Formation of Activated States of Indoleacetic Acid and Cytokinins: An Experimental Approach to a Hypothesis Concerning Signal Transduction

Abstract

Heterocyclic compounds such as IAA or cytokinins are involved in plant regulation. Some of the effects of these hormones are related with H 2 O 2 or the promotion of the formation of free radicals. Cytokinins also play an active role in preventing aging and senescence in plant cells. They seem to act either by means of direct scavenging of free radicals or preventing their formation. Recently peroxides have been found to transduce messages, but both peroxides and free radicals have a short half-life which makes it difficult for them to act as a messengers between the primary production sites and the responding sites such as DNA. They may, however, secondarily oxidize key molecules such as ACC producing ethylene, which in turn can act as a secondary messenger. In this paper we show that IAA and cytokinins are able to form excited states either in the dark in the presence of pyridoxal phosphate, H 2 O 2 and linolenic acid or in the light in the presence of riboflavin. These systems are also able to promote ethylene formation from ACC. We also show that different substituents in the hormone molecules can significantly modify their reactivity, thus suggesting a possibility for hormone regulation.