|Alchanati, I - TEXAS A&M UNIVERSITY|
|Benedict, C - TEXAS A&M UNIVERSITY|
Submitted to: Biochemistry of Cotton Workshop
Publication Type: Proceedings
Publication Acceptance Date: September 24, 1994
Publication Date: N/A
Technical Abstract: Phytoalexins are antibiotics that accumulate in plant cells in response to microbial attack. In this role they have a critical part in the resistance to most potential pathogens that attack the plant. Inoculation of cotton stele tissue with conidia of Verticillium dahliae induces the biosynthesis sesquiterpenoid phytoalexins such as: desoxyhemigossypol (dHG), desoxyhemigossypol-6-methyl ether (dMHG), hemigossypol (HG), hemigossypol-6-methyl ether (MHG) and gossypol (G). Methylation of the 3-hydroxyl group of phytoalexins from cotton stele tissue substantially reduces toxicity to pathogens. Adding the methyl group approximately doubles the amount of phytoalexin required for the same inhibitory effect on almost all fungi. This effect of methylation was true for both dHG and HG. The methylation reduces the water solubility of the phytoalexins. Thus, dHG but not dMHG is sufficiently toxic and soluble to completely inhibit most fungi without the aid of surfactant. The role of the phytoalexins in disease resistance has been studied extensively, but there has been only a limited amount of work describing the individual enzymes catalyzing the biosynthesis of the sesquiterpenoid phytoalexins. In this paper we describe the isolation and characterization of the dHG-O-methyltransferase. We propose that this enzyme catalyzes the transfer of a methyl group from S-adenosyl-L- methionine (SAM) to a ring hydroxyl group on dHG to form dMHG.