Simpson, G.M.2012-05-282013-01-042013-05-292013-01-04198519851985http://hdl.handle.net/10388/etd-05282012-152639This study was designed to determine how endogenous AbA levels in wheat plants changed when drought stress was imposed at various stages of its development and to select a stage of development at which changes in AbA levels were most sensitive to drought stress. Sensitivity in this sense was synonymous with the production of large amounts of AbA in response to drought stress. The variety used in this study was Pitic 62 and the plants were grown under controlled environmental conditions. At each of the five stages of development studied, tillering, stem elongation, booting, inflorescence emergence and milk development stages,stress was imposed on the plants up to five days of stress. Control plants were sampled on days corresponding to alternate days of stress. Parameters of plant water status studied were total leaf water potential, leaf osmotic potential, leaf pressure potential and relative water content. Changes in these parameters were related to changes in AbA levels, stomatal resistance and dry matter accumulation. It was found that there were clear differences in drought-induced increases in AbA levels between the stages of development. There was also a tendency to produce greater AbA levels in response to stress at later stages of development. The implications of these findings have been discussed. Relative increases in AbA levels were found not to differ greatly from stage to stage suggesting the possibility that it may be an inherent capability of the cultivar or crop.en-UStext