Physiological features of drought resistant plants
Various physiological characters which are related to drought resistance are photosynthetic rate, transpiration rate, osmotic concentration etc. These factors are briefly discussed below:
1. Osmotic adjustment
As a plant, detect a water deficit stress, it may accumulate a variety of osmotically active compounds such as amino acids, sugars and ion inside its cells, resulting in a lower of the cell osmotic potential. Water present in intercellular spaces then flows towards the inside of those cells. This process called “Osmotic adjustment”, was proposed as a potential factor that could enable plants to maintain turgor and survive better at low water status. It has however been argued that osmotic adjustment probably does not allow the plant to draw much extra water from the soil and that is could come at a cost in yield potential.
2. Cell membrane stability
The ability to survive dehydration is influenced by a cells ability to survive at reduced water content. This can be considered complementary to Osmotic adjustment because both traits will help maintain leaf growth during drought. Crop varieties differ in dehydration tolerance and an important factor for such differences in the capacity of the cell membrane to prevent electrolyte leakage at decreasing water content or cell membrane stability (CMS). The maintenance of membrane function is assumed to mean that cell activity is also maintainer. Measurements of CMS have been used in different crops and are known to be correlated with yields under high temperature and possibly under drought stress.
3. Epicuticular wax
In sorghum, drought resistance is a trait that is highly correlated with the thickness of the Epicuticular wax layer. Experiments have demonstrated that rice varieties with a thick cuticle layer retain their leaf turgor for longer periods of time after the onset of a water stress.
4. Partitioning and stem reserve mobilization
As photosynthesis becomes inhibited by drought, the grain filling process becomes increasingly reliant on stem reserve Utilization. 72 numerous studies have reported that stem reserve mobilization capacity is related to yield under water stress in wheat, rice. A few studies also indicated that this mechanism maintained grain yield under water stress at grain filling stage. The drought tolerance mechanism is stimulated by a decrease in gibberellic acid concentration and an increase in abscisic acid concentration.
5. Seedlings drought traits
For emergence from deep sowing (to exploit dry upper soil), this practiced to help seedlings reach the receding moisture profile and to avoid high soil surface temperatures which inhibit germination. Screening at these stage provides practical advantage specially when managing large amount of germplasms.
6. Accumulation of ABA
The benefit of ABA accumulation under drought has been demonstrated (Innes et al. 1984). It appears to pre-adapt plants to stress by reducing stomatal conductance, rates of cell division, organ size and increasing development rate. However, high ABA can also result in sterility problems since high ABA levels may abort developing florets.
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