Introductory Crop Physiology (1+1)

Drought Resistance

Drought resistance

1. Drought avoidance/ drought postponement
2. Drought tolerance

Drought avoidance/ drought postponement: Ability to maintain tissue hydration or plants ability to maintain a high level of water status or turgor under conditions of increasing soil water deficits.
Dehydration tolerance: Ability to function while dehydrated is called as dehydration tolerance mechanism which maintains tissue hydration during drought

Reduction in water loss

a) Reduction in transpiration area
b) Stomatal behaviour: It is governed by
• Uptake/lose of K – changes in osmotic potential of guard cells
• Metabolic changes involving organic acids ex: Malate
• Hormones – ABA and cytokinines
c) Waxiness
d) Leaf rolling

e) High hydraulic resistance by decreasing the diameter of xylem

f) Root to shoot signaling: (Conservative approach) ABA synthesized in drying roots moves to the shoot and regulates leaf conductance, leaf expansion and thus brings about reduction in water lose ( Drought postponement)

• Water is conserved for further use in later stages
• Early warning/signal
g) WUE: Balance between water used or water availability with respect to biomass production (at canopy level). At whole plant level it is the ratio between the photosynthesis and transpiration. When there is decline water potential- shoot growth is completely ceased but root growth will continue even under severe stress condition

h) Root characteristics: Uptake of water


Mechanism which are related to the ability to function while dehydrated
1. Membrane integrity: Ability of a cell to maintain structure and function of membrane especially to prevent electrolyte leakages.
2. Osmotic adjustment: Adaptional response to decrease the water potential in the extreme environment resulting in increased accumulation of compounds like proline, glycine betain, manitol, sorbitol, etc in the cell is called as osmoregulation or osmotic adjustment. Mechanism to maintain the turgor even at low water potential is extremely important for saline adaptation.
3. Stress proteins: Proteins of smaller molecular weight are synthesized by organisms as a physiological response to environmental stress for cellular protection. eg., heat shock proteins, dehydrins, osmotins, etc

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