Protein Synthesis Linked with Resistance of Oat Leaves to Crown Rust Fungus

Abstract

Blasticidin S completely supressed the resistance expression of Shokan 1 oat leaves to Puccinia coronata avenae race 226 when 5×10^-6M aqueous solution of the chemical was supplied to the plants for 4hr from stem cut-ends from 8 or 12hr after inoculation. This blasticidin S effect was decreased as the initiation of the chemical supply was delayed to 14 or more hr after inoculation, and no effect was found by the supply after 24hr. The ratio of ¹⁴C-leucine incorporation into acid insoluble fraction to total uptake increased in the resistant-responding leaves to 1.2- to 1.35-fold of non-inoculated control, when the leaves were fed with ¹⁴C-leucine for 1 and 4hr from 14 to 24hr and 14 to 18hr after inoculation, respectively. No obvious increase in the ratio of incorporation was observed during the period of experiments in the leaves which were inoculated with compatible race 203. Blasticidin S markedly inhibited the incorporation of ¹⁴C-leucine into acid insoluble fraction in all cases including the blasticidin S treatment was initiated at 24hr after inoculation, in which no effect of blasticidin S on the resistance was detected. It was suggested that protein synthesis causally linked with resistance expression of Shokan 1 leaves to race 226 occurred between 14 and 24hr after inoculation. Peroxidase isozymes and phenylalanine ammonia-lyase activity increased in leaves inoculated with race 226, but the increases were not reduced by the blasticidin S treatment. It was assumed, therefore, that the resistance in this host-pathogen system involved the synthesis of protein(s) other than these enzymes.