A potential role for cellulase in hormone-controlled elongation

Abstract

Summary Measurements were made of the effects of indoleacetic acid (IAA), gibberellic acid (GA) and cycloheximide (CH) on growth, protein content and cellulase activities of segments derived from the apex of decapitated, etiolated epicotyls of Pisum sativum L. var. Alaska. Increasing amounts of CH caused increasing inhibition of both endogenous and hormonestimulated elongation, whereas certain critical levels of CH converted the expansion elicited by high levels of IAA into elongation. This CH-evoked conversion from expansion into elongation was accompanied by a partial decrease in protein accumulation and cellulase activity. Cellulase activity per segment increased in proportion to total growth (fresh weight) in tissues elongating in response to high levels of GA or low levels of IAA. In contrast, cellulase activity per segment rose markedly in tissues expanding in response to high levels of IAA. It is concluded that the amount of IAA present in the tissue governs the level of certain growth-limiting-proteins (GLP). These GLP, in turn, control the amount and direction of growth (i.e., elongation or expansion). It is suggested that cellulase should be considered as a candidate for the role of a GLP whose activity is modulated by IAA.