WATER RELATIONS OF COTTON FLOWER PETALS AND FRUIT

Water needed for expansion is believed to enter plant tissue in respon se to a growth-induced water potential gradient that occurs as turgor is reduced during relaxation of cell walls or in response to increased solutes. Under water stress, the cotton flower petal continues to exp and when all leaves on the plant are wilted and new leaf expansion has ceased in the shoot tips. This study was undertaken to determine if w ater for expansion entered the petal in response to a gradient or to i ncreased solutes. Water potentials of cotton petal, leaf, bract and fr uit were determined pre-dawn and midday in dryland and irrigated field plots. The mechanism by which petal expansion occurs appears not to b e associated with a growth-induced water potential gradient or to incr eased solutes because the gradient is reversed from that needed to dri ve expansion. The water potential of the petal tissues was consistentl y higher than that of the subtending leaves and bracts both during and after anthesis, and under different water stress conditions. How this reversal in water potential gradient is established and maintained sh ould provide insight into mechanisms involved in growth during water s tress.