Gene expression during leaf senescence. New Phytol 126:419-448

Cell Biology Department, Institute of Grassland and Environment Research, Plas Gogerddan, Aberystwyth, Dyfed, SY23 3EB, Wales, UK
New Phytologist (Impact Factor: 7.67). 02/1994; 126(3):419 - 448. DOI: 10.1111/j.1469-8137.1994.tb04243.x


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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    • "The initiation and progression of leaf senescence are known to be influenced by various internal and external factors (Smart, 1994; Nam, 1997; Park et al., 1998; Weaver et al., 1998 "
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    ABSTRACT: Medicinal importance of Picrorhiza (Picrorhiza kurrooa Royle ex Benth. - a herb of western Himalayan region) and its endangered status in Red Data Book presses an urgent need for intensive R&D interventions towards ensuring its availability for the medicinal use, its sustainability and improvement. The present study was conducted on Cathepsin B cysteine protease in Picrorhiza. Cathepsin B cysteine protease has been reported to function in diverse processes such as senescence, abscission, programmed cell death, fruit ripening and in response to pathogen and pest attacks. A full-length cDNA- Pk-cbcp encoding cathepsin B-like cysteine protease was cloned from Picrorhiza. The full length Pk-cbcp cDNA consisted of 1369 bp with an open reading frame of 1080 bp, 80 bp 5′ untranslated region and 209 bp 3′ untranslated region. The deduced Pk-cbcp protein contained 359 amino acids with a molecular weight of 39.981 kDa and an isoelectric point of 5.75. Secondary structure analysis revealed Pk-cbcp had 28.97% α-helices, 14.48% β-turns, 19.50% extended strands and 37.05% random coils. Semiquantitative PCR analysis revealed 157% higher expression of Pk-cbcp during senescence compared to that of pre-senescence. Further, application of phytohormones abscisic acid, jasmonic acid and cytokinin influenced the temporal expression status of Pk-cbcp. Abscisic acid and jasmonic acid increased the expression level whereas cytokinin reduced the expression. The findings suggest the role of Pk-cbcp in leaf senescence in Picrorhiza which may be differentially mediated through phytohormones.
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    • "It has been well documented that this ultimate phase of development leading to leaf abscission results in a massive coordinated degradation of macromolecules transported out of senescing leaves (Masclaux-Daubresse et al. 2010). Senescencerelated cell changes are first detected in the chloroplasts (Dodge 1970), whereas the mitochondria and nucleus remain intact until advanced senescence (Smart 1994; Inada et al. 1998). The breakdown of chloroplasts is associated with a decrease in photosynthesis that occurs alongside chlorophyll degradation (Humbeck et al. 1996; Lu & Zhang 1998). "
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    ABSTRACT: Brassica napus L. is an important crop plant, characterised by high nitrogen (N) levels in fallen leaves, leading to a significant restitution of this element to the soil, with important consequences at the economic and environmental levels. It is now well established that the N in fallen leaves is due to weak N remobilisation that is especially related to incomplete degradation of foliar proteins during leaf senescence. Identification of residual proteins in a fallen leaf (i.e. incompletely degraded in the last step of the N remobilisation process) constitutes important information for improving nutrient use efficiency. Proteome analysis of the vascular system (petioles) and blades from fallen leaves of Brassica napus was performed, and the 30 most abundant residual proteins in each tissue were identified. Among them, several proteins involved in N recycling remain in the leaf after abscission. Moreover, this study reveals that some residual proteins are associated with energy metabolism, protection against oxidative stress, and more surprisingly, photosynthesis. Finally, comparison of blade and petiole proteomes show that, despite their different physiological roles in the non-senescing leaf, both organs redirect their metabolism in order to ensure catabolic reactions. Taken together, the results suggest that a better degradation of these leaf proteins during the senescence process could enable improvements in the N use efficiency of Brassica napus.
    Plant Biology 10/2014; 17(2). DOI:10.1111/plb.12241 · 2.63 Impact Factor
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    • "The senescence-associated degradation contributes strongly to the remobilization of growth-limiting nutrients such as nitrogen, phosphorus, and sulphur from senescing organs towards other parts of the plant (Snapp and Lynch, 1996; Masclaux-Daubresse et al., 2008). Besides ageing, leaf senescence can be induced and accelerated by a variety of biotic and abiotic stresses (Smart, 1994), including shade and darkness (Biswal and Biswal, 1984; Rousseaux et al., 1996; Weaver and Amasino, 2001). "
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    ABSTRACT: Phytochrome is thought to control the induction of leaf senescence directly, however, the signalling and molecular mechanisms remain unclear. In the present study, an ecophysiological approach was used to establish a functional connection between phytochrome signalling and the physiological processes underlying the induction of leaf senescence in response to shade. With shade it is important to distinguish between complete and partial shading, during which either the whole or only a part of the plant is shaded, respectively. It is first shown here that, while PHYB is required to maintain chlorophyll content in a completely shaded plant, only PHYA is involved in maintaining the leaf chlorophyll content in response to partial plant shading. Second, it is shown that leaf yellowing associated with strong partial shading in phyA-mutant plants actually correlates to a decreased biosynthesis of chlorophyll rather than to an increase of its degradation. Third, it is shown that the physiological impact of this decreased biosynthesis of chlorophyll in strongly shaded phyA-mutant leaves is accompanied by a decreased capacity to adjust the Light Compensation Point. However, the increased leaf yellowing in phyA-mutant plants is not accompanied by an increase of senescence-specific molecular markers, which argues against a direct role of PHYA in inducing leaf senescence in response to partial shade. In conclusion, it is proposed that PHYA, but not PHYB, is essential for fine-tuning the chlorophyll biosynthetic pathway in response to partial shading. In turn, this mechanism allows the shaded leaf to adjust its photosynthetic machinery to very low irradiances, thus maintaining a positive carbon balance and repressing the induction of leaf senescence, which can occur under prolonged periods of shade.
    Journal of Experimental Botany 03/2014; 65(14). DOI:10.1093/jxb/eru060 · 5.53 Impact Factor
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