Nitrogen Stress Induces <i>Magnaporthe grisea </i>(Hebert) Barr to Secrete Protoplast-Disrupting Proteins

Abstract

Experiments were conducted to determine the effect of nitrogen stress on the gene expression of <i>Magnaportlze</i>

<i>grisea </i>(Hebert) Barr, a casual agent of blast disease of rice and other graminaceous species, Concentrated culture

filtrate extracts of the fungus grown in nitrogen deficient medium exhibited strong disruptive activity against the

protoplasts of different plant species including rice. However, the same activity was not observed in culture filtrate

extracts of the fungus grown in nitrogen rich medium. The results suggest that nitrogen stress induces the fungus to

secrete protoplast-disrupting factors. The nitrogen stress elicited protoplast-disrupting activity was found to be

conserved among different host-limited forms of the pathogen. The microscopic events preceding the protoplast

death and the rapidity of the response evinced plasma membrane to be the site of action of protoplast-disrupting

factors. Preliminary characterization of culture filtrate extracts suggested the heat labile proteins of 20.4 to 22.4 kDa

to be the prime candidates for protoplast-disrupting factors.