Ultrastructure of Tomato Leaf Tissue Treated with the Pseudomonad Phytotoxin Coronatine and Comparison with Methyl Jasmonate. David A. Palmer. Department of Plant Pathology, Oklahoma State University, Stillwater, Oklahoma 74078. Carol L. Bender. Department of Plant Pathology, Oklahoma State University, Stillwater, Oklahoma 74078. MPMI 8:683-692. Accepted 11 May 1995. Copyright 1995 The American Phytopathological Society.

Coronatine is a chlorosis-inducing phytotoxin produced by several pathovars 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 leaves was maintained, the toxin induced thickening of cell walls and shrinkage 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 more pronounced on coronatine-treated tissue than on healthy tissue, despite the accumulation of proteinase inhibitors in toxin-treated tissue. 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 symptoms similar to untreated healthy tissue. Methyl jasmonate and coronafacic acid, compounds structurally similar to coronatine, induced the accumulation of proteinase inhibitors but did not affect chloroplast size or induce chlorosis. Our results show that the virulence factor coronatine does not cause massive cellular destruction in the tomato leaves. Furthermore, the proteinase inhibitors induced in the plant do not slow pathogen growth, and coronatine does not act solely by mimicking methyl jasmonate.