Aging and senescence of the leaf organ

Abstract

Leaf senescence is a sequence of biochemical and physiological events comprising the final stage in leaf development. It encompasses the period from a fully expanded mature state up to the death, thereby limiting longevity. The changes occurring during leaf senescence are very complex but highly regulated, and are genetically programmed with actions coordinated at the cellular, tissue, organ, and organism levels. A major breakthrough in our molecular understanding of this phenomenon has been achieved through the characterization of various mutants and senescence-associated genes, including regulatory genes. In particular, a genetic screening and assay system for leaf senescence has been well established in Arabidopsis, which led leaf senescence into the realm of genetic subject along with the rich genetic and genomic resources in this model plant. These advances have not only revealed the existence of a complex regulatory network of senescence-associated signaling pathways, but have also allowed us to postulate the molecular mechanisms for signal perception, execution, and regulation. The key regulatory genes identified to date encode a variety of proteins, including transcription regulators and signal-transduction proteins, regulators of protein degradation, proteins associated with phytohormone pathways, and regulators of metabolism. Elucidation of their roles in leaf senescence and analyses of senescence regulatory pathways, including systemslevel approaches, will increase our knowledge of the networks involved in senescence activity.

Micro-scale chlorophyll analysis and developmental expression of a cytokinin oxidase/dehydrogenase gene during leaf development and senescence

“…Numerous studies since have shown the cytokinins to be key regulators of senescence. For reviews of the role of cytokinin in development and senescence see Gan and Amasino (1996), Jameson (2003), Lim and Hong (2007) and Werner and Schmülling (2009). However, the key cytokinin regulatory genes have not been monitored during sequential leaf senescence.…”

Stem girdling influences concentrations of endogenous cytokinins and abscisic acid in relation to leaf senescence in cotton

“…Leaf senescence is considered the result of complex interaction between external factors such as drought, high salinity and low temperatures (Marani et al 1985;Lim and Nam 2007) and internal factors such as plant hormones (Yong et al 2000;Dong et al 2008). Cytokinin and ABA are commonly identified phytohormones during research on leaf senescence.…”

Betacyanin accumulation and guaiacol peroxidase activity in Beta vulgaris L. leaves following copper stress

“…Given that senescence is a catabolic process that leads to nutrient recycling, chloroplast degeneration is one of the earliest events in the process. It is accompanied by a decrease in photosynthetic activity, chlorophyll degradation, and protein loss [39].…”