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The current study explored the role of ionic copper (CuCl

Numerous advances have been made to mitigate the repercussion of toxic metals on photosynthetic prokaryotes, i.e. cyanobacteria. One strategy is exogenous supplementation of plant growth regulators (PGRs). This perhaps intensifies the resistance ability of cyanobacteria to encounter the environmental stresses by augmenting their physiological functioning and decontaminant efficiency. Thus, the aim of the present study was to determine if the PGRs auxin (indole-3 acetic acid, IAA; 300 nM) and cytokinin (kinetin, KN; 10 nM) are able to mitigate the toxic environmentally relevant doses of chromium (CrVI; 100 and 150 µM) in cyanobacteria (Nostoc muscorum ATCC 27,683 and Anabaena sp. PCC 7120). The response was assessed by estimating oxidative stress [in vitro and in vivo (superoxide radical; O2·−, hydrogen peroxide H2O2 and malondialdehyde equivalents contents; MDA)], feasible alteration in whole cell oxygen evolution, ascorbate–glutathione cycle and their metabolites. Intracellular Cr accumulation raised the production of ROS by down-regulating the photosynthetic rate due to decreased pigment contents (Chl a; chlorophyll a, Car; carotenoids and PC; phycocyanin) and reduced growth despite the accelerated activity of the ascorbate–glutathione (AsA-GSH) cycle enzymes (viz. APX; ascorbate peroxidase, GR; glutathione reductase and DHAR; dehydroascorbate reductase). Concurrently, exogenous PGRs (auxin and cytokinin) moderated the negative effects of Cr on the growth, by lowering the cellular Cr accumulation and ROS level and by modulating the pigment system, photosynthesis and a further rise in the efficiency of AsA-GSH cycle, thereby acting as positive regulators of the metal detoxification machinery. Thus, exogenous application of PGRs (auxin and cytokinin) could improve the growth in cyanobacteria in Cr-polluted environments, hence maintaining productivity in paddy cultivation as well as having potential to be used as bio-remediator in metal-contaminated aquatic systems.

This review explains the transport, mobility, resistance and detoxification of toxic metalloid arsenic (As) in plants. Arsenic is ubiquitously present in Earth’s crust; however, numerous human interventions such as rapid industrialization use of As-based pesticides, insecticides and discharge of industrial wastes in water bodies leads to cumulative increase in As in the environment and has become a global challenge. Arsenic exists in different organic and inorganic forms, but inorganic forms such as pentavalent arsenate (AsV) and trivalent arsenite (AsIII) are more toxic and actively taken up by plants. Its toxicity is marked by generation of reactive oxygen species (ROS) that are capable of degrading various biomolecules of the cellular systems. To keep the ROS under the limit, plants have an array of enzymatic antioxidants such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione-S-transferase (GST); and non-enzymatic antioxidant like ascorbate, proline, and cysteine. Contrary to this, As-hyper-accumulator plants survive under high concentration of As through the strenuous action of Asv reduction into AsIII followed by the vacuolar compartmentalization of complex or inorganic As. Hence, this review focuses on the potential sources of As in the environment, its speciation and toxicity, and tolerance strategies in plants.

Background Cyanobacteria are well known for their inherent ability to serve as atmospheric nitrogen fixers and as bio-fertilizers; however, increased contaminants in aquatic ecosystem significantly decline the growth and function of these microbes in paddy fields. Plant growth regulators play beneficial role in combating the negative effects induced by heavy metals in photoautotroph. Current study evaluates the potential role of indole acetic acid (IAA; 290 nm) and kinetin (KN; 10 nm) on growth, nitrogen metabolism and biochemical constituents of two paddy field cyanobacteria Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120 exposed to two concentrations of chromium (CrVI; 100 μM and 150 μM). Results Both the tested doses of CrVI declined the growth, ratio of chlorophyll a to carotenoids (Chl a/Car), contents of phycobiliproteins; phycocyanin (PC), allophycocyanin (APC), and phycoerythrin (PE), protein and carbohydrate associated with decrease in the inorganic nitrogen (nitrate; NO3— and nitrite; NO2—) uptake rate that results in the decrease in nitrate and ammonia assimilating enzymes; nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT) except glutamate dehydrogenase (GDH). However, exogenous supplementation of IAA and KN exhibited alleviating effects on growth, nitrogen metabolism and exopolysaccharide (EPS) (first protective barrier against metal toxicity) contents in both the cyanobacteria, which probably occurred as a result of a substantial decrease in the Cr uptake that lowers the damaging effects. Conclusion Overall result of the present study signifies affirmative role of the phytohormone in minimizing the toxic effects induced by chromium by stimulating the growth of cyanobacteria thereby enhancing its ability as bio-fertilizer that improved fertility and productivity of soil even in metal contaminated condition.