Apical Dominance, Water Deficit and Axillary Inflorescence Growth in Zea mays: The Role of Abscisic Acid

In the sweet corn cultivar, Iochief, an episode of water deficitduring early tassel development results in a subsequent promotionof the growth of the lower axillary inflorescences. This responseis also produced by the application of abscisic acid (ABA) atthis period of growth to well-watered plants, and the hypothesisthat the response to water deficit was due to an increase inendogenous ABA concentration was examined. The ABA contentsof the tassel, leaf and axillary inflorescences were found toincrease during water stress, the increase in the tassel andaxillary buds being most rapid in the first 2 days of waterdeficit. This increase in free ABA content was followed after4 days of water deficit by a progressive increase in the concentrationof ‘bound’ ABA in the tissues. There was littleincrease in free ABA concentration after 4 days water deficit;this paralleled the subsequent growth response of the axillaryinflonscences which also was unaffected by prolonging the epidoseof water deficit beyond 4 days. In order to establish whether the response of the axillary inflorescencesto ABA was dependent upon the presence of the tassel, ABA wasapplied to watered plants with or without the developing tassel.As had been previously found with water stress, removing thetassel inhibited the response of the plant to applied ABA. Zea mays, apical dominance, water stress, inflorescence growth, abscisic acid