The Relation between Bacterial Toxic Action and Plant Growth Regulation

Abstract

Coronatine is an extracellular toxin produced by Pseudomonas coronafaciens var, atropurpurea (REDDY and GODKIN), the incitant of the chocolate spot disease on Italian ryegrass (Lolium multiflorum LAM.). Coronatine induces the necrosis with chlorotic halo symptoms of the disease in host leaves as well as in nonhosts and thus is nonspecific. Coronatine, at low concentration of 0.3μg to 30μg/ml, also induces marked hypertrophy only on potato tuber tissues. When a potato tuber cylinder was incubated with coronatine before the extensibility measurement, the plasticity was greater than that of the control. The results suggest that coronatine is required to increase the plasticity of the cell wall for cell expansion. These results indicate that coronatine may be characterized as a substance with high auxin-like activity. However, physiological data show that coronatine has a tissue specificity. It is clearly different from IAA. The difference in the tissue specificity strongly suggests that the two substances have different primary site of action. On the other hand, coronatine and IAA have fundamentaly the same final steps in increasing cell size. The steps involve some process which enhance the plasticity of the cell wall. Histological and physiological data show that the most sensitive site for coronatine injury may be in the cytoplasm. On the other hand, coronatine-induced hypertrophy of potato tuber tissues were markedly inhibited by N, N-dicyclohexylcarbodiimide, one of the inhibitors of membrane-bound ATPase. This results suggests a close association between coronatine and membrane-bound ATPase. In addition, coronatine changes the permeability 24 to 48 hours before the development of hypertrophy on potato tuber tissues. Thus, these results suggests that the disruption of the cytoplasm induced by coronatine may be due to secondaly effects brought about indirectly by physiological changes of the plasma membrane.