Correlation between activity of ribonucleases and potato virus Y biosynthesis in tobacco plants

Abstract

Tobacco plants, leaf discs and protoplasts infected with two strains of the potato virus Y (PVYOand PVYN) were studied during the period of the acute infection stage. The following characteristics of the host plants were monitored: dynamic changes in the ribonuclease (RNase) activities in relation to the virus multiplication; changes in subcellular localization of RNases, phosphomonoesterase (PME) and phosphodiesterase (PDE); and connection of RNase activities with host plants resistance. Activities of RNases in both the crude homogenates and the partially purified enzyme preparations from the diseased discs were markedly increased during the experimental period when compared to the discs from healthy plants. The courses of both curves were coincident and correlated with the multiplication curve of the PVYOand PVYNstrains. Changes in the content and in the subcellular localization of RNase, PME and PDE isozymes were determined in mesophyll protoplasts prepared from the healthy and PVYNinfected plants of Nicotiana tabacum L. cv. Samsun. In the chloroplast and cytosol fractions of the infected protoplasts, activities of RNase as well as PME and PDE were increased. The enhanced content of the RNase isozymes was also found in the infected leaves after electrophoretic separation. A linear correlation (P<0.001) was found between the content of the potato virus YNand the tobacco host resistance to virus multiplication. This was established on the basis of enhanced levels of RNases, using susceptible, tolerant and resistant plants.