Indian J. Plant Physiol •• Vol. XXVIII No.2 pp. 107-114 (June 1985)
EFFECT OF WATER STRESS ON PHOTOSYNTHESIS AND WATER RELATIONS OF WHEAT VARIETIES D.C. UPRETY and G.S. SIROHI
Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi.1l0 012 SUMMARY
The analysis of the effect of water stress on the photosynthesis and
water relations of wheat varieties 'C 306' and 'Kalyansona' showed that
stress affected both stomatal and nonstomatal components of photosyn­
thesis. The comparatively higher photosynthesis in variety C 306 under
water stress conditions might probably be by the maintenance of higher
turgor due to higher water potential of its leaves. The variability in
photosynthesis could not be explained in terms of the stomatal resistance
values.
Water deficit in plants brought about by drought influences various
physiological processes which are associated with the reduction in turgor such
as stomatal behaviour, photosynthesis and growth (Sullivan and Ross, 1919).
However. many crop species have evolved physiological and morphological
adaptations to drought conditions. Despite the economic effects of water
deficits in decreasing the photosynthesis and growth of plants. no efforts have
been made to understand the variability on the response of water stress in the
Indian wheat varieties.
In the present studies the effect of water stress on the growth and yield of
wheat varieties, have been taken with a view to differentiate various physiological
components of the response i.e., water relations of leaf tissues, leaf area develop­
ment, stomatal resistance and CO 2 gas exchange.
MATERIALS AND METHODS
Two varieties of wheat. ·C 306' and 'Kalyansona" were raised in
rectangular cement pots (30x20 em) kepc under natural conditions during the
crop seasons of 1982-83 and 1983-84. The results of 1983-84 experiment are
presented in this communication. Each pot with 8 plants was adequately
fertilized for maintaining optimum growth. Drought treatment was given by
restricting irrigation at three stages (i) tillering, (ii) anthesis and (iii) seed
108
D.C. UPRETY AND G.S. SIROm
development. The'Se are three independent stress treatments. Plants were
reirrigated when they wilted. Observations on photosynthesis and water rela­
tions were taken at 7, 5 and 3 days after drought-treatment at tiIlering. anthesis
and seed development stages respectively. The sampling time was adjusted on
the basis of wilting response in both the varieties. Observations were also taken
after reirrigation on wilting at each stage.
Net photosynthesis (P net) was calculated from CO2 exchange measure­
ments made on main stem leaves using single leaf chamber. The depletiOll of
COl! concentration of the air that had passed through the chamber was measured
with an infrared gas analyser (ADC Ltd., Hoddesdon. U.K.) (Parkinson, 198I).
Leaf area development was studied with the help of leaf area meter
(LiCor). Specific leaf area was calculated as leaf area per unit dry weight.
A null-balance diffusion porometer (liCor LI 1600) was used on the
intact leaves to measure the stomatal resistance. Observations were taken in the
forenoon between 11 to 11.45 AM under full sunlight in the youngest fully
expanded leaf of mothershoot.
Total dry matter and the grain yield were also measured at the time of
harvest.
Water relations in leaf tissues were measured by estimating their relative
water content (RWC) and water potential (.fo) by following the methods described
by Weatherley (1970) and Leach et al (1982) respectively. Soil water content
was measured by gravimetric dry weight basis.
RESULTS AND DISCUSSION
The immediate effect of water stress on the photosynthetic process was
the enhancement of diffusion resistance, reduction in the leaf area development
and depression in the net photosynthesis. The stomatal resistance was signi­
ficantly increased due to water stress treatment in both the varieties at all the
three stages, however, during the seed development stage, leaves of both the
varieties exhibited very high diffusion resistance, Varietal difference in stomatal
resistance was not significant (Table I).
Water stress treatment significantly reduced the net photosynthesis in both
the varieties at al1 the three stages of growth. However, the reduction in P(net)
was comparatively less in C 306 (10%) as compared to Kalyansona (58%). The
varietal difference for net photosynthesis was found significant at all the stages
0.413
Treatment
Interaction
NS
NS
Variety
1.18
Reirrigated
1.14
Control
1.33
1.40
Reirrigated
Drought
2.17
1.32
Tillering
stage
0.853
NS
NS
2.87
3.20
2.58
3.10
4.34
2.97
Anthesis
stage
0.626
0.626
NS
NS
13.62
5.70
13.56
11.30
9.74
10.86
Tillering
stage
0.594
0.372
0.556
0.372
0.728
8.20
3.14
8.02
6.00
4.64
6.18
Seed development
stage
0.594
IS.64
7.84
16.58
14.02
11.66
15.54
Anthesis
stage
-------------------­ - - -
B. Net photosynthesis (P net)
(tJ.1 CO. m- I S_l)
0.731
NS
3.16
8.53
2.91
3.08
8.16
2.63
Seed development
stage
--------------------­
Drought
Control
Treatment
A. Stomatal resistance (S/cm-1)
The effect of water stress on stomatal resistance and photosynthesis of wheat varieties
C.D. at 5% P.
Kalyansona
C306
Variety
Table I
~
{Il
c;IJI
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"1:1
~
c;IJI
{Il
l'!'l
{Il
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l'!'l
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NS
NS
NS
NS
7.34
NS
CD at 5% P. Variety
Treatment
Interaction
Kalyansona
187.30
180.10
166.60
135.80
Control
Drought
ReirrigatecJ
NS
15.13
NS
16660
135.80
171.29
126.68
182.50
179.10
171.60
147.80
Control
Drought
Reirrigated
C 306
Anthesis Seed
stage develop­
ment
stage
(A) Specific Leaf Area (cml/g)
Tillering
stage
Treatment
27.28
19.95
26.31
24.32
23.00
24.75
Tillering
stage
NS
1.58
NS
14.75
26.91
17.82
25.06
26.37
26.08
23.80
24.55
Anthesis Seed
stage
develop­
ment
stage
(B) Final dry matter production
0.58
NS
NS
9.12
7.66
8.8\
8.07
7.78
7.93
Tillering
stage
5.57
9.06
6.50
8.12
7.81
8.75
6.62
7.81
Anthesis Seed
stage develop­
ment
stage
(C) Grain Yield (g/plant)
Effect of water stress on the leaf area development, dry matter production and grain yield of wheat
varieties
Variety
Table II
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WATER STRESS ON PHOTOSYNTHESIS
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except at tillering. It was recorded that the net photosynthesis in Kalyansona
was higher (about 30% more) than e 306. (Table I).
The water stress treatment brought about significant reduction in the leaf
area development in both the varieties. This is apparent from the values of
specific leaf area. Varietal difference for this character was not significant
(Table II).
In case of 'Kalyansona' water stress treatmellt at tillering and anthesis
stages, brought about significant decrease in final dry matter production.
Whereas, in the case of 'e 306', the stress at tillering and seed development stage
did not affect the dry mattcr production. The reduction was only significant at
anthesis stage. The varietal difference was not significant (Table II).
Stress treatment at all the three stages, significantly reduced the grain
yield in 'Kalyansona', whereas in 'e 306', reduction was observed due to drought
treatment at anthesis and seed development stages only (Table II).
One of the immediate effect of water stress on the leaf tissues was on its
water potentiaL Stress at anthesis stage, resulted in 83% reduction in Kalyansona
as compared to 23% reduction in e 306. Similarly drought at later stage caused
about 65% reduction in Kalyansona and 36% reduction in e 306. Water stress
effect at tillering stage was not significant. It was also noted that under irrigated
conditions, there was no significant difference in the *" of leaves between
Kalyansona and e 306 (Table III).
The effect of water stress on RWe of leaves was not significant at tillering
and anthesis stages. However, at the later stage, the depression in Rwe was
significantly lower in 'Kalyansona' than 'e 306' (Table lIT).
The moisture content in the soil was more or less similar in both the
varieties at various stages of growth (Table III). It was interesting to note that
when plants were rewatered at wilting stage, the differences caused by drought
for various characters were almost nullified.
Thus it was noted that under water stress conditions, the net photosynthesis
(P net) values were significantly higher in 'e 306' as compared to 'Kalyansona'.
However, stomatal resistance does not show significant variation. It appears to
be a unique relationship between the turgor pressure and stomatal resistance
(with stomatal resistance increasing markedly near zero turgor induced by
drought). This is consistant with the observation recorded by Turner, (1979)
that adaptation of stomata to waterstress parallels osmotic adjustment to bulk
CD at 5% P
Kalyansona
C306
Variety
Table III
3.82
NS
8.20
8.20
NS
NS
NS
2.813
2.813
Interaction
1.139
1.139
NS
NS
Treatment
NS
NS
NS
NS
14.0
NS
NS
NS
NS
Variety
27.0
15.0
84.00
4.2
91.00
11.6
91.33
-13.0
-12.1
-8.0
Roirrigated
19.0
25.0
S.O
48.61
83.28
13.5
112.00
90.48
86.13
-243
-25.3
Drought
14.0
3.5
12,0
15.5
91.91
-14.3
-15.3
-8.3
-10.0
Centrol
27.0
83.10
90.56
90.33
-12.6
-12.3
-6.6
5.8
Reirrigated
20.0
55.90
81.S4
14.0
87.66
26.0
-17.6
79.90
-20.0
89.36
89.69
--13.6
Anthesis Seed
stage develop­
ment
stage
Tillering
stase
Anthesis Seed
stage develop­
ment
stage
Tiltering
stage
-14.6
Anthesis Seed
stage
development
stage
(C) Soil water conten (%)
(B) Relative water content %
-8.6
-7.S
Tillerins
stale
(A) Leaf water potential (ifJ)
Drought
Control
Treatment
Effect of water stress on the water relations of wheat varieties
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W ATEA STAESS ON PHOTOSYNTHESIS
113
leaf tissue. Cultivar differences in response of drought to stomatal resistance
and photosynthesis may represent their abilities to adjust osmotically in these
two varieties. This gives little consideration to stomata in affecting the
process of gas exchange in these cases. This might be due to poor ability of
stomata to adapt to the stress (Ludlow, 1980).
The question arises, as to how the high photosynthesis has been main­
tained under water stress conditions in C 306. In this regard, the water relations
of these two varieties were looked into. It was seen that there was very little
effect of drought on the relative water content (RWC) of leaves and that too
after the seed development stage. However, the variability was significantly
reRected in the drought induced reduction of water potential of leaves. The
chemical energy potential of water in 'c 306' remained high even under water
stress conditions. It may be argued that the osmotic adjustment that leads to
an increase in turgor must have decreased tissue elasticity (Davis and Kakso,
1979), because there waS very little change in relative water content (RWC) as
compared to leaf water potential ("') in ·C 306'. The higher '" in 'c 306' leaf,
not only maintained its turgor under adverse condition but also helped in the
photosynthetic functions of leaves. It appears that the photosynthesis as such
(gas exchange capacity) is not much affected by the relative water content of the
tissue but by the turgor maintained due to chemical potential of water thus
allowing the leaf tissues to exchange the CO2 efficiently in C 306.
It thus appears that water stress affected both water relations as well as
stomatal and nonstomatal components of photosynthesis in wheat leaves. Among
the water relations the varietal differences were reflected in the leaf water poten­
tial. Variety 'c 306' appeared to maintain comparatively higher water poten­
tial than 'Kalyansona' under water stress conditions. However, little effecl on
the relative water content indicated that the osmotic adjustment which lead to
turgor maintenance might have been helped by tissue elasticity rather than higher
water content. As suggested by Richter and Wagner (1982) components of total
water potential permit plants to resist the negative effect of water stress on
photosynthesis. The significantly higher P (net) values in C 306 under water
stress conditions appeared to be more affected by the maintenance of turgor
rather than the behaviour of stomates. The varietal differences which were
observed in the net photosynthesis and not in the stomatal resistance showed
that in these cases little consideration was found for stomata to affect the process
of gas exchange.
ACKNOWLEDGEMENT
This research work has been financed partly by the grant made by the
I
.
114
D.C. UPRETY AND G.S. SIROHI
United States Department of Agriculture, Office of Industrial Corporation and
Development, authorized by Public Law 480.
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