Occurrence of Methyl (+)-Abscisate as an Artefact of Extraction

Abstract

Alkaline methanolic extracts of avocado (Persea gratissima) fruit contain large amounts of methyl (+)-abscisate but little or no (+)-ABA is liberated by alkaline hydrolysis of the aqueous solution left after extraction of ether-soluble acidic and neutral compounds. No methyl (-t-)-abscisate is detectable in acetone or acidic methanol extracts but (+)-ABA can be released by alkaline hydrolysis of the aqueous solution in these experiments. It is concluded that methyl (-f)-abscisate is an artefact of extraction caused by the methanolysis of a conjugate in neutral or basic conditions. Reports of neutral inhibitors in plant extracts require re-examination because some of the inhibitory activity may be attributable to methyl (+)-abscisate formed during methanol extraction. (+)-ABA biosynthesised from (+)-[3'-14C]mevalonolactone by avocados had a higher specific activity than had the bound (+)-ABA; this suggests that free (+)-ABA is formed first and the conjugate is derived from this, rather than the reverse.