IAA-oxidase activity in light grown cucumber hypocotyls treated with helminthosporol.

Helminthosporol (H-ol) promoted the growth of light grown cucumber hypocotyls. The IAA-oxidase activity per dry weight of the hypocotyl of H-ol treated materials was less than that of controls. There was an inverse relationship between IAA-oxidase activity and H-ol induced elongation of the hypocotyl. However, when IAA-oxidase activity per plant was compared between H-ol treated materials and controls there was no essential difference. It is concluded that the apparent inhibitory effect of H-ol on IAA-oxidase activity is not directly related to the mechanism of H-ol action.