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: Drought stress has a considerable impact on the ecosystem and agriculture. Continuous water deficit induces early leaf senescence in plants. During this process, chloroplasts are degraded and photosynthesis drastically drops. The objective of this investigation was to look into the regulation of nitrogen and carbon metabolism during water deficit. Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase; EC 18.104.22.168) and the total protein contents inform us of the sink-source relation in plants. Glutamine synthetase (GS, EC 22.214.171.124) isoenzymes are good markers of plastid status (GS2) and the nitrogen metabolism (GS1). Tolerant and sensitive wheat (Triticum aestivum L.) genotypes were tested, which are widely used in agriculture. The amount of protein, Rubisco and GS isoforms in leaves were measured during the grain filling period, as indicative traits that ultimately determine the onset and stage of senescence. The symptoms of senescence first appeared on the oldest and finally on the youngest leaves. Drought stress disrupted the sequentiality of senescence in the sensitive varieties. An untimely senescence appeared in flag leaves, earlier than in the older leaves. Total protein and Rubisco contents decreased and the GS2 isoenzyme declined considerably in the youngest leaves. In the tolerant varieties, however, these physiological parameters did not change under drought, only the sequential senescence of leaf levels accelerated in some cases compared to the control, well-watered plants. Our results revealed that GS is a good indicator of drought stress, which can be applied for the characterization of wheat cultivars in terms of drought stress tolerance.Plant Physiology and Biochemistry 03/2013; 67C:48-54. · 2.78 Impact Factor
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ABSTRACT: The present study tries to examine the influence of natural and oxidative stress [hydrogen peroxide (H2O2) treatment]-induced senescence on peroxidase (POD) activity in neem (Azadirachta indica A. juss) leaves. Data indicated that incubation of detached leaves in presence of H2O2 has induced POD(s), that enzyme activity is also enhanced in natural senescing leaves. Changes in POD activity and protein loss during H2O2-promoted senescence has shown similarity with natural senescence suggests that the underlying regulatory mechanisms might be the same in both stresses, at least in neem. Initial induction of POD activity under H2O2 stress suggests that PODs play a very important role during the early phases of leaf senescence. Reduction in POD activity along with the increase in protein loss at latter stages suggests that there was no correlation between PODs and senescence, at least in neem.International Journal of Current Research. 06/2013; 5(6):1463-1467.
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ABSTRACT: Aims The effects of elevated CO2 on leaf area index (LAI) vary among studies. We hypothesized that the interactive effects of CO2 and nitrogen on leaf area loss have important roles in LAI regulation. Methods We studied the leaf area production and loss using nodulating soybean and its non-nodulating isogenic line in CO2-controlled greenhouse systems. Results Leaf area production increased with elevated CO2 levels in the nodulating soybean stand and to a lesser extent in the non-nodulating line. Elevated CO2 levels accelerated leaf area loss only in nodulating plants. Consequently, both plants exhibited a similar stimulation of peak LAI with CO2 elevation. The accelerated leaf loss in nodulating plants may have been caused by newly produced leaves shading the lower leaves. The nodulating plants acquired N throughout the growth phase, whereas non-nodulating plants did not acquire N after flowering due to the depletion of soil N. N retranslocation to new organs and subsequent leaf loss were faster in non-nodulating plants compared with nodulating plants, irrespective of the CO2 levels. Conclusion LAI regulation in soybean involved various factors, such as light availability within the canopy, N acquisition and N demands in new organs. These effects varied among the growth stages and CO2 levels.Plant and Soil 11/2013; 373:627-639. · 2.64 Impact Factor