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.

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.

Arsenate and arsenite-induced inhibition and recovery in two diazotrophic cyanobacteria Nostoc muscorum and Anabaena sp.: study on time-dependent toxicity regulation.

Exposure time, metal bio-accumulation, and upregulation of ascorbate-glutathione (AsA-GSH) cycle are the key factor that provide tolerance against heavy metal stress. Thus, the current study is an endeavor to prove our hypothesis that regulation of arsenate (AsV: 50, 100, and 150 mM) and arsenite (AsIII: 50, 100, and 150 µM) toxicity is time dependent (48-96 h) due to modulation in bio-accumulation pattern, AsA-GSH cycle, and non-enzymatic antioxidants in two paddy field cyanobacteria Nostoc muscorum ATCC27893 and Anabaena sp. PCC7120. After 48 h, reduction in growth associated with increased sensitivity index, As bio-accumulation, and oxidative stress was observed which further intensified after 96 h but the degree of damage was lesser than 48 h. It denotes a significant recovery in growth after 96 h which is correlated with decreased As bio-accumulation and oxidative stress due to increased efficiency of AsA-GSH cycle and non-enzymatic antioxidants. Both the species of As caused significant rise in oxidative biomarkers as evident by in -vitro analysis of O2·-, H2O2, and MDA equivalent contents despite appreciable rise in the activity antioxidative enzymes APX, DHAR, and GR. The study concludes that among both forms of arsenic, AsIII induced more toxic effect on growth by over-accumulating the ROS as evident by weak induction of AsA-GSH cycle to overcome the stress as compared to AsV. Further, with increasing the time exposure, apparent recovery was noticed with the lower doses of AsV, i.e., 50 and 100 mM and AsIII, i.e., 50 and 100 µM; however, the toxicity further aggravated with higher dose of both AsV and AsIII. Study proposes the deleterious impact of AsV and AsIII on cyanobacteria N. muscorum and Anabaena sp. but the toxicity was overcome by time-dependent recovery.

Effect of Time Interval on Arsenic Toxicity to Paddy Field Cyanobacteria as Evident by Nitrogen Metabolism, Biochemical Constituent, and Exopolysaccharide Content.

Arsenic poisoning in aquatic ecosystem is a global concern that obstructs the productivity of agricultural lands (paddy fields) by targeting the growth of cyanobacteria. The cyanobacteria also tolerate and accumulate elevated concentration of arsenic (As) inside the cell and excrete out from cells in less toxic forms after the successive time interval. Thus to validate this, the study was carried out at two different time intervals, i.e., 48 h and 96 h. Two redox forms of As arsenate (AsV) and arsenite (AsIII) at different concentrations (50, 100, and 150 mM AsV; 50, 100, and 150 µM AsIII) caused substantial reduction in growth, pigments (Chl a/Car and phycobiliproteins: phycocyanin, allophycocyanin, and phycoerythrin), inorganic nitrogen ( nitrate (NO3-) and nitrite (NO2-)) uptake, activity of enzymes (NR, NiR, GS, and GOGAT) of nitrogen metabolism, biochemical constituents (protein, carbohydrate, and exopolysaccharide (EPS) contents of Nostoc muscorum, and Anabaena sp. PCC7120. The tested doses of AsV and AsIII after 48 h of exposure exhibited adverse impact on these parameters, but after 96 h with lower doses of AsV (50 mM and 100 mM) and AsIII (50 µM and 100 µM), significant recovery was recorded. Contrary to this, at higher dose of AsV (150 mM) and AsIII (150 µM), the adverse impact was further aggravated with increasing time exposure. Contrary to the activity of NR, NiR, GS, and GOGAT, GDH activity (alternative NH3+ assimilating enzyme) was found to increase, and after 96 h, the activity showed declining trend but still higher than the control. The biochemical constituent EPS (first protective barrier) under scanning electron microscope showed more accumulation of dry adsorbent in the case of AsIII stress hence displayed more toxic nature of AsIII than AsV. The study concludes that with increasing time exposure, the recovery in growth and related parameters mainly at lower doses of AsV and AsIII points toward adaptability of cyanobacteria which was more pronounced in Nostoc muscorum.

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.

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.

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.

Oxygen toxicity and antioxidative responses in arsenic stressed Helianthus annuus L. seedlings against UV-B.

In order to know the impact of elevated level of UV-B on arsenic stressed Helianthus annuus L. var. DRSF-113 plants, certain physiological (growth - root and shoot lengths, their fresh masses and leaf area; photosynthetic competence and respiration) and biochemical parameters (pigments - Chl a and b, Car, anthocyanin and flavonoids; reactive oxygen species - superoxide radicals, H2O2; reactive carbonyl group, electrolyte leakage; antioxidants - superoxide dismutase, peroxidise, catalase, glutathione-S-transferase, proline) of their seedlings were analysed under the simultaneous exposures of two arsenic doses (6mgkg-1 soil, As1; and 12mgkg-1 soil, As2) and two UV-B doses (1.2kJm-2d-1, UV-B1; and 3.6kJm-2d-1, UV-B2). As1 and As2 alone declined all the studied growth parameters - along with photosynthetic pigments which were further aggravated after the simultaneous exposures of predefined levels of UV-B. Each As exposure was accompanied by significant accumulation of As in root, shoot and leaves and was substantiated by simultaneous exposures of UV-B doses which manifested into suppressed growth, decreased chlorophyll contents and photosynthesis. In similar conditions, other photo-shielding pigments, viz. carotenoids, anthocyanin and flavonoids along with respiration and oxidative stress markers such as O2•¯, H2O2; and indicators of cell membrane damage like MDA (malondialdehyde), RCG (reactive carbonyl group), electrolyte leakage were enhanced by As, and became more pronounced after the simultaneous exposures of UV-B doses. As doses stimulated the activities of SOD, POD, CAT, GST and Pro which got further accelerated after the simultaneous exposures of UV-B doses.