Loss of photosynthesis signals a metabolic reprogramming to sustain sugar homeostasis during senescence of green leaves: Role of cell wall hydrolases

Abstract

Leaf senescence is always associated with decline in photosynthesis, consequently a loss of cellular sugar. On the other hand, execution of senescence program needs energy and leaves, therefore, tend to collect sugars from other sources to sustain energy homeostasis. This sugar reprogramming induced by loss of sugar involves operation of a complex catabolic network. The exact molecular mechanism of induction and regulation of the network, however, is not fully resolved but the current literature available suggests sugar starvation as a signal for induction of several senescence-associated genes including the genes coding for the enzymes for degradation of cellular constituents and their conversion to respiratory sugars. The late expression of genes coding for the cell wall hydrolases and enhancement in the activity of these enzymes late during senescence are indicative of the cell wall polysaccharides as the last source of sugars to sustain energy homeostasis for execution of the senescence program.