Biochemical Changes During Bean Leaf Growth, Maturity, and Senescence

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Abstract
A detailed study was made of the content per leaf lamina of several biochemical components during growth and the entire lifespan of the primary leaf of bean, Phaseolus vulgaris L., var. Dwarf Horticultural Bush. Total DNA measured spectrofluorometrically was retained even after abscission and withering of the lamina. Possible reasons for the lack of DNA degradation in very old leaves are presented. Using improved extraction methods it was found that both putative cytoplasmic polyribosomes and the total organelle plus cytoplasmic ribosomal RNAs rose to a peak during leaf growth, declined rapidly, and finally levelled off during maturity and senescence. Even 37 d old senescent leaves retained polysomes as large as hexamers. Organelle rRNA peaked late in the growth phase and about 4 d after the peak in cytoplasmic rRNA. During leaf maturity and senescence, both of these rRNA types decreased in parallel. Total protein and chlorophyll peaked at different times during leaf growth, declined at a steady rate during maturity, and then declined faster in the senescence phase. The trends are compared with each other and to the literature.

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