INDOLE-3-BUTYRIC ACID IN ARABIDOPSIS-THALIANA .3. IN-VIVO BIOSYNTHESIS

Indole-3-butyric acid (IBA) was identified by HPLC and GC-MS as one of the reaction products after incubation of sterile cultures of Arabido psis thaliana seedlings with labeled indole-3-acetic acid (IAA). This is the first demonstration of IBA biosynthesis in a dicotyledonous pla nt. After 1h of incubation most of the IBA was found in the free form, while after longer periods of incubation most of it was detected in c onjugated forms. Formation of IBA conjugates was inhibited by the addi tion of unlabeled IBA. The biosynthesis of IBA and its conjugates was followed throughout the development of the seedlings and at different pH values. All parts of the plant (isolated roots, leaves, shoots and flowers) were able to convert IAA to IBA to the same extent. IAA was m ore readily transported than IBA in mature Arabidopsis plants. Feeding of labeled phenylacetic acid (PAA) and alpha-naphthylacetic acid (NAA ) to Arabidopsis seedlings resulted in a new small peak which was hydr olyzed by 7NNaOH, but the formation of compounds with longer side chai ns (analogous to IBA) could not be detected.