| Abstract | e metabolism of a biologically active abscisic acid (ABA) analogue, ( + )-( l’SJ’S)-2’,3’-dihydroabscisic acid [( +)-4-(1E,3Z)-(4S,5S)-4-(4-carboxy-3-methyl-1,3-butadienyl)-4-hydroxy-3,3,5-trimethyl~clohexanone], which cannot form phase & acid was studied in a cell suspension culture of bromegrass (Bromus inermis). The analogue induced freezing tolerance in bromegrass cells similar to (S)-( + )-ABA and was oxidized to (l’S,2’S)-8’-hydroxy-2’,3’-dihydroabscisic acid [4-(1E,3Z)-(3R,4S,5S)-4-(4-carboxy-3-methyl-l,3-butadienyl)-~hydroxy-3-hydroxymethyl-3,5-dimethylcyclohexanone]. The enantiomer ( -)-(l’RJ’R)- 2’,3’dihydroabscisic acid, which was inactive in inducing freezing tolerance, was converted to two metabolites, viz., the corresponding enantiomeric (l’RJ’R)-8’-hydroxy-2’,3’-dihydroabscisic acid [4-(1E,3Z~3S,4R,5R)-4-(4_carboxy-3-methyl-l,3-butadi~yl)~-hydroxy-3-hydroxymethyl-3,5-dimethylcyclohexanone] and reduction product (-)-l-(lE,3Z)-( lR,4S,6R)-1-(4-carboxy-3-methyl-1,3-butadienyl)-2,2,6-trimethylcyclohexan-l+diol. Both enantiomers of the analogue were transformed to the glucose esters. The structures of the metabolites were established by both spectroscopic analyses and chemical syntheses. The metabolite 8’-hydroxy-2’,3’-hydroxyabscisic acid is a cyclohexanone analogue of 8’-hydroxyabscisic acid, the transient oxidation product in the metabolism of ABA to phaseic acid. Like phaseic acid, the racemic form of 8’-hydroxy-2’,3’-dihydroabscisic acid was inactive in inducing freezing tolerance in bromegrass cells, suggesting that ABA and (+)-(l’&?‘S)-2’,3’-dihydroabscisic acid were the active compounds. |
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