Comparison of Protein and mRNA Syntheses in Tobacco Leaves Infected with the Yellow or the Ordinary Strain of Cucumber Mosaic Virus

Abstract

Infection of tobacco (Nicotiana tabacum L. cv. Ky57) leaves with the yellow strain of cucumber mosaic virus (CMV(Y)) resulted in large chlorotic spot formation, while no clear symptom appeared with the ordinary strain of the virus (CMV(O)) except for faint yellowing. In spite of the marked difference in symptom appearance on the tobacco between the two virus strains, the time course and extent of the virus titer and coat protein synthesis were essentially similar for both strains. In the leaves inoculated with CMV(O), 80 s ribosome concentration and host protein synthesis decreased temporarily, and then they were recovered moderately when the virus titer reached a maximum. 70 s ribosome concentration decreased to a small extent, and poly(A)-mRNA synthesis and polysome concentration were little affected throughout the experimental periods. In the leaves infected with CMV(Y), in comparison with CMV(O), poly(A)-mRNA synthesis and polysome concentration first decreased almost simultaneously, and followed by the decrease of host protein synthesis, and then 80 s and 70 s ribosome concentrations decreased significantly in the order. Thus, it is suggested that a series of such reactions lies at the basis of symptom appearance. Incidentally, no increase in activities of protease and ribonuclease was observed in the leaves inoculated with the two virus strains.