Chlorophyll decomposition in senescing leaves and ripening fruits: Functional and evolutionary perspectives

Progress in the understanding of chlorophyll breakdown was very slow until the identification of major catabolites and enzyme systems by Matile and coworkers (Matile et al., 1999). The recent identification of the gene for chlorophyllase from ethylenetreated Valencia orange peel (Jacob-Wilk et al., 1999) was an important step towards elucidation of the developmental and hormonal regulation of chlorophyll catabolism in senescing plant systems. Notwithstanding the functional similarities between senescing leaves and ripening fruits, the evolutionary significance of chlorophyll decomposition in these systems seems to be different. Whereas in senescing leaves chlorophyll breakdown appears to be a component of the retrieval of nitrogen from dying organs, in fleshy fruits the disappearance of chlorophyll exposes the bright pigments, carotenoids and anthocyanins, which render the fruit attractive for seed dispersing animals. There are, however, important fruits which retain their chlorophyll throughout, or, at least, until the very late stages of ripening. Following Cipollini et al. (1991), it seems that such stay-green fruits have the potential advantage of extended photosynthesis; which presumably outweighs the seed-dispersal advantage of the attractive, bright colored fruit.