Discuss the drought resistance mechanism in plants.
Answers
Response of Plants to Drought Stress
Plants growing in drought stress may have the ability to control / avoid stress by escaping (Enduring Drought) or tolerating stress (by developing succulent or Non-succulent habit). These two capabilities are collectively termed as Drought Tolerance.
i. Drought Evading Plants
These plants remain under dormant / perennation to avoid stress period by seeds and shoots. Such plants complete their life-cycle in few weeks within the rainy season (eg. CO 16 variety of sorghum). They are called as Ephemerals. These plants also prolong their life cycle for some time based on the necessity. They reduce water loss by certain mechanism.
ii. Succulents
These (CAM) plants store enough water in their tissues. Their stomata open at night. They have thick leaves and possess modifications (such as phyllodes and phylloclades) under water stress conditions. They fix carbon during day time with the help of malic acid and CO2, which is released internally during respiration.
iii. Non-succulents
These plants endure drought with the following adaptive features:
Succulents-Pineapple
Smaller leaves with thick cuticle
Sunken stomata with hair (pubescence) eg. Nerium
Shedding their leaves during summer to avoid excess water loss
Dehydration of protoplasm
Reducing enzyme activity
Favouring the syntheses of ABA (stress hormone) and Ethylene (senescence hormone)
Closing stomata due to increase ABA concentration, thereby reducing water loss
Nerium
Thus, because of these special features, succulents and non-succulents grow well under drought conditions. They are not or least affected by stress. Similarly, the arid zone plants also develop mechanisms to tolerate water stress, hence they are not adversely affected in terms of growth and yield. But, the non-arid zone plants suffer heavy loss in growth and yield because they do not have above said mechanisms to tolerate the stress.
iv. Drought Resistant Plants
These plants resist the water stress situations due to the following adaptive features / mechanisms. Therefore, these plants can be grown in drought facing / arid-zone areas.