Pistil development in Cleome flowers IV. Effects of growth-regulating substances on female abortion in Cleome spinosa Jacq.

Abstract

Summary Pistil development in flower buds of andromonoecious Cleome spinosa Jacq . is inhibited by sprays with NAA and with gibberellins, and promoted by Ethephon and zeatin. The action of gibberellins and Ethephon is not exerted via the fruits, gibberellin directly causing pistil abortion, whereas Ethephon requires the presence of endogenous gibberellins. Although exogenous auxin reduces pistil development, the main action of endogenous auxin in female abortion is rather to increase the sink activity of subjacent developing fruits, thus changing the competition for cytokinins from the roots. Hence, the intermittent formation of perfect and male flowers in zones on the inflorescence can be ascribed to a lack of cytokinins in flower buds on top of simultaneously developing fruits with a high sink activity.