PROGRAMMED SENESCENCE OF PLANT ORGANS

The senescence of plant organs associated with reproductive developmen t has been studied extensively during the past century, and it has lon g been recognized that th is type of death is internally programmed. T he regulation of organ senescence as well as its biochemical and genet ic determinants has been an historically rich area of research. Certai n plant hormones have been implicated as regulators or modulators of o rgan senescence and many of the biochemical pathways associated with t he senescence syndrome have been elucidated. The genetic basis of orga n senescence has also been well established by the identification of m utations that impair the senescence program and recently, transgenic p lants have been used to critically determine the role of specific enzy mes and hormonal signals in mediating programmed senescence of plant o rgans, Here, we review the current understanding of the processes that regulate leaf, flower and fruit senescence, emphasizing the rate that programmed organ senescence plays in the adaptive fitness of plants.