drought resistences changes in morphological and physiological characters

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.

12. G.S.Jeena.,& R.K`Shukla.,(2017)

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.