Synergistic regulation of hydrogen sulfide and nitric oxide on biochemical components, exopolysaccharides, and nitrogen metabolism in nickel stressed rice field cyanobacteria.

The present study examined the regulatory mechanism of hydrogen sulfide (H2S) and nitric oxide (NO) in nickel (Ni) stressed cyanobacteria viz., Nostoc muscorum and Anabaena sp. by analyzing growth, photosynthetic pigments, biochemical components (protein and carbohydrate), exopolysaccharides (EPS), inorganic nitrogen content, and activity of enzymes comprised in nitrogen metabolism and Ni accumulation. The 1 µM Ni substantially diminished growth by 18% and 22% in N. muscorum and Anabaena sp. respectively, along with declining the pigment contents (Chl a/Car ratio and phycobiliproteins), and biochemical components. It also exerted negative impacts on inorganic uptake of nitrate and nitrite contents; nitrate reductase and nitrite reductase; and ammonium assimilating enzymes (glutamine synthetase, glutamate synthase, and glutamate dehydrogenase exhibited a reverse trend) activities. Nonetheless, the adverse impact of Ni can be mitigated through the exogenous supplementation of NaHS [sodium hydrosulfide (8 µM); H2S donor] and SNP [sodium nitroprusside (10 µM); NO donor] which showed substantial improvement on growth, pigments, nitrogen metabolism, and EPS layer and noticeably occurred as a consequence of a substantial reduction in Ni accumulation content which minimized the toxicity effects. The accumulation of Ni on both the cyanobacterial cell surface (EPS layer) are confirmed by the SEM-EDX analysis. Further, the addition of NO scavenger (PTIO; 20 µM) and inhibitor of NO (L-NAME; 100 µM); and H2S scavenger (HT; 20 µM) and H2S inhibitor (PAG; 50 µM) reversed the positive responses of H2S and NO and damages were more prominent under Ni stress thereby, suggesting the downstream signaling of H2S on NO-mediated alleviation. Thus, this study concludes the crosstalk mechanism of H2S and NO in the mitigation of Ni-induced toxicity in rice field cyanobacteria.

Silicon nanoparticles: Comprehensive review on biogenic synthesis and applications in agriculture.

Recent advancements in nanotechnology have opened new advances in agriculture. Among other nanoparticles, silicon nanoparticles (SiNPs), due to their unique physiological characteristics and structural properties, offer a significant advantage as nanofertilizers, nanopesticides, nanozeolite and targeted delivery systems in agriculture. Silicon nanoparticles are well known to improve plant growth under normal and stressful environments. Nanosilicon has been reported to enhance plant stress tolerance against various environmental stress and is considered a non-toxic and proficient alternative to control plant diseases. However, a few studies depicted the phytotoxic effects of SiNPs on specific plants. Therefore, there is a need for comprehensive research, mainly on the interaction mechanism between NPs and host plants to unravel the hidden facts about silicon nanoparticles in agriculture. The present review illustrates the potential role of silicon nanoparticles in improving plant resistance to combat different environmental (abiotic and biotic) stresses and the underlying mechanisms involved. Furthermore, our review focuses on providing the overview of various methods exploited in the biogenic synthesis of silicon nanoparticles. However, certain limitations exist in synthesizing the well-characterized SiNPs on a laboratory scale. To bridge this gap, in the last section of the review, we discussed the possible use of the machine learning approach in future as an effective, less labour-intensive and time-consuming method for silicon nanoparticle synthesis. The existing research gaps from our perspective and future research directions for utilizing SiNPs in sustainable agriculture development have also been highlighted.

Modulation of salt stress in paddy field cyanobacteria with exogenous application of gibberellic acid: growth behavior and antioxidative status.

The present study explores the possible function of gibberellic acid (GA: 20 µM) in reducing salt (NaCl) induced toxicity in two diazo-trophic cyanobacteria i.e. Nostoc muscorum and Phormidium foveolarum. The physiological and biochemical parameters viz. growth, photosynthetic pigments (chlorophyll a, carotenoids, and phycocyanin), photosynthetic and respiratory rates, oxidative stress biomarkers (superoxide radicle, hydrogen peroxide, and malondialdehyde contents) antioxidant activities (superoxide dismutase, peroxidase, catalase, and glutathione-S-transferase) and non-enzymatic antioxidants were studied under both the doses i.e. 40 mM (LC 10) and  mM (LC 30) of NaCl. The growth, photosynthetic pigments and photosynthetic rate were found to be declined under concentration-dependent manner of NaCl. Contrastingly, the respiratory rate, oxidative stress biomarkers, and the activity of antioxidant enzymes i.e. superoxide dismutase (SOD), peroxidases (POD), catalase (CAT), and glutathione-S-transferase (GST) together with contents of non-enzymatic antioxidants (proline and cysteine) were found to increase in the test cyanobacteria. PSII photochemistry in both the cyanobacteria was negatively affected showing an inhibitory effect of NaCl on JIP parameters, while an enhancement effect was noticed in the values related to energy flux parameters. Further, the addition of GA to the growth medium caused an alleviating effect as it completely mitigated NaCl toxicity induced by a lower dose i.e. 40 mM of NaCl, while it partially alleviated the growth and photosynthetic parameters of 80 mM NaCl stressed cyanobacteria. Supplementation of GA significantly reduced the contents of oxidative stress tested cyanobacteria due to an improved antioxidant system (increased activities of enzymatic and non-enzymatic antioxidants) as evident from the biochemical analysis. In brief, our findings reflect the possible role of GA as a potential modulator of salt toxicity. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-022-01266-5.

Silicon and nitric oxide-mediated mechanisms of cadmium toxicity alleviation in wheat seedlings.

The individual impact of silicon (Si) and nitric oxide (NO, as sodium nitroprusside) on metal toxicity in various plant species has been well documented; however, their combined action in the regulation of metal stress has never been tested yet. Therefore, this study investigates the effects of the combined application of Si and NO in the mitigation of Cd toxicity in wheat seedlings. Seedlings grown on Cd has a significantly declined growth due to an increased accumulation of Cd and oxidative stress markers (due to downregulation of antioxidant defense system particularly ascorbate-glutathione cycle) and a decreased accumulation of NO and Si. Additionally, the altered leaf and root structures resulted into a declined photosynthetic efficiency. However, the addition of Si and NO alone as well as combined significantly alleviated Cd toxicity in wheat seedlings by lowering the accumulation of Cd and oxidative stress markers and improving leaf and root structures, which are collectively responsible for a better photosynthetic rate under Cd toxicity, and hence an improved growth was noticed. Particularly, the application of Si and NO in combination lowered the oxidative stress markers via upregulating the antioxidant defense system (particularly AsA-GSH cycle) suggesting the increased efficacy of Si + NO against the Cd toxicity in wheat seedlings as compared to their alone treatments.

Differential response of copper nanoparticles and ionic copper on growth, chlorophyll fluorescence, oxidative stress, and antioxidant machinery of two paddy field cyanobacteria.

The current study explored the role of ionic copper (CuCl2; 0.2 µM and 1 µM) and synthesized copper nanoparticles (CuNPs; 0.2 mM and 1 mM) in the two paddy field cyanobacteria (Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120) with respect to growth, photosynthetic pigments, photosynthetic efficiency (O2 evolution and photochemistry of photosystem II; PS II), oxidative stress biomarkers, and antioxidant system. The low doses of ionic Cu (0.2 µM) and CuNPs (0.2 mM) showed stimulating effects on growth, pigment content (chlorophyll a, phycobiliproteins, and carotenoids), oxygen evolution, and PS II photochemistry. High doses of Cu/CuNPs (1 µM Cu and 1 mM CuNPs) caused a decline in the above-mentioned parameters. The values of fluorescence kinetics parameters: ϕP0, FV/F0, ϕE0, Ψ0, and PIABS, except for F0/FV, associated with PS II photochemistry in tested cyanobacteria and subjected to the high doses of ionic Cu and CuNPs, were decreased, while energy fluxes, ABS/RC, TR0/RC, ET0/RC, and DI0/RC, were increased. Conversely, treatment with low doses of Cu and CuNPs caused a reverse trend, indicating normalization of PS II performance. Although the activity of enzymatic antioxidants (superoxide dismutase SOD; peroxidase POD; catalase CAT and glutathione-S-transferase GST) in both cyanobacteria exposed to high doses of ionic Cu and CuNPs was accelerated considerably, the oxidative stress remained high. Conversely, at low doses of ionic Cu and CuNPs, a significant enhancement in the activities of enzymatic antioxidants decreased the levels of oxidative stress biomarkers. Nevertheless, in Anabaena sp., the levels of biomarkers were greater than those of the control. The current study concluded that compared to synthesized CuNPs, ionic Cu at elevated concentration had a damaging effect on growth, photosynthetic pigments, and PS II photochemistry via increased oxidative stress, and this effect was enhanced in Anabaena sp. than N. muscorum.

Interplay of hydrogen peroxide and nitric oxide: systemic regulation of photosynthetic performance and nitrogen metabolism in cadmium challenged cyanobacteria.

In the present study, the potential role of hydrogen peroxide (H2O2) and nitric oxide (NO) has been well recorded in the induction of cadmium (Cd) stress tolerance in cyanobacteria. In this regard, H2O2 and SNP (sodium nitroprusside, NO donor), were applied to Nostoc muscorum and Anabaena sp. exposed to Cd (6 µM) stress, to analyze different physiological and biochemical parameters. Results revealed that treatment of Cd reduced the growth, pigment contents, photosynthetic oxygen yield and performance of PS II photochemistry (decreased chlorophyll a fluorescence parameters, i.e., ФPo, Ψo, ФEo, PIABS along with Fv/Fo and increased the energy flux parameters, i.e., ABS/RC, TRo/RC, ETo/RC, DIo/RC along with Fo/Fv. Similarly, uptake of nitrate (NO3 -) and nitrite (NO2 -), as well as the activities of nitrate and ammonia assimilating enzymes along with carbohydrate content, were severely affected by Cd toxicity and notwithstanding this, glutamate dehydrogenase (GDH) activity exhibited reverse trend. Exogenous application of a very low dose (1 µM) of H2O2 (only for 3 h) and NO (SNP; 10 µM) notably counteracted Cd-induced toxicity. Nevertheless, the positive impact of H2O2 got reversed under the treatment of PTIO (NO scavenger) and LNAME (inhibitor of nitric oxide synthase; NOS) while NO could work efficiently even in the presence of NAC (H2O2 scavenger) and DPI (inhibitor of NADPH oxidase); hence indicated towards the H2O2 mediated NO signaling in averting Cd induced toxicity in test cyanobacteria. In conclusion, current finding demonstrated a positive cross-talk between H2O2 and NO for providing tolerance to cyanobacteria against Cd stress.

Phytohormone up-regulates the biochemical constituent, exopolysaccharide and nitrogen metabolism in paddy-field cyanobacteria exposed to chromium stress.

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.

Fascinating impact of silicon and silicon transporters in plants: A review.

Silicon (Si) is a metalloid which is gaining worldwide attention of plant scientists due to its ameliorating impact on plants' growth and development. The beneficial response of Si is observed predominantly under numerous abiotic and biotic stress conditions. However, under favorable conditions, most of the plant can grow without it. Therefore, Si has yet not been fully accepted as essential element rather it is being considered as quasi-essential for plants' growth. Si is also known to enhance resilience in plants by reducing the plant's stress. Besides its second most abundance on the earth crust, most of the soils lack plant available form of Si i.e. silicic acid. In this regard, understanding the role of Si in plant metabolism, its uptake from roots and transport to aerial tissues along with its ionomics and proteomics under different circumstances is of great concern. Plants have evolved a well-optimized Si-transport system including various transporter proteins like Low silicon1 (Lsi1), Low silicon2 (Lsi2), Low silicon3 (Lsi3) and Low silicon6 (Lsi6) at specific sub-cellular locations along with the expression profiling that creates precisely coordinated network among these transporters, which also facilitate uptake and accumulation of Si. Though, an ample amount of information is available pertinent to the solute specificity, active sites, transcriptional and post-transcriptional regulation of these transporter genes. Similarly, the information regarding transporters involved in Si accumulation in different organelles is also available particularly in silica cells occurred in poales. But in this review, we have attempted to compile studies related to plants vis à vis Si, its role in abiotic and biotic stress, its uptake in various parts of plants via different types of Si-transporters, expression pattern, localization and the solute specificity. Besides these, this review will also provide the compiled knowledge about the genetic variation among crop plants vis à vis enhanced Si uptake and related benefits.

Nostoc muscorum and Phormidium foveolarum differentially respond to butachlor and UV-B stress.

Present study deals with responses of two cyanobacteria viz. Nostoc muscorum and Phormidium foveolarum against butachlor [2-chloro-2,6-diethyl-N-(butoxymethyl) acetanilide] (low dose; 5 µg mL-1 and high dose; 10 µg mL-1) and UV-B (7.2 kJ m-2) alone, and in combination. Butachlor and UV-B exposure, alone and in combination, suppressed growth of both the cyanobacteria. This was accompanied by inhibitory effect on whole cell oxygen evolution and photosynthetic electron transport activities. Both the stressors induced the oxidative stress as there was significant increase in superoxide radical (O2 ·-) and hydrogen peroxide (H2O2) contents resulting into increased lipid peroxidation and electrolyte leakage. In N. muscorum, low dose of butachlor and UV-B alone increased the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), while activity of all these enzymatic antioxidants declined significantly at treatments with high dose of butachlor alone, and with low and high doses of butachlor and UV-B in combination. In P. foveolarum, enhanced activity of SOD, CAT and POD (except POD at high dose of butachlor and UV-B combination) was noticed. Ascorbate level in N. muscorum declined progressively with increasing intensity of stress while in P. foveolarum varied response was noticed. Proline contents increased progressively under tested stress in both the organisms. Overall results suggest that N. muscorum was more sensitive than P. foveolarum against butachlor and UV-B stresses. Hence, P. foveolarum may be preferred in paddy field for sustainable agriculture.

Liquid assisted pulsed laser ablation synthesized copper oxide nanoparticles (CuO-NPs) and their differential impact on rice seedlings.

Hydroponic experiments were conducted to investigate impact of laser ablated copper oxide nanoparticles (CuO-NPs) on rice seedlings. The present work demonstrates that exposure of lower concentrations (5, 10, 20, and 50 µM) of CuO-NPs enhance growth (in terms of fresh and dry weight and length), of rice seedlings. However, at higher concentrations (100, 200, and 500 µM) of CuO-NPs, growth (in terms of length, fresh weight and dry weight) decreased significantly (P < 0.05). Further, photosynthetic pigments (total chlorophyll and carotenoids) and protein contents were also found to be in accordance with the results of growth. This had occurred due to enhanced level of CuO-NPs accumulation at higher doses which also enhanced the level of oxidative stress markers such as hydrogen peroxide (H2O2) and malondialdehyde (MDA). Chlorophyll a fluorescence parameters (Fv/Fm and qP and except NPQ) and amount of some minerals (Ca, Mg, Na, and K) increased at lower concentrations of CuO-NPs. In contrast, the levels of Fv/Fm and qP were significantly (P < 0.05) reduced at higher concentration of CuO-NPs, which might be due to enhanced accumulation of Cu and oxidative stresses markers. Our results showed that lower dosages of pulsed laser ablated CuO-NPs (5, 10, 20, and 50 µM) might be beneficial for growth and development of rice seedlings.

Kinetin alleviates chromium toxicity on growth and PS II photochemistry in Nostoc muscorum by regulating antioxidant system.

The present study was undertaken to evaluate the metal toxicity alleviating effects of kinetin (KN, 10 nM) on growth, photosynthetic pigments and photochemistry of PS II in the cyanobacterium Nostoc muscorum exposed to chromium (CrVI) stress (100 and 150 µM). Chromium declined growth, photosynthetic pigments (chlorophyll a, phycocyanin and carotenoids), photosynthetic oxygen evolution rate and parameters of fluorescence kinetics (ϕP0, FV/F0, ϕE0, Ψ0 and PIABS except F0/FV) in concentration dependent manner, while stimulating effects on respiration, energy flux parameters (ABS/RC, TR0/RC, ET0/RC and DI0/RC), oxidative stress biomarkers i.e., superoxide radical (SOR), hydrogen peroxide (H2O2) and lipid peroxidation (TBARS contents) and antioxidative enzymes: superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and glutathione-S-transferase (GST), were observed. However, upon addition of KN in the growth medium an alleviating effect against chromium induced toxicity on growth, photosynthetic pigments and photochemistry of PS II was recorded. This had occurred due to substantial reduction in levels of oxidative stress biomarkers: SOR, H2O2 and TBARS contents with concomitant rise in activity of antioxidative enzymes: SOD, POD, CAT and GST and appreciable lowering in the cellular accumulation of chromium. The overall results demonstrate that KN application significantly alleviated chromium induced toxicity on growth performance of the cyanobacterium N. muscorum due to significant improvement in photosynthetic pigments and photochemistry of PS II by up-regulating the activity of antioxidative enzymes, and declining cellular accumulation of chromium. Furthermore, Cr induced toxicity at lower dose (100 µM) was found to be ameliorated more efficiently in N. muscorum following supplementation of KN.

Simultaneous exposure of sulphur and calcium hinder As toxicity: Up-regulation of growth, mineral nutrients uptake and antioxidants system.

The current study was carried out to investigate the role of exogenous sulphur (K2SO4: S; 60 mg S kg-1 sand) and calcium (CaCl2: Ca; 250 mg Ca kg-1 sand) individually as well as in combination (S + Ca) in ameliorating the inhibitory effect of As (Na2HAsO4·7H2O: As1; 15 mg As kg-1 sand and As2; 30 mg As kg-1 sand) by analyzing biomass accumulation, mineral nutrients uptake, photosynthetic pigments content, redox status of the cell, enzymatic and non-enzymatic defense system in Brassica juncea L. seedlings. Biomass accumulation, uptake of mineral nutrients, photosynthetic pigments (chlorophyll a, b and carotenoids) content and the activity of proline dehydrogenase (ProDH) declined with increasing accumulation of As in root as well as leaves in As dose dependent manner. Contrary to this, exogenous application of S, Ca and S + Ca, markedly reduced the negative impact of As on above captioned traits except ProDH activity. On the other hand, ROS and their biomarkers (superoxide radical; O2˙-, hydrogen peroxide; H2O2, malondialdehyde; MDA equivalents content and membrane damage; electrolyte leakage), activities of enzymatic (superoxide dismutase; SOD, peroxidase; POD, catalase; CAT and glutathione-S-transferase; GST) and non-enzymatic antioxidant i.e. proline (Pro) content and its enzyme pyrroline-5-carboxylate synthetase; P5CS activity were increased in root and leaves under As stress. While, exogenous application of S, Ca and S + Ca, further enhanced the activities of above mentioned enzymes and Pro content thereby causing considerable reduction in O2˙-, H2O2, MDA equivalents content and electrolyte leakage. This study suggests that exogenous application of S and/or Ca efficiently (particularly S + Ca) lowered the negative impact of As on biomass accumulation in Brassica seedlings by improving the uptake of essential mineral nutrients', content of photosynthetic pigments, activities of enzymatic and content of non-enzymatic antioxidants.

Toxicity assessment of arsenate and arsenite on growth, chlorophyll a fluorescence and antioxidant machinery in Nostoc muscorum.

The present study deals with impact of varied doses of arsenite (AsIII; 50, 100 and 150 µM) and arsenate (AsV; 50, 100 and 150 mM) on growth, photosynthetic pigments, photochemistry of photosystem II, oxidative biomarkers, (O2•¯, H2O2 and MDA equivalents contents) and activity of antioxidant enzymes in diazotrophic cyanobacterium Nostoc muscorum after 48 and 96 h of the treatments. The reduction in growth, pigment contents (Chl a, Phy and Car) and PS II photochemistry was found to increase with enhanced accumulation of test metal in cells, and the damaging effect on photosynthetic pigments showed the order (Phy > chl a> Car). The negative effect on PS II photochemistry was due to significant decrease in the value of JIP kinetics ϕP0, FV/F0, ϕE0,Ψ0 and PIABS except F0/FV and significant rise in values of energy flux parameters such as ABS/RC, TR0/RC, ET0/RC and DI0/RC. Both the species of arsenic caused significant rise in oxidative biomarkers as evident by in vitro and in vivo analysis of (O2•¯, H2O2 and MDA equivalents contents) despite of appreciable rise in the activity antioxidative enzymes such as SOD, POD, CAT and GST. The study concludes that in among both forms of arsenic, arsenite effect was more dominant on growth, photosynthetic pigments; oxidative stress biomarkers as evident by weak induction of anti-oxidative defense system to overcome the stress as compared to arsenate.

Pretilachlor toxicity is decided by discrete photo-acclimatizing conditions: Physiological and biochemical evidence from Anabaena sp. and Nostoc muscorum.

The current study was undertaken to elucidate the impact of the herbicide pretilachlor (3 µg ml-1 and 6 µg ml-1) on cyanobacteria, Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120 under three levels of photoacclimatization (suboptimum, 25 µmol photon m-2 s-1; optimum, 75 µmol photon m-2 s-1; and supra-optimum, 225 µmol photon m-2 s-1) by analyzing certain physiological (biomass accumulation, photosynthesis, Chl a fluorescence and respiration) and biochemical parameters (photosynthetic pigments‒ chlorophyll a, carotenoids and phycocyanin; reactive oxygen species‒ O2•¯, H2O2, lipid peroxidation; antioxidant system‒ superoxide dismutase, peroxidise, catalase and glutathione-S-transferase). The light conditioning played the most prominent role in deciding the extent of herbicide toxicity on both the tested cyanobacteria as the maximum toxicity was observed in suboptimum light acclimatized cyanobacterial cells corroborated by the least growth in the same cells. The impact of pretilachlor treatment on photosystem II photochemistry viz. φP0, Ñ°0, φE0, PIABS, ABS/RC, TR0/RC, ET0/RC and DI0/RC was also altered by light acclimatization. The percent rise in oxidative stress markers (SOR and H2O2) and consequent lipid peroxidation (MDA equivalents) were also highest in suboptimum light acclimatized cells exposed to pretilachlor which could not be prospered with compatible antioxidant performance. Conversely, supra-optimum light acclimatized cells of both the cyanobacteria was found to accelerate the activities of all the studied enzymes and thus able to counterbalance the pretilachlor toxicity and supported the healthier growth.

Exogenous IAA differentially affects growth, oxidative stress and antioxidants system in Cd stressed Trigonella foenum-graecum L. seedlings: Toxicity alleviation by up-regulation of ascorbate-glutathione cycle.

In the present study, effect of exogenous indole-3-acetic acid at their different levels (i.e. low; IAAL, 10µM and high; IAAH, 100µM) were studied on growth, oxidative stress biomarkers and antioxidant enzymes (SOD, POD, CAT and GST), and metabolites (AsA and GSH) as well as enzymes (APX, GR and DHAR) of ascorbate-glutathione cycle in Trigonella foenum-graecum L. seedlings grown under cadmium (Cd1, 3mgCd kg(-1) soil and Cd2, 9mgCd kg(-1) soil) stress. Cadmium (Cd) at both doses caused reduction in growth which was correlated with enhanced lipid peroxidation and damage to membrane as a result of excess accumulation of O2(•-) and H2O2. Cd also enhanced the oxidation of AsA and GSH to DHA and GSSG, respectively which give a clear sign of oxidative stress, despite of accelerated activity of enzymatic antioxidants: SOD, CAT, POD, GST as well as APX, DHAR (except in Cd2 stress) and GR. Exogenous application of IAAL resulted further rise in the activities of these enzymes, and maintained the redox status (> ratios: AsA/DHA and GSH/GSSG) of cells. The maintained redox status of cells under IAAL treatment declined the level of ROS in Cd1 and Cd2 treated seedlings thereby alleviated the Cd toxicity and this effect was more pronounced under Cd1 stress. Contrary to this, exogenous IAAH suppressed the activity of DHAR and GR and disturbed the redox status (< ratios: AsA/DHA and GSH/GSSG) of cells, hence excess accumulation of ROS further aggravated the Cd induced damage. Thus, overall results suggest that IAA at low (IAAL) and high (IAAH) doses affected the Cd toxicity differently by regulating the ascorbate-glutathione cycle as well as activity of other antioxidants in Trigonella seedlings.

Interactive effects of herbicide and enhanced UV-B on growth, oxidative damage and the ascorbate-glutathione cycle in two Azolla species.

A field experiment was conducted to investigate the impact of alone and combined exposures of herbicide pretilachlor (5, 10 and 20µgml(-1)) and enhanced UV-B radiation (UV-B1; ambient +2.2kJm(-2) day(-1) and UV-B2; ambient +4.4kJm(-2) day(-1)) on growth, oxidative stress and the ascorbate-glutathione (AsA-GSH) cycle in two agronomically important Azolla spp. viz., Azolla microphylla and Azolla pinnata. Decreased relative growth rate (RGR) in both the species under tested stress could be linked to enhanced oxidative stress, thus higher H2O2 accumulation was observed, that in turn might have caused severe damage to lipids and proteins, thereby decreasing membrane stability. The effects were exacerbated when spp. were exposed to combined treatments of enhanced UV-B and pretilachlor. Detoxification of H2O2 is regulated by enzymes/metabolites of AsA-GSH cycle such as ascorbate peroxidase (APX) and glutathione reductase (GR) activity that were found to be stimulated. While, dehydroascorabte reductase (DHAR) activity, and the amount of metabolites: ascorbate (AsA), glutathione (GSH) and ratios of reduced/oxidized AsA (AsA/DHA) and GSH (GSH/GSSG), showed significant reduction with increasing doses of both the stressors, either applied alone or in combination. Glutathione-S-transferase (GST), an enzyme involved in scavenging of xenobiotics, was found to be stimulated under the tested stress. This study suggests that decline in DHAR activity and in AsA/DHA ratio might have led to enhanced H2O2 accumulation, thus decreased RGR was noticed under tested stress in both the species and the effect was more pronounced in A. pinnata. Owing to better performance of AsA-GSH cycle in A. microphylla, this study substantiates the view that A. microphylla is more tolerant than A. pinnata.

Evaluating the combined effects of pretilachlor and UV-B on two Azolla species.

The present study assessed the comparative responses of two agronomic species of Azolla (A.microphylla and A. pinnata) exposed to man-made and natural stressors by evaluating biomass accumulation, pigments (chlorophyll a and b and carotenoid contents), photosynthetic activity and nitrogen metabolism. The study was carried out in field where two species of Azolla were cultured and treated with various concentrations (5, 10 and 20 µg ml(-1)) of herbicide; pretilachlor [2-chloro-2,6-diethyl-N-(2-propoxyethyl) acetanilide] and enhanced levels (UV-B1: ambient +2.2 kJ m(-2) day(-1) and UV-B2: ambient +4.4 kJ m(-2) day(-1)) of UV-B, alone as well as in combination. Biomass accumulation, photosynthetic pigments; chlorophyll a, b and carotenoids, photosynthetic oxygen yield and photosynthetic electron transport activities i.e. photosystem II (PS II) and photosystem I (PS I) in both the species declined with the increasing doses of pretilachlor and UV-B radiation, which further declined when applied in combination. The lower doses (5 and 10 µg ml(-1)) of pretilachlor and UV-B (UV-B1 and UV-B2) alone, damaged mainly the oxidation side of PS II, whereas higher dose (20 µg ml(-1)) of pretilachlor alone and in combination with UV-B1 and UV-B2 caused damage to PS II reaction centre and beyond this towards the reduction side. A significant enhancement in respiration was also noticed in fronds of both the Azolla species following pretilachlor and UV-B treatment, hence indicating strong damaging effect. The nitrate assimilating enzymes - nitrate reductase and nitrite reductase and ammonium assimilating enzymes - glutamine synthetase and glutamate synthase were also severely affected when treated either with pretilachlor and/or UV-B while glutamate dehydrogenase exhibited a stimulatory response. The study suggests that both the species of Azolla showed considerable damage under pretilachlor and UV-B treatments alone, however, in combination the effect was more intense. Further, in comparison to A. pinnata, A. microphylla exhibited greater resistance against tested doses of both the stresses, either alone or in combination.

A lucrative technique to reduce Ni toxicity in Raphanus sativus plant by phosphate amendment: Special reference to plant metabolism.

Nickel (Ni) contamination is one of the serious environmental problems. It creates hazard in soil environment and also in crop quality. In the present study, response of Raphanus sativus (radish) to Ni (50mgkg(-1) soil) under different concentrations (100, 200, 500 and 1000 DAPmgkg(-1) soil) of phosphate as soil amendment was investigated after 40 days of growth. Ni-treated plants without amendment showed reduction in their growth as a result of appreciable decrease in the photosynthetic activity. Under this treatment, Ni accumulation significantly enhanced lipid peroxidation and level of oxidants showing oxidative stress and it was also associated with decrease in the activities of antioxidative enzymes except super oxide dismutase (SOD). Application of phosphate in Ni contaminated soil resulted into significant improvement in plant growth. Under phosphate amendment, the status of oxidative biomarkers: SOR, TBARS and H2O2 were under control by the higher activity of antioxidants: APX, CAT, POD, GST and DHAR compared to Ni contaminated soil without amendment. Principal component analysis (PCA) was performed to show the significant changes in biochemical traits under control and phosphate amendment. The values of PS II transient kinetics: Phi-E0, Psi-0 and PIABS increased and values of energy fluxes: ABC/RC, Tro/RC, Eto/RC and Dio/RC decreased in plants grown in Ni contaminated soil under phosphate amendment as compared to without amendment. Among all doses of phosphate amendment soil amended at 500mg DAPkg(-)(1) soil the yield of plant was the highest and Ni accumulation was the lowest. As compared to plants grown in Ni treated soil without amendment the yield of plant at 500mg DAPkg(-1) soil showed about 70% increment and the reduction in Ni accumulation was 63% in shoot and 64% in root. Because of these beneficial effects this technique can be easily applied at metal contaminated agricultural fields to reduce food chain contamination and to improve food quality.

Arsenic contamination, consequences and remediation techniques: a review.

The exposure to low or high concentrations of arsenic (As), either due to the direct consumption of As contaminated drinking water, or indirectly through daily intake of As contaminated food may be fatal to the human health. Arsenic contamination in drinking water threatens more than 150 millions peoples all over the world. Around 110 millions of those peoples live in 10 countries in South and South-East Asia: Bangladesh, Cambodia, China, India, Laos, Myanmar, Nepal, Pakistan, Taiwan and Vietnam. Therefore, treatment of As contaminated water and soil could be the only effective option to minimize the health hazard. Therefore, keeping in view the above facts, an attempt has been made in this paper to review As contamination, its effect on human health and various conventional and advance technologies which are being used for the removal of As from soil and water.

Silicon-mediated alleviation of Cr(VI) toxicity in wheat seedlings as evidenced by chlorophyll florescence, laser induced breakdown spectroscopy and anatomical changes.

Silicon (Si)-mediated alleviation of Cr(VI) toxicity was examined in wheat seedlings using an in vivo approach that involves chlorophyll fluorescence, laser induced breakdown spectroscopy (LIBS) and anatomical changes. Exposure to Cr(VI) significantly reduced the growth and photosynthetic activities (chlorophyll fluorescence) in wheat which was accompanied by remarkable accumulation of this element in tissues. However, addition of Si to the growth medium alleviated the effects of Cr(VI). The LIBS spectra were used as a fingerprint of the elemental compositions in wheat seedlings, which showed a reduction in Cr accumulation following Si addition. Nutrient element levels (Ca, Mg, K and Na) declined in wheat following the addition of Cr (VI), as recorded by LIBS and inductively coupled plasma atomic emission spectroscopy (ICAP-AES). However, addition of Si along with Cr(VI) increased the contents of nutrient elements in wheat. LIBS, ICAP-AES and AAS showed a similar distribution pattern of elements measured in wheat. Anatomical observations of leaf and root revealed that Cr(VI) affected internal structures while Si played a role in protection from toxic effects. The results showed the suitability of chlorophyll fluorescence as a parameter and appropriateness of LIBS technique and anatomical procedures to elucidate Si-mediated alleviation of Cr(VI) toxicity. Furthermore, our results suggest that the measured parameters and techniques can be used non-invasively for monitoring the growth of crops under different environmental conditions.