Effect of Phytohormones Applications in the Amelioration of Water and Salt Stress Legumes

Abstract

Draught and salt stress are the two major economic constraints in Pakistan. Irrigation of crop plants with poor quality irrigation water often results in both salt stress and water stress in the dryer part of the irrigation cycle. Modulation of the varied responses of draught and salinity can be made in the balance of the growth regulators (Itai and Benzionii 1976, Naqvi et al, 1983). The delivery of growth hormones from the roots to the shoots is reduced by subjecting the roots to osmotic stress (Shaw and Loomis 1965, Bnizioni et al, 1967 Silton et al, 1967). During water stress the internal concentration of ethylene and ABA increases with a subsequent decrease in cytokinin was noted. Hubick et al (1986) reported that in sun flower plants the effect of drought and GAS and ethylene was minimal, stressed roots has 32 times more ABA than controls. The levels of cytokinins in the shoots of droughted plants were about half those in stressed shoots and glucosylation of cytokinin was noted. Tal and Imber (1970) and Aharoni et al, (1977) suggest that the endogenous level of auxins and GA may also decrease during drought. Some of growth inhabitation normally observed in osmotically stressed plants are reported to by direct application of growth regulators (O’ Leary and Prisco, 1980). Several phytohormones can reduce the stress-induced inhibition of plants. Even in halophytes, salt injury has been counteracted by GA3 (Starck et al, 1975). Cytokinin prevented the salt-induced necrosis of tobacco leaves and promoted the incorporation of amino acids into protein of sodium chloride-stressed tissues of pea roots (Benzioni et al, 1979). The role of ABA accumulation in the stomatal control of transcription and water use efficiency is the best documented example of hormone-mediated adaptation to change in the environment. ABA can also stimulate physiological response thought to be involved in adaptation to sodium chloride (La Rosa et al), 1985). Physiological adaptations to water stress indicate that plants are capable of internal osmotic adjustment by producing various metabolites (Kramer, 1980). Accumulation of O-methyl Scylloinositol and ononitol were noted in the leaves of several water-stressed Vigna species (Ford, 1982). How hormones control in this aspect would be particularly valuable if evaluated against a background knowledge of physiological adaptation of the plant to its environment. Moreover, biochemical changes are demonstrated to occur as plants rehydrate. We need to know whether these changes contribute to the ability of plants to grew in dry areas. Present attempts are: (a) screening of the varieties which may be relatively resistant to water and salt stress (b) effects of phytohormones applications in the amelioration of water and salt stresses and (c) measurement of myo-inositol level from the plants under stress and the effect of applied growth regulators on its le vel. Moreover, the nitrogen fixation process is sensitive to water stress in a number of legumes (Sprent 1971, 1972; Engin and Sprent 1973; Pankhurat and Sprent 1975). Investigations were also made on the effect of slat and growth regulators o nitrogenase activity of the nodules.