Interaction of engineered nanoparticles with various components of the environment and possible strategies for their risk assessment.

Nanoparticles are the materials with at least two dimensions between 1 and 100 nm. Mostly these nanoparticles are natural products but their tremendous commercial use has boosted the artificial synthesis of these particles (engineered nanoparticles). Accelerated production and use of these engineered nanoparticles may cause their release in the environment and facilitate the frequent interactions with biotic and abiotic components of the ecosystems. Despite remarkable commercial benefits, their presence in the nature may cause hazardous biological effects. Therefore, detail understanding of their sources, release interaction with environment, and possible risk assessment would provide a basis for safer use of engineered nanoparticles with minimal or no hazardous impact on environment. Keeping all these points in mind the present review provides updated information on various aspects, e.g. sources, different types, synthesis, interaction with environment, possible strategies for risk management of engineered nanoparticles.

Plant peroxiredoxins: catalytic mechanisms, functional significance and future perspectives.

Peroxiredoxins (Prx) are a family of thiol dependent peroxidases found in almost all kingdoms. In plants, five major classes of Prx are known. They are known to catalyze the decomposition of peroxides and as they lack a prosthetic group, the catalytic cycle results in the generation of an inactive form of Prx. In order to regain the active form, Prx rely on external electron donors such as thioredoxins, glutaredoxins, cyclophilins, NADPH-dependent thioredoxin reductase C (NTRC) etc. In addition to their well established role in antioxidative defense, Prx are also reported to play an important role in growth and development, dessication tolerance in dormant seeds, protection of photosynthesis, defense against pathogens and redox signaling. Prx are also known to establish an alternate water-water cycle for the detoxification of H2O2, parallel to ascorbate-dependent H2O2 detoxification. But the relative contribution of Prx in detoxifying H2O2 compared to ascorbate peroxidase is not known so far due to experimental limitations. In view of the above, the present review focuses on the recent developments on Prxs.

Proline improves copper tolerance in chickpea (Cicer arietinum).

The present study suggests the involvement of proline in copper tolerance of four genotypes of Cicer arietinum (chickpea). Based on the data of tolerance index and lipid peroxidation, the order for copper tolerance was as follows: RSG 888 > CSG 144 > CSG 104 > RSG 44 in the selected genotypes. The basis of differential copper tolerance in chickpea genotypes was characterized by analyzing, antioxidant enzymes (superoxide dismutase, ascorbated peroxidase and catalase), phytochelatins, copper uptake, and proline accumulation. Chickpea genotypes showed stimulated superoxide dismutase activity at all tested concentrations of copper, but H(2)O(2) decomposing enzymes especially; ascorbate peroxidase did not increase with 25 and 50 microM copper treatments. Catalase activity, however, increased at lower copper concentrations but failed to stimulate at 50 microM copper. Such divergence in responses of these enzymes minimizes their importance in protecting chickpea against copper stress. The sensitive genotypes showed greater enhancement of phytochelatins than that of tolerant genotypes. Hence, the possibility of phytochelatins in improving copper tolerance in the test plant is also excluded. Interestingly, the order of proline accumulation in the chickpea genotypes (RSG 888 > CSG 144 > CSG 104 > RSG 44) was exactly similar to the order of copper tolerance. Based on hyperaccumulation of proline in tolerant genotype (RSG 44) and the reduction and improvement of lipid peroxidation and tolerance index, respectively, by proline pretreatment, we conclude that hyperaccumulation of proline improves the copper tolerance in chickpea.

Peroxiredoxins: a less studied component of hydrogen peroxide detoxification in photosynthetic organisms.

Peroxiredoxins (Prx) are ubiquitous thiol-dependent peroxidases capable of reducing a broad range of toxic peroxides and peroxinitrites. A cysteinyl residue of peroxiredoxins reacts with the peroxides as primary catalytic center and oxidizes to sulfenic acid. The regeneration of the reduced form of Prx is required as a next step to allow its entry into next catalytic cycle. Several proteins, such as thioredoxin, glutaredoxin, cyclophilin, among others, are known to facilitate the regeneration of the reduced (catalytically active) form of Prx in plants. Based on the cysteine residues conserved in the deduced amino acid sequence and their catalytic mechanisms, four groups of peroxiredoxins have been distinguished in plants, namely, 1-Cys Prx, 2-Cys Prx, Type II Prx and Prx Q. Peroxiredoxins are known to play an important role in combating the reactive oxygen species generated at the level of electron transport activities in the plant exposed to different types of biotic and abiotic stresses. In addition to their role in antioxidant defense mechanisms in plants, they also modulate redox signaling during development and adaptation. Besides these general properties, peroxiredoxins have been shown to protect DNA from damage in vitro and in vivo. They also regulate metabolism in thylakoids and mitochondria. The present review summarizes the most updated information on the structure and catalysis of Prx and their functional importance in plant metabolism.