CHANGES IN IAA-OXIDASE AND PEROXIDASE ACTIVITIES IN HYPOCOTYLS OF <i>LUPINUS ALBUS</i>, L, AFTER TREATMENT WITH INDOLE-3-ACETIC ACID

Abstract

The variation in IAA-oxidase and peroxidase activities in etiolated lupine hypocotyls treated with IAA is studied. Intact plants sprayed with 10^-3 M IAA solution, show an increase of IAA-oxidase in the hypocotyls after 6 h of treatment. After 24 h, the activity is the same as that of untreated plants. The effect of IAA varies with the age of the seedlings as well as with the localization along the hypocotyl. Only those zones with low growth or with recently stopped growth, exhibit an increase of IAA-oxidase after treatment with IAA, the increase being supressed by cicloheximide. When whole hypocotyls of different ages are incubated in IAA solutions, reproducible results are only obtained if plants are decapitated before the treatments. 24 h after decapitation IAA-oxidase decreases 30 % in relation to non decapitated seedlings. Decapitated seedling hypocotyls incubated with IAA show an increase of specific activity at 10^-4 M IAA, and a decrease at 10^-3 M IAA. Cicloheximide reinforces the IAA effect in both cases. Hypocotyl sections from decapitated seedlings show, after incubation with 10^-4 M IAA, variations in IAA-oxidase that are dependent on the localization of sections along the hypocotyl as well as the age of seedlings. In sections with active growth, the IAA treatment decreases the activity while in slowly growing sections or sections with recent growth, the activity is increased in comparison with the control sections. These results suggest that the effect of IAA on IAA-oxidase, depends of the endogenous IAA leve1 in addition to the exogenous IAA added. Peroxidase activity does not show a variation similar to that of IAA-oxidase in al1 the assays, indicating that the different isoperoxidases do not have an identical capacity to destroy IAA.