Abstract
Coronatine is an extracellular toxin produced by Pseudomonas coronafaciens var. atropurpurea (Reddy and Godkin) Stapp, the incitant of the chocolate spot disease on Italian ryegrass (Lolium multiflorum Lam.). Coronatine induced the necrosis with chlorotic halo symptoms of the disease in host leaves as well as in non-hosts and thus is nonspecific. Coronatine, at low concentration of 0.05mM to 0.5mM, also induced marked hypertrophy only on potato tuber tissues. When a potato tuber cylinder was incubated with coronatine before the extensibility measurment, the plasticity was greater than that of the control, suggesting that coronatine is required to increase the plasticity of the cell wall for cell expansion. Coronatine-induced water uptake was quantitatively inhibited by tree entirely different type of inhibitors, suggesting that water uptake by potato tuber tissue in the presence of coronatine externally added is linked to the general aerobic metabolism and corresponds closely to outgrowth of potato tuber tissue. Coronatine-induced tissue deformability of potato cylinder was reduced by treatment with actinomycin D and cycloheximide. These results suggest that RNA and protein syntheses seem to be essential prior to cell expansion and tissue deformation. It can be therefore concluded that coronatine may control the syntheses of enzymes which loosen the cell wall before expansion of the cell by turgor pressure. The rapid increase in cell expansion of potato tissue treated with coronatine was accompanied by disapperance of starch grains in the cell. We conclude from the experiments described above that the effect of coronatine on cell enlargement depends on both increases in the plasticity of the cell wall and in osmotic pressure in the cell sap.
