The role of free radicals in the decomposition of the phytoalexin desoxyhemigossypol

Abstract

The cotton phytoalexin desoxyhemigossypol (dHG) decomposed rapidly in solution to give hemigossypol (HG). The rate of decomposition was retarded by the reducing agents ascorbic acid, reduced glutathione and cysteine, by the metal chelator diethylenetriaminepentaacetic acid, and by the enzyme catalase. However, the chelator, ethylenediaminetetraacetic acid did not reduce the rate of decomposition and the enzyme superoxide dismutase increased the rate of decomposition. Solutions of the phytoalexin desoxyhemigossypol-6-methyl ether were significantly more stable than were those of dHG. Oxygen-18 from water but not from oxygen gas was incorporated into HG during this decomposition. A hydroperoxynaphthalenone which loses hydrogen peroxide is proposed as an intermediate to explain this observation. The formation of hydrogen peroxide may be involved in the toxicity of this phytoalexin to plant pathogens such as Verticillium dahliae.