Bean halo-blight toxin

Abstract

Pseudomonas phaseolicola causes a disease of beans commonly called halo blight. The halo is a chlorotic zone which appears in the leaf round each infection site. It has been interpreted as the effect of a toxin produced at, and diffusing away from, the infection site. The zone characteristically contains a relatively large amount of the amino acid ornithine¹. When Ps. phaseolicola was grown in a defined liquid culture medium at 18°C the filter-sterilised medium, when applied to bean leaves, caused the chlorosis symptom of the disease². From such media I have isolated a substance, 80–90% pure, which, when introduced to the leaf at a level of 100 ng per g fresh weight, causes both chlorosis and accumulation of ornithine. I report here the highly unusual structure of this compound. Its extreme lability in the presence of weak acids has made its isolation difficult, but has helped in the resolution of its structure.