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Nanobiotechnology deals with the synthesis of nanostructures using living organisms. Among the use of living organisms for nanoparticle synthesis, plants have found application particularly in metal nanoparticle synthesis. Use of plants for synthesis of nanoparticles could be advantageous over other environmentally benign biological processes as this eliminates the elaborate process of maintaining cell cultures. Biosynthetic processes for nanoparticles would be more useful if nanoparticles were produced extracellularly using plants or their extracts and in a controlled manner according to their size, dispersity and shape. Plant use can also be suitably scaled up for large-scale synthesis of nanoparticles. In view of this, we have reviewed here the use of plants or their extracts in the synthesis of silver and gold nanoparticles for various human applications.

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The human population is increasing at an alarming rate, whereas at the same time agricultural productivity is decreasing due to the effect of various environmental problems. In particular, cold stress is a serious threat to the sustainability of crop yields. Indeed, cold stress can lead to major crop losses. Various phenotypic symptoms in response to cold stress include poor germination, stunted seedlings, yellowing of leaves (chlorosis), reduced leaf expansion and wilting, and may lead to death of tissue (necrosis). Cold stress also severely hampers the reproductive development of plants. The major negative effect of cold stress is that it induces severe membrane damage. This damage is largely due to the acute dehydration associated with freezing during cold stress. Cold stress is perceived by the receptor at the cell membrane. Then a signal is transduced to switch on the cold-responsive genes and transcription factors for mediating stress tolerance. Understanding the mechanism of cold stress tolerance and genes involved in the cold stress signaling network is important for crop improvement. Here, I review cold stress tolerance mechanisms in plants. The major points discussed are the following: (1) physiological effects of cold stress, (2) sensing of cold temperatures and signal transduction, and (3) the role of various cold-responsive genes and transcription factors in the mechanism of cold stress tolerance. cold stress / signal transduction / cold-responsive genes / transcription factors

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The mechanism behind enhanced salt tolerance conferred by the overexpression of glyoxalase pathway enzymes was studied in transgenic vis-à-vis wild-type (WT) plants. We have recently documented that salinity stress induces higher level accumulation of methylglyoxal (MG), a potent cytotoxin and primary substrate for glyoxalase pathway, in various plant species [Yadav, S.K., Singla-Pareek, S.L., Ray, M., Reddy, M.K. and Sopory, S.K. (2005) MG levels in plants under salinity stress are dependent on glyoxalase I and glutathione. Biochem. Biophys. Res. Commun. 337,[61][62][63][64][65][66][67]. The transgenic tobacco plants overexpressing glyoxalase pathway enzymes, resist an increase in the level of MG that increased to over 70% in WT plants under salinity stress. These plants showed enhanced basal activity of various glutathione related antioxidative enzymes that increased further upon salinity stress. These plants suffered minimal salinity stress induced oxidative damage measured in terms of the lipid peroxidation. The reduced glutathione (GSH) content was high in these transgenic plants and also maintained a higher reduced to oxidized glutathione (GSH:GSSG) ratio under salinity. Manipulation of glutathione ratio by exogenous application of GSSG retarded the growth of non-transgenic plants whereas transgenic plants sustained their growth. These results suggest that resisting an increase in MG together with maintaining higher reduced glutathione levels can be efficiently achieved by the overexpression of glyoxalase pathway enzymes towards developing salinity stress tolerant plants.