ON THE CLAIMED ‘ADAPTIVE’ NATURE OF IAA-OXIDASE AND AN EFFECT OF GREEN LIGHT ON IAA-OXIDASE ACTIVITY

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Abstract
This paper examines the claim by Galston and Dalberg (Am. J. Botany, 41, 373 (1954), that IAA-oxidase is an adaptive enzyme, by which was meant that it is an enzyme formed as a consequence of the presence of IAA. Certain of the published evidence is rejected as irrelevant to the question.It is shown here that crude IAA-oxidase preparations from etiolated pea buds show a lag phase in IAA destruction whereas this is not so with enzyme from hook tissue or older stem tissue.Pretreatment of hook tissue or older tissue with IAA did not increase IAA-oxidase activity. It is confirmed that IAA-oxidase preparations from buds pretreated with IAA gave more destruction of IAA, when measured after 60 minutes, than did enzyme from untreated buds. This difference occurred because of elimination of the lag phase in destruction and not because of induced formation of enzyme.The lag phase in IAA-oxidase activity with enzyme extracted from buds was increased by exposing the seedlings to 3 minutes of weak green light (maximum transmission 520 mμ) at 16 hours before harvest. Pretreatment of such light-treated buds with IAA did not completely eliminate the lag phase in IAA-oxidase activity. It is suggested that these effects of green light are a new photo-effect in plants.

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