Detection of a necrosis-inducing factor of nonhost plant leaves produced by Pseudomonas syringae pv. tomato

A necrosis-inducing factor (NIF) was extracted from two virulent strains of Pseudomonas syringae pv. tomato sonicated cells. The factor had an approximate molecular weight of 108 000, contained 90% protein and 10% polysaccharide, and was partially purified by affinity chromatography, gel chromatography, gel electrophoresis, and electrophoresis on cellulose acetate strips. The factor caused loss of electrolytes within 48 h and necrosis on bean, pepper, and cucumber leaves but not on tomato leaves of different cultivars. Similar fractions extracted from cells of P. fluroescens did not show any activity. Activity was destroyed by pronase or by hydrolysis with HCl indicating that the activity is due to the protein component. The factor did not show any pectolytic or cellulolytic activity. The factor was produced at a maximum after 24 h of growth of P. syringae pv. tomato and was more abundant when extracted from cells grown in rich medium.