Leaf senescence is a type of programmed cell death characterized by loss of chlorophyll, lipids, protein, and RNA. Cytokinins are a class of plant hormones that play roles in many aspects of plant growth and development, including leaf senescence, apical dominance, the formation and activity of shoot meristems, nutrient mobilization, seed germination, and pathogen responses. They also appear to mediate a number of light- regulated processes, such as de-etiolation and chloroplast differentiation. It is known that the concentrations of endogenous cytokinins decline in plant tissues as senescence progresses. This observation provides the opportunity to manipulate the senescence program in transgenic plants to enhance biomass and seed production, through the regulated expression of cytokinin biosynthesis genes
