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plant senescence
Plant senescence is the process of aging in plants. It is a heavily studied subject just as it is in the other kingdoms of life. Plants, just like other forms of organisms, seem to have both unintended and programmed aging. Leaf senescence is the cause of autumn leaf color in deciduous trees.
==Programmed senescence==
Programmed senescence seems to be heavily influenced by plant hormones. The hormones abscisic acid and ethylene are accepted by most scientists as the main causes, but at least one source believes gibberellins, brassinosteroids and strigolactones are equally responsible. Cytokinins and probably other hormones such as auxins (and maybe also jasmonic acid and salicylic acid) help to maintain the plant cell but when they are withdrawn or if the cell cannot receive the cytokinin and the others it may then undergo apoptosis or senescence.〔Ivanova M., and Rost T.L., (1998). Cytokinins and the Plant Cell Cycle: Problems and Pitfalls of Proving their function. Plant Cell Proliferation in Growth and Development. Ed J.A. Bryant and D. Chiatante. Johon Wiley & Sons Ltd.〕 Cytokinin (and possibly salicylic acid) may particularly inhibit shoot senescence whereas auxin (and maybe jasmonic acid) may particularly inhibit root senescence at normal non-artificial levels. Gibberellin and ethylene may be indicators of sugar and oxygen deficiencies respectively so they may also normally act to preserve leaves from senescence but encourage roots to die off. Abscisic acid is known to be an indicator of water deficiency and if strigolactones are an indicator of nutrient deficiencies coming from the root other than water, then these may stimulate shoot senescence and inhibit root die-offs as well.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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