RESPONSES OF PLANTS TO WATER STRESS AND REMEDIAL MANAGEMENT STRATEGIES, ESPECIALY IN RICE

2. RESPONSES OF PLANTS
TO WATER STRESS AND
REMEDIAL MANAGEMENT
STRATEGIES, ESPECIALY
IN RICE
PRABHASMITA SHATPATHY
Adm No: 01PP/11
DEPT. OF PLANT PHYSIOLOGY
OUAT, BBSR

3. CONTENTS
• Introduction
• Plants’ morphological response to water stress
• Physiological response to water stress
• Biochemical response to water stress
• Remedial management strategies

4. INTRODUCTION
WHAT IS WATER STRESS?
• A major abiotic stress
• Induced by many environmental
conditions.
a) No rainfall (drought)
b) High salt conc.
c) Low temp.
d) Transient loss of turgor at mid day

5. RESPONSES OF PLANTS TO
WATER STRESS

6. Altered cellular
metabolism
Physiological and
Developmental events
Salt
Drought
Flooding
Extreme
temperature
Ozone

8. MORPHOLOGICAL RESPONSE TO
WATER STRESS

9. 1) GROWTH CHANGES:
 Reduction in cell and leaf expansion (ex: Populus).
Effect of water stress on leaf expansion of sunflower
(Boyer , 1970)

10.  Leaf growth rate is reduced. Leaf area is reduced.
Dependance of leaf growth on turgor pressure in sunflower
Y= yield threshold
(The pressure below
which the cell wall
resists nonreversible
deformation)
m= wall extensibility
(the responsiveness of
the wall to pressure)
Ѱp= turgor pressure
of the plant
(Matthews et al. 1984.)

11.  Leads to leaf abscission in some cases (ex: Populus,
cotton, paper birch).
CONTROL
-5 BARS -12 BARS -24 BARS
Leaves of young cotton plants abscise in response to water stress
(Courtesy: B. L.
McMichael)

12. Stem length is reduced (ex: soybean,
potato, okra).
Cell thickness is increased. Because
reduced cell volume causes increase in
solute conc. of cell. This in turn
compresses plasma membrane &
increase thickness.

13.  Root growth is increased as with
reduced leaf expansion, more C
translocated towards roots. This increases
water supply.
 Wax deposition on leaf surface is
increased, which reduces cuticular
transpiration & increases reflection

14. 2) YIELD:
• Water stress causes reduction in yield. Because
 Water stress → disrupt assimilate partitioning→
reduced leaf area → reduced photosynthetic
surface → reduced light interception → reduced
dry matter production.
 Water stress → stomata closes → reduce intake of
CO2 → reduced photosynthesis → reduced dry
matter production

15. Effect of drought on yields of corn and soybean crops in the
United States
Crop yield (percentage of 10-year average)
Year Corn Soybean
1979 104 106
1980 87 88 Severe drought
1981 104 100
1982 108 104
1983 77 87 Severe drought
1984 101 93
1985 112 113
1986 113 110
1987 114 111
1988 80 89 Severe drought
(Source: U.S Department of Agriculture 1989)

16. Taiz & Geiger,2002

17. 3) LEAF ORIENTATION AND LEAF MOVEMENT :
• Leaf movement can provide additional protection against
heating during water stress.
• Additional strategies for adapting leaf area to drought:
Loss of leaves
Wilting (changes angle of the leaf)
Morphology (vertical leaves)
Leaf rolling (in grasses)
• Reduction of radiation load results in less evaporation.

18. Strong effect of water stress on leaf position in soybean
Well Watered
Mild water stress Severe water stress
(Courtesy: D. M. Oosterhuis)

19. PHYSIOLOGICAL RESPONSE TO
WATER STRESS

20. Physiological changes due to water stress

21. 1) STOMATAL CLOSURE :

22. • Advantage: less loss of water
Disadvantage: less transport of CO2.
• Two types:
1) Hydro passive stomatal closure:
• Occurs in Ferns and Lycopods.
• Loss of water from stomatal guard cells,
turgor drops, stoma closes

23. 2) Active stomatal closure :
• Occurs in Angiosperms and Gymnosperms.
• This is mediated by ABA i.e produced by roots and leaves
during water stress and transported into guard cells.
• ROS (ex: H2O2 ) is produced which causes inhibition of
membrane proton pumps & influx of Ca2+. Increased
Ca2+ level causes efflux of anions from cells, which in
turn causes efflux of K+.
• Malate Starch. It reduces the osmotic potential
& turgor pressure. Cell volume reduces & stomata closes.

24. Passive stomatal closure Active stomatal closure

25. 2) PHOTOSYNTHETIC RESPONSES
Effects of water stress on photosynthesis:
1- early effect: mostly via stomatal closure
2- late effect: metabolic breakdown
Reasons for reduction in photosynthesis :
• Reduction in photochemical efficiency of PSI & PSII and
quantum generation.
• Disruption of cyclic & non-cyclic types of electron
transport during the light reaction of photosynthesis.

26. • Qualitative and quantitative changes in
photosynthetic pigments (reduced or even no
pigmentation). This reduces chlorophyll &
carotenoids (function as an accessory pigment
for photosynthesis ) synthesis.
• Low Co2 uptake due to stomatal closure.
• Damage of the photosynthetic apparatus
through the production of ROS (like
superoxide and hydroxyl radicals).

27. • Poor assimilation rates in photosynthetic
leaves (due to reduced photosynthetic
metabolites & enzymes activity, low
carboxylation efficiency and inhibition of
chloroplast activity).
• Rapid decrease in the amount of RubisCO
which in turn leads to lower activity of the
photosynthetic enzymes.

28. Effect of water stress on photosynthesis of Fraxinus
americana and F. pennsylvanica trees (Cregg et al, 2009)

29. Effect of water stress on photosynthetic rate of two olive
cultivars (Guerfel et al., 2009)

30. Effect of water stress on photosynthesis
of sunflower (Boyer, 1970)

31. 3) CHLOROPHYLL CONTENTS
• Decrease in chlorophyll content under water deficit
due to pigment photo-oxidation and chlorophyll
degradation.
• Both the chlorophyll a and b are prone to soil
dehydration (Farooq et al., 2009).
• Drought or heat stress produce ROS such as O2
-
and H2O2, can lead to lipid peroxidation and
consequently, chlorophyll destruction (Mirnoff,
1993; Foyer et al., 1994).

32. (A) Plants grown under
well watered
conditions
(B) Plants of the same
age after two
cycles of drought-
stress treatment
Ajay K. GargAjay K. GargAjay K. Garg
(Ajay K. Garg,2002)

33. • This causes reduction in the net photosynthesis
and dry matter production.
• But, with decreasing chlorophyll content, green
colour of the leaf changes into yellow, which
increases the reflectance of the incident
radiation (Schelmmer et al., 2005). It seems that
this mechanism can protect photosynthetic
system against stress.

34. Chlorophyll content (mg g-1 FWof Leaf ) in 5 rice cultivars grown
under simulated water stress
Variety
Control
(No stress)
Water stress at PI
stage
Parijata 3.08 1.50
Sidhant 2.78 1.41
Mandakini 3.07 1.37
Lalat 3.18 1.61
Manaswini 2.96 1.43

35. 4) OSMOLYTE ACCUMULATION
• Under drought, the maintenance of leaf turgor may be
achieved by osmotic adjustment with the accumulation
of compatible solutes or osmolytes in cytoplasm.
• The cell actively accumulates solutes. It reduces the
solute potential, which promotes the flow of water into
the cell.
• These osmolytes include proline, glycinebetaine,
mannitol, sucrose, soluble carbohydrates etc.

37. Proline content (μmol/g of leaf tissue) in 5 traditional rice cultivars
grown under simulated physiological drought stress (Borah et al, 2012)
Variety
Control
(deionized
water)
Simulated
osmotic drought
of 0.15 bar
Simulated
osmotic drought
of 0.25 bar
Borah 0.001 0.0131 0.161
Laodubi 0.003 0.132 0.253
Beriabhanga 0.061 0.068 0.171
Leserihali 0.057 0.053 0.204
Kolajoha 0.052 0.075 0.083

38. 5) WATER RELATIONS
• Relative water content (RWC), leaf water potential
(LWP), stomatal resistance, rate of transpiration,
leaf temperature and canopy temperature are
important characteristics of plant water relations.
• Exposure of plants to drought stress substantially
decreased the LWP, RWC and transpiration rate
(Siddique et al., 2001).

39. Leaf water potential of eight maize genotypes grown under
control and water stress conditions (Neto and Prisco, 2004)
Genotype Control Stress
BR3123 -0.22 -0.49
BR5004 -0.24 -0.51
BR5011 -0.34 -0.62
BR5026 -0.21 -0.37
BR5033 -0.29 -0.32
CMS50 -0.15 -0.37
D766 -0.25 -0.40
ICI8447 -0.30 -0.45

40. Dawn (0500h) & midday (1300h) estimates of leaf water potential of 2 rice cultivars
(IR 28 & Kinandang Patong) subjected to well watered (control) & water stress
treatments during a 29 period (Goday et al., 2012)

41. BIOCHEMICAL RESPONSE TO
WATER STRESS

42. 1) GENERATION OF ROS (REACTIVE OXYGEN SPECIES)
AND PRODUCTION OF ANTIOXIDANT ENZYMES
• ROS, such as H2O2, O2
-, OH⁻ and OH2, are
by-products in electron transport chains
and have unpaired electrons that can
attract electrons from other components.

43. • ROS can therefore cause damage to a variety of
compounds such as DNA, RNA, proteins, lipids
and chlorophyll and thus damage membranes
and change cell metabolism and eventually lead
to senescence.
• So plants have evolved various ROS scavenging
mechanisms. These include many antioxidant
systems, both enzymatic and non-enzymatic.

44. • Enzymatic antioxidants, such as superoxide
dismutase, peroxidase, ascorbate peroxidase,
catalase, polyphenol oxidase and gluthathione
reductase can detoxify ROS.
• The non-enzymatic anti oxidants, including
vitamins (A, C and E), glutathione, carotenoids
and phenolic compounds, can scavenge ROS by
donating an electron or a hydrogen atom.

45. :
Water
stress
damage membranes
macromolecules
SOD
catalase
ascorbate peroxidase
glutathione reductase
ascorbate
glutathione
carotenoids
anthocyanins
osmolytes
proteins
amphphillic molecules

46. 2) PRODUCTION OF STRESS PROTEINS AND CHAPERONES
• Proteins increase and decrease in response to water
stress.
• Heat-shock proteins (Hsps) and late embryogenesis
abundant (LEA)-type proteins are two major types of
stress-induced proteins during water stress.
• LEA-proteins accumulate in dehydrating leaves, and
during seed ripening
• The LEA-like proteins are thought to act as
chaperones.

47. • Function:
a) protect enzymatic activities (Reyes et al.,
2005)
b) prevent misfolding and denaturation of
important proteins (Xiong and Zhu, 2002)
c) Protect macromolecules such as
enzymes, lipids and mRNAs from dehydration

48. Overall response:

49. REMEDIAL MANAGEMENT
STRATEGIES FOR DROUGHT,
ESPECIALLY IN RICE

50. • Drought management strategies need to focus
on maximum extraction of available soil
moisture and its most efficient use in crops for
increasing yield.
• Types of strategies:
(a) Agronomic
(b) Genetic

51. In order to plan crop yield improvement programs for a
given target drought-prone area the following steps are
essential:
• Characterize the major patterns of drought stress and
their frequency of occurrence in the target environment
• Evaluate crop response to the major drought patterns
(simulation modeling)
• Match crop phenology (growth period, sowing,
flowering, and seed filling) with most favourable period
of soil moisture and climatic regimes

52. • Develop a strategy for the optimal use of
supplementary irrigation, when available
• Increase available soil water to crop through
agronomic management practices
• Identify plant traits that would maximize (i) use
of available soil moisture in transpiration (ii)
production of biomass per unit water transpired,
and (iii) partitioning into seed, thereby
conferring enhanced crop water productivity.

53. (a) Agronomic management strategies:
International Rice Research Institute (IRRI, Phillipines)
adopts two main strategies for coping with drought.
1. Drought escape: This involves
• avoiding drought through adapted cropping
calendars
• planting short duration varieties
• providing access to additional water resources like
irrigation.

54. 2. moderate drought (by reducing unproductive
water losses):
This helps in saving water for productive
transpiration. This can be done
• by dry direct seeding
• by adopting aerobic rice production
• by better water and nutrient management.

55. Use of ground water efficiently:
SPRINKLER IRRIGATION BED & FURROW IRRIGATION
DRIP IRRIGATION

56. Other strategies are:
• Use of drought tolerant varieties:
Example: Sahbhagi dhan
• Adoption of early maturing varieties well adapted
to direct seeding and varied levels of moisture
stress.
• Use of quality seeds.
• Increase level of fertilizer use in areas of moderate
and low fertilizer use

57. • Amelioration of inland salinity/alkalinity affected
areas.
• Practicing deep summer ploughing.
• Adoption of appropriate rain water management
devices for better moisture conservation and
utilization (dams, reservoirs etc.).
• Transvasement - Building canals or redirecting
rivers for irrigation purpose in drought-prone
areas.

58. Rain water harvesting structures
Dams

59. (b) Genetic management strategies:
• Genetic management strategies for drought focus
on maximum extraction of available soil moisture
and its efficient use in crop establishment and
growth to maximize biomass and yield.
• So for this, Various approaches have so far been
tested to produce stress tolerant plants using
classical genetic methods as well as improved plant
breeding techniques.

60. • Select genotypes that have improved yield in
dry environments.
• Potentially important traits for plant breeding
for stress resistance include:
i. water-extraction efficiency
ii. water-use efficiency
iii. hydraulic conductance
iv. osmotic and elastic adjustments
v. modulation of leaf area.
vi. Plant emergence characteristics/vigor
vii.Phenology/ Elasticity of development
viii.Nutrient acquisition/Uptake efficiency

61. ix. Photosynthesis, Radiation Use Efficiency
x. Deep Root development
xi. Hormonal regulation (ABA, GA, Ethylene)
xii. Osmotic Adjustment/RWC
xiii. Canopy temperature
xiv. Stay green/ Delayed senescence
xv. Grain number maintenance
xvi. Grain fill duration and rate
xvii. Harvest Index under Drought
xviii. Yield and its components

62. • Genetic engineering method is also adopted to produce
transgenic plants with improved stress tolerance.
New pathways for the biosynthesis of various
compatible solutes (ex: proline and betaine) are
introduced into plants, which improved stress tolerance.
ex: Transgenic rice plants overexpressing the p5cs gene
that encodes P5CS produced more proline and exhibited
better performance, reduced free radical levels and
higher biomass under osmotic stress.

63. A number of sugar alcohols like mannitol,
trehalose, myo-inositol, D-ononitol and sorbitol
have been targeted for the engineering of
compatible solute overproduction.
Ex: Trehalose overproducing transgenic rice
plants showed high tolerance to different
abiotic stresses and maintained optimal K+/Na+
ratios necessary for cellular functions.

64. LEA protein accumulates in plants in response
to water stress and have several functions in
plant resistance to drought.
Ex: Over expression of a barley group 3 LEA
protein gene, HAV1 in transgenic rice,
showed better stress tolerance under salt and
drought stress than wild-type plants.

65. CONCLUSION
• Knowledge should be gained on survival mechanisms
which may be used for improving drought tolerant
cultivars for areas where proper irrigation sources are
scarce or drought conditions are common.
• our knowledge about causes and consequences of the
water stress in plants still has many dark areas, and we
need to enhance our efforts in furthering our
appreciation of the issue.

66. REFERENCES
• http://en.wikipedia.org/wiki/Redox
• Shakeel Ahmad Anjum, Morphological, physiological and biochemical responses of
plants to drought stress, African Journal of Agricultural Research Vol. 6(9), pp. 2026-
2032, 4 May, 2011.
• Apel K, Hirt H (2004). Reactive oxygen species: metabolism, oxidative stress, and signal
transduction. Annu. Rev. Plant Biol., 55: 373-399
• Cornic G (2000). Drought stress inhibits photosynthesis by decreasing stomatal
aperture - not by affecting ATP synthesis. Trends Plant Sci.,5: 187-188
• Nayyar H, Walia DP (2003). Water stress induced proline accumulation in contrasting
wheat genotypes as affected by calcium and abscisic acid. Biol. Plant., 46: 275-279
• Benjamin JG, Nielsen DC (2006). Water deficit effects on root distribution of soybean,
field pea and chickpea. Field Crops Res., 97:248-253
• Jaleel CA, Gopi R, Sankar B, Gomathinayagam M, Panneerselvam R(2008). Differential
responses in water use efficiency in two varieties of Catharanthus roseus under
drought stress. Comp. Rend. Biol.,331: 42-47