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 dicotyledonousand monocotyledonous plants. A simple method, using analysisby HPLC to measure the conversion of naphthaleneacetamide (NAM)to naphthaleneacetic acid (NAA) was employed for the detectionof 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 andorange. In addition to the presence of the conversion activity,we confirmed that radioactivity from ³H-IAM was incorporatedinto IAA in a cell-free system from O. sativa C5924. An extractof roots of rice seedlings exhibited twice the activity of thatin an extract of shoots. IAM hydrolase activity was observedin calluses from all lines of rice callus examined, irrespectiveof whether they were wild or cultivated lines, with the exceptionof O. grandiglumis W1194 and O. branchyantha W656, while otherspecies of Gramineae exhibited no activity. These results suggestthe possibility that this enzyme may play a specific role inrice. (Received August 23, 1990; Accepted November 29, 1990)