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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    • "Further studies on the levels of chlorophylls a and b, soluble proteins, and unsaturated fatty acids and on the chloroplast ultrastructure, chloroplast number, and differences in gene expression have provided strong evidence to support that chloroplast ultrastructure regeneration is responsible for the functional stay-green trait of CN17 (Luo et al. 2013). In fact, plants have also evolved sophisticated response mechanisms to adapt to different developmental events during different growth stages and to reprogram gene expression at the transcriptional level (Smart 1994). Therefore, transcript profiling has been widely used to determine how plants transcriptionally respond to developmental events during leaf senescence (Luo et al. 2013). "
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    ABSTRACT: Leaf senescence is a notably important trait that limits the yield and biomass accumulation of agronomic crops. Therefore, determining the chromosomal position of the expression sequence tags (ESTs) that are associated with leaf senescence is notably interesting in the manipulation of leaf senescence for crop improvement. A total of 32 ESTs that were previously identified during the delaying leaf senescence stage in the stay-green wheat cultivar CN17 were mapped to 42 chromosomes, a chloroplast, a mitochondrion, and a ribosome using in silico mapping. Then, we developed 19 pairs of primers based on these sequences and used them to determine the polymorphisms between the stay-green cultivars (CN12, CN17, and CN18) and the control cultivar MY11. Among the 19 pairs of primers, 5 pairs produced polymorphisms between the stay-green cultivar and the non-stay-green control. Further studies of Chinese Spring nullisomic-tetrasomics show that JK738991 is mapped to 3B, JK738983 is mapped to 5D, and JK738989 is mapped to 2A, 4A, and 3D. The other two ESTs, JK738994 and JK739003, were not assigned to a chromosome using the Chinese Spring nullisomic-tetrasomics, which indicates that these ESTs may be derived from rye DNA in the wide cross. In particular, the ESTs that produce polymorphisms are notably useful in identifying the stay-green cultivar using molecular marker-assisted selection. The results also suggest that the in silico mapping data, even from a comparison genomic analysis based on the homogeneous comparison, are useful at some points, but the data were not always reliable, which requires further investigation using experimental methods.
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    • "Although experiments, where leaf senescence induced by girdling leads to a decreased photosynthetic activity, have been reported frequently (Parrott et al. 2007), there are only a few studies concerning the activity of photosynthetic apparatus and electron transfer in the senescence process (Lichtenthaler and Babani 2004). Although it is well known that plant senescence is always accompanied by yellowing and Chl decomposition, observation of leaf color and determination of Chl content is insufficient to determine the process of leaf senescence, particularly in relation to changes in photosynthetic apparatus performance and structure (Smart 1994). The measurement of Chl fluorescence is able to elucidate more comprehensively and profoundly the changes in photosynthetic apparatus structure and performance in the process of leaf senescence in plants. "
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    ABSTRACT: Senescence constitutes the final stage of a plant organ and tissue development and is a subject to gene control and strict regulation. By the late growing season, when Alhagi sparsifolia entered the natural senescence period, a girdling treatment was conducted on the phloem to increase the sugar content in leaves and to investigate carbohydrate-induced leaf senescence. After the semi-girdling and full-girdling treatment, organic matter could not leave leaves due to the destruction of sieve tubes. This led to constantly increasing sugar contents in leaves. Girdling was shown to greatly accelerate the senescence of plants. In girdled leaves, chlorophyll (Chl) a, Chl b, carotenoids (Car), and both ratios of Chl a/b and Chl/Car were significantly reduced. On the donor side of PSII, the oxygen-evolving complex was damaged under high concentrations of carbohydrates, which was manifested as the emergence of the K phase in fluorescence kinetic curves. On the acceptor side of PSII, the high carbohydrate content also led to the disruption of electron transport and reduced light-use efficiency, which was manifested as a reduction in numerous fluorescence parameters. We believe that the emergence and development of plant senescence was not necessarily induced by the high content of carbohydrates, because even a decrease in the carbohydrate concentration could not arrest the senescence process. Although the high content of carbohydrates in plants was capable of inducing plant senescence, this kind of senescence was likely a pathological process, including degradations of physiological functions.
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