Drought stress accounts for more crop production losses than any other factor. The presentation discusses the causes and effects of drought stress on plants and various tolerance mechanisms. It outlines that drought avoidance mechanisms include increased water absorption and transport, deep root systems, and reduced transpiration. Physiological responses include osmolyte accumulation, antioxidant production, and hormonal changes. Developing crops with drought tolerant traits through both conventional and molecular breeding approaches will be important for improving productivity under increasing drought conditions from climate change.

1. Presented by:
PhD student: Mohaned Mohammed

2. Drought stress and tolerance mechanisms
in crops:
What is drought:
Is a period or conduction of unusually dry weather with a
geographic area where there is a lack of precipitation.
Drought stress account fro more production losses than all
other factors combined.
Fraction of world arable land subject to drought (abiotic
stress) 26%.
Drought is caverned by various factors, the most prominent
are:
 Extreme of temp
 Photon irradiance
 Paucity of water

3. The characteristic 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

4. Major reasons of drought
Atmospheric factors:
High temp
High wind
Air pollution
Soil factors:
• Low temp
• Excessive soil salinity
• Receding water content

5. Different type of drought
 Meteorological drought:
Due to prolonged period with less than average
precipitation.
 Agricultural drought:
Which affect crop production or ecology of range.
 Hydrological drought:
When the water reserves available in sources such as
lack and reservoirs fall be low statistical avreage.

6. Effect drought stress on plants
Effect on growth:
Reduction of turgor pressure, due to cell size will be
smaller.
Effect on photosynthesis:
Photosynthesis decreases due to distruption of PS II
(photo system II), stomatal closure and decrease in
electron transport.
Decrease in nuclear acid and proteins

7. Protease activity, RNAase activity, RNA hydrolysis and
DNA content falls down.
effect on Nitrogen metabolism.
Nitrate reductase activity, nitrite reductase activity
insensitive.
Effect on carbohydrate metabolism;
Loss of starch and carbohydrate translocation decrease.

8. Mechanism of drought tolerance:
 Drought scape:
It is defined as ability of a plant to complete its life cycle
before supply of water in soil is depleted. These plant
known as drought scapers.
 Drought avoidance:
It is ability of plant to maintain relatively water balance
despite a shortage of soil moisture.

9.  Drought tolerance:
It is ability of plant to withstand water deficit with low
tissue water potential.

10. Mechanisms of resistance to drought
Morphological response to drought:
 Increase in water absorption and transportation,
declination of transpiration.
 Developed root system and higher ratio of root to
shoot.
 Thick leaf
 Small leaf area
 Thick cuticle
 Developed veins and bundle
 Smaller and more stomata

11. Physiological and biochemical basis of drought stress
tolerance in plants:
 Increase in capacity of resistance to dehydration of
cytoplasm: rapid accumulation of proline,
glycinebetaine, and ion etc.
 Synthesis of specific proteins like LEA.
 Reduced ROS accumulation.
 Increase in antioxidative enzymes.
 Decreased efficiency of Rubisco.

12.  Phytohormone play vital role in drought tolerance in
plants.
Under drought condition, endogenous contents of
auxins, gibberellins, cytokine, usually decrease while
those of abscisic acid and ethylene increase.
 There are many signals that induce stomatal closure
among these the best known signal is ABA.

14. Summary
 In the days of global warming, the effect of drought
stress on crop productivity is expected to increase.
 The crop plant have involved certain resistance
mechanism agaist drought stress.
We should identify these mechanism and traits
And we introgress these into succeptable genotypes
 Only conventional breeding is not sufficient in
development of drought tolerant varieties.

15.  Non conventional approaches i.e. molecular breeding
can play a significant role in the sphere of abiotic stress
mainly drought tolerance.
 Genomic regions carrying drought tolerant gene can
contribute for abiotic stress tolerance.