Gene expression during leaf senescence
ABSTRACT Leaf senescence is a hiphly-controlled sequence of events comprising the final stage of development. Cells remain viable during the process and new gene expression is required. There is some similarity between senescence in plants and programmed cell death in animals. In this review, different classes of senescence-related genes are defined and progress towards isolating such genes is reported. A range of internal and external factors which appear to cause leaf senescence is considered and various models for the mechanism of senescence- initiation are described. The current understanding of senescence at the wrganelle and molecular levels is presented. Finally, same ideas are mooted as to why senescence occurs and why it should be studied further.
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ABSTRACT: Supraoptimal concentrations of indoleacetic acid (IAA) stimulated ethylene production, which in turn appeared to oppose the senescence-retarding effect of IAA in tobacco leaf discs. Kinetin acted synergistically with IAA in stimulating ethylene production, but it inhibited senescence. Silver ion and CO(2), which are believed to block ethylene binding to its receptor sites, delayed senescence in terms of chlorophyll loss and stimulated ethylene production. Both effects of Ag(+) were considerably greater than those of CO(2). IAA, kinetin, CO(2), and Ag(+), combined, acted to increase ethylene production further. Although this combination increased ethylene production about 160-fold over that of the control, it inhibited senescence. Treatment with 25 mul/l of ethylene in the presence of IAA enhanced chlorophyll loss in leaf discs and inhibited by about 90% the conversion of l-[3,4-(14)C] methionine to (14)C(2)H(4) suggesting autoinhibition of ethylene production.The results suggest that ethylene biosynthesis in leaves is controlled by hormones, especially auxin, and possibly the rate of ethylene production depends, via a feedback control system, on the rates of ethylene binding at its receptor sites.Plant physiology 12/1979; 64(5):805-9. · 6.56 Impact Factor
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ABSTRACT: A non-green catabolite of chlorophyll (Chl) the fluorescent compound FC 2, is produced when intact senescent chloroplasts of barley (Hordeum vulgare L.) are incubated in the presence of ATP. The origin of FC 2 has now been demonstrated by employing senescent chloroplasts containing Chl (14)C-labelled in the pyrrole-rings: upon incubation in the presence of ATP, (14)C-labelled FC 2 is generated. The production of FC 2 requires the hydrolysis of ATP as demonstrated by the failure of the β, γ-imido analogue to support the reaction. Adenosine triphosphate can partially be replaced by UTP but GTP and CTP, as well as ADP and AMP, are ineffective. The system responsible for FC 2 production can also be fueled with glucose-6-phosphate, fructose-6-phosphate and glucose-1-phosphate; other sugar-phosphates including glyceraldehyde-3-phosphate have no effect. Adenosine triphosphate is also required for the release of FC 2 from chloroplasts. When chloroplasts are incubated in the presence of UTP or hexose-monophosphates which support the generation of FC 2 within the organelles, the catabolite is not released. It is concluded that the envelope of senescent chloroplasts is equipped with translocators for the cytosolic compounds which provide the metabolic energy and cofactors required for the action of the catalyst(s) responsible for the oxidative cleavage of Chl-porphyrin and possibly also for the dismantling of Chl-protein complexes. Moreover, a translocator may be involved in the release of the primary catabolites of Chl from chloroplasts.Planta 05/1992; 187(2):230-5. · 3.35 Impact Factor
- American Journal of Botany - AMER J BOT. 01/1964; 51(3).