Ethylene: Interorgan signaling and modelling of binding site structure

Ethylene is involved in many developmental processes including the senescence of petals in ethylene sensitive flower species such as carnation, orchids and Petunia. The mode of action of ethylene in petal senescence may be its effect on the expression of numourous genes, among them genes coding for enzymes directly involved in cell death and genes encoding ethylene biosynthetic enzymes or components of the ethylene perception and signal transduction route(s). In carnation, a range of different senescence-related (SR) genes were isolated by Woodson and co-workers. Expression of most of these genes increased during the rise in ethylene production while treatment with the ethylene inhibitor 2,5-norbornadiene generally was inhibitory, indicating that expression is controlled by ethylene [1]. Based on homology studies with other known proteins, putative roles of some of the proteins in petal senescence is expected. Among the carnation SR genes, besides from the ethylene biosynthetic genes ACC synthase and ACC oxidase, the following activities have been reported: beta-glucosidase, beta-galactosidase, glutathione-S-transferase, carboxyphosphonoenolpyruvate mutase and thiol protease [1 and references therein]. Although some of these enzymes may be directly or indirectly involved in the processes leading to petal senescence, definite proof of their function e.g in transgenic plants, is lacking.