Effect of isoprothiolane on Pyricularia oryzae Cavara (I). Cell wall regeneration of protoplasts.

Abstract

Effects of isoprothiolane (IPT) on the regeneration process of protoplasts isolated from hyphae of Pyricularia oryzae Cav. were examined by electron, phase-contrast and fluorescence microscopies. Electron microscopy revealed that freshly-prepared protoplasts were completely devoid of cell wall. The plasmalemma became corrugated, and small, vesicle-like protrusions appeared from it before any sign of incipient cell wall regeneration, regardless of the presence or absence of IPT. Electron-dense, particle-like wall materials were deposited on the original protoplasts prior to budding within 2hr after incubation; they were loosely organized along the plasmalemma and developed to form cell walls of fibrillar structure in controls. The overall features and developmental process of cell walls formed in the presence of 20ppm IPT were similar to those in controls, whereas cell walls formed in the presence of 50ppm IPT were thinner and less compact than those of controls. Protoplasts incubated in the regenerating medium formed bud-like protrusions by 2hr after incubation. Regardless of the presence or absence of IPT they continued to repeat budding-like divisions until 8hr, resulting in chains of budded cells. Normal hyphae arose from either original protoplasts or budded cells in chains at 8hr. By 24hr after incubation in control solutions nearly 50% of incubated protoplasts had produced hyphae. However, hyphae arose from only 1% of protoplasts in 20ppm IPT and were never produced in 50ppm, even after 24hr. IPT evidently interfered with cell wall regeneration of protoplasts of P. oryzae, but whether the observed effect was the expression of the primary or secondary action of IPT remains uncertain.