Dynamic changes in the activities of glucose-6-phosphate dehydrogenase, ribulose bisphosphate carboxylase and ribonuclease in tobacco leaves, leaf discs and mesophyll protoplasts in relation to TMV multiplication.

摘要

Multiplication of tobacco mosaic tobamovirus (TMV) differed in leaves of intact 2-month-old tobacco cv. Samsun plants, leaf discs and mesophyll protoplasts when inoculated with purified TMV at 100μg/ml. Most TMV was synthesized in leaves of whole plants (7.2 mg TMV/g fresh weight), followed by leaf discs (2.04 mg TMV/g fresh weight). Activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) fell rapidly after 10 days to 60-65% of healthy controls. In infected leaf discs, enzyme activity gradually declined after inoculation. A linear correlation was observed between ribonuclease activity and TMV multiplication in infected leaves and infected leaf discs. In protoplasts, ribonuclease activity was significantly increased by virus infection, but its activity was not correlated with TMV multiplication. Activity of RUBISCO and glucose-6-phosphate hydrogenase was not detected in protoplasts. From the results it is suggested that: in leaves of intact plants, TMV-RNA is synthesized from intermediates produced in the oxidative pentose phosphate pathway and by host RNA degradation; in leaf discs, TMV-RNA is preferentially synthesized from nucleoside precursors obtained from host rRNA, but also from intermediates produced in the oxidative pentose phosphate pathway; and in protoplasts, TMV-RNA is preferentially synthesized from nucleoside precursors from degraded host RNA. The involvement of the reductive pentosephosphate pathway in TMV-RNA biosynthesis was minimal in the 3 plant systems studied.