DIFFERENTIAL-EFFECTS OF CALMODULIN ANTAGONISTS ON INDOL-3-YLACETIC ACID-INDUCED AND GIBBERELLIC ACID-INDUCED BIPHASIC GROWTH-RESPONSES

The effects of chlorpromazine and calmidazolium on rapid IAA- and GA3-induced changes in growth rate of etiolated pea stems were measured. During the initial period of up to 160 min after hormone application, the responses to both IAA and GA3 were seen to be biphasic, showing two acceleration peaks. Chlorpromazine or calmidazolium applied simultaneously with the hormones blocked the first IAA-induced acceleration peak, but did not affect the second one. In contrast, the first GA3-induced peak was not prevented by chlorpromazine or calmidazolium, while the second one was completely abolished. The results support the concept that the active calmodulin-calcium complex may be an essential component of hormone-controlled stem elongation. They also point to differential mechanisms of IAA and GA3 actions.