Effects of virus infection on the chlorophyll content, photosynthetic rate and carbon metabolism of Tolmiea menziesii

Abstract

Leaves from variegated Tolmiea menziesii plants, previously found to be virus-infected, have severely lowered chlorophyll (Chl) levels. Yet, infected plants appeared to grow as rapidly in a greenhouse as green, uninfected control plants. On a Chl basis, the photosynthetic (PS) rate of variegated leaves significantly exceeded that of control leaves. The area-based PS rate of the variegated leaves was less than that of the controls at low light levels, but approached the latter's rate at higher intensity. Both types of leaves had similar CO 2 compensation points and extents of oxygen inhibition of PS. The variegated leaves had an increased Chl a b ratio and a decreased content of light-harvesting Chi a + b protein. Leaf discs prepared from variegated leaves, when photosynthesizing with 14CO 2, produced more labelled glycine and less sucrose than did control discs. The level of PS carbon reduction cycle intermediates was approximately equal in both disc types. We conclude that variegated leaves have a significantly lower amount of antenna Chl but not less reaction center Chl. The increase in labelled glycine in the variegated discs apparently results from viral demand for that metabolite in coat protein and nucleic acid synthesis. Withdrawal of glycine by the virus may be responsible for the lower Chl content of the infected leaves.