Distribution of Indoleacetic Acid Oxidase and Inhibitors in Light-Grown Cotton

Extracts of green plant tissues exhibiting IAAoxidase activity characteristically contain inhibitors of the enzyme (4, 11). The high concentration of such inhibitors prompted the discoverers of IAAoxidase to suggest that the system does not function in green tissue (16). Later, Galston and Dalberg (6) found that in etiolated tissue the in vitro IAAoxidase activity increases with age or IAA treatment. Similar studies of this enzyme in green tissue have been handicapped by the presence of the inhibitory substances. As will be pointed out in the discussion, the limiting effect of this handicap on other work has clearly left the adaptation and distribution of IAA-oxidase in green plants an open question. The recent finding that riboflavin and light will reduce or eliminate the effect of native inhibitors (11) has provided a method to survey the potential IAA destroying capacity of various green tissues and facilitated the present study. Cotton contains an IAA-oxidase-inhibitor system (11). This paper presents evidence for an increase, with age, of IAA-oxidase activity in light-grown cotton tissues. The evidence is compatible with the in vivo function of the enzyme proposed by Galston and Dalberg (6).