The Effect of Methionine on Ethylene and 1-Aminocyclopropane-1-Carboxylic Acid Production byBipolaris sorokiniana

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Abstract
Research was initiated to determine the effect of exogenous methionine on the ability of the fungal pathogen Bipolaris sorokiniana to produce ethylene and intermediates of the ethylene biosynthetic pathway of higher plants. When grown on leaf-blade infusion media of the host (Poa pratensis) supplemented with methionine, the pathogen produced ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) was secreted into culture filtrates, and the protein fraction of the pathogen had low ACC synthase activity. On the leaf-blade infusion media without methionine, ethylene production was negligible to nondetectable, the initial level of ACC in the leaf-blade infusion media was decreased, and ACC synthase activity of the protein fraction of the pathogen was high. Addition of ACC to the leaf-blade infusion media resulted in low ethylene production by the pathogen compared with that produced with the addition of methionine. Differences in the use of ACC and methionine for ethylene production by the pathogen suggests that the pathogen does not efficiently convert ACC to ethylene and that ethylene may be produced via more than one pathway. The low ACC synthase activity of the protein fraction of the pathogen after 10 days'' growth on leaf-blade infusion media with methionine suggests that methionine or a metabolite of methionine may decrease the production of ACC synthase.