Inhibition of ornithine decarboxylase activity by phaseolotoxin: implications for symptom production in halo blight of French bean

摘要

The effects of crude toxin preparations obtained from Pseudomonas syringae pv. phaseolicola [P. savastanoi pv. phaseolicola] and purified phaseolotoxin (PT) on enzyme inhibition were studied. Both substances inhibited ornithine decarboxylase, whichis an important enzyme in the control of senescence and the cell cycle. Inoculation of Phaseolus vulgaris leaves with P. s. pv. phaseolicola resulted in chlorosis of the leaves around the site of inoculation. The chlorotic region contained chlorophyll catabolites similar to those in senescence-associated leaves. It is suggested that the chlorosis was associated with the destruction of chlorophyll and not just the inhibition of chlorophyll synthesis. The application of putrescine to infected plants prevented the chlorotic halo forming. It is suggested that the inhibition of ornithine decarboxylase in vivo may contribute to the chlorotic symptoms. The role of PT in the pathogenesis of halo blight in P. vulgaris is discussed.