Indian J.Plant Physioi., Vol. XXX, No.4, pp.
321-331,
1987
,
,
PHYSIOLOGICAL SIGNIFICANCE'OF ZINC AND IRON-RETROSPECT AND PROSPECT O.K.OARO·
Department of Plant Physiology, Institute of Agricultural Scienc~s",
Banaras Hindu University, Varanasi-al 005 The constraint arising out of iron and zinc deficiency in the Indiall'
agricultural field is recurringly expanding owing to a general negligence in the
of such vital elements. The level of mineral nutrients in soil, or of an externally
applied fertilizer, is an important factor that seems to influence the growth and
yield potentiality of a crop. If the level of an element is lower than the optimum,
the growth will not be up to the mark, and the plants may show symptoms of
deficiency. On the other hand, if the soil nutrient is above the optimum requirement
of crop, it may develop signs of toxicity. So it is important to find out a suitable
level of nutrient elements for different crops. Coupled with these, the processes.
involved in senescence are important because they occur during grain fill, and
evidences suggest that earl} senescence may be yield limiting. Iron is involved ill
energy producing and utilizing processes in plants and is important in many redox.
reactions. In higher plants the essentiality of Fe for development and maintenance
of photosynthetically active tissues has been recognized because Fe is involved in
the synthesis of chrolophyll (Miller et al., 1984). Presently, Zn is also recognised
as an essential .compotent in several dehydrogenases, proteinases etc. A large
number of growth and metabolic effects of Fe and Zn remain unexplained relative
to their roles as biocatalysts. Furthermore, iron is an integral part of the nitrogen­
fixing complex, i.e., nitrogenase, leghaemoglobin and ferredoxins (Evans and
Russel, 1971). While presenting the work done at Banaras Hindu University with
my reseerch colleague Dr. A, Hemantaranjan, I would cover the physiological
significance of zinc fertilization in wheat and the effect(s) of iron and zinc fertiliza­
tion on senescence in french bean (PhaseolWl vulgaris L.) with reference to nodula­
tion and nitrogen fixation.
use:
EtI'eet of various levels of zinc on the growth and yield of wheat Triticum aestivum (1..)
Fertilization of zinc in the form of zinc sulphate produces distinct improve­
ment in the growth and yield of wheat plants. As shown in Table 1, there are
*Based on Presidential address delivered at 29th AnnI;Ull General Body meeting of the Indian
societY for Plant Physiology at the University of Agricultural Sciences. Dbarwad (Kamataka) 011
December 30,1986,
~:':~~:~~~F'
I
322
O.Jt.·GARG
Table 1: Effect of various levels of zinc on indole-3-acetic acid content, chlorophyll
'a' and chlorophyll 'b' contents of leaves in wheat at different stages of
growth, average of 4 replications in each case
Treatment
Zn IIII kg-I soil
Age: of plants (daya after aowiq)
SO
65
80
95
1.10
1.20
1.30
1.45
1.60
1.35
0.88
0.00
1.10
1.20
1.25
1.45
1.20
0.65
1.45
2.30
2.65
3.50
3.65
3.00
0.85
0.00
1.00
1.15
1.40
1.45
1.20
078
3.15
4.15
5.10
5.95
6.10
5.20
1.18
0.85
2.00
2.60
3.50
3.55
3.00
1.00
A. Indole-3-ocetic ucid ("" kg-I fresh weight)
o (Control)
3
6
9
12
15
C.D. at5%
1.10
1.20
1.40
1.50
1.60
1,30
0.85
1.20
1.30
1.50
1.60
1.80
1.50
0.80
B. ChlorophyU 'a' (mg g-l fresh weight)
o (Control)
3
6
9
12
IS
C.D.at5%
2.15
3.20
4.25
5.00
5.15
4.65
1.12
3.00
4.00
5.10
5.90
6.00
5.30
l.S5
C. Chlorophyll 'b' (mg g-1 fresh weight)
o (Control)
3
6
~
12
IS
C.D. at 5%
2.55
4.00
5.20
6.45
6.60
5.45
1.00
3.95
5.10
7.00
8.?5
8.90
7.50
1.22
increases in indole-3-acetic acid, chlorophyll 'a' and 'b' contents in wheat leaves
specially at 9 acd 12 mg kg-I soil (ppm) at 65 day of growth. The growth
characters viz., area of leaf and total dry weight of plants (Table 2) reveal the
same trend of increase and decrease at the levels of 9 and 12 mg kg- I soil of added
zinc. However, a decline may be seen at 15 mg kg- I soil. The yield attributes viz..
number of ear heads, yield of seeds per plant and the bulk weight of 1000 seeds
were improved with the progressive rise of zinc in the soil, up to 12 mg kg_I. as
shown in table 3. It is possible because of the greater availability of this element
in the soil, This happens because zinc plays a specific role in plant metabolism,
particularly in the synthesis of auxin (Tsu~ 1948), which is essentially required in
the growth and development of plants. Besides this, it is a constituent of several
important enzymes like carbonic anhydrase, alcoholic dehydrogenase, etc, (Vallee
J
r
a
323
PHYSIOLOGICAL SIGNIFICANCE OF ZINC AND IRON
Table II : Effect of various levels of zinc on the area of leaves and total dry
matter content (g) of wheat at different stages of growth; average of 4
replications in each case
Treatment
Zn mg kg-l soil
Age of plants (days after sowing)
50
65
80
95
A. Areao/lea/(cm)
o(Control)
3
6
9
12
15
C.D. at 5%
33.20
42.07
49.64
59.95
61.27
44.49
0.08
60.62
72.41
76.85
111.65
113.25
87.75
0.13
69.75
84.60
95.87
115.63
121.86
92.11
0.81
73.06
89.46
103.33
117.00
124.10
94.00
0.99
16.40
16.83
19.63
24.38
18.91
20.05
23.54
27.40
27.97
21.25
2.39
B. Total dry Weight (g)
o (Control)
3
6
9
12
15
C.D.at5%
5.30
6.16
7.65
9.46
10.20
7.84
2.51
11.55
12.47
14.78
17.90
18.58
15.32
2.27
25.60
18.86
4.76
Table III : Effect of various levels of zinc on certain yield characters of wheat at
the time of harvest; average of 4 replications in each Case
Treatment
Zn rog kg-l soil
Murober of ear
heads
Length of ear
heads
(em)
o (Control)
3
6
9
12
15
C.D. at 5%
10.00
11.00
12.00
15.00
16.00
13.00
1.28
9.74
11.25
11.50
12.35
12.45
11.50
1.70
Yield of seeds
per plant
(g)
13.58
18.65
19.95
22.78
22.95
20.00
0.06
Bulk weight
of 1000
seeds (g)
38.34
44.10
47.05
52.90
53.25
45.38
0.16
and Wacker. 1970). Synthesis of nucleic acid and protein also essentially require
zinc (Scrutton et al., 1971). This is further supported with the observation on
physiological changes (Table 1). Porokhnevich and Vakulchuk (1975) reported an
increase in the number and photoactive surface of chloroplasts per unit leaf
area without any decrease in the chlorophyll content of chloroplasts under
the influence of applied zinc, which ultimately increased the grain yield of
barJey. It may be presumed that the enzyme content is increased due to
324
O.L'GAllG
the 'enhanCed levers of zinc which might have favoured chlorophyll content in
leaves even after the post-flowering stage (Voica. 1969). Indole-3-acetic acid is
also responsible for the inhibition ot' the destruction of chlorophyll 'a' and 'b'
{Mishra and Biswal, 1980; Hemantaranjan and Garg, 1984). Obviously, these
phYSiological chmrges could have led the plants tOr better photosynthesis for a
longer period and resulted into the greater dry matter production and improved
,grain yield. Yield decreased at higher levels of zinc application, as it was observed
at IS rng kg- I soil of zinc, which may be due to the toxic effect of zinc at this level.
In the light of vital role played by zinc in plant metabolism and of results
()f this investigation, if there is greater availability of zinc at cellular level within
an optimum range (9 and 12 mg kg- I soil), the growth and yield potentiality of
.of plants will stand improved.
hoo and zioc fertilizatioD 011 leaf seoeseeaee iD freoeb beea (Phaseolus .ulgaris L.)
The results indicate that chlorophyll 'a' and 'b' IAA and nitrate reductase
activity in leaves increased with increased concentrations of Fe. However, a
.decline in the above physiological changes were noted at 20 mg kg- I soil of Fe
(Table 4 and S). These were found lObe increased at the levels of zinc application
too. Increases in the amount of chlorophyll 'a' and 'b', indole-3-acetic acid
concentrations and nitrate reductase activity were recorded in leaves treated with
the combination of Fe and Zn. The combinations of 5 Fe
5 Zn Jp.g kg-I soil
.howed maximum increases in all the parameters noted above. Iron @ 10 mg kg-1
also increased nitrate reductase activity compared to individual Fe or Zn treat­
ments. The increases were optimum at 40 day stage. beyond which a gradual
.decrease was recorded. These decreases were rapid in control plants which showed
lower amounts of chlorophyll in the yellow leaves. Treated plants remained healthy
and green at the later stage of growth. This indicated that chlorophyll destruction
:started at the post-flowering stage (40 to 4S days after sowing) in control plants,
which is considered early senescence, and chlorophyll 'a' and 'b' would reduce
photosynthetic duration. One of the striking phenomen()n of senescence is the loss
.of chlorophyll (Patterson and Moss, 1979; Hemantaranjan and Garg, 1984 and
Garg et aI., 1986). During senescence, enzyme and structural protein lysis follow
rapidly after membrane degradation of chloroplasts. The kil;letics of decay have
been described for a number of stroma enzymes (Hall et al., 1979; Peoples and
Dallings, 1978). Carbonic anhydrase, a zinc metallo-enzyme, is largely localized in
the stroma of chloroplasts where it exerts a buffering action by mediating PH
.changes and prevents chloroplasts proteins from being denatured (Jacobson et al.,
1975). Chlorophyll is formed in higher plants from the precursor ct-aminolevuUnic
acid. This pathWay may be activated by Fe,· and may be related to aconitase
+
325
PHYSIOLOGICAL SIGNIFICANCE OF ZINC AND UlON
Table IV : Effect(s) of Fe and Zn fertilization on chlorophyU 'a' and 'b' of french
bean leilves at three dates of growth
Chlorophyll 'a'
Treatment
Fe' Zn
20 days
mg kg-1 soil
o (Control)
0
5
0
0
10
0
20
5
0
0 10
0 20
5
5
]0 10
20 20
C.D. at 5%
1.30
2.00
2.90
1.90
J.85
1.90
2.00
3.50
3.15
3.00
0.90
40 days
Chlorophyll 'b,
60 days
mg g-1 fresh weight
2.40
1.80
3.30
3.00
3.65
4.00
3.10
2.90
2.75
3.00
2.80
3.10
3.25
2.96
5.60
5.90
5.00
4.75
4.50
4.20
1.20
1.00
20 days
2.25
2.95
3.85
2,80
2.70
2.85
2.95
4.45
4.15
3.95
0.90
40 days
60 days
mg ar1 fresh weight
3.85
3.05
4.95
4.50
5.15
5.90
2.25
3.95
4.15
3.80
4.20
3.85
4.40
4.00
7.05
6.65
6.15
5.80
5.65
5.lS
1.30
],05
Table V : EffcctsCs) of Fe and Zn fertilization on indole-3-acetic acid and nitrate
reductase activity of french bean leaves at different stages of growth
Treatment
Zn
Fe
Indole-3-acetic acid
20 days
mgkg-l soH
o (Control)
0
0
5
0
10
0
20
0
5
0 10
0 20
5
5
10 10
20 20
C.D.atS%
40 days
mg g-l fresh weight
1.21
0.96
1.42
1.10
1.44
1.13
1.40
1.08
1.20
1.56
1.28
1.63
1.67
1.33
1.51
1.88
1.58
1.94
1.44
1.71
0.36
0.90
Nitrate reductase activity
60 days
20 days
40 days
p. mol h-l
0.91
1.31
1.38
1.33
I.4S
1.51
1.58
1.81
1.80
1.60
0.22
0.30
1.21
1.41
1.07
1.00
1.04
1.06
2.12
2.10
2.06
0.31
60 days
ar1 fresh wt
1.32
2.33
2.66
2.26
2.10
2.20
2.23
3.48
3.44
3.40
0.39
1.22
2.21
2.57
2.16
2.02
2.11
2.14
3.39
3.33
3.21
0.41
activity and the formation of ferredoxin. Ferredoxin may be necessary to activate
the a-aminolevulinic acid (ALA) synthesizing enzyme. With Fe-deficient plants,
ferredoxin would be limiting and could directly affect chlorophyll biosynthesis
(Miner et aI" 1984). The increases in the level of IAA might have delayed the
senescence of leaves in Zn- and Fe-treated plants since IAA is known to inhibit
~hlorophyll· loss during senescence in wheat (Mishra and Biswal, 1980;
Hemantaranjan and Garg, 1984). The higher increases of IAA in the Zn-treated
''F-;;;.:'~c~~'':;::;;c':~~pt
I
!
326 O.K. GARG
plants than Fe-treated plants may have been related with Zn-involvemcnt in
auxin metabolism (Takaki and Kushizaki, 1970). Further, maximum nitrate
reductase activity at the 4O-day stage of growth may have been because of rapid
growth and requirement fer higher energy to reduce N. Nitrate reductase in an
Fe-containing enzyme and Fe may play a key role in changing the oxidation
state through electron transfer (Hall, 1977; Smith, 1984). A marked reduction in
nitrate reductase activity of control plants indicated the importance of Fe and Zn
individually or in combination for the maintenance of nitrate reductase activity in
plants. This led to the conclusion that iron alone or in combination with zinc
applied contri buted to the inhibition of senescence in french bean plants.
boa and zinc fertilization in relation to nodulation aDd nitrogen fixation in french
bean
Iron alone (at a concentration of 5 or 10 mg kg- 1 soil) as well as in
combination with the idential concentration(s) of zinc, initiated significant nodule
formation (Table 6). The nudule processing under the laboratory conditions have
shown the appearance of N:~ -fixing bacteroids Rhizobia sp.) inside the newly
formed nodules. As a matter of fact, french bean plants grown in Varanasi soils.
lack nitrogen-fixing nodules. The availability of iron and zinc in the soil is not
more than 0.60 and 2-3 mg kg- 1 soil respectively, which is near the deficiency
level in the soil. During the course of investigations no exogenous supplementation
of Rhizobium was made in the experimental soil. At a threshold level of 5 mg kg-I
soil the two salts (ferrous sulphate and zinc sulphate) exhibited maximum nodula­
tion and an increase in the leghaemoglobin content. Fe at 5 and 10 mg kg-I soil
Table VI: Effects(s) of Fe and Zn on nodule number, dry matter yield and their
leghaemoglobin content in french been at two dates of growth
Treatment
Fe
Zn
Mumber of nodules
40 days
mg kg-1 soil
o(Control)
0
0
5
0
10
0
20
20
5
0
10
0 20
5
5
10 to
20 20
C.D.at5%
80 days
4 plants-1
0.0
0.0
46.0
30.0
47.0
59.0
21.0
30.0
22.0
14.0
19.0
27.0
34.0
21.0
76.0
59.0
70.0
54.0
51.0
66.0
18.0
11.0
Dary matter yield
40 days
g pOt-1
0.0
0.10
0.19
0.07
0.05
0.06
0.07
0.26
0.22
0.21
0.08
80 days
0.0
0.95
1.10
0.77
0.41
0.60
0.79
1.30
1.18
1.13
0.18
Lcghaemoglobin
40 days
80 days
mg 4 plants- 1
0.0
0.0
0.61
0.06
0.32
0.12
0.03
0.49
0.02
0.33
0.52
0.03
0.52
0.03
0.18
1.04
0.89
0.16
0.84
0.15
0.16
0.10
b 1
q ".
r
PHYSIOLOGICAL SIGNIFICANCBOF ZINC AND IRON
327
.and Zn at 5, 10 and 20 mg kg~1 soil showed a trend of increase in the number of
nodules, dry matter yield and leghaemo81obin content. In contrast, Fe (@ 20 mg
kg~1 soil) alone or in combination with Zn (@ 20 mg kg-I soil) revealed a consider­
able decrease in the above at both the stages.
In the present investigation a significant increase in total dry matter and
in l'il'O nitrogen fixation were also found on the addition of either of the two salts
(alone or in combination) at a concentration of 5 or 10 mg kg- I soil (Table 7). at
all the three stages of growth. Finally. at harvest, the data recorded for the yield
attributes were also better over the control (Tab1e 8) and specially at a concentra­
1ion of 5 or 10 mg kg- 1 soil of the two salts (alone or in combination.
The increases in nodulation and leghaemoglobin content at different levels
of Fe and Zn are probably associated with their specific physiolopical roles in
-plant and Rhizobium growth up to a certain level; the decrease in activities with
the higher Fe and/or Zn levels might be due to a possible inter-molecular inter­
ference with the plant/microbe nutrition. Rai et al. 0984) reported that iron and
its inter relationship with other micronutrients is an important factor controlling
1he nitrogenase-make up and activity inside the nodules. Extrinsic factors, which
limit the synthesis and functions of leghaemoglobin, ferredoxin and active iron
(Fe++) of nodules, are of great importance. The in vivo nitrogen fixation might be
due to the fact that at the levels of initial fixation of dinitrogen, the energetic
-electrons required for the reduction are carried by ferredoxin, a low molecular
weight protein containing several per cent iron (Dart, 1979). It is all the more
important to mention at this point that nitrogenase activity is due primarily to an
iron-molybdenum (Fe-Mo) co-factor (Pienkos et al., 1977 and Shah el al., 1977)
which is an active site of component-I of nitrogenase and the site to which
molecular nitrogen binds and is subsequently reduced during Nz-fixation
{Shah el al., 1978}. Naturally then, an Fe-deficiency below the critical level
is expected to block the formation of nitrogenase enzyme precursor.
Therefore, on supplementation with a readily assimilable Fe-salt. the Fe­
deficiency was made up leading to possible activation of the nitrogenase complex•
.and hence the significant nitrogen fixation. Such roles of exogenous Fe has already
been examined in a Nz-fixing photosynthetic microbial system (Vaishampayan,
1984)•.
The fore going discussion stimulate the idea that iron may affect the produc­
1ion of nitrogen by french bean plants in three ways. It may act directly on the
initiation, development and enzymatic functions of nodules, it may influence the
.efficiency of host~Rhizobium symbiosis, or it may play an essential role in plant'
metabolism and growth independent of symbiosis. The role of zinc in the initiation
j;
328
O.K. GAllO
matter
Table VII : Effectll(s) of Fe and Zn fertilization on the total dry
yield and
total nitrogen content in french bean at different stages of growth
Il1I q-l soil
0 ·0
0
5
0
10
0
20
0
5
0 10
0 20
5
5
.0 10
20 20
CD. at 5%
Total oitropn
Total dry matter
Treatment
Zn
Fe
40 days
80 days
9.72
12.96
18.92
11.92
12.80
·.5.92
13.90
27.20
24.88
22.72
2.20
g 3 plants-1
23.94
33.31
37.11
32.14
33.00
36.13
36.00
·48.35
45.66
42.24
1.90
106 days
(Maturity)
36.00
51.13
54.00
45.41
47.44
51.60
51.43
63.00
60.61
57.13
1.98
40 days
50.00
60.60
67.20
58.50
54.39
57.00
58.10
74.80
72.00
69.00
3.10
80 days
106 days
(Maturity)
m, 3 plants-1
191.20
300.10
326.00
275.50
251.SO
265.00
270.50
354.00
348.00
335.00
4.10
372.50
603.60
655.00
556.80
507.30
538.60
543.80
724.90
702.60
682.30
11.10
Table VIII: Effect(s) of Fe and Zn fertiliZJltion on certain yield characters of
french bean
Treatmcnt
Zn
Fe
mg
I
5
10
20
0
0
0
5
10
Number of pods
per plant
Number of seeds
per pod
Weight of seeds
per plants (g)
Wci8btof
1000 seeds (g)
q-l soil
o(Control)
0
0
0
5
10
20
5
10.
20 20
C.D. at5%
4.00
6.00
7.00
6.00
6.00
6,00
7.00
10.00
9.00
6.50
1.80
4.00
5.00
5.SO
4.50
5.00
5.00
5.50
6.00
6.00
5.00
2.00
6.15'
14.00
18.40
12.15
14.98
16.00
18.00
32.20
28.24
16.71
3.10
410.20
463.00
479.00
442.50
440.00
446.00
451.00
538.80
529.20
508.00
49.00
of nodules, increase in leghaemoglobin content, total dry matter production; total
nitrogen and yield attributes cannot be ruied out at the moment. There is report
that zinc nutrition has been helpful in nodulation and nitrogen fixation in chickpea
(Yadavand Lhukla. 1983). The findings of Clarkson and Hanson (1980) strenthen
the facts mentioned above to a great extent and convey an important informatioD
that plant cell has need for stable metalloenzyme eomplexes in which co-ordinatioD
is b~iadJy tetrahedral and zinc has been reported to be the most competent
J-.
PHYSIOLOGICAL SIGNIFICANCE OF ZINC AND IRON
element to fulfil this need. Its saturated d orbitals and small size favour tetra­
hedral complexes which give importance of zinc by taking part in various processes
of plant metabolism. This is very clear from the present experimental findings,
especially when zine was combined with iron. This lead to the conclusion that the
french bean plants which grow in the soils of Varanasi lack the N2-fixing nodules.
This may be in response to the proper nutritional deficiency apparent from the
fore going experiments. The addition of various levels of Fe and/or Zn to Varanasi
soils created a condition conducive to the formation of nodules morphologically
similar to those present in the legume plants of other areas. Our microbial culture­
experiments have confirmed the bssociation of some Ni1ixing Rhizobium strain
in these nodule$. and the phenomena clearly indicate the existence of Rhizobia in
and/or around the Varanasi soil. However under specific nutritional state of tbe
soil. as stated above, these Rhizobia can undergo a symbiotic relation with bean
plants for a significant yield of nitrogen and can finally increase the yield of french
bean plants (Table 8) by the efficient nitrosen f>upply to the photosynthetic parts
and delaying senescence of leaves.
CONCLUSIONS
In spite of the specific and significant role(s) of iron and zinc in plant
metabolism zinc and/or iron deficiency in crop plants is prevelent in Indian
agricultural fields. During the last few years some critical experiments were
performed with the cereal crop wheat and pulse crop french bean with the applica­
tion of zinc (in wheat) and zinc and iron (in french bean) in the deficient soils of
Varanasi (Zn-availability-O.60 mg kg- 1 soil and Fe-availability-2.0 to 3.0
mg kg- 1 soil). The effect of various levels of zinc on the growth and yield of
wheat proved that increasing levels of zinc upto 12 mg kg-1 soil provided required
availability of this element to wheat plants and thereby improved their growth and
yield.
Experiments on the effect(s) of iron and/or zinc fertization on the yield of
french bean with special reference to senescence showned tbat iron alone or in
combination of zinc contributed to tbe inhibition of senescence in french bean
leaves and increased the yield. Furthermore, french bean plants grown in Varanasi
soils lack nitrogen fixing nodules. The addition of various levels of Fe and Zn to
Varanasi soils (especially @ 5 or 10 mg kg- 1 soil) created a condition conducive to
the formation of nodules morpholosically similar to tbose present in legume
plants grown elsewhere. Our results indicated that Rhizobia sp. existed in soils of
Varanasi. However, under certain nutritional status of the soil (low Fe and Zn),
these Rhizobia probably fail to make a functional symbiotic nitrogen-fixing
complex in the bean plants.
330
O.K. GAllG
On the basis of the conclusions, discussed, it may be suggested that zinc and
iron command a great significance in maintaining a 'physiological balance' in crop
plants. The growers should, therefore, take care that these nutrients are not
<lecificient in the soil.
It is optimistically expected that major advances in combatting zinc and
iron problems will continue to be made in the coming years by utilizing genotypic
variation. The door that has been opened by such investigations will permit the
researchers to examine the physiological significance and practicability of zinc and
iron nutrition in other economic crops.
REFERENCES
OarkSOIl, T. and Hanson. B.J. (1980). 'I'b8 mineral nutrition of higher plants. Ann. Rev. Plant
Physiol., 31 : 239·298.
Dart, P. 1979.10 : A Treatise on Dinitropn FIXation, Section UI (R.W.H. Hardy and W.S.
Silver Eds.). lohn Wiley and Sons, Inc., New York, p. 419.
Evans. H.J. and Russel, S.A. (1971). lh : The Chemistry and Biochemistry of Nitrogen fixation,
l.R. Postgate (Ed.), Plenum Press, London, pp. 191-215.
(larg, O.K., Hemantaranjan A. and Ramesh. C. 1986. Effect of iron and zinc fertilization on
senescence in french bean (Piroseolus vulgaris L.). I. Plant Nutr., 9: 251-266.
Hall, D.G. 1977. Iron-Sulphur proteins and energy conversion systems. p. 67-80. In R. Buvet, J.J.
Allen and J.R. Massue (ed). Living systems as energy con'ferters. North Holland Publ.,
Amsterdam.
Han, N.P., Keys. J.A. and Merrett, J.M. (1978). Ribulose di-phosphate corboxylase protein
during flag leaf senescence. I. Exp. Bot., 29 : 31-37.
Hemantaranjan, A. and Garg. O.K. (1984), Effect of zinc fertilization on the senescence of wheat
varieties. Indian I. Plant Physiol., Z8 : 239-246 •
.Jacobson, B.S., Pong, P. and Health, R.L. (1975). Carbonic anhydrase of spinach. Studies on its
location, inhibition and physiological fonction. Plan t Physiol., SS : 468-474.
Miller, G.W., Pushnik, J.C. and Welkie G.W. (1984). Iron chlorosis, a world wide problem, the
relation of chlorophyll biosynthesis to iron, I. Plant Nutr., 7 : 1-22.
Misbra, A.N. and Biswal, U.C. (1980). Effect of phytohormones on chlorophyll degradation
during agini of chloroplasts in vivo and in vitro. Protoplasma. lOS: 1-8.
Patterson, T.G. and Moss, D.N. (1979). Senescens in fiield grown wheat. Crop Sci.,
l' :635-640..
Peoples, M.B. and Dallings, M.J. (1978). Degradation of ribulose 1-5 diphosphate carboxylase
by proteolytic enzymes from crude extracts of wheat leaves. Planta, 188: 153-160.
Pienkos. P.T., Shan V.K. and Brill, W.J •. (1977). Molybdenum cofactor from molybdoenzymes and
in vitro reconstitution of nitrogenase and nitrate reductase. Proc. Nat. Acad. Sci.
U.S.A., 74: 5468-5471.
Porokhnevich, N.V. and Vakulchuk, M.N. (1975). Changes in plastid apparatus per unit leaf area
and yield of barley given different zinc rates. I. Agrokhimiya. 8 : 90·94.
PHYSIOLOGICAL SIGNIFICANCE OF ZINC AND IllON
,
i
331
Rai, R., V. Prasad, Choudhary S.K. and Sinha. N.P. (1984). Iron nutrition and symbiotic nitrogen
fixation of lentil (Lens cuJinaries) genotypes in calcareous soil. J. Plant Nutr., 5 : 905­
913.
Rawlings, I. Shah. V.K., ChisneIl, J.R. Brill, W.l. Zimmerman, R. E. Munk and W.H. Orme­
Jobnson (1977). Novel metal cluster in the iron-molybdenum co-factor ofnitrogena~
(nitrogen-fixation). J. Bioi. Chem.,2.53: 1001-1004.
Scrutton, M.C., Wu, C.W. and Goldthwait, D.A. (1971). The presence and pOssible role of zinc
in the RNA polymerase obtained from E. coli. Proc. Nat. Acad. Sci., U.S., 68 : 2497­
2501.
Shah, V.K., Cbisnell l.R. ahd Brill, W.l. (1977). lsnlation of an iron-molybdenum co-factor from
nitrogenase (nitrogen-fixation). Proc. Nat. Acad. Sci., U.S.A., 74 : 3249-3253.
Shah, V.K., Chisnell J.R.land Brill, W.J. (1978). Acetylene reduction by the iron-molybdenum
co-factor from nitrogenase. BiQchem. Biophys. Res. Commun., 81 : 232-236.
Smith, B.N. (1984). Iron in higher plants: storage and metabolic role. J. Plant Nutr., 7 : 759-766.
Takaki, H. and Kushizaki. M. (1970), Accumulation offree tryptophan and tryptnmine in zinc.
deficient maize seedlings. Plant and Cell Physiol., Z : 793-804.
Tsui, C. (1948). The role of zinc in auxin synthesis in tomato plants. Amer. J. Bot., 3S : 172-179.
Vallee, B.L. and Wacker, W.E.C. (1970). In 'Proteins' (H. Neurath ed.) 2nd ed., S. Academic
Press, New York.
Vaishampayan, A. (1984). Copper -iron interactions. in a N1·fixing cyanobacterium. J. Plant Nutr.~
7: 567-573.
Voica, C. (1969). Influence of B, Mn, Cu, Zn and Mo on some of the phyyioiogical processes of
seedlings of barley cv. Bruker. Studii Cere. BioI., Zl : 151-155.
Yadav, O.P. and Shukla, U.C. (1983). Effect of zinc on nodulation and nitrogen fixation in
chickpea (Cicer arietinum L.) J. A,ric. Sci., 101 : 559-563.