Ionylideneacetic Acids and Abscisic Acid Biosynthesis by Cercospora rosicola

Abstract

Several compounds having the basic a-ionylideneacetic acid structure were tested in Cercospora rosicola resuspensions. At 100/IM, all the compounds inhibited abscisic acid (ABA) biosynthesis. Time studies with unlabelled and deuterated (2Z,4E)- and (2E',4E)-a-ionylideneacetic acids showed rapid conversions into both (2Z,4E)- and (2E',4E)-4/-keto-a-ionylideneacetic acids as major products. Incorporation of the label into ABA was specific for the 2Z,4is-isomer. Minor products, identified by GC-MS, were (2Z,4E)- and (2is,4is)-4'-hydroxy-a-ionylideneacetic acids and (2Z,4E)-l'-hydroxy-a-ionylideneacetic acid. The conversion to (2Z,4ii)-l '-hydroxy-a-ionylideneacetic acid has not been previously reported and was specific for the 2Z,4is-isomer. A time study for the conversion of methyl esters of [2H3]-(2Z,4E)- and [2H3]-(2E,4E)-4'-keto-a-ionylideneacetates showed a slow introduction of the l'-hydroxyl group and specificity for 2Z,4E-isomer. Conversion of the ethyl esters of (2Z,42s)- and (2E,4is)-l'-hydroxy-a-ionylideneacetates into the ethyl esters of both ABA and (2E,4is)-ABA demonstrated that ABA can be formed by oxidation of the 4'-position after the insertion of the 1 '-hydroxy group. The ethyl 1 '-hydroxy acids were also isomerized to the corresponding ethyl (2Z,4E)- and ethyl (2E,4E)-3'-hydroxy-β-ionylideneacetates. Ethyl (2Z,4E)-1 '-hydroxy acid also gave small amounts of ethyl l',4'-rnms-diol of ABA. These results suggest that ABA may be formed through a (2Z,4E)-1 '-hydroxy-α-ionylidene-type intermediate in addition to the previously proposed route through (2Z,4E)-4'-keto-α-ionylideneacetic acid. © 1985, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.