HORMONAL-CONTROL OF EAR ABORTION IN A STRESS-SENSITIVE MAIZE (ZEA-MAYS) INBRED

A cold-sensitive maize (Zea mays L.) inbred was used as a model for in vestigating the interactions between growth regulators, reproductive d evelopment, and environmental stress. In this genotype, a chilling tre atment given just before floral transition caused the topmost ear to a bort and be replaced at maturity by a sterile, leaf-like, structure. E xogenous applications of the synthetic auxin 2,4-dichlorophenoxyacetic acid or of the cytokinin benzyladenine respectively mimicked or preve nted the abortive response caused by chilling. Chilling also induced a moderate decrease in the content of endogenous indoleacetic acid (IAA ) in the apical shoot tissues. By contrast, zeatin-type cytokinins dec reased dramatically (5-8 fold), both in the apical shoot tissues and i n the xylem exudate of chilled plants. Overall, the ratio of free-IAA to zeatin-cytokinins was increased in the apical shoot of chilled plan ts. Our results suggest that: (1) ear abortion induced by chilling mig ht be related to an altered cytokinin content; (2) the number of devel oping ears may be limited by the endogenous levels of cytokinins just before floral transition; and (3) cytokinins may have a potential for increasing yield in maize.