Changes in the flow of early products of photosynthetic carbon fixation associated with the replication of TYMV

Abstract

In leaves of Chinese cabbage systemically infected with turnip yellow mosaic virus (TYMV), the following metabolic changes are closely related in time to the period of virus replication: (i) a diversion of the products of photosynthetic carbon fixation away from sugars and into organic and amino acids; (ii) an increase in the activity of the enzymes phosphoenol pyruvate carboxylase and aspartate amino transferase. Tests with various host-virus combinations suggest that these changes are specific for TYMV rather than the host species. We suggest that these changes are induced by the virus and are directly connected with the requirements of virus replication. The findings support the view that TYMV is primarily a parasite of the chloroplast. The following properties are permanently changed by TYMV infection, and the observed reductions occur only toward the end of the period of virus replication: (i) rate of carbon fixation, (ii) concentration of fraction I protein and ribulose diphosphate carboxylase activity. Previous work has shown that these changes also occur with other viruses.