ULTRASTRUCTURE OF TOMATO LEAF TISSUE TREATED WITH THE PSEUDOMONAD PHYTOTOXIN CORONATINE AND COMPARISON WITH METHYL JASMONATE

Coronatine is a chlorosis-inducing phytotoxin produced by several path ovars of Pseudomonas syringae, Light and electron microscopy were used to determine the effect of coronatine on tomato leaf tissue, Although the structural integrity of cells in coronatine-treated chlorotic lea ves was maintained, the toxin induced thickening of cell walls and shr inkage of chloroplasts, Coronatine also stimulated the accumulation of large cubical protein particles and smaller proteinaceous spheres in leaf parenchyma cells; this was coincident with a dramatic increase in proteinase inhibitor activity, Growth of P. syringae pv. tomato was m ore pronounced on coronatine-treated tissue than on healthy tissue, de spite the accumulation of proteinase inhibitors in toxin-treated tissu e, Tomato leaf tissue infected with a coronatine-producing strain of P . s. pv. tomato exhibited symptoms similar to tissue treated with the purified toxin, while tissue infected with a COR(-) mutant showed symp toms similar to untreated healthy tissue, Methyl jasmonate and coronaf acic acid, compounds structurally similar to coronatine, induced the a ccumulation of proteinase inhibitors but did not affect chloroplast si ze or induce chlorosis, Our results show that the virulence factor cor onatine does not cause massive cellular destruction in the tomato leav es, Furthermore, the proteinase inhibitors induced in the plant do not slow pathogen growth, and coronatine does not act solely by mimicking methyl jasmonate.