Some Correlated Events in Aging Leaf Tissues of Tree Tomato and Tobacco

Leaves from solanaceous species of Nicotiana and Cyphomandra were examined. Ultrastructural studies of chloroplasts, coupled with both chemical and cytophotometric analyses of leaf tissues, showed that chloroplast substructures, which would become quite conspicuous during senescence, appeared well in advance of nucleic acid and protein declines in leaf composition. Subsequent to these declines, which included chlorophyll loss, there was a breakdown of the chloroplast thylakoid systems. Specific fine structure changes during rapid leaf expansion included the appearance of plastoglobuli within chloroplasts. As leaves matured, plastoglobuli became rare and plastosomes became abundant. In leaves of both tobacco and tree tomato, nucleic acid, protein, and chlorophyll losses were observed before leaves reached their mature dimensions.