Rôle of ammonia in infection of Phaseolus vulgaris by Pseudomonas spp

Abstract

Leaves of French bean ( Phaseolus vulgaris) cv. Canadian Wonder and Red Mexican were infiltrated with suspensions of Pseudomonas phaseolicola (Races 1,2), P. mors-prunorum or P. fluorescens to give a hypersensitive (incompatible), susceptible (compatible) or no response. They were also infiltrated with solutions of ammonia. Measurement of ammonia in treated and untreated tissues showed that concentrations were insufficient to account for the damage associated with the hypersensitive response, but they were high enough to explain symptoms in susceptible leaves. Similar amounts of ammonia were evolved from leaves kept in light, or dark, after inoculation treatments which also had no effect on the responses of leaves to the bacteria. After exposure to chloroform vapour leaves gave off about the same amounts of ammonia as did susceptible leaves after inoculation; senescent leaves evolved much less. In vitro, each of the four bacteria produced about the same amounts of ammonia but at rates far too low to explain leaf damage if production in vivo were at similar rates. Treatment of leaves with cycloheximide 30 min before inoculation with incompatible bacteria suppressed the leakage of electrolytes normally associated with the hypersensitive response and also suppressed this response, though at the concentrations used it had no effect on growth of the bacterium in vitro. Cycloheximide had no effect on electrolyte leakage caused by ammonia. Calcium nitrate (0·05 to 0·3 n) had little or no effect on production of ammonia by, or responses of, leaves inoculated with incompatible bacteria. These results show that ammonia plays no part in the hypersensitive responses of bean leaves to incompatible species of Pseudomonas.