Steroid Phytohormones: Function, Mechanism of Action, Significance

Abstract

In plants, steroid hormones serve as endogenous signaling molecules. Brassinosteroids act as positive growth regulators or as compounds responsible for plant stress tolerance. Phytoecdysteroids probably show an antifeedant activity. It is assumed that the brassinosteroid signal transduction is mediated by the membrane receptor system whereas the ecdysteroid action is still unclear. This review summarizes possibilities of identifying plant proteins capable of binding to steroid hormones in order to get a better insight into their function. Methods of studying the mechanism of action of steroid phytohormones include gene knock-out or knock-down technologies or direct isolation of steroid-binding proteins. The approach is illustrated by the known mechanisms as well as by identification of the Rubisco enzyme as a steroid-binding protein.