Journal of Experimental Botany, Vol. 55, No. 404,
Sulphur Metabolism in Plants Special Issue, pp. 1927–1937, August 2004
DOI: 10.1093/jxb/erh192 Advance Access publication 16 July, 2004
Interactions between selenium and sulphur nutrition
in Arabidopsis thaliana
P. J. White1,*, H. C. Bowen1, P. Parmaguru1, M. Fritz1, W. P. Spracklen1, R. E. Spiby1, M. C. Meacham1,
A. Mead1, M. Harriman2, L. J. Trueman1, B. M. Smith1, B. Thomas1 and M. R. Broadley3
1
Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK
2
Norsk Hydro, ASA, N-0240 Oslo, Norway
3
Plant Science Division, School of Biosciences, University of Nottingham, Sutton Bonington Campus,
Loughborough, Leicestershire LE12 5RD, UK
Received 11 March 2004; Accepted 4 May 2004
Abstract
Introduction
Selenium (Se) is an essential plant micronutrient, but is
toxic at high tissue concentrations. It is chemically
similar to sulphur (S), an essential plant macronutrient.
The interactions between Se and S nutrition were
investigated in the model plant Arabidopsis thaliana
(L.) Heynh. Arabidopsis plants were grown on agar
containing a complete mineral complement and various concentrations of selenate and sulphate. The Se/S
concentration ratio in the shoot ([Se]shoot/[S]shoot)
showed a complex dependence on the ratio of selenate
to sulphate concentration in the agar ([Se]agar/[S]agar).
Increasing [S]agar increased shoot fresh weight (FW)
and [S]shoot, but decreased [Se]shoot. Increasing [Se]agar
increased both [Se]shoot and [S]shoot, but reduced shoot
FW. The reduction in shoot FW in the presence of Se
was linearly related to the shoot Se/S concentration
ratio. These data suggest (i) that Se and S enter
Arabidopsis through multiple transport pathways with
contrasting sulphate/selenate selectivities, whose activities vary between plants of contrasting nutritional
status, (ii) that rhizosphere sulphate inhibits selenate
uptake, (iii) that rhizosphere selenate promotes sulphate uptake, possibly by preventing the reduction in
the abundance and/or activity of sulphate transporters
by sulphate and/or its metabolites, and (iv) that Se
toxicity occurs because Se and S compete for a biochemical process, such as assimilation into amino
acids of essential proteins.
Selenium (Se) is an oxygen group element (Group VIA)
with chemical properties similar to sulphur (S) and tellurium
(Te). Selenium displays metalloid characteristics and it
occurs in several different oxidation states as selenide
(Se2ÿ), elemental selenium (Se0), selenite (Se4+), and
selenate (Se6+). Selenium can also form direct Se-carbon
bonds and is found in a variety of organic compounds such
as methylated compounds, selenoamino acids, and selenoproteins (Martens and Suarez, 1997a). Since the radii of S2ÿ
and Se2ÿ are similar (0.174 and 0.191 nm, respectively), Se
can replace S in metal sulphides. Thus, Se is associated with
pyrite and other sulphide minerals in unweathered rocks and
mineral ores (Huston et al., 1995). The S/Se/Te concentrations in igneous rocks approximate 520/0.05–0.09/0.001 ppm
(Bisbjerg, 1972). However, the behaviour of S and Se
differs during weathering because S2ÿ is readily oxidized to
S6+, whilst Se2ÿ oxidation stops at Se4+ unless the oxidation
potential is very high. The geochemical balance of S:Se in
sea-water is 8 000 000:1, contrasting with 3000:1 in
sedimentary rocks (Bisbjerg, 1972). Enrichment of marine
sediments with Se occurs as a result of weathering and
erosion of rocks, atmospheric deposition, and marine bioaccumulation of Se (Martens and Suarez, 1997b). Selenium
is present in all sedimentary rocks formed during the
Carboniferous to Quaternary Periods (360 My to the
present). However, Se is most prominent in shales formed
during the Late Cretaceous to early Tertiary periods.
Depending upon the parent rock, soil Se concentrations
are toxic to plant growth in some regions of the world and
insufficient in others (Rosenfeld and Beath, 1964; Shrift,
Key words: Mutants, phylogeny, selenate, sulphate, toxicity,
uptake.
* To whom correspondence should be addressed. Fax: +44 (0) 24 7657 4500. E-mail: [email protected]
Journal of Experimental Botany, Vol. 55, No. 404, ª Society for Experimental Biology 2004; all rights reserved
1928 White et al.
1969; Dhillon and Dhillon, 2003). Inputs of Se to soils arise
from both natural (biogenic) and anthropogenic processes
(Nriagu, 1989). Anthropogenic gaseous and particulate Se
emissions are more mobile in the atmosphere than biogenic
emissions, because they arise at higher temperatures.
Anthropogenic Se tends to be largely deposited to soils in
rainwater, which contains 0.00001–0.001 ppm Se, rather
than through dry deposition (De Gregori et al., 2002). A
correlation between industrialization and Se deposition has
been inferred from the Se content of historical plant and soil
samples (Haygarth et al., 1993). Selenium also accumulates
in soils through the use of fertilizers and irrigation water
containing Se (Bisbjerg, 1972). In fertilizers, ammonium sulphate contains up to 36 ppm, phosphate rocks up to 55 ppm,
and single superphosphate up to 25 ppm Se (Swaine, 1962;
Bisbjerg, 1972). However, since single superphosphate has
generally been replaced by triple superphosphate, which
contains up to 4 ppm Se, fertilizer inputs of Se to soils have
fallen.
Plant species differ in their ability to accumulate Se and
have been divided into three groups: ‘non-accumulator’,
‘Se-indicator’, and ‘Se-accumulator’ plants (Rosenfeld and
Beath, 1964; Shrift, 1969; Brown and Shrift, 1982; Wu,
1998; Ihnat, 1989; Dhillon and Dhillon, 2003; Ellis and
Salt, 2003). Most plants contain less than 25 lg Se gÿ1 dry
matter and are termed non-accumulators (Fig. 1). Such
plants are incapable of tolerating high Se in the environment, and Se toxicity occurs below about 10–100 lg Se gÿ1
dry matter, although the exact value depends critically upon
the selenate:sulphate ratio in the rhizosphere solution
(Table 1; Fig. 2). These plants tolerate low Se concentrations in the rhizosphere by restricting Se uptake and
movement to the shoot (Wu et al., 1988; Wu and Huang,
1992). Several plant species can grow adequately in both
seliniferous and non-seliniferous soils, and can contain up
to 1000 lg Se gÿ1 dry matter without consequence. Such
species include members of the genera Aster, Astragalus,
Atriplex, Castilleja, Comandra, Grayia, Grindelia, Gutierrezia, Machaeranthera, Mentzelia, and Sideranthus. These
are termed ‘Se indicator’ plants. A few species of the genera
Astragalus, Happlopappus (Oonopsis section), Machaeranthera (Xylorhiza section), Morinda, Neptunia and Stanleya are Se accumulators, and their shoot tissue may contain
up to 20–40 mg Se gÿ1 dry matter when grown under
natural conditions (Rosenfeld and Beath, 1964; Shrift,
1969). These species are capable of tolerating high tissue
Se concentrations, but they are rarely observed on nonseleniferous soils. However, despite these differences in
Se accumulation between plant species, and unlike other
mineral nutrients such as Ca, Mg, and K (Broadley et al.,
2003, 2004), there is no evidence for systematic differences
in the Se concentrations in shoots between angiosperm
orders. Over 95% of the variation in shoot Se concentration
can be attributed to within-order variance, which is likely
to reflect species-specific differences. Differences in the
Fig. 1. The mean relative Se concentrations in shoots of 185 angiosperm
species. The species are: (1) Sorghum bicolor, (2) Agropyron trachycaulum, (3) Agropyron cristatum, (4) Atriplex lentiformis, (5) Bromus
inermis, (6) Atriplex rosea, (7) Sorghum vulgare, (8) Panicum miliaceum,
(9) Atriplex halimus, (10) Atriplex vesicaria, (11) Atriplex leucoclada,
(12) Bellis perennis, (13) Glycine max, (14) Atriplex hortensis, (15)
Atriplex pseudocampanulata, (16) Asclepias syriaca, (17) Picris
hieracioides, (18) Lotus corniculatus, (19) Trifolium subterraneum,
(20) Atriplex polycarpa, (21) Atriplex undulata, (22) Atriplex deserticola, (23) Lolium multiflorum, (24) Bromus sativa, (25) Atriplex
semibaccata, (26) Lycopersicon peruvianum, (27) Zea mays, (28)
Securigera varia, (29) Atriplex nummularia, (30) Dactylis glomerata,
(31) Panicum coloratum, (32) Panicum virgatum, (33) Bouteloua
curtipendula, (34) Lycopersicon pennellii, (35) Sporobolus cryptandrus,
(36) Panicum obtusum, (37) Echinochloa crus-galli, (38) Sorghum sp.,
(39) Lactuca sativa, (40) Medicago sativa, (41) Eragrostis trichodes,
(42) Setaria leucopila, (43) Medicago lupulina, (44) Schizachyrium
scoparium, (45) Atriplex canescens, (46) Elytrigia pontica, (47)
Cichorium endivia, (48) Lolium perenne, (49) Buchloe dactyloides,
(50) Trifolium pratense, (51) Phleum pratense, (52) Artemisia frigida,
(53) Sophora sericea, (54) Malvastrum coccineum, (55) Oreocarya spp.,
(56) Bouteloua gracilis, (57) Ranunculus repens, (58) Daucus carota,
(59) Munroa squarrosa, (60) Solanum tuberosum, (61) Salsola pestifer,
(62) Xanthium strumarium, (63) Kochia scoparia, (64) Spinacia
oleracea, (65) Hordeum vulgare, (66) Xanthium spp., (67) Euphorbia
spp., (68) Atriplex inflata, (69) Gutierrezia sarothrae, (70) Holcus
lanatus, (71) Cynara cardunculus, (72) Atriplex breweri, (73) Phaseolus
vulgaris, (74) Lycopersicon esculentum, (75) Pastinaca sativa, (76)
Secale cereale, (77) Alopecurus pratensis, (78) Atriplex sp., (79)
Hibiscus cannabinus, (80) Cynodon dactylon, (81) Triticum aestivum,
(82) Agropyron repens, (83) Potentilla anserina, (84) Sinapis alba, (85)
Atriplex muelleri, (86) Beta vulgaris, (87) Gossypium hirsutum, (88)
Machaeranthera grindelioides, (89) Astragalus argyroides, (90) Astragalus macrotropis, (91) Astragalus monspessulanus, (92) Astragalus
schistosus, (93) Astragalus sinicus, (94) Astragalus szovitzii, (95)
Astragalus tribuloides, (96) Atriplex atacamensis, (97) Astragalus
bakaliensis, (98) Astragalus globiceps, (99) Astragalus lilacinus, (100)
Astragalus sessiliceps, (101) Astragalus interpositus, (102) Astragalus
campylorrhynchus, (103) Astragalus chaborasicus, (104) Astragalus
glycyphyllos, (105) Astragalus bungeanus, (106) Astragalus miser, (107)
Astragalus recollectus, (108) Astragalus refractus, (109) Astragalus
siliquosus, (110) Astragalus scorpioides, (111) Astragalus venosus,
(112) Agrostis stolonifera, (113) Astragalus falcatus, (114) Astragalus
galegiformis, (115) Astragalus odoratus, (116) Astragalus hamosus,
(117) Sorghum3drummondii, (118) Avena sativa, (119) Astragalus
adsurgens, (120) Astragalus alopecuroides, (121) Astragalus alpinus,
(122) Astragalus campylosema, (123) Sporobolus airoides, (124)
Astragalus onobrychis, (125) Astragalus rugosus, (126) Astragalus
vulpinus, (127) Astragalus pulchellus, (128) Astragalus vesicarius, (129)
Astragalus platysematus, (130) Astragalus ponticus, (131) Astragalus
alopecurus, (132) Astragalus caraganae, (133) Astragalus chinensis,
(134) Astragalus luristanicus, (135) Solanum melongena, (136)
Selenium and sulphur nutrition
ability of plants to tolerate Se are thought to be a consequence of differences in their Se metabolism (Shrift, 1969;
Brown and Shrift, 1982; Wu, 1998; Terry et al., 2000; Ellis
and Salt, 2003; Montes-Bayón et al., 2003). The assimilation of Se into organoselenium compounds is thought to
compete with S assimilation. Both selenocysteine and
selenomethionine can be incorporated into proteins, which
may impair their stability and functional activities. This is
thought to account for Se toxicity in non-accumulator
plants. In the Se-tolerant accumulator plants the formation
of selenomethionine appears to be restricted and selenocysteine is converted to non-protein amino acids such
as Se-methylselenocysteine, selenocystathionine, and the
dipeptide c-glutamyl-Se-methylselenocysteine.
Plants acquire Se from the soil solution. The uptake of
Se by plant roots is influenced by the chemical form and
concentration of Se in the soil solution, soil redox conditions, pH of the rhizosphere, and the presence of competing anions such as sulphate and phosphate (Mikkelsen et al.,
1989b; Blaylock and James, 1994; Dhillon and Dhillon,
2003). Selenium can be taken up by plant roots as selenate
2ÿ
(SeO2ÿ
4 ), selenite (SeO3 ) or as organoselenium compounds
such as the amino acids selenocysteine and selenomethionine. When present at comparable concentrations, the uptake
of selenate is generally greater than that of selenite (HurdKarrer, 1935; Rosenfeld and Beath, 1964; Ulrich and Shrift,
1968; Bisbjerg and Gissel-Nielsen, 1969; Gissel-Nielsen,
1973; Asher et al., 1977; Smith and Watkinson, 1984;
Mickelsen et al., 1987; Bañuelos and Meek, 1989; Arvy,
1993; de Souza et al., 1998; Zayed et al., 1998; Hopper and
Astragalus canadensis, (137) Astragalus boeticus, (138) Astragalus
sulcatus, (139) Vicia villosa, (140) Astragalus austriacus, (141)
Abelmoschus esculentus, (142) Raphanus sativus, (143) Lotus tenuis,
(144) Agropyron desertorum, (145) Astragalus fraxinifolius, (146)
Astragalus scorpiurus, (147) Trifolium angustifolium, (148) Brassica
rapa, (149) Pisum sativum, (150) Festuca arundinacea, (151) Astragalus
asper, (152) Astragalus demetrii, (153) Cucumis sativus, (154) Astragalus incanus, (155) Stipa comata, (156) Astragalus tephrosioides, (157)
Allium cepa, (158) Atriplex nuttallii, (159) Setaria italica, (160) Lactuca
serriola, (161) Polypogon monspeliensis, (162) Taraxacum officinale,
(163) Brassica oleracea, (164) Lepidium sativum, (165) Brassica napus,
(166) Oxalis stricta, (167) Pascopyrum smithii, (168) Helianthus annuus,
(169) Oryzopsis hymenoides, (170) Tragopogon pratensis, (171) Linum
usitatissimum, (172) Brassica juncea, (173) Eurotia lanata, (174) Oryza
sativa, (175) Stanleya pinnata, (176) Brassica nigra, (177) Astragalus
bisulcatus, (178) Haplopappus fremontii, (179) Trifolium repens, (180)
Brassica carinata, (181) Astragalus racemosus, (182) Aster occidentalis,
(183) Sinapis spp., (184) Astragalus pectinatus, (185) Machaeranthera
ramosa. To obtain these values, data from the 182 studies described in the
40 papers listed in Appendix 1 were subjected to a residual maximum
likelihood (REML) analysis, using procedures described previously
(Broadley et al., 2001, 2003, 2004). The data are relative values on
a linear scale that approximate to lg Se gÿ1 shoot dry matter. Negative
values can arise from the REML fitting procedures (Thompson and
Wellham, 2000). A dashed line is drawn at a mean relative shoot Se
concentration of 100. Only 34 of the species studied had a mean relative
shoot Se concentration higher than this. Inset: Frequency distribution of
the mean relative Se concentration in shoots of angiosperm species
excluding the two highest Se-accumulator plants.
1929
Parker, 1999; Pilon-Smits et al., 1999; Shanker and
Srivastava, 2001; Montes-Bayón et al., 2003; Zhang et al.,
2003), but the uptake of Se is often most effective as organic
selenium compounds, such as those present in extracts from
Se-accumulator plants (Rosenfeld and Beath, 1964; MontesBayón et al., 2003). Colloidal elemental selenium and metal
selenides are not available to plants (Hurd-Karrer, 1935;
Peterson and Butler, 1966). Once it has been taken up by
roots, selenate is readily transported to the shoot via the
xylem (Asher et al., 1977; Smith and Watkinson, 1984;
Gissel-Nielsen, 1987; Wu et al., 1988; Arvy, 1993; de Souza
et al., 1998; Zayed et al., 1998; Hopper and Parker, 1999),
and Se appears to be redistributed within the plant, particularly from older to younger leaves, in a manner analogous
to S (Rosenfeld and Beath, 1964).
Selenate is thought to enter root cells through sulphate
transporters in the plasma membrane. In most plant species,
a small family of genes encode sulphate transporters (Smith
et al., 2000; White, 2003). The overexpression of these
genes in transgenic plants increases Se uptake (Terry et al.,
2000). Historically, it was observed that selenate and
sulphate competed for influx to roots (Leggett and Epstein,
1956; Pettersson, 1966; Ulrich and Shrift, 1968; Shennan
et al., 1990), and exhibited similar Michaelis constants
for high-affinity transport (Km=15–20 lM). However,
when plants are supplied with mixtures of selenate and
sulphate, the Se:S concentration ratio in the rhizosphere
solution is rarely identical to the Se:S concentration ratio in
plant tissues (Hurd-Karrer, 1937; Bell et al., 1992; Barak
and Goldman, 1997; Feist and Parker, 2001; Ellis and Salt,
2003; Suarez et al., 2003). This suggests that the transporters responsible for the uptake and translocation of these
anions are selective for either sulphate (in non-accumulator
plants in which the Se/S ratio is lower in shoot tissues than
in the rhizosphere solution), or selenate (in Se-accumulator
plants in which the Se/S ratio is higher in shoot tissues than
in the rhizosphere solution). Remarkably, there is often no
correlation between the shoot Se and S concentrations of
different plant species (or even ecotypes of the same
species) growing in the same environment (Feist and
Parker, 2001). Both selenate and sulphate are accumulated
in plant cells against their electrochemical gradient (Brown
and Shrift, 1982; Smith et al., 2000), and an H+-coupled
mechanism with a stoichiometry of one anion to three
protons has been proposed. This is consistent with an
increase in sulphate (Leggett and Epstein, 1956; Vange
et al., 1974) and selenate (Ulrich and Shrift, 1968) uptake
by roots as the rhizosphere is acidified.
The toxicity of selenate is progressively reduced by the
presence of increasing sulphate in the rhizosphere solution
(Hurd-Karrer, 1935; Rosenfeld and Beath, 1964; Mikkelsen
et al., 1989b), not only because high sulphate concentrations
in the rhizosphere reduce selenate uptake per se (HurdKarrer, 1935; Gissel-Nielsen, 1973; Pratley and McFarlane,
1974; Mikkelsen et al., 1988; Mikkelsen and Wan, 1990;
1930 White et al.
Table 1. Selenium toxicity in some Se-nonaccumulator plants
The critical shoot tissue Se concentrations correspond to a 10% reduction in the yield of plants grown in the presence of added selenate.
Plant
Medium
Sulphate in
rhizosphere
Critical concentration
(mg Se kgÿ1 dry wt.)
Reference
Alfalfa (Medicago sativa)
Alfalfa (Medicago sativa)
Soil
Hydroponics
Hydroponics
Hydroponics
Hydroponics
Hydroponics
Soil
Soil
Soil
Soil, upland
Soil, flooded
Hydroponics
Hydroponics
Hydroponics
Hydroponics
Hydroponics
Soil
Hydroponics
25–30
19
94
73
340
25
83
3
3
<2
160
81
320
590–900
290
490–840
210
3
330
Soltanpour and Workman (1980)
Mikkelsen et al. (1987)
Bermudagrass (Cynodon dactylon)
Buffalograss (Buchloe dactyloides)
Bush bean (Phaseolus vulgaris)
Crested wheatgrass (Agropyron desertorum)
Mustard (Brassica juncea)
Pea (Pisum sativum)
Rice (Oryza sativa)
Rice (Oryza sativa)
ND
0.5 mM, pH 4.5
0.5 mM, pH 7.0
0.25 mM
0.25 mM
4 mM
0.25 mM
ND
ND
ND
8.9 mM
(saturated soil)
1.875 mM
0.5 mM
0.25 mM
0.5 mM
0.25 mM
ND
1.875 mM
Ryegrass (Lolium perenne)
Ryegrass (Lolium perenne)
Seaside bentgrass (Agrostis stolonifera)
Strawberry clover (Trifolium fragiferum)
Tall fescue (Festuca arundinacea)
Wheat (Triticum vulgare)
White clover (Trifolium repens)
Bell et al., 1992; Wu and Huang, 1992; Zayed and Terry,
1992, 1994; Barak and Goldman, 1997; Zayed et al., 1998;
Hopper and Parker, 1999; Pezzarossa et al., 1999; Grieve
et al., 2001; Feist and Parker, 2001; Vickerman et al., 2002),
but also because they lower the tissue Se/S quotient and
(presumably) the relative incorporation of selenocysteine
and selenomethionine into proteins. Interestingly, in the
long term, shoot S concentrations can be increased, especially at low rhizosphere sulphate concentrations, by increasing the selenate concentration in the soil solution (Smith and
Watkinson, 1984; Bañuelos et al., 1990; Mikkelsen et al.,
1988; Mikkelsen and Wan, 1990; Bell et al., 1992; Barak
and Goldman, 1997; Kopsell and Randle, 1997; Takahashi
et al., 2000; Feist and Parker, 2001;Yoshimoto et al., 2002;
Suarez et al., 2003). It is thought that this results from either
selenate or Se metabolites antagonizing the inhibition of
transport activity or repression of transcription of sulphate
transporter genes by sulphate and its metabolites. Sulphate
transport is reduced when sulphate supply does not limit
growth and the cellular sulphate is abundant. Repression of
sulphate transporter activities by sulphate, cysteine or
glutathione,
and
positive
regulation
by
o-acetylserine, have all been proposed (Hawkesford and
Smith, 1997; Bolchi et al., 1999; Smith et al., 2000;
Takahashi et al., 2000; Vidmar et al., 2000; Terry et al.,
2000).
Selenium is an essential element for all animals, including
humans (Rayman, 2000, 2002; Dhillon and Dhillon, 2003).
The US recommended dietary allowance is 55–70 lg dÿ1
and the UK reference nutrient intake is 60–70 lg dÿ1.
However, human diets in several countries lack sufficient Se
(Mikkelsen et al., 1989b; Rayman, 2000, 2002). To address
this dietary Se deficiency, agronomists and plant breeders
are pursuing two complementary strategies to develop crops
Wu et al. (1988)
Wu et al. (1988)
Wallace et al. (1980)
Wu et al. (1988)
Tripathi and Misra (1974)
Tripathi and Misra (1974)
Prasad and Arora (1980)
Mikkelsen et al. (1989a)
Smith and Watkinson (1984)
Hopper and Parker (1999)
Wu et al. (1988)
Hopper and Parker (1999)
Wu et al. (1988)
Tripathi and Misra (1974)
Smith and Watkinson (1984)
with enhanced Se content. The first strategy is through improvements in crop husbandry. For this strategy to succeed,
it is important to determine the potential for different crops
to accumulate Se by characterizing the responses of their
growth and Se content to the application of Se and S
fertilizers. The second strategy is to develop crop genotypes
with improved Se accumulation and tolerance traits, through
conventional breeding or GM approaches. This second
strategy is likely to benefit from knowledge of the genes
that impact on Se accumulation and tolerance. A common
approach to identify and confirm candidate genes impacting
on a specific trait is to utilize the genetic resources available
for the model brassica, Arabidopsis thaliana (L.) Heynh.
However, before the potential of any candidate genes can be
realized in crop plants, a deeper understanding of the
possible physiological consequences of their manipulation
should be obtained. In this paper, a comprehensive characterization of the interactions between Se and S nutrition has
been undertaken in Arabidopsis. This should inform the
subsequent identification of candidate genes impacting on
Se accumulation and their potential for manipulating the
phenotype of crop plants.
Materials and methods
Seeds of the Arabidopsis accession Columbia-5 glabrous1 (Col-5,
no. N1644) were obtained from the Nottingham Arabidopsis Stock
Centre (Nottingham, UK). Seeds were washed in 70% (v/v) ethanol/
water, rinsed in distilled water, and surface-sterilized using NaOCl
(1% active chlorine). Seeds were then rinsed in sterile, distilled water,
and sown in unvented, polycarbonate culture boxes (Hammond et al.,
2003), at a density of 10 seeds per box, on 75 ml of 0.8% (w/v) agar
containing 1% (w/v) sucrose and a basal salt mix formulated
according to Murashige and Skoog (1962). This formulation was
termed MS medium and contained 1.73 mM sulphate. A medium
Selenium and sulphur nutrition
Fig. 2. The relationship between the shoot fresh weight of 21-d-old
Arabidopsis (Columbia gl1) plants and (A) the sulphate concentration in
agar containing a complete mineral complement with (open circles) or
without (closed circles) 100 lM selenate, or (B) the selenate concentration in agar containing a complete mineral complement including 1.73
mM (closed circles) or 50 lM (open circles) sulphate. Data are expressed
as mean 6SE from 4 or 5 replicate experiments.
containing 50 lM sulphate was also employed (MS-S medium), in
which sulphate was replaced by chloride. Selenium was added to MS
and MS-S media as sodium selenate and the sulphate concentration
was manipulated by replacing the chloride in MS-S medium. Boxes
were placed in a growth room maintained at 24 8C. Plants were
provided with 16 h of light daily. Illumination was provided by
a bank of fluorescent tubes (100 W 84; Philips, Eindhoven, The
Netherlands) giving a photon flux density between 400 and 700 nm of
50–80 lmol photons mÿ2 sÿ1 at plant height. Plants were harvested
21 d after sowing. The shoot and roots of individual plants were
separated and weighed. Shoot and root material from individual
culture boxes were bulked separately for mineral analyses. The S and
Se contents of plant material were determined by atomic emission
spectroscopy by inductively coupled plasma (Jobin-Yvon JY-24
Atomic Emission Spectrophotometer; ICA, Middlesex, UK).
Results
The shoot fresh weight (FW) of Arabidopsis plants
growing on agar containing all essential mineral nutrients
1931
and no selenium was greater when the agar contained
higher sulphate concentrations ([S]agar; Fig. 2A). When
plants were grown in the absence of Se, a maximal shoot
FW was obtained at [S]agar greater than about 500 lM.
When Arabidopsis were grown on agar containing a selenate concentration ([Se]agar) of 100 lM, the shoot FW
was less than that observed in plants growing in the
absence of selenate at a comparable [S]agar. When plants
were grown with a [Se]agar of 100 lM, maximal shoot
FW was not obtained even in the presence of 20 mM
[S]agar (Fig. 2A). The shoot FW of Arabidopsis plants
growing on agar lacking selenium was greater when the
[S]agar was 1.73 mM than when [S]agar was 50 lM
(Fig. 2B). When Arabidopsis were grown at a [S]agar of
1.73 mM, shoot FW was reduced to values lower than
those observed in the absence of Se when [Se]agar was
greater than about 10 lM. In comparison, when Arabidopsis were grown at a [S]agar of 50 lM, shoot FW was
reduced at a [Se]agar as low as 1 lM (Fig. 2B). These
data indicate (i) that increasing [Se]agar prevented Arabidopsis growing at low [S]agar and (ii) that the toxic effect
of [Se]agar on Arabidopsis growth could be mitigated by
increasing [S]agar.
In general, increasing the [Se]agar increased the shoot Se
concentration ([Se]shoot) of Arabidopsis plants growing
with a [S]agar of 1.73 mM or 50 lM (Fig. 3A). When the
[Se]agar was insufficient to affect growth, [Se]shoot was
greater when plants were grown at a lower [S]agar (Fig. 3A).
When Arabidopsis plants were grown on agar containing
a [Se]agar of 100 lM, a [Se]shoot of about 0.06 lg mgÿ1
shoot FW was observed at [S]agar <5 mM, but the [Se]shoot
showed a tendency to decrease at higher [S]agar (Fig. 3B).
These data are consistent with previous observations
suggesting that sulphate in the rhizosphere inhibits selenate
uptake by plant roots (Hurd-Karrer, 1935; Gissel-Nielsen,
1973; Pratley and McFarlane, 1974; Mikkelsen et al., 1988;
Mikkelsen and Wan, 1990; Bell et al., 1992; Wu and
Huang, 1992; Zayed and Terry, 1992, 1994; Barak and
Goldman, 1997; Zayed et al., 1998; Hopper and Parker,
1999; Pezzarossa et al., 1999).
The shoot S concentration ([S]shoot) was greater in plants
grown with a [Se]agar of 100 lM, compared with plants
grown in agar lacking Se (Fig. 4A). Similarly, increasing
the [Se]agar increased the [S]shoot of Arabidopsis plants
growing with a [S]agar of 1.73 mM or 50 lM (Fig. 4B). This
effect was observed at lower [Se]agar when plants were
grown at lower [S]agar. These data are consistent with
previous observations that increasing the selenate concentration in the rhizosphere increases shoot S concentrations
(Smith and Watkinson, 1984; Mikkelsen et al., 1988;
Bañuelos et al., 1990; Mikkelsen and Wan, 1990; Bell
et al., 1992; Kopsell and Randle, 1997; Takahashi et al.,
2000; Feist and Parker, 2001;Yoshimoto et al., 2002;
Suarez et al., 2003). These observations have been
interpreted as the consequence of either selenate or Se
1932 White et al.
Fig. 3. The relationship between the shoot selenium concentration
([Se]shoot) of 21-d-old Arabidopsis (Columbia gl1) plants and (A) the
selenate concentration in agar ([Se]agar) containing a complete mineral
complement including 1.73 mM (closed circles) or 50 lM (open circles)
sulphate, or (B) the sulphate concentration in agar ([S]agar) containing
a complete mineral complement with (open circles) or without (closed
circles) 100 lM selenate. Data are expressed as mean 6SE from 4 or 5
replicate experiments. Note the minimal [Se]shoot of plants grown on agar
lacking added selenate. A parallel regression analysis on the logtransformed data of panel (A) indicated that [Se]shoot increased
significantly with increasing [Se]agar (P<0.001) and that there was
a consistent difference in [Se]shoot of plants grown in the presence of 1.73
mM or 50 lM [S]agar when the [Se]agar was insufficient to affect growth.
An ANOVA on the log-transformed data of (B) indicated a significant
effect of [Se]agar on [Se]shoot (P<0.001), but that increasing [S]agar had no
significant effect. Statistical analyses were performed on the values from
all replicate experiments.
Fig. 4. The relationship between the shoot sulphur concentration
([S]shoot) of 21-d-old Arabidopsis (Columbia gl1) plants and (A) the
sulphate concentration in agar ([S]agar) containing a complete mineral
complement with (open circles) or without (closed circles) 100 lM
selenate, or (B) the selenate concentration in agar ([Se]agar) containing
a complete mineral complement including 1.73 mM (closed circles) or 50
lM (open circles) sulphate. Data are expressed as mean 6SE from 4 or 5
replicate experiments. An ANOVA on the log-transformed data of (A)
indicated a significant effect of [Se]agar (P<0.001), but no significant
effect of [S]agar, on [S]shoot. A parallel regression analysis on the logtransformed data of (B) indicated that [S]shoot increased significantly with
increasing [Se]agar (P<0.001) and that there was a consistent difference in
the [S]shoot of plants grown in the presence of 1.73 mM or 50 lM [S]agar
(P<0.05). Statistical analyses were performed on the values from all
replicate experiments.
metabolites antagonizing the repression of sulphate transporters by sulphate and its metabolites.
The shoot FW/root FW of Arabidopsis is about 5.2 when
plants are grown under the conditions described here, and
most of the Se and S in these plants is in the shoot. Thus, it
is possible to address whether Se and S enter Arabidopsis
through the same transport pathway by comparing the
quotients [Se]shoot/[S]shoot and [Se]agar/[S]agar obtained under contrasting conditions. If Se and S are transported by
the same pathway, then [Se]shoot/[S]shoot should be linearly
related to [Se]agar/[S]agar. When Arabidopsis was grown at
50 lM [S]agar the relationship between [Se]shoot/[S]shoot and
[Se]agar/[S]agar appeared to be linear, but the gradient was
significantly lower than unity, suggesting that the transport
pathway selected for suphate over selenate (Fig. 5A). This
has been observed in other members of the Brassicaceae,
such as Brassica juncea, Brassica napus, Brassica nigra,
Brassica oleracea, and Lesquerella fendleri, and in Seindicator and non-accumulator plants grown in a variety of
soils (Hurd-Karrer, 1937; Bell et al., 1992; Barak and
Goldman, 1997; Kopsell and Randle, 1999; Feist and
Parker, 2001; Grieve et al., 2001; Suarez et al., 2003).
Selenium and sulphur nutrition
Fig. 5. The relationship between the shoot Se/S concentration ratio
([Se]shoot/[S]shoot) and the agar Se/S concentration ratio ([Se]agar/[S]agar)
in Arabidopsis (Columbia gl1) plants grown in the presence of (A)
contrasting [Se]agar and [S]agar of 1.73 mM (closed circles) or 50 lM
(open circles), or (B) contrasting [S]agar and a [Se]agar of 100 lM. Data are
the quotients of the mean values for 4 or 5 replicate experiments presented
in Figs 3 and 4.
By contrast, selenate is accumulated preferentially over
suphate in Se-accumulator plants, such as Astragalus
bisulcatus and Stanleya pinnata, another member of the
Brassicaceae (Bell et al., 1992; Feist and Parker, 2001; Ellis
and Salt, 2003). When plants were grown at 1.73 mM
[S]agar the relationship between [Se]shoot/[S]shoot and
[Se]agar/[S]agar appeared to follow a hyperbolic relationship
(Fig. 5A). The initial gradient at low [Se]agar was steeper
than that observed in plants grown at a [S]agar of 50 lM, but
the gradient declined as [Se]agar was increased. This implies
that plants grown at a [S]agar of 1.73 mM were less selective
for sulphate over selenate than their counterparts grown at
a [S]agar of 50 lM, particularly at low selenate concentrations. When plants were grown in the presence of
a [Se]agar of 100 lM, and the [Se]agar/[S]agar was reduced
by increasing the [S]agar, it was observed that the gradient of
the relationship between [Se]shoot/[S]shoot and [Se]agar/
1933
[S]agar was shallower at low [S]agar than at high [S]agar
(Fig. 5B). This is consistent with the data from plants grown
at constant [S]agar (Fig. 5A) and again suggests that the
selectivity of the transport pathway for sulphate over
selenate is lower at higher [S]agar. Assuming that both
low [S]agar and high [Se]agar lead to the induction of the
same sulphate transporters in the plasma membranes of
Arabidopsis roots (cf. Takahashi et al., 1997, 2000;
Shibagaki et al., 2002; Yoshimoto et al., 2002; Maruyama-Nakashita et al., 2003), and that both sulphate and
selenate enter the plants through these proteins, the data
presented here suggest that the inducible sulphate transporters are more selective for sulphate than the constitutively active sulphate transporters. These observations
provide physiological evidence for the presence of multiple
sulphate transporters in Arabidopsis roots with contrasting
sulphate/selenate selectivities that dominate transport
across the plasma membrane under contrasting nutritional
conditions.
It is thought that the competition between Se and S for
assimilation into amino acids and proteins may account for
the toxicity of Se in most plants (Shrift, 1969; Brown and
Shrift, 1982; Terry et al., 2000; Ellis and Salt, 2003). If this
is the case then Se toxicity should be related to the tissue Se/
S concentration ratio. It was observed that the growth of
Arabidopsis (expressed as the shoot FW obtained in the
presence of selenate divided by the shoot FW obtained in
the absence of selenate at the same sulphate concentration)
was approximately linearly related to the shoot Se/S
concentration ratio (Fig. 6). This is consistent with the
accumulation of Se in the shoot tissues inhibiting growth
through its interactions with S metabolism.
Discussion
This paper reports a comprehensive characterization of
the interactions between Se and S nutrition in the model
brassica, Arabidopsis thaliana. Arabidopsis plants were
grown on agar containing various concentrations of selenate and sulphate to determine how interactions between
these two anions affect growth and shoot concentrations of
Se and S. These studies indicated that several transport
proteins, with contrasting selectivities, could mediate the
uptake of selenate and sulphate into plants, and that
the relative activities of these transporters were governed
by the nutritional status of the plant. They also indicated
that Se toxicity was directly related to the [Se]shoot/[S]shoot,
suggesting that Se toxicity occurs because Se and S
compete for a biochemical process, such as assimilation
into the amino acids of essential proteins.
The hypothesis that several transport proteins, with
contrasting anion selectivities and regulation by plant
nutritional status, mediate the uptake of selenate by
Arabidopsis could be tested either (i) by characterizing
selenate and sulphate uptake by Arabidopsis mutants
1934 White et al.
Fig. 6. The relationship between the growth of Arabidopsis (Columbia
gl1) plants (expressed as the shoot FW obtained in the presence of
selenate divided by the shoot FW obtained in the absence of selenate at
the same sulphate concentration) and the [Se]shoot/[S]shoot quotient. Data
were derived from the mean values for 4 or 5 replicate experiments
presented in Figs 2, 3, and 4. Plants were grown in the presence of
contrasting [Se]agar and [S]agar of 1.73 mM (closed circles) or 50 lM
(open circles), or contrasting [S]agar and a [Se]agar of 100 lM (closed
squares). Data from conditions yielding the lowest growth were excluded.
The linear regression y= ÿ0.02093+1.012, where y is plant growth and x
is the [Se]shoot/[S]shoot, had an R2 value of 0.595.
misexpressing specific sulphate transporters grown with
contrasting mineral nutrition, or (ii) by combining data on
selenate and sulphate fluxes through plant sulphate transporters, perhaps expressed in yeast mutants lacking their
endogenous sulphate transporters (Smith et al., 1995;
Cherest et al., 1997), with gene expression studies. Arabidopsis mutants misexpressing sulphate transporters are
available for these studies (Terry et al., 2000; Shibagaki
et al., 2002; Yoshimoto et al., 2002; Maruyama-Nakashita
et al., 2003), and it has already been observed that mutants
overexpressing sulphate transporters have a greater selenate
uptake (Terry et al., 2000), whereas mutants lacking
sulphate transporters have a lower selenate uptake (Shibagaki et al., 2002), than wild-type plants. However the anion
selectivity of these mutants has not been investigated.
Similarly, although suphate uptake by yeast mutants expressing only plant sulphate transporters has been characterized, there appears to be no complementary data on
selenate uptake. Thus, testing the hypothesis developed in
this paper remains a future research objective.
Selenium toxicity has been used as a screen to identify
genes that impact on Se accumulation by Arabidopsis
(Rose, 1997; Shibagaki et al., 2002). It has been observed
that mutants lacking root selenate/sulphate transporters and/
or enzymes involved in the reduction and assimilation of
selenate survive the presence of high Se concentrations in
the rhizosphere (Rose, 1997; Shibagaki et al., 2002). This is
consistent with the physiological observations reported
here. Since selenate enters plants through sulphate transporters, mutants lacking root sulphate transporters will
exhibit reduced selenate uptake and will be less sensitive
to Se toxicity in the rhizosphere. Mutants that are unable to
assimilate Se into amino acids and proteins are thought to
be less likely to be sensitive to cellular Se toxicity. An
alternative approach to identify genes that impact on
[Se]shoot would be to map quantitative gene effects to
specific chromosomal loci (QTL) in mapping populations
of Arabidopsis that differ in their ability to accumulate and/
or tolerate Se, as has been done for several other mineral
elements (Payne et al., 2004).
In the future, it is hoped that knowledge of the physiology of Se accumulation, the interactions between Se and S,
and the genes impacting on Se accumulation and Se
tolerance in Arabidopsis can be used to develop crops with
increased Se content. This will inform strategies to address
the Se deficiency in human diets prevalent in several
countries.
Acknowledgements
This work was supported by the UK Biotechnology and Biological
Sciences Research Council (BBSRC), the UK Department for
Environment, Food and Rural Affairs (Defra) and the European
Union (Project QLK1-1999-00498: Garlic and Health). PP was
supported by a Fellowship from the Food and Agriculture Organization of the United Nations. RES was supported by a BBSRC
CASE Studentship sponsored by Hydro Agri Ltd. (UK). WPS was
supported by a Rank Prize Fund Vacation Studentship. We thank
John Hammond (HRI) for help with the figures.
Appendix
Papers from which data were combined in the residual maximum
likelihood (REML) analysis presented in Fig. 1. Study numbers are
given in brackets.
Arthur MA, Rubin G, Woodbury PB, Schneider RE, Weinstein
LH. 1992. Uptake and accumulation of selenium by terrestrial plants
growing on a coal fly ash landfill. Part 2. Forage and root crops.
Environmental Toxicology and Chemistry 11, 1289–1299. [1–6]
Arthur MA, Rubin G, Schneider RE, Weinstein LH. 1992.
Uptake and accumulation of selenium by terrestrial plants growing on
a coal fly ash landfill. Part 3. Forbs and grasses. Environmental
Toxicology and Chemistry 11, 1301–1306. [7–14]
Bañuelos GS, Ajwa HA, Mackey B, Wu L, Cook C, Akohoue
S, Zambruzuski S. 1997. Evaluation of different plant species used
for phytoremediation of high soil selenium. Journal of Environmental Quality 26, 639–646. [15–18]
Bañuelos GS, Ajwa HA, Wu L, Guo X, Akohoue S,
Zambrzuski S. 1997. Selenium-induced growth reduction in
Brassica land races considered for phytoremediation. Ecotoxicology
and Environmental Safety 36, 282–287. [19–20]
Bañuelos GS, Cardon GE, Phene CJ, Wu L, Akohoue S,
Zambrzuski S. 1993. Soil boron and selenium removal by three
plant species. Plant and Soil 148, 253–263. [21]
Bañuelos GS, Meek DW. 1989. Selenium accumulation in
selected vegetables. Journal of Plant Nutrition 12, 1255–1272.
[22–23]
Bañuelos GS, Zayed A, Terry N, Wu L, Akohoue S,
Zambrzuski S. 1996. Accumulation of selenium by different plant
species grown under increasing sodium and calcium chloride salinity.
Plant and Soil 183, 49–59. [24–27]
Selenium and sulphur nutrition
Baumgartner DJ, Glenn EP, Moss G, Thompson TL, Artiola
JF, Kuehl RO. 2000. Effect of irrigation water contaminated with
uranium mill tailings on Sudan grass, Sorghum vulgare var. sudanense, and fourwing saltbush, Atriplex canescens. Arid Soil Research
and Rehabilitation 14, 43–57. [28–29]
Bell PF, Parker DR, Page AL. 1992. Contrasting selenate-sulfate
interactions in selenium-accumulating and nonaccumulating plant
species. Soil Science Society of America Journal 56, 1818–1824.
[30–41]
Bisbjerg B, Gissel-Nielsen G. 1969. The uptake of applied
selenium by agricultural plants. I. The influence of soil type and plant
species. Plant and Soil 31, 287–298. [42–53]
Davis AM. 1972. Selenium accumulation in a collection of
Atriplex species. Agronomy Journal 64, 823–824. [54]
Davis AM. 1986. Selenium uptake in Astragalus and Lupinus
species. Agronomy Journal 78, 727–729. [55]
Duckart EC, Waldron LJ, Donner HE. 1992. Selenium uptake
and volatilization from plants growing in soil. Soil Science 153,
94–99. [56]
Fleming GA. 1962. Selenium in Irish soils and plants. Soil
Science 94, 28–35. [57–58]
Furr AK, Parkinson TF, Gutenmann WH, Pakkala IS, Lisk
DJ. 1978. Elemental content of vegetables, grains, and forages fieldgrown on fly ash amended soil. Journal of Agricultural and Food
Chemistry 26, 357–359. [59–62]
Gissel-Nielsen G, Bisbjerg B. 1970. The uptake of applied
selenium by agricultural plants. 2. The utilization of various selenium
compounds. Plant and Soil 32, 382–396. [63–82]
Goodson CC, Parker DR, Amrhein C, Zhang Y. 2003. Soil
selenium uptake and root system development in plant taxa differing
in Se-accumulating capability. New Phytologist 159, 391–401.
[83–87]
Gupta UC, Gupta SC. 2002. Quality of animal and human life as
affected by selenium management of soils and crops. Communications in Soil Science and Plant Analysis 33, 15–18. [88–91]
Hamilton JW, Beath OA. 1963. Selenium uptake and conversion
by certain crop plants. Agronomy Journal 55, 528–531. [92–95]
Hamilton JW, Beath OA. 1963. Uptake of available selenium by
certain range plants. Journal of Range Management 16, 261–265.
[96–99]
Hamilton JW, Beath OA. 1964. Amount and chemical form of
selenium in vegetable plants. Journal of Agricultural and Food
Chemistry 12, 371–374. [100–101]
Hossner LR, Woodard HJ, Bush J. 1992. Growth and selenium
uptake of range plants propagated in uranium mine soils. Journal of
Plant Nutrition 15, 2743–2761. [102–107]
Hurd-Karrer AM. 1935. Factors affecting the absorption of
selenium from soils by plants. Journal of Agricultural Research 50,
413–427. [108]
Hurd-Karrer AM. 1937. Selenium absorption by crop plants as
related to their sulphur requirement. Journal of Agricultural Research 54, 601–608. [109–111]
Mbagwu JSC. 1983. Selenium concentrations in crops grown on
low-selenium soils as affected by fly-ash amendment. Plant and Soil
74, 75–81. [112–129]
Miller JT, Byers HG. 1937. Selenium in plants in relation to its
occurrence in soils. Journal of Agricultural Research 55, 59–68.
[130–137]
Pezzarossa B, Piccotino D, Shennan C, Malorgio F. 1999.
Uptake and distribution of selenium in tomato plants as affected
by genotype and sulphate supply. Journal of Plant Nutrition 22,
1613–1635. [132–135]
Pratley JE, McFarlane JD. 1974. The effect of sulphate on the
selenium content of pasture plants. Australian Journal of Experimental Agriculture and Animal Husbandry 14, 533–538. [136–138]
1935
Retana J, Parker DR, Amrhein C, Page AL. 1993. Growth and
trace element concentrations of five plant species grown in a highly
saline soil. Journal of Environmental Quality 22, 805–811. [139]
Robinson WO, Edgington G. 1945. Minor elements in plants,
and some accumulator plants. Soil Science 60, 15–28. [140]
Shane BS, Littman CB, Essick LA, Gutenmann WH, Doss GJ,
Lisk DJ. 1988. Uptake of selenium and mutagens by vegetables
grown in fly ash containing greenhouse media. Journal of Agricultural and Food Chemistry 36, 328–333. [141–148]
Smith GS, Watkinson JH. 1984. Selenium toxicity in perennial
ryegrass and white clover. New Phytologist 97, 557–564. [149]
Terry N, Carlson C, Raab TK, Zayed AM. 1992. Rates of
selenium volatilization among crop species. Journal of Environmental Quality 21, 341–344. [150]
Wadge A, Hutton M. 1986. The uptake of cadmium, lead and
selenium by barley and cabbage grown on soils amended with refuse
incinerator fly ash. Plant and Soil 96, 407–412. [151–153]
Wan HF, Mikkelsen RL, Page AL. 1988. Selenium uptake by
some agricultural crops from central California soils. Journal of
Environmental Quality 17, 269–272. [154–156]
Watson MC, Banuelos GS, O’Leary JW, Riley JJ. 1994. Trace
element composition of Atriplex grown with saline drainage water.
Agriculture, Ecosystems and Environment 48, 157–162. [157–159]
Williams C, Thornton I. 1972. The effect of soil additives on the
uptake of molybdenum and selenium from soils from different
environments. Plant and Soil 36, 395–406. [160–169]
Wu L, Huang Z-Z. 1992. Selenium assimilation and nutrient
element uptake in white clover and tall fescue under the influence of
sulphate concentration and selenium tolerance of the plants. Journal
of Experimental Botany 43, 549–555. [170–177]
Wu L, Huang Z-Z, Burau RG. 1988. Selenium acumulation and
selenium-salt cotolerance in five grass species. Crop Science 28,
517–522. [178–181]
Zayed A, Lytle CM, Terry N. 1998. Accumulation and volatilization of different chemical species of selenium by plants. Planta
206, 284–292. [182]
References
Arvy MP. 1993. Selenate and selenite uptake and translocation in
bean plants (Phaseolus vulgaris). Journal of Experimental Botany
44, 1083–1087.
Asher CJ, Butler GW, Peterson PJ. 1977. Selenium transport in root
systems of tomato. Journal of Experimental Botany 28, 279–291.
Bañuelos GS, Meek DW. 1989. Selenium accumulation in selected
vegetables. Journal of Plant Nutrition 12, 1255–1272.
Bañuelos GS, Meek DW, Hoffman GJ. 1990. The influence of
selenium, salinity, and boron on selenium uptake in wild mustard.
Plant and Soil 127, 201–206.
Barak P, Goldman IL. 1997. Antagonistic relationship between
selenate and sulfate uptake in onion (Allium cepa): Implications for
the production of organosulfur and organoselenium compounds.
Journal of Agricultural and Food Chemistry 45, 1290–1294.
Bell PF, Parker DR, Page AL. 1992. Contrasting selenate–sulfate
interactions in selenium-accumulating and nonaccumulating plant
species. Soil Science Society of America Journal 56, 1818–1824.
Bisbjerg B. 1972. Riso report no. 200: Studies on selenium in
plants and soils. Copenhagen, Denmark : Danish Atomic Energy
Comission Research Establishment Riso.
Bisbjerg B, Gissel-Nielsen, G. 1969. The uptake of applied
selenium by agricultural plants. I. The influence of soil type and
plant species. Plant and Soil 31, 287–298.
Blaylock MJ, James BR. 1994. Redox transformations and plant
uptake of selenium resulting from root–soil interactions. Plant and
Soil 158, 1–12.
1936 White et al.
Bolchi A, Petrucco S, Tenca PL, Foroni C, Ottonello S. 1999.
Coordinate modulation of maize sulfate permease and ATP
sulfurylase mRNAs in response to variations in sulfur nutritional
status: stereospecific down-regulation by L-cysteine. Plant
Molecular Biology 39, 527–537.
Broadley MR, Bowen HC, Cotterill HL, Hammond JP,
Meacham MC, Mead A, White PJ. 2003. Variation in the shoot
calcium content of angiosperms. Journal of Experimental Botany
54, 1431–1446.
Broadley MR, Bowen HC, Cotterill HL, Hammond JP, Meacham MC, Mead A, White PJ. 2004. Phylogenetic variation
in the shoot mineral concentration of angiosperms. Journal
of Experimental Botany 55, 321–336.
Broadley MR, Willey NJ, Wilkins JC, Baker AJM, Mead A,
White PJ. 2001. Phylogenetic variation in heavy metal accumulation in angiosperms. New Phytologist 152, 9–27.
Brown TA, Shrift A. 1982. Selenium: toxicity and tolerance in
higher plants. Biological Reviews 57, 59–84.
Cherest H, Davidian J-C, Thomas D, Benes V, Ansorge W,
Surdin-Kerjan Y. 1997. Molecular characterization of two high
affinity transporters in Saccharomyces cerevisiae. Genetics 145,
627–635.
De Gregori I, Lobos MG, Pinochet H. 2002. Selenium and its
redox speciation in rainwater from sites of Valparaiso region
in Chile, impacted by mining activities of copper ores. Water
Research 36, 115–122.
de Souza MP, Pilon-Smits EAH, Lytle CM, Hwang S, Tai J,
Honma TSU, Yeh L, Terry N. 1998. Rate-limiting steps in
selenium assimilation and volatilization by Indian mustard. Plant
Physiology 117, 1487–1494.
Dhillon KS, Dhillon SK. 2003. Distribution and management of
seleniferous soils. Advances in Agronomy 79, 119–184.
Ellis DR, Salt DE. 2003. Plants, selenium and human health. Current
Opinion in Plant Biology 6, 273–279.
Feist LJ, Parker DR. 2001. Ecotypic variation in selenium accumulation among populations of Stanleya pinnata. New Phytologist
149, 61–69.
Gissel-Nielsen G. 1973. Uptake and distribution of added
selenite and selenate by barley and red clover as influenced by
sulphur. Journal of the Science of Food and Agriculture 24,
649–655.
Gissel-Nielsen G. 1987. Fractionation of selenium in barley and
rye-grass. Journal of Plant Nutrition 10, 2147–2152.
Grieve CM, Poss JA, Suarez DL, Dierig DA. 2001. Lesquerella
growth and selenium uptake affected by saline irrigation water
composition. Industrial Crops and Products 13, 57–65.
Hammond JP, Bennett MJ, Bowen HC, Broadley MR, Eastwood
DC, May ST, Rahn C, Swarup R, Woolaway KE, White PJ.
2003. Changes in gene expression in Arabidopsis shoots during
phosphate starvation and the potential for developing smart plants.
Plant Physiology 132, 578–596.
Hawkesford MJ, Smith FW. 1997. Molecular biology of higher
plant sulphate transporters. In: Cram J et al., eds. Sulphur
metabolism in higher plants. Leiden, The Netherlands: Blackhuys
Publishers, 13–25.
Haygarth PM, Cooke AI, Jones KC, Harrison AF, Johnston AE.
1993. Long-term change in the biogeochemical cycling of
atmospheric selenium: deposition to plants and soil. Journal of
Geophysical Research 98, 16769–16776.
Hopper JL, Parker DR. 1999. Plant availability of selenite and
selenate as influenced by the competing ions phosphate and sulfate.
Plant and Soil 210, 199–207.
Hurd-Karrer AM. 1935. Factors affecting the absorption of
selenium from soils by plants. Journal of Agricultural Research
50, 413–427.
Hurd-Karrer AM. 1937. Selenium absorption by crop plants as
related to their sulphur requirement. Journal of Agricultural
Research 54, 601–608.
Huston DL, Sie SH, Suter GF, Cooke DR, Both RA. 1995. Traceelements in sulfide minerals from Eastern Australian volcanichosted massive sulfide deposits. 1. Proton microprobe analyses of
pyrite, chalcopyrite, and sphalerite, and 2. Selenium levels in
pyrite—comparison with delta-s-34 values and implications for the
source of sulfur in volcanogenic hydrothermal systems. Economic
Geology and the Bulletin of the Society of Economic Geologists
90, 1167–1196.
Ihnat M. 1989. Plants and agricultural materials. In: Ihnat M, ed.
Occurrence and distribution of selenium. Boca Raton, Florida:
CRC Press, 33–104.
Kopsell DA, Randle WM. 1997. Selenate concentration affects
selenium and sulfur uptake and accumulation by ‘Granex 33’
onions. Journal of the American Society for Horticultural Science
122, 721–726.
Kopsell DA, Randle WM. 1999. Selenium accumulation in a rapidcycling Brassica oleracea population responds to increasing
sodium selenate concentrations. Journal of Plant Nutrition 22,
927–937.
Leggett JE, Epstein E. 1956. Kinetics of sulfate absorption by
barley roots. Plant Physiology 31, 222–226.
Martens DA, Suarez DL. 1997a. Mineralization of seleniumcontaining amino acids in two California soils. Soil Science
Society of America Journal 61, 1685–1694.
Martens DA, Suarez DL. 1997b. Selenium speciation of marine
shales, alluvial soils, and evaporation basin soils of California.
Journal of Environmental Quality 26, 424–432.
Maruyama-Nakashita A, Inoue E, Watanabe-Takahashi A,
Yamaya T, Takahashi H. 2003. Transcriptome profiling of
sulfur-responsive genes in Arabidopsis reveals global effects of
sulfur nutrition on multiple metabolic pathways. Plant Physiology
132, 597–605.
Mikkelsen RL, Haghnia GH, Page AL. 1987. Effects of pH and
selenium oxidation state on the selenium accumulation and yield of
alfalfa. Journal of Plant Nutrition 10, 937–950.
Mikkelsen RL, Mikkelsen DS, Abshahi A. 1989a. Effects of
soil flooding on selenium transformations and accumulation
by rice. Soil Science Society of America Journal 53, 122–127.
Mikkelsen RL, Page AL, Bingham FT. 1989b. Factors affecting
selenium accumulation by agricultural crops. In: Selenium in
agriculture and the environment. Soil Science Society of America,
Special Publication 23, 65–94.
Mikkelsen RL, Page AL, Haghnia GH. 1988. Effect of salinity and
its composition on the accumulation of selenium by alfalfa. Plant
and Soil 107, 63–67.
Mikkelsen RL, Wan HF. 1990. The effect of selenium on sulfur
uptake by barley and rice. Plant and Soil 121, 151–153.
Montes-Bayón M, LeDuc DL, Terry N, Caruso JA. 2003. Selenium
speciation in wild-type and genetically modified Se accumulating
plants with HPLC separation and ICP-MS/ES-MS detection.
Journal of Analytical Atomic Spectrometry 17, 872–879.
Murashige T, Skoog F. 1962. A revised medium for rapid growth
and bioassays with tobacco tissue cultures. Physiologia Plantarum
15, 473–497.
Nriagu JO. 1989. A global assessment of natural sources of
atmospheric trace metals. Nature 338, 47–49.
Payne KA, Bowen HC, Hammond JP, Hampton CR, Lynn JR,
Mead A, Swarup K, Bennett MJ, White PJ, Broadley MR.
2004. Natural genetic variation in caesium (Cs) accumulation by
Arabidopsis thaliana. New Phytologist 162, 535–548.
Peterson PJ, Butler GW. 1966. Colloidal selenium availability to
three pasture species in pot culture. Nature 212, 961–962.
Selenium and sulphur nutrition
Pettersson S. 1966. Active and passive components of sulfate uptake
in sunflower plants. Physiologia Plantarum 19, 459–492.
Pezzarossa B, Piccotino D, Shennan C, Malorgio F. 1999. Uptake
and distribution of selenium in tomato plants as affected by
genotype and sulphate supply. Journal of Plant Nutrition 22,
1613–1635.
Pilon-Smits EAH, de Souza MP, Hong G, Amini A, Bravo RC,
Payabyab ST, Terry N. 1999. Selenium volatalization and
accumulation by twenty aquatic plant species. Journal of
Environmental Quality 28, 1011–1018.
Prasad T, Arora SP. 1980. Studies on 75Se accumulation in rice
plants and its effect on yield. Journal of Nuclear Agriculture
Biology 9, 77–78.
Pratley JE, McFarlane JD. 1974. The effect of sulphate on
the selenium content of pasture plants. Australian Journal
of Experimental Agriculture and Animal Husbandry 14, 533–538.
Rayman MP. 2000. The importance of selenium to human health.
Lancet 356, 233–241.
Rayman MP. 2002. The argument for increasing selenium intake.
Proceedings of the Nutrition Society 61, 203–215.
Rose AB. 1997. Selenate-resistant mutants of Arabidopsis. In: Cram
J et al., eds. Sulphur metabolism in higher plants. Leiden, The
Netherlands: Blackhuys Publishers, 217–219.
Rosenfeld I, Beath OA. 1964. Selenium: geobotany, biochemistry,
toxicity, and nutrition. New York: Academic Press.
Shanker K, Srivastava MM. 2001. Uptake and translocation of
selenium by maize (Zea mays) from its environmentally important
forms. Journal of Environmental Biology 22, 225–228.
Shennan C, Schachtman DP, Cramer GR. 1990. Variation in
[75Se]selenate uptake and partitioning among tomato cultivars and
wild species. New Phytologist 115, 523–530.
Shibagaki N, Rose A, McDermott JP, Fujiwara T, Hayashi H,
Yoneyama T, Davies JP. 2002. Selenate-resistant mutants of
Arabidopsis thaliana identify Sultr1;2, a sulfate transporter required for efficient transport of sulfate into roots. The Plant
Journal 29, 475–486.
Shrift A. 1969. Aspects of selenium metabolism in higher plants.
Annual Review of Plant Physiology 20, 475–494.
Smith FW, Ealing PM, Hawkesford MJ, Clarkson DT. 1995.
Plant members of a family of sulfate transporters reveal functional
subtypes. Proceedings of the National Academy of Sciences, USA
94, 11102–11107.
Smith FW, Rae AL, Hawkesford MJ. 2000. Molecular mechanisms
of phosphate and sulphate transport in plants. Biochimica et
Biophysica Acta 1465, 236–245.
Smith GS, Watkinson JH. 1984. Selenium toxicity in perennial
ryegrass and white clover. New Phytologist 97, 557–564.
Soltanpour PN, Workman SM. 1980. Use of NH4HCO3-DTPA
soil test to assess availability and toxicity of selenium to alfalfa
plants. Communications in Soil Science and Plant Analysis 11,
1147–1156.
Suarez DL, Grieve CM, Poss JA. 2003. Irrigation method affects
selenium accumulation in forage Brassica species. Journal of
Plant Nutrition 26, 191–201.
Swaine DJ. 1962. Technical Communication 52: The traceelement content of fertilisers. London : Comonwealth Agricultural
Buraux.
Takahashi H, Watanabe-Takahashi A, Smith FW, Blake-Kalff
M, Hawkesford MJ, Saito K. 2000. The roles of three functional
sulphate transporters involved in uptake and translocation
of sulphate in Arabidopsis thaliana. The Plant Journal 23,
171–182.
1937
Takahashi H, Yamazaki M, Sasakura N, Watanabe A, Leustek T,
de Almeida Engler J, Engler G, Van Montagu M, Saito K.
1997. Regulation of sulfur assimilation in higher plants: a sulfate
transporter induced in sulfate-starved roots plays a central role in
Arabidopsis thaliana. Proceedings of the National Academy of
Sciences, USA 94, 11102–11107.
Terry N, Zayed AM, de Souza MP, Tarun AS. 2000. Selenium in
higher plants. Annual Review of Plant Physiology and Plant
Molecular Biology 51, 401–432.
Thompson R, Welham SJ. 2000. REML analysis of mixed models.
In: Payne RW, ed. The guide to GenStat—part 2: statistics.
Oxford, UK: VSN International, 413–503.
Tripathi N, Misra SG. 1974. Uptake of applied selenium by plants.
Indian Journal of Agricultural Science 44, 804–807.
Ulrich JM, Shrift A. 1968. Selenium absorption by excised
Astragalus roots. Plant Physiology 43, 14–20.
Vange MS, Holmern K, Nissen P. 1974. Multiphasic uptake of
sulfate by barley roots. I. Effects of analogues, phosphate, and pH.
Physiologia Plantarum 31, 292–301.
Vickerman DB, Shannon MC, Bañuelos GS, Grieve CM, Trumble JT. 2002. Evaluation of Atriplex lines for selenium accumulation, salt tolerance and suitability for a key agricultural insect
pest. Environmental Pollution 120, 463–473.
Vidmar JJ, Tagmount A, Cathala N, Touraine B, Davidian J-CE.
2000. Cloning and characterization of a root specific high-affinity
sulfate transporter from Arabidopsis thaliana. FEBS Letters 475,
65–69.
Wallace A, Mueller RT, Wood RA. 1980. Selenate toxicity effects
on bush beans grown in solution culture. Journal of Plant
Nutrition 2, 107–109.
White PJ. 2003. Ion transport. In: Thomas B, Murphy DJ, Murray
BG, eds. Encyclopaedia of applied plant sciences. London:
Academic Press, 625–634.
Wu LL. 1998. Selenium accumulation and uptake by crop and
grassland plant species. In: Frankenberger WT, Engberg RA, eds.
Environmental chemistry of selenium. New York: Marcel Dekker,
657–686.
Wu L, Huang Z-Z. 1992. Selenium assimilation and nutrient
element uptake in white clover and tall fescue under the influence
of sulphate concentration and selenium tolerance of the plants.
Journal of Experimental Botany 43, 549–555.
Wu L, Huang Z-Z, Burau RG. 1988. Selenium acumulation and
selenium-salt cotolerance in five grass species. Crop Science 28,
517–522.
Yoshimoto N, Takahashi H, Smith FW, Yamaya T, Saito K. 2002.
Two distinct high-affinity sulfate transporters with different inducibilities mediate uptake of sulfate in Arabidopsis roots. The
Plant Journal 29, 465–473.
Zayed A, Lytle CM, Terry N. 1998. Accumulation and volatilization of different chemical species of selenium by plants. Planta
206, 284–292.
Zayed AM, Terry N. 1992. Selenium volatilization in broccoli as
influenced by sulfate supply. Journal of Plant Physiology 140,
646–652.
Zayed AM, Terry N. 1994. Selenium volatilization in roots and
shoots: effects of shoot removal and sulfate level. Journal of Plant
Physiology 143, 8–14.
Zhang Y, Pan G, Chen J, Hu Q. 2003. Uptake and transport of
selenite and selenate by soybean seedlings of two genotypes. Plant
and Soil 253, 437–443.