Release of Nitrogen From Chloroplasts During Leaf Senescence in Rice (Oryza sativa L.)

Abstract

In order to ascertain the possibility that nitrogen associated with chloroplasts serves as a major source of nitrogen redistributed from senescent leaves, chloroplasts were isolated from rice leaves and changes with leaf age in total leaf nitrogen and chloroplast nitrogen were examined. Results presented here show that decrease in total leaf nitrogen during leaf senescence was closely correlated with decrease of chloroplast nitrogen and roughly 85–95 per cent of leaf nitrogen released from senescent leaves during the experimental period could be accounted for by a loss of chloroplast nitrogen. By dividing chloroplast nitrogen into two fractions, i.e. lamellar and stroma fractions, the question of which fraction was more deeply concerned with the loss of leaf nitrogen was clarified. Results suggested that in the vegetative stage of plant growth the stroma was mainly responsible for the loss of leaf nitrogen. On the other hand, nitrogen was released from lamellar and stromal fractions at almost the same rate during the reproductive stage.