ON THE MODE OF ACTION OF ISOVALERIC ACID IN STIMULATING THE GERMINATION OF AGARICUS BISPORUS SPORES

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Abstract
Summary: Isovaleric acid and isoamyl alcohol have been identified as metabolites of Agaricus bisporus. They are produced in all its developmental stages. These observations relate two earlier reports on germination in this fungus, namely, the stimulation of germination by mushroom hyphae growing in the neighbourhood of A. bisporus spores, and the promotion of germination in this species by application of isovalerate or isoamyl alcohol. The physiological effect of this acid is, at least partly, brought about by metabolic events. Mushroom spores readily convert [14C]‐isovalerate into cell constituents. After an incubation period of 1 day, approximately 12% of the radioactivity of the non‐volatile water‐soluble fraction was localized in succinate, fumarate, malate and citrate; 85% was found in glutamate, pyrrolidone carboxylate, γ‐aminobutyrate, proline, alanine, aspartate, glycine and serine. Only 3% of the carbon of the labelled isovalerate was used for glyconeogenesis. One of the first steps of isovalerate metabolism in the spores is a CO2 fixation reaction (carboxylation of β‐methylcrotonyl‐CoA, formed from isovaleryl‐CoA). The ‘triggering’ reaction of isovalerate in germination of mushroom spores probably consists in a removal of the CO2‐self‐inhibitor by participation of β‐methylcrotonyl‐CoA carboxylase. The possibility of additional metabolic effects of exogenous isovalerate relevant to its germination‐stimulating activity is noted.