Abstract
The present paper dealts with the results of studies on the breakdown of chlorophyll in tobacco leaves systemically infected with CMV. The major findings are as follows: chlorophyllase activity gradually decreases and chlorophyll contents rapidly decreases as viral infection progresses. High content of pheophytin, a form lacking magnesium in chlorophyll, is found in the mosaic and yellowish areas of infected leaves but the amounts of chlorophyllides and pheophorbides are negligible in the same areas. Pheophytin is never produced from chlorophyll by the optimal reaction of chlorophyllase or proteolytic enzyme. These results suggest that the breakdown of chlorophyll in the leaves showing mosaic is mainly due to the conversion of chlorophyll to pheophytin by the alteration of intracellular environment that occurs as a result of viral infection.
The concentration of carotenoids increases also in the mosaic and yellowish areas of infected leaves. Especially, xanthophyll. a yellow pigment, increases markedly.
The content of fraction I protein in infected leaves dereases remarkably as the symptoms progress. The decrease of fraction I protein content is found to be closely correlated with the breakdown of chlorophyll. But, the mechanisms by which these two materials are degraded appear to be different.
