Plant Physiol. (1967) 42, 1797-1799
Short Communication
Photosynthesis in Chlorophyllous Stem Tissue and Leaves
of Cercidium floridum: Accumulation and
Distribution of 14C from 14C021
Michael S. Adams2, Boyd R. Strain, and Irwin P. Ting
Department of Life Sciences and Dry-Lands Research Institute,
University of California, Riverside, California 92502
Received August 3. 1967.
The contribttiion of ph,otosynthesis by green
stem tissue to the total carbohydrate economy of
plants has been of interest to physiologists and
ecologists (6,9, 10, 11, 12). Priestley (11) suggested thait it seemed unlikely that stem photosynthesis contributed significantly to the requirements o,f most deciduous trees during leafless
seasons. Pearson and Lawrence (9,10) measuired
photosynthetic activity in the stem cortex of the
quaking a'spen (Populus tremuiiiloides) with an iodinestarch test, and suiggested that corticular photosynthesi,s was a significant factor in its distribultion
within a maAinly coniferous vegetative formation.
Strain and Johnson (12) measuired CO., absorption
by green stems of P. tremuloides and agreed wvitlh
the latter w;orkers. With the desert shruib occotillo
(Fouquieria splendens), however, Mooney and
Strain (6) were nolt able tio detect net CO., absorption dulring a drought-induiced leafless condition.
Nevertheless, the adaptive significance of stem
photosyntheslis by woody desert perennials, which
mnay be leafless dturing dry seasons, remains an
attractive hypothesis. In this report, we present
evidence that stem photosynthesis by the Palo Verdle
(Cercidium floridumt Benth.) is quiatlitatively sim'ilar
to leaf photosynthesis when the plants are in leaf,
and is of such a magnituide that it cou1ld be biologically signifi-canit.
Cercidiutm floridumn is a small leguminouis tree
occturring in washes and sandy areas below 400 m
in the Colorado Desert of California, in Ariizoia,
and in the states of Baja California and Sonora,
Mexico (7). The smal,l leaves (1-2 cm) beal- 1 to
3 pairs of pinnae. Typical;ly, the trees are leafless
during mtuch of the year (14); however, in some
years the leaves may persist. Cannon (3) described
the location of the chlorophyll in the sftems.
1 Supported by a grant, GB-4146, from the National
Science Foundation.
2 National Aeronautics and Space Administration
predoctoral fellow.
Plants were selecoted from several under inves'tigation at tihe Universilty of California's lloyd
Desert Research Laboratory, near Palm Desert,
California. Experiments were conducted oni foliated and leafless stems, approximately 2 mm in
diameter. The stems were exposed to closel atmospheres containing 14CO., and aiir for 10 or 20
minute periods. The intact tissue wias pl,aced in
50 ml glas.s test tubes which containel 5 ,uc
NaH'4CO (ispecific activity _ 52 ^,uc/imole) in
0.7 ml 10 mM tris buiffer (pH 7.4). A pipet was
inserted and the system sealed with Apiezon Q.
Excess 85 % lactic acid was injected throtugh the
pipet to releiase 14CO from the NaH'-*CO. The
sealed tuibe was immersed in a 1-liter glass jar
containing distilled water and ice to control temperature. Temperature was measured with a
shielded mercury thermometer sealed in a similarly
immersed test tuibe. At the end of the 10 or 20
minuite periods, the leaves and/or stems were washed
in dlisitililed water and frozen under (Iry ice. The
tisstue was returned to the laboratory wilile frozen
and extracted within 2 hoturs.
Suirface area was determined by measirements
taken at the beginning of the experiment. Clilorophyll was extracited wiith cold 80 % acetonie and
analyzed by the meithod of Arnon (1). T'is'ises
varied from 0.300 to 0.716 g fresh weight.
The products of photosynthesis were analyzed
essentially by the methods of Bliight and Dyer (2)
and Canvin and Beevers (4), as previloulsly r eported (13). After grinding in l,iquid No, neutral
(carbohydrates), basic (amino acidcs), ancd ac-idic
(organic phosiphates and acids) fractions were
separated by ion exchange chromatography. Aliquots (0.2 ml) of the fractions were cotunted for
radioactivity, and results expressed as disintegrations per minute (dpm) cm-2 hr-1. Similar aliiqliots
of ithe llipid-containing chiloro,form component were
counted. In some experiments, the methanol-chloroform-insoluble fraction was counted using CabO-Sil Gel a,s a suspension medium.
In general, in leaves and stems the h'ighest levels
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PLANT PHYSIOLOGY
Table I. Photosynthetic Accumulation of 14C fronit 14O,0 in the Alcohol-soluble Fractionl by Leaf-Bearing Sten
and Leaf Tissue of Cercidium Floridum
Stems and leaves were exposed to 5 ,c of 14CO2 in a closed svstem for 10 or 20 minutes, frozen, and subsequently extracted with chloroform-methanol and water. The aqueous fraction wvas separated into neutral, basic
and acidic components by ion exchange chromatography. T -- 310.
Stem
Leaf
10 mmin
5.98
Total dpm*
Component (% of total)
62.7
72.2
Neutral (carbohydrates)
18.3
27.5
Basic (amino acids)
9.5
9.8
Acidic (organic
phosphates +
organic acids)
* Total levels of activity inl the fractions are expressed as dpm
cmn 2 hr
ponents are expressed as % of total activity.
Table II. Photosynthetic Accunmulation of 14C front
of Cercidium floridum
Stems were exposed to 5 UC of 14CO2 in a closed
system for 20 minutes at 330 and 410, frozen, and
subsequently extracted witlh chloroform-methanol and
water. The aqueous fraction was separated into neutral,
basic and acidic components by ion exchange chromatography.
14CO, by Leafless Stem Tissue
Total dpm*
Component (% of total)
Neutral (carbohydrates)
Basic (amino acids)
Acidic (organic)
330
4.4i
410
5.91
83.0
12.1
4.9
77.5
17.9
4.6
phosphates +
organic acids)
0.242
0.061
Insoluble (dpm)
* Total levels of activity in the fractions are expressed
as dpm cm-2 hr-I X 10-5. Levels in the individual
components are expressed as % of total activity.
of activity were found in the neutral fraction. The
basic fraction contained more activity than the
acidic fraction (tables I and II). Thus, leaves and
stems accumulated similar proportions of the 14C.
These ratios of activity (in the 3 fractions are expected for photosynthesis (8). Levels of activiity
found in the lipid fraction were very low, constituiting less )than 2 % of ithe total activity.
When foliated stems were expo,sed to 14CO0
(Jnfly 6, 1967), the mean rate of accumulation of
'C in the leaves was 5.75 X 105 dpm cm 2 hr-1, and
4.11 X 105 dpm cm-2 hr-1 in the stem (table I).
Translo-cation between leaves and stems during
short-time intervals probably was not significant
(see later). Accumulation of 14C in the alcoholsoluble fracti-on during the 20 minute experimental
periio-d was essentially linear, and thtus photosynthesis was not limited by CO2.
The total chlorophyll was 3.38 mg dMn2 in the
leaves and 4.13 mg dm-2 in the stems. Pearson and
20 min
4.18
10 mill
4.04
20 milm
5.52
65.3
22.9
11.8
63.4
26.1
10.5
X 10
Levels
Le.
in the individual com-
Lawrence (10) also reported more chlorophvll in
aspen cortex than in leaves in spring, but this ratio
reversed in summer. Their valtues determined for
aspen cortex and leaves in May were only slightly
higher than those presented here for C. floridtum.
The rates of accumulation of 14C in the alcoholsoluble fraction per unit chlorophyll for leaves and
stems were 190 X 105 dpm mg-' hr-1 and 100 X 10"
(Ipm mg-1 hr-1 respectively. The lower rate of
accumulation by stems despite higher chlorophyll
concentrations cotuld possibly be accounted for by
a greater expected CO, difftusion resistance of
stems, differences in albedo, or a greater depth of
the chlorophyllous layer resulting in less radiant
einergy absorption by the chiloroplasts.
When drought-induced leafless stems were exposed to 14CO0 at 330 (Atuguist 9, 1967), total acciumtulation in the alcohol- soluhble fraction was similar
to that of stems with leaves at 310 (4.46 X 105 as
compared to 4.18 X 105 dpm cm-2 hr-1). At 410,
accumulation was 5.91 X 105 dpm cm-2 hr1 (table
II). Accumulation in insoluble components was
low during these short-time periods. These data
suiggest ithat translocation from leaves to stems
l)robably did not influience the data froom the July 6
experiment (cf. 5).
Our results indicate that photolsynthetic activity
in small stems of Cercidiun floridumr is comparable
to that of leaves when compluted on a rate per tunit
area. Addition,all experimen-lts are planned to sttudy
possible seasonal changes in the levels of activity
in d1ifferent fractions, and possible seasional (lifferences in rates of total photoisynithesis in leaves and
stems.
Literature Cited
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Plant Physiol. 24: 1-15.
2. BLIGH, E. G. AND W. J. DYER. 1959. A rapid
method of total lipid extraction and purification.
Can. J. Biochem. Physiol. 37: 911-17.
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ADAMS ET AL.-PHOTOSYNTHESIS IN CHLOROPHYLLOUS STEM TISSUE
3. CANNON, W. A. 1908. The topography of the
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1799
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