Inhibition of Ethylene Production by Rhizobitoxine

Rhizobitoxine, an inhibitor of methionine biosynthesis in Salmonella typhimurium, inhibited ethylene production about 75% in light-grown sorghum seedlings and in senescent apple tissue. Ethylene production stimulated by indoleacetic acid and kinetin in sorghum was similarly inhibited. With both apple and sorghum, the inhibition could only be partially relieved by additions of methionine. A methionine analogue, alpha-keto-gamma-methylthiobutyric acid, which has been suggested as an intermediate between methionine and ethylene, had no effect on the inhibition.Incorporation of (14)C from added methionine-(14)C into ethylene was curtailed by rhizobitoxine to about the same extent as was ethylene production. These results suggest that rhizobitoxine interferes with ethylene biosynthesis by blocking the conversion of methionine to ethylene and not indirectly by inhibiting the biosynthesis of methionine. Ethylene production by Penicillium digitatum, a fungus which produces ethylene via pathways not utilizing methionine as a precursor, was not affected by rhizobitoxine.