PHOTOSYNTHETIC 14 C0 2 ASSIMILATION BY
RICE LEAVES UNDER THE INFLUENCE
OF BLUE LIGHT
BY V. S. R.
DAS ANO
P. V.
RAJU
Department of Botany, S. V. University, Tirupati (A.P.)
lr is realised that during photosynthetic carbon reduction, amino-acid~
and other reduced carbon compounds are rapidly formed besides the
quantitatively principal products, the carbohydrates (Calvin and
Bassham, 1962). The flow of newly incorporated carbon into noncarbohydrate constituents is assumed to be the result of a drainage of
intermediates from the carbon reduction cycle and by the utilization of
photochemically generated cofactors (Bassham et al., 1964). Such a
diversion of carbon may be influenced by the environment to a degree.
The present investigation has been attempted to find out if activating light of shorter wavelength and consequently of higher energy
can accelerate the incorporation of 14 C0 2 into secondary photosynthetic
products. For instance, Hess and Tolbert ( 1964) have shown that in
Clzlamydomonas previously adapted to blue light, a large proportion of
glycolate products was formed with a corresponding decrease of
incorporation into Krebs cycle acids. Even in higher plants Nichiporovich ( 1956) had reported results to suggest an influence of blue light
on the formation of photosynthetic products. However, he found that
blue light caused an increased production of amino-acids with decrea~e
in organic acids. In the work reported here the effect of blue monochromatic light on the pattern of photosynthesis of carbon compounds
by intact rice leaves under field conditions was studied.
MATERIAL AND
METHODS
•
Rice plants (Ory::a satil'a, cultivar Pumbavulu) were grown in
pots on black loam soil mixed with compost. A bout two-month-old
plants which were in tillering stage formed the experimental material.
r
The carbon dioxide assimilation experiments were conducted on
leaves attached to the potted plants in direct sunlight (white light).
Experiments in blue light were conducted by placing the potted plants
in sunlight screened through a specially constructed wooden frame
fitted with a blue paper. The predominant spectral transmission of
this blue paper was in the range of 4200-4400 A.
'
The gas-feeding assembly consisted of a hard glass specimen tube
fitted with a two-holed rubber stopper. Through one of the holes an
P-1
2
V. S. R. DAS AND 1'. V. RAJU
' L '-shaped glass tube was inserted and into the other a straight glass
tube was fitted. This assembly was connected through the straight
glass tube to a hard glass test-tube into which about 25 em. of the intact
leaf tip was introduced. Three micromoles of NaH 14 C0 3 (approximate
activity 3 · 3 x I 03 cpm.) and twelve micro moles of NaH 12 C0 3 were initially taken into the specimen tube before connecting it to the test-tube
3 mi. of 0· 5 N HCI was introduced into the specimen tube through the
' L' tube to liberate carbon dioxide.
After ten minutes exposure to 14 CO., in white or blue light the
leaves (only the portions exposed) were immediately immersed in hot
80% ethanol, were extracted with the same solvent and the alcohol
extract was concentrated to a small volume. Suitable aliquots of the
ethanolic extracts were dried on planchets and the activity fixed was
counted using a thin window G.M. counter. The alcoholic extract wa~
analysed by two-directional chromatography on Whatman No. I paper
using the solvent systems. phenol saturated with water in the first direction and n-butanol: propionic acid: water in the second. Agfa rapid
X-ray films were used for developing the radioautograms. The
chromatograms were sprayed individually with aniline phthalate, ninhydrin or bromophenol blue to detect ~ugars. amino-acids and organic
acids respectively. The amount of radio-carbon incorporated into
individual substances was estimated by cutting out the corresponding
portions from unsprayed chromatograms. eluting the material and by
counting the activity in the eluate.
RESULTS
AND
IJISCLJSSIOt-;
In white light, sucrose and glucose put together, comprise the major
product of photosynthesis at the end of ten minutes (Fig. I). Organic
acids including citric acid and presumably glyceric acid were also quite
prominent. Phosphoglyceric acid (PGA). alanine and other aminoacids became radioactive to <1 lesser extent.
Photosynthesis for ten minutes in blue light had also resulted in
the formation of carbohydrate as the major product although in this
case only sucrose was formed instead of sucrose and glucose as in white
light. On the other hand, there was a considerable decrease of
incorporation of carbon into organic acids in blue light with a corresponding increase of radioactivity into amino-acids. particularly alanine.
tyrosine. glycine and to a smaller extent phenylalanine and leucine were
also active in blue light (Fig. 2). Sugar phosphates decreased while
relatively more phosphoglyceric acid was formed than in white light.
The distribution of newly incorporated carbon into various fractions under the two different qualities of light is shown in Table I.
The present results on the pattern of incorporation of carbon are
taken to represent the effect of quality of light rather than the differences in intensities since the experiments were conducted under bright
't
'
IN BU F LIGHT
' C0 2 ASSIMILATION
TABLE
1
Distribution of radioactivity in the different products of photo,\)'llthesis
by rice leaves expressed as percentage of total activity reco\'ered
from paper chromatogram
Per cent. activity
Product
White light
Blue light
Sugar(s)
53·3
49·0
Alanine
11·0
38·8
6·3
8·0
20·1
3·0
9·3
1·2
Other amino-acids
Organic acids
Sugar phosphates
light well above the saturation. The pattern of photoassimilation of
carbon dioxide by rice leaves under blue light reported here agrees with
the results obtained by Nichiporovich (1956) on different plants,
inasmuch as the blue light results in an enhanced incorporation of carbon
into amino-acids. But there was no increased incorporation of carbon
into glycolate products in rice leaves under blue light as reported by
Hess and Tolbert (1964) in Chlamydomonas.
That several amino-acids arc produced as a result of direct photosynthetic activity rather than through the dark biochemical reactions
is borne out by the work of Helle bust and Bidwell ( 1963) and that of
Bassham et a/. (1964). Blue light is supposed to increase the content
of chlorophyll b but the precise relation of this change in pigments to the
enhanced synthesis of amino-acids during photosynthesis is not clear
at present.
AcKNOWLEDGEMENT
This investigation was supported by a grant-in-aid
Department of Atomic Energy, Government of India.
from the
SUMMARY
Photoassimilation of carbon dioxide by intact rice leaves was studied
in white and blue light. The most striking difference between the
pattern of carbon flow into various compounds under the two different
qualities of light was the occurrence of an accelerated synthesis of amino-
4
V.
S. R. DAS ANIJ P. V. RAJU
acids, particularly alanine, under blue light with a corresponding decrease
of incorporation into organic acids and sugar phosphates.
REFERENCES
CALVIN, M. AND BASSHAM, J. A. (1962).
W. A. Benjamin, N.Y.
The Photosynthesis of Carbon Compounds.
BASSHAM, J. A., BRONISLAWA, MORAWlECKA AND MARTHA KIRK (1964).
synthesis during photosynthesis. Biochim. Biophys. Acta, 90, 542.
Protein
HEss, J. AND ToLBERT, N. E. (1964). Changes in chlorophyll b and C"0 2 fixatior.
products by Chlamydomonas adapted in blue light. Plant. Physiol., 39, Suppl.
XIV.
NtcHIPOROY!CH, A. A. (1956). Tracer atoms used to study the products of photosynthesis depending on the conditions under which the process takes place.
Proc. Int. Conf Peacejid Uses of Atomic Energy, Geneva, 12, 340.
HELLEBUST, J. A. AND BIDWELL, R. G. S. (1963). Sources of carbon for the synthesis
of protein amino-acids in attached photosynthesizing wheat leaves. Can. J.
Bot., 41, 985.
EXPLANATION OF PLATE
FIGS. l and 2.
Radioautographs of paper chromatograms from products of
I 0 minutes photosynthesis by rice leaves. Fig. I. In white light. Fig. 2. In blue
light.
IND. J. PLANT PHYSIOLOGY
. VOL. VIII, PL. l
GLYCOLIC
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StiGAll 110HOI'l10$lMIAT£S-
FIG. I
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Cl'l"RtC ACit)
AW.NINE~
S'ERllfE
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\.
SUCRosr~
SUGAR MOI'tOPH.OSPtfATE~.~
SUGA~ DIPHOSP~ATES~
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FIG. 2
V. S. R. Das and P. V. Raju