5. EFFECTS OF WATER DEFICITS ON
PHYSIOLOGICAL, MORPHOLOGICAL AND
BIOLOGICAL PROCESSES
1. Water deficit at cellular level
i. Cell Division: It is less affected as compared to cell
elongation.
ii. Ex. Radish leaves DNA content reduced to 40% of
control leaves at W.P. of -2 bars and to 20% at -8 bar.
iii. Cell Enlargement: Reduction in T.P. causes in cell
enlargement, which in turn decreases root and shoot
elongation.
iv. Also interferes with stomatal opening.
6. 2. Leaf Expansion : In maize, rate of leaf enlargement
is greatest when leaf water potential is in the range -1.5
to -2.5 bars.
As leaf water potential falls to -9 to -10 bars, leaf
elongation vertically ceases, photosy. Was slightly
impaired.
3. Turgor: Lag in absorption behind transpiration → loss
in turgor → due to rise in transpiration→ due to
increase in atmospheric dryness with onset of drought.
4. Plant structures:
Leaf area, cell size & intercellular volume are usually
decreased.
Cutinization, hairiness, stomatal frequency and
thickness of both palisade layers increased.
7. 5. Root development: It is affected by soil
water potential in a number of ways
In G’nut & wheat wt. of root decreased but
number of root is same approx.
Roots grow towards water in the soil.
6. Photosynthesis: Water stress can reduced
photosy.by
Reduction in leaf area
Closure of stomata
Reduction in activity of dehydrated
protoplasmic machinery
Reduce photosyn. surface
8. Reduce the production of dry matter
The leaf water potential at which stomata close
varies with
A. Position of the leaf
B. Leaf age
C. Growth condition
D. Rate of stress
7. Respiration: It increases in early stage
afterwards decreases as it is severe.
Severe dehydration of tissues caused a burst of
respiration in some species results of hydrolysis of
starch to sugars
9. In general reduction in photosynthesis, commences
W.P. commences to zero.
It decline more or less turgor pressure to a value of
zero.
8.Distribution of assimilates: Distribution pathway
is highly resistant to water stress.
Velocity of assimilatory movement was influenced
by water stress as low as -30 bars in wheat.
Effect of water deficit distribution of assimilates to
various plant organs will depends on
I. Stage & development of plants
II. Pre-history of stress
III. Degree of stress
IV. Degree of sensitivity to stress of organs
10. 9.Photorespiration: It is unaffected
by short term stress in certain
conditions but substrate for
photorespiration depleted.
10.Protoplasmic effects of water
deficit: Removal of water surrounding
protein molecules may cause changes
in configuration affecting permeability,
hydration, viscosity & enzyme activity.
11. 11. Carbohydrate metabolism: In cotton as a
result of stress, the sugar content increases &
starch content decreases.
By contrast, in stems, the conc. Of both sugars and
starch increases indicating reduced water supply
not only affects photosynthesis but also the ability
of plants to utilize the products of photosyn.is still
more impaired.
12. Enzyme activity: In maize increase in water
stress cause nitrate reductase activity decline at
much greater rate than peroxidase activity.
Levels of enzymes involving hydrolysis and
degradation usually either remains same or
increase.
12. 13. Nitrogen metabolism: Hydrolysis of proteins
occur in wilted plants is accompanied by increased
amino acids.
Synthesis of RNA & proteins are decreased in
sugar beet before visible wilting occurs.
14. Nucleic acid: its synthesis is unaffected by
moderate stress in older leaves, but Rnase activity
increases which degrade RNA.
Reduced growth of stressed seedling due to
alternation of nucleotide composition Of the RNA.
13. 15. Ageing: It produces changes in the course of
protein synthesis and water stress greatly
accelerate the change normally associated with
senescence.
16. Growth regulators:
A. ABA: In water stress plants , ABA synthesized
and released from mesophyll to chloroplast and
travels to guard cells where it
a. Inhibit K+ uptake
b. Inhibit H+ release
c. Promote leakage of malate from guard cells.
These effects cause guard cells to lose turgor.
Loss of turgor decreases stomatal aperture.
14. B. Cytokinins: In stressed sunflower plants,
cytokinin content in root exudates was reduced.
In detached lettuce leaves, water stress had the
effects of decreasing cytokinin as ABA increased.
C. Gibberellins: GA declined in tomato shoot, root
following stress applied by flooding roots.
D. Auxins: IAA in sorghum leaves decreased as a
result of water stress.
Water stress can directly affect the action of IAA in
shoots.
E. Ethylene: In cotton plants, water stress induced
abscission of leaves that is promoted by plants.
15. Water stress in cotton, bean plants, ethylene level
are elevated rapidly in both leaves and petioles.
17.Reproductive and grain development:
A. flowering: Moisture regimes during this period
largely determines the no. of fruits which will be
produced.
B. Fruit enlargement: Severe stress during this
period results in small or shriveled grains.
C. Ripening: Water stress has no effect on yield
component but may effect length of ripening period.
16. 18. Crop yield: Effect of water stress
on yield depends on stage at which it
occurs.
At early stage, no. of primordial
branches may be reduced.
Drastic effect of stress was observed
at flowering stage.
17. EFFECTS ON CEREALS
On floral initiation, anthesis (wheat&
rice).
At ripening stage (reduc. in test wt.).
Plant height, leaf area.
Leaf rolling, drying, premature death of
leaf.
Reduc. in photosyn. & dry matter
production.
18. EFFECTS ON PULSES & FRUIT CROPS
• Flower abortion .
• Stress during pod filling reduces test weight.
• In fruits, shedding of fruits. Ex. June drop of
apples & citrus.
• In some cases, drought prevails causes
premature flowering which results in
reduced yield, size of pods, seeds & fruits.
19. MOST SENSITIVE STAGES OF MAJOR CROPS
1. Rice: panicle initiation, flag leaf & milky
2. Sorghum: booting & flowering
3. Maize: tasseling & silking
4. Groundnut: peg penetration & pod development
5. Sunflower: head formation and early grain
forming
6. Pearl millet: booting & flowering
7. Finger millet: flowering
8. Soybean: flowering & pod filling
9. Cotton : square formation & boll development
10. Black & Green gram: flow. & early pod develop.
20. EFFECTS OF STRESS IN MAIZE
Tasseling and silking stage ( most
harmful) , grain filling reduc. yield
drastically than at vegetative stage.
Pollen develop. slower leads to reduc.
fertility → reduc. in grain no. wt. per
ear.
During anthesis shorten duration of
grain filling by causing premature
desiccation of endosperm & by limiting
embryo volume.
21. EFFECT OF WATER STRESS IN
SUNFLOWER
Drought tolerant crop
Deeper root system → due to stress at
veg. stage
Yield and oil content decreases
Interesting fact
1. under normal cond. Oil content and
seed is high than seed protein content.
2. In mild stress cond. Seed protein
content high in hybrids than that of oil
content.
22. EFFECTS OF WATER IN SOYBEAN
Leaf expansion rate reduced
Leaf flipping movement seen
Water stress causes early flowering & reproductive
growth
Leaf clamping
Effect of water stress in
groundnut:
Fairly drought tolerant
Low rainfall, prolonged dry spell decrease its yield
Photosyn. , carbohy. ,chlorophyll , enzymatic
activity ,internodal length , pod & kernel
development reduced.
23. EFFECTS OF WATER STRESS IN COTTON
o Affect both production & distribution of
carbohydrates.
o Reduction of leaf area
o Mummified dry bolls ( younger bolls)
o Older bolls size reduced
o Stress during peak flowering and early pod
develop. reduced yield
24. GROWTH STAGES REDUCTION IN YIELD
WITH ONE DAY OF
STRESS(Kg lint/ha)
Squaring 9.2
Peak flowering 18.8
Late flowering 16.1
Boll maturation 3.6
Hearn and Constable 1984
25. METHODS FOR MITIGATE ADVERSE
CONDITIONS OF WATER STRESS IN CROPS
1. RICE:
a) Seed hardening KCl 1% with CCC 50 ppm & foliar
spray of 1000ppm CCC → increased grain yield
up to 5723 kg/ha
b) Foliar spray of murate of potash 2% at flower
initiation → 400 kg/ha
c) Foliar spray of 0.3 ppm of brassinolide at panicle
initiation and flowering → 605t/ha
2. SORGHUM : kaolin 3% foliar spray → 10%
26. 3.RAGI: Seeds treated with CCC 5 ppm → 12%
4. BAJRA: Combined spray of 0.5% ZnSO4 & 0.5%
CuSO4 together with boric acid 0.2% → 16.8%
Soaking Bajra seed with 2% KCl or NaCl for 16 hrs
→ 329 kg/ha
5.SOYBEAN: Kaolin 3% or liquid paraffin at 1% as
foliar spray → 10%
Foliar spray of salicylic acid 100 mg/lit on 30 & 45
DAS → 16%
6.BLACKGRAM: Foliar spray of KCl at 0.5% during
flowering → 100 kg/ha
28. BENEFICIAL EFFECTS OF WATER STRESS
1.Moderate water stress improved the quality of
Apples, Pears, Peaches and Plums.
2.Water stress increases the alkaloid content in
datura.
3.Water stress increases the percentage of oil in
soybean but decreases the yield of oil per acre.
4.Protein content of wheat increased by water
stress during maturation.
5. Although water stress decreases total vegetative
growth , it generally increases the rubber content in
rubber plants.
29. WATER STRESS IN RELATION TO DISEASES
AND INSECT RESISTANCE
1. Development of bark cankers is usually
correlated with decreased water content of
the bark.
2.The incidence of blossom end rot of
tomato fruits is said to be higher on plants
subjected to severe water stress.
3. Trees with low water stress have high
oleoresin exudation pressures, which
seems to be unfavorable to the
establishment of beetles.
33. TREATM
ENTS
WATER STRESS NORMAL WATER CONDITI
ON
NITROG
EN
(mg/pot) NITROG
EN
(mg/pot)
GRAIN STRAW TOTAL GRAIN STRAW TOTAL
UNINOCUL
ATED
62.0 59.0 121.0 182.0 72.0 254.0
Os 4 71.0 23.0 94.0 202.0 69.0 271.0
Ew24 93.0 40.0 133.0 250.0 107.0 357.0
11a 124.0 51.0 175.0 252.0 85.0 337.0
17bt 150.0 87.0 237.0 263.0 96.0 359.0
M 10 132.0 81.0 213.0 260.0 71.0 331.0
Os 2 162.0 53.0 216.0 207.0 73.0 280.0
SEm± 6.4 5.8 4.4 11.9 4.0 8.7
C.D.(0.05
)
18.5 16.8 12.7 25.8 24.6 13.7
Indian journal of plant phy.(april-june,1997) Sangeeta paul IARI newdelhi
34. LEAF EXPANSION IN
BRASSICA SPECIES IN
RESPONSE TO WATER
STRESS (LEAF WATER
POTENTIAL,R.W.C. , &
SOLUTE POTENTIAL AT
ZERO TURGOR IN
BRASSICA SPECIES)
35. SPS./STRESS
TREATMENT
LEAF W.P.(MPa) R.W.C. S.P AT ZERO
T.P.(MPa)
BEFORE STRESS PERIOD
B.juncea -0.45 0.81 -1.01
B.napus -0.64 0.94 -1.32
END OF STRESS PERIOD
B.J Control -0.89 0.78 -1.14
Stressed -1.33 0.74 -1.49
B.N Control -0.98 0.81 -1.24
Stressed -1.58 0.69 -1.57
AFTER REWATERING, TWENTY FOUR HOURS
B.J Control -0.85 0.76 -1.20
Stressed -1.14 0.72 -1.38
B.N Control -0.90 0.81 -1.27
Stressed -1.24 0.74 -1.50
36. EFFECT OF WATER& RECOVERY ON LEAF
AREA (CM SQUARE/PLANT)
SPECIES STRESS PERIOD RECOVERY PERIOD
CONTROL STRESSED CONTROL STRESSED
B. juncea 135.0 106.8 149.4 125.2
B.napus 81.5 70.2 102.5 81.0
A.KUMAR & J.ELSTON
37. EFFECT OF WATER STRESS
ON PHOTOSYNTHESIS AND
WATER RELATIONS OF WHEAT
VARIETIES (EFFECT OF WATER
STRESS ON STOMATAL
RESISTANCE &
PHOTOSYNTHESISOF WHEAT
VARIETIES)
38. VARIET
Y
TREAT
MENT
STOMATAL RESIST
ANCE
(S/cm
inverse
)
NET PHOTO
SYN. (P
net)
(µl
CO2
per m
sq. sec
inverse
T.S. A.S. S.D.S. T.S. A.S. S.D.S.
C-306 Control 1.32 2.97 2.63 10.86 15.54 6.18
Drought 2.17 4.34 8.16 9.74 11.66 4.64
Reirriga
ted
1.40 3.10 3.08 11.30 14.02 6.00
Kalyans
ona
Control 1.14 2.58 2.91 13.56 16.58 8.02
Drought 1.33 3.2 8.53 5.70 7.84 3.14
Reirriga
ted
1.18 2.87 3.16 13.62 13.62 8.20
D.C.Uprety and G.S. Sirohi, IARI New Delhi
40. VARIETI
ES
Stem
CONTRO
L
Leaf Seed
HG-75 1.841 1.951 1.738 2.271 0.675 0.573
IC-11521 1.894 1.500 2.044 1.379 0.864 0.483
DURGAJ
AY
2.357 2.820 2.234 2.987 1.097 1.172
FS-277 1.466 1.763 1.594 2.034 0.927 0.643
19-1-55 2.079 1.637 1.445 1.623 0.902 0.920
CONTROL STRESS CONTROL STRESSSTRESS
EFFECT OF WATER STRESS ON DRY WEIGHT OF STEM,LEAF,SEEDS IN FIVE
GUAR VAR.AT HARVEST.(CLUSTER BEAN) (g/plant)
SOURCE: INDIAN JOURNAL OF PLANT
PHYSIOLOGY M.S Kuhad and I.S Sheoran
42. RESPONSE OF AVENA SPECIES
LEAF PHOTOSYNTHESIS AND
STOMATAL CONDUCTANCE TO
WATER STRESS (RATIO OF
PHOTOSYNTHESIS(Pn) &
STOMATAL CONDUCTANCE (gs)
OF OAT SPECIES IN RESPONSE
TO WATER STRESS AT
VEGETATIVE AND FLOWERING
STAGES OF CROP GROWTH.
44. EFFECT OF ETHEREL ON
SOME MORPHOLOGICAL &
BIOCHEMICAL PARAMETERS
IN SOYABEAN GERMINATING
UNDER MOISTURE STRESS (
EFFECT OF MOISTURE
STRESS ON GERMINATION,
VIGOUR INDEX &
GERMINATION RELATIVE
INDEX)
