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

Abstract

In the sweet corn cultivar, Iochief, an episode of water deficit during early tassel development results in a subsequent promotion of the growth of the lower axillary inflorescences. This response is also produced by the application of abscisic acid (ABA) at this period of growth to well-watered plants, and the hypothesis that the response to water deficit was due to an increase in endogenous ABA concentration was examined. The ABA contents of the tassel, leaf and axillary inflorescences were found to increase during water stress, the increase in the tassel and axillary buds being most rapid in the first 2 days of water deficit. This increase in free ABA content was followed after 4 days of water deficit by a progressive increase in the concentration of ‘bound’ ABA in the tissues. There was little increase in free ABA concentration after 4 days water deficit; this paralleled the subsequent growth response of the axillary inflonscences which also was unaffected by prolonging the epidose of water deficit beyond 4 days. In order to establish whether the response of the axillary inflorescences to ABA was dependent upon the presence of the tassel, ABA was applied to watered plants with or without the developing tassel. As had been previously found with water stress, removing the tassel inhibited the response of the plant to applied ABA.