Leaves senescence

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

P is crucial for several aspects of plant metabolism, especially the energy and sugar metabolism, and several enzymatic reactions, including photosynthesis. Plants have therefore developed mechanisms for the uptake and efficient use of P. Maize plants recycled N quicker from old to young tissue when P is deficient, leading to earlier leaf senescence (Usuda 1995). P-deficient plants invest more resources into root development and therefore have an increased root-to-shoot biomass ratio compared to well-nourished plants. Furthermore, they accumulate more carbohydrates in leaves and allocate more carbon to the roots (Hermans et al. 2006). 

Bean, cultivar Rnto 0.05 24/day, 3-5 days 50, leaf senescence (chlorosis) 125, 127... 

Garcia-Plazaola, J.I., Hernandez, A., and Becerril, J.M., Antioxidant and pigment composition during autumnal leaf senescence in woody deciduous species differing in their ecological traits. Plant Biol, 5, 557, 2003. 

Hoch, W.A., Zeldin, E.L., and McCown, B.H., Physiological significance of anthocyanins during autumnal leaf senescence. Tree Physiol, 21, 1, 2001. 

Lee, D.W. et al., Pigment dynamics and autumn leaf senescence in a New England deciduous forest, eastern USA, Ecol Res., 18, 677, 2003. 

Lee DW. 2002. Anthocyanins in autumn leaf senescence. In Gould KS, Lee DW, Eds. Anthocyanins in Leaves. Advances in Botanical Research. Amsterdam Academic Press, Vol 37 pp. 37-53. 

Davies, K.M. Grierson, D. (1989). Identification of cDNA clones for tomato (Lycopersicon esculentum) mRNAs that accumulate during fruit ripening and leaf senescence in response to ethylene. Planta 179, 73-80. 

The tubers start to become freeze tolerant (LD50 at -5°C) toward the end of October, prior to leaf senescence (Ishikawa and Yoshida, 1985). Tolerance increases to -11°C by mid-December. Increased low temperature tolerance did not appear to be due to changes in tuber moisture content the role of inulin depolymerization in increased cold tolerance has not been assessed. 

Becker, W. and Apel, K., Differences in gene expression between mature and artificially induced leaf senescence, Planta, 189, 74-79, 1993. 

Developmental stages I. From planting until approximately 70% canopy closure (approx. 75 days) II. From the end of stage I until approximately 50% flower opening (approx. 70 days) III. From the end of stage II until leaf senescence (approx. 60 days). 

Leaf senescence is characterized by loss of chlorophyll, leaf yellowing, degradation of proteins, membrane lipids, and RNA, and recycling to young tissues.453 Delay of leaf senescence by exogenous application of cytokinins has been confirmed by numerous studies,454 suggesting that cytokinins are key components in the regulation of leaf senescence. 

Incubation of spinach leaf starch granules with extrachloroplastic phosphorylase resulted in the formation of glucose 1-phosphate (Steup et al., 1983). Hammond and Preiss (1983) reported a large increase in cytosolic phosphorylase from spinach leaf in a time course that approximates the time of leaf senescence (i.e., when starch chloroplast must be hydrolyzed and exported to active sinks). 

A transgenic reduction in MIPS activity has also been reported. Antisense suppression of MIPS in transgenic potato resulted in a sevenfold reduction in inositol, and resulted in reduced apical dominance, altered leaf morphology, precocious leaf senescence and a decrease in overall tuber yield. The altered leaf morphology was found to be due to cell enlargement in the leaves. The authors of this study found that in addition to inositol, galactinol, and raffinose levels were reduced. In contrast, increases were observed for hexose phosphates, sucrose, and starch. The authors further concluded that many different inositol metabolites may have contributed to the development of the phenotypes observed (Keller et al., 1998). 

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