Drought stress occurs when there is a period of unusually dry weather within an area causing a lack of precipitation. Plants have developed three main mechanisms to deal with drought stress: drought escape by completing their lifecycle before the dry season, drought avoidance by maintaining high tissue water potential through deeper roots and reduced transpiration, and drought tolerance by withstanding low water potential through processes like osmotic adjustment. The effects of drought stress on plants include reduced growth due to lower turgor pressure, decreased photosynthesis, and changes to carbohydrate and protein metabolism.

1. DROUGHT STRESS
SUBMITTED BY: MUZAMIL TASSEN
ROLLNO: IUBC1IBB112
4th semester2016-20
Islamia university Bahawalpur

2. Introduction
 Drought is a period or condition of unusually dry weather
within a geographic area where there is a lack of precipitation.
 The characteristics features of drought stress is low water
potential due to high solute concentration.
 Low water supply causes soil mineral toxicities and can make
a plant more susceptible to damage from high irradiance.

3. MECHANISM OF DROUGHT STRESS
 DROUGHT ESCAPE: It is defined as the ability of a plant
to complete its life cycle before supply of water in soil is depleted
and form dormant seeds before the onset of dry season. These
plants are known as drought escapers since they escape drought
by rapid development.

4.  DROUGHT AVOIDANCE: It is the ability of plants to
maintain relatively high tissue- water potential despite a shortage
of soil moisture. Drought avoidance is performed by maintenance
of turgor through roots grow deeper in the soil, stomatal control
of transpiration and by reduction of water loss through reduced
epidermal i.e. reduced surface by smaller and thicker leaves.

5.  DROUGHT TOLERANCE: It is the ability to withstand
water deficit with low tissue water potential. Drought tolerance is
the maintenance of turgor through osmotic adjustment (a process
which induces solute accumulation in cell), increase in elasticity
in the cell and decrease in cell size.

6. Figure: Drought Avoidance : Reduced surface by smaller
and thicker leaves

7. Mechanisms of resistance to drought and
the methods to increase the resistance
 Increase in water absorption and transportation, declination of
transpiration
 Developing root system
 Thick leaf and cuticle
 Developed veins and bundle smaller and more stomata

8.  Physiology and biochemistry:
 Stomatal regulation
 Increase in capacity of resistance to dehydration of
cytoplasm: Rapid accumulation of Pro, glycinebetaine,
Lea protein, dehydrin, osmotins and ion etc.: ABA
accumulation→stomatal closure

9. EFFECT OF DROUGHT STRESS
 Effect on Growth: Reduction in Turgor Pressure, due to cell sizes
will be smaller.
 Effect on Photosynthesis: Photosynthesis decreases due to
disruption of PS II (Photo System II), stomatal closure, decrease
in electron transport.
 Decrease in nuclear acids and proteins: Protease activity↑, free
aa↑, RNAase activity↑，RNA hydrolysis, DNA content falls
down.
 effect on Carbohydrate metabolism: Loss of starch and increase in
simple sugars, carbohydrate translocation decreases.