The Presence of an Enzyme that Converts IndoIe-3-acetamide into IAA in Wild and Cultivated Rice

The enzymatic conversion of indole-3-acetamide (IAM) to IAA, which is the second step in the IAM pathway (tryptophan → IAM → IAA) was investigated in calluses derived from various dicotyledonous and monocotyledonous plants. A simple method, using analysis by HPLC to measure the conversion of naphthaleneacetamide (NAM) to naphthaleneacetic acid (NAA) was employed for the detection of IAM hydrolase activity. Among calluses from 27 plants tested, only callus from a cultivated strain of rice (Oryza sativa C5924) had high conversion activity similar to that of crown gall cells, and very weak activity was found in calluses from lucern and orange. In addition to the presence of the conversion activity, we confirmed that radioactivity from 3H-IAM was incorporated into IAA in a cell-free system from O. sativa C5924. An extract of roots of rice seedlings exhibited twice the activity of that in an extract of shoots. IAM hydrolase activity was observed in calluses from all lines of rice callus examined, irrespective of whether they were wild or cultivated lines, with the exception of O. grandiglumis W1194 and O. branchyantha W656, while other species of Gramineae exhibited no activity. These results suggest the possibility that this enzyme may play a specific role in rice.