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Environmental and Stress Physiology

Influence of Water Deficits on the Abscisic Acid and Indole-3-Acetic Acid Contents of Cotton Flower Buds and Flowers

U.S. Department of Agriculture, Agricultural Research Service Western Cotton Research Lab, Phoenix, Arizona 85040, Plant Stress and Health Physiology Laboratory, Weslaco, Texas 78596

A field experiment was conducted during the summer of 1988 to test the hypothesis that water deficit affects the abscisic acid (ABA) and indole acetic acid (IAA) concentrations in cotton (Gossypium hirsutum L.) flower buds in ways that predispose young fruits (bolls) that subsequently develop from them to increased abscission rates. Water deficit had little effect on the ABA content of flower buds but increased the ABA content of flowers as much as 66%. Water deficit decreased the concentrations of free and conjugated IAA in flower buds during the first irrigation cycle but increased them during the second cycle. Flowers contained much less IAA than buds. Water deficit slightly increased the conjugated IAA content of flowers but had no effect on the concentration of free IAA in flowers. Because water deficit slightly increased the ABA content but did not decrease the IAA content of flowers, any carry-over effect of water deficit on young boll shedding might have been caused by changes in ABA but not from changes in IAA.