morphological and physiological characters changes - Drought Resistence
- 1. BASICSOFDROUGHTTOLERANCE– MORPHOLOGICAL ANDPHYSIOLOGICAL CHARACTERS PBG-301 FUNDAMENTALS OF PLANT BREEDING(2+1)
- 2. BASICS OF DROUGHT RESISTENCE ◦ Drought resistance (DR) is defined as the mechanism causing minimum loss of yield in a water deficit environment relative to the maximum yield in a water constraint free management of the crop. ◦ Plants have evolved several mechanisms to cope with water deficit stress which includes drought escape and drought tolerance.
- 3. CHARACTERS ◦ MORPHOLOGICAL ◦ Increase in water absorption and transportation, declination of transpiration a. Developed root system and higher ratio of root to shoot. ◦ Thick leaf, smaller leaf area and thick cuticle ◦ Developed veins and bundle，smaller and more stomata (cuticular resistance& hydraulic resistance) ◦ PHYSIOLOGICAL ◦ Stomatal regulation: ABA accumulation→stomatal closure ◦ Increase in capacity of resistance to dehydration of cytoplasm: Rapid accumulation of Pro, glycinebetaine, Lea proteiChanges in stomatal resistance ◦ Maintenance of turgor ◦ Changes in dehydration tolerance ◦ Changes in allocation of assimilates, dehydrin, osmotins and ion etc. • Changes in radiation interception
- 4. Changes in root density and depth Transcriptome Sequencing of Chickpea (Cicer arietinum L.) Genotypes for Identification of Drought-Responsive Genes Under Drought Stress Condition
- 5. Changes in hydraulic resistance When water is left in the profile, a decrease in root resistance may increase the reservoir of water available to the plant. With a limited volume of water in the soil, an increase in hydraulic resistance in the root saves water during vegetative growth for use during reproductive growth.
- 6. Changes in leaf area Through a reduction in leaf size or by the shedding or death of leaves Case study Atmospheric and soil water influences on the plant water balance Several recent studies with sunflower have shown that water stress during vegetative development reduces leaf size by about two-thirds (Fig. 1a). Water stress reduced the leaf area index from 6 in irrigated plants to 2 in unirrigated plants. Ritchie (1974) demonstrated that, provided the soil surface is dry, once the leaf area index decreases below about 3, evapotranspiration decreases approximately linearly with leaf area to give zero evapotranspiration at zero leaf area.
- 7. Changes in radiation interception. An alternate mechanism for adaptation to stress without irreversibly affecting leaf area is through changes in leaf angle or orientation. These changes reduce the radiation load on the leaves and allow the plant to dissipate less energy as latent heat. Important features of the mechanisms responsible for changes in leaf orientation are that they operate only during stress and that their recovery is rapid when stress is relieved. Case study Adaptation of rice environments In rice, leaf rolling under controlled environment conditions decreased the rate of transpiration by up to 50% (O’Toole et al 1979a).In the field, reduction in evapotranspiration from an equivalent degree of leaf rolling is likely to be smaller, due to an increase in the sensible heat and vapor pressure deficit within the canopy when the soil surface is dry or because of more rapid evaporation of water when the soil surface is wet.
- 8. Gilbert, ME., & Medina, v.(2016)
- 9. Changes in cuticular resistance (Hübl 1963, Turner et a1 1978a, Muchow et a1 1980)
- 10. Even if changes in waxiness fail to change leaf reflectance, they may change the resistance of the cuticle to water loss. O’Toole et a1 (1979b) reported that differences in cuticular resistance correlated with differences in epicuticular wax deposition in rice Physiological mechanisms Changes in stomatal resistance. The ability of stomata to regulate water loss provides an important mechanism for reducing water loss during drought. Crop plants show a range in sensitivity of stomata to water deficits. Case study Stomatal responses to air humidity and to soil drought Turner (1974) showed that, under field conditions, stomatal resistance increased markedly at values of leaf water potential ranging from -0.8 MPa in field beans to below –2.7 MPa in cotton. Varietal differences in stomatal response to water stress have been reported in sorghum and wheat (Blum 1974, Jones 1977)
- 11. Maintenance of turgor As water is removed from a cell with the development of water deficits, the solutes inside the plasmalemma are concentrated and the osmotic potential is lowered. The degree of concentration depends on tissue elasticity. For a given change in water potential, the greater the elasticity, the greater the concentration of solutes. (Turner and Jones 1980). Changes in dehydration tolerance. When drought stress becomes prolonged or severe and other mechanisms of adaptation fail or have been exhausted, the ability of tissues to withstand dehydration becomes important. Slow Rates of drying enhance dehydration tolerance (Gaff 1980), possibly due to the accumulation of solutes such as sugars and proline that protect proteins and aid in recovery.
- 13. Changes in allocation of assimilates Manipulation of nitrogen and water supplies has been used to demonstrate that excessive growth leading to a depletion of the water supply in the vegetative phase can lead to little reproductive growth and a severe yield reduction (Barley and Naidu 1964, Passioura 1972). Under such circumstances, transfer of nutrients and assimilates stored into roots , stems, and leaves to the grain should reduce the drastic effects of the depleted water reserves. CASE STUDY In such severe conditions, the proportion of preflowering assimilates that move to the grain increases from the usual 0-20% (20-40% in rice; Murata and Matsushima 1975) to as high as 60-70% (Gallagher et al 1976, Passioura 1976). However, in all cases in which this phenomenon has been studied, the actual amount of preflowering assimilates transferred to the grain has not increased. Rather, the proportion of postflowering assimilates in the grain has decreased (Passioura 1976, Bidinger et al 1977, Rawson et al 1977b). Although a high harvest index does not necessarily indicate a greater degree of translocation to the grain, the wide variation in harvest index among cultivars does suggest that variation for this character might exist in a broadly based gene pool.
- 14. REFERENCE Leaf morphology and reflectance in relation to water and temperature stress. Pages 295-308 in N. C. Turner and P. J. Kramer, eds. Adaptation of plants to water and high temperature stress. Wiley Interscience, New York. Murata, Y., and S. Matsushima. 1975. Rice. Pages 73-99 in L. T. Evans, ed. Crop physiology: some case histories. Cambridge University Press, Cambridge.