Combined Application of Citric Acid and Cr Resistant Microbes Improved Castor Bean Growth and Photosynthesis while it Alleviated Cr Toxicity by Reducing Cr+6 to Cr3+

Chromium is highly harmful to plants because of its detrimental effects on the availability of vital nutrients and secondary metabolites required for proper plant growth and development. A hydroponic experiment was carried out to analyze the effect of citric acid on castor bean plants under chromium stress. Furthermore, the role of two chromium-resistant microorganisms, Bacillus subtilis and Staphylococcus aureus, in reducing Cr toxicity was investigated. Different amounts of chromium (0 µM, 100 µM, 200 µM) and citric acid (0 mM, 2.5 mM, and 5 mM) were used both alone and in combination to analyze the remediation potential. Results showed that elevated amounts of chromium (specifically 200 µM) minimized the growth and biomass because the high concentration of Cr induced the oxidative markers. Exogenous citric acid treatment boosted plant growth and development by improving photosynthesis via enzymes such as superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase, which decreased Cr toxicity. The application of citric acid helped the plants to produce a high concentration of antioxidants which countered the oxidants produced due to chromium stress. It revealed that castor bean plants treated with citric acid could offset the stress injuries by decreasing the H2O2, electrolyte leakage, and malondialdehyde levels. The inoculation of plants with bacteria further boosted the plant growth parameters by improving photosynthesis and reducing the chromium-induced toxicity in the plants. The findings demonstrated that the combination of citric acid and metal-resistant bacteria could be a valuable technique for heavy metal remediation and mediating the adverse effects of metal toxicity on plants.

Soil applied glycine betaine with Arbuscular mycorrhizal fungi reduces chromium uptake and ameliorates chromium toxicity by suppressing the oxidative stress in three genetically different Sorghum (Sorghum bicolor L.) cultivars

Background Chromium is the most toxic pollutant that negatively affects a plant’s metabolic activities and yield. It reduces plant growth by influencing the antioxidant defence system’s activities. In the present study, a completely randomized block design experiment with three plants/pot in three replication was conducted on three varieties of sorghum viz. SSG 59–3, HJ 513 (multi-cut) and HJ 541 (single-cut) for amelioration of chromium toxicity (2 & 4 ppm) by exogenous application of GB (50 & 100 mM) with and without AMF in soil. The ameliorative effects were tested at two growth stages viz. vegetative (35 DAS) and grain filling (95 DAS), in terms of Cr uptake, grain yield, antioxidative defence system parameters (viz. enzymes – SOD, APX, CAT, GR, POX and metabolites – proline, glutathione, ascorbate, β-carotene) and indices of oxidative stress parameters (viz. PPO, H2O2, and MDA). Results The results delineated that Cr uptake and indices of oxidative stress were increased with increasing concentration of Cr stress in all the varieties (HJ 541, HJ513 & SSG 59–3) at both the growth stages (35 & 95 DAS). At higher concentration (4 ppm), Cr stress decreased the grain yield (45–50%) as compared with controls. Polyphenoloxidase activity, MDA and H2O2 content increased at both growth stages in all the varieties. However, antioxidative enzymes and metabolite activities increased due to Cr stress but this increase was not sufficient to counteract with ROS generated under Cr stress which was enhanced on the application of AMF and GB either individually or in combination (spiked in soil). It decreased the indices of oxidative stress and ameliorated the Cr toxicity and increased grain yield (65–70%) in all the varieties. Conclusions Both GB and AMF improved the antioxidative activities and stress tolerance capacity of the plant. Glycine betaine at both 50 and 100 mM level, significantly ameliorated Cr toxicity. However, AMF concomitantly with GB further boosts up the amelioration behaviour of the plant against Cr toxicity, at both growth stages in all the varieties. The combination of 100 mM GB with 10 g AMF was observed most effective among all the treatments. Among the varieties, SSG 59–3 had the lowest chromium uptake, indices of oxidative stress, and highest antioxidative system’s activity as compared to HJ 513 followed by HJ 541 variety. Thus AMF and GB either individually or in combination may be used to maintain plant yield attributes under Cr toxicity.

Seed Priming with Brassinosteroids Alleviates Chromium Stress in Rice Cultivars via Improving ROS Metabolism and Antioxidant Defense Response at Biochemical and Molecular Levels

This research was performed to explore the vital role of seed priming with a 0.01 µM concentration of brassinosteroids (EBL) to alleviate the adverse effects of Cr (100 µM) in two different rice cultivars. Seed priming with EBL significantly enhanced the germination attributes (germination percentage, germination energy, germination index, and vigor index, etc.), photosynthetic rate as well as plant growth (shoot and root length including the fresh and dry weight) under Cr toxicity as compared to the plants primed with water. Cr toxicity induced antioxidant enzyme activities (SOD, POD, CAT, and APX) and ROS level (MDA and H2O2 contents) in both rice cultivars; however, a larger increment was observed in YLY-689 (tolerant) than CY-927 (sensitive) cultivar. EBL application stimulatingly increased antioxidant enzyme activities to scavenge ROS production under Cr stress. The gene expression of SOD and POD in EBL-primed rice plants followed a similar increasing trend as observed in the case of enzymatic activities of SOD and POD compared to water-primed rice plants. Simultaneously, Cr uptake was observed to be significantly higher in the water-primed control compared to plants primed with EBL. Moreover, Cr uptake was significant in YLY-689 compared to CY-927. In ultra-structure studies, it was observed that EBL priming relieved the rice plants from sub-cellular damage. Conclusively, our research indicated that seed priming with EBL could be adopted as a promising strategy to enhance rice growth by copping the venomous effect of Cr.

Biochar Mediated-Alleviation of Chromium Stress and Growth Improvement of Different Maize Cultivars in Tannery Polluted Soils

Soil pollution with heavy metal is a serious problem across the globe and is on the rise due to the current intensification of chemical industry. The leather industry is one of them, discharging chromium (Cr) in huge quantities during the process of leather tanning and polluting the nearby land and water resources, resulting in deterioration of plant growth. In this study, the effects of biochar application at the rate of 3% were studied on four maize cultivars, namely NK-8441, P-1543, NK-8711, and FH-985, grown in two different tannery polluted Kasur (K) and Sialkot (S) soils. Maize plants were harvested at vegetative growth and results showed that Cr toxicity adversely not only affected their growth, physiology, and biochemistry, but also accumulated in their tissues. However, the level of Cr toxicity, accumulation, and its influence on maize cultivars varied greatly in both soils. In this pot experiment, biochar application played a crucial role in lessening the Cr toxicity level, resulting in significant increase in plant height, biomass (fresh and dry), leaf area, chlorophyll pigments, photosynthesis, and relative water content (RWC) over treatment set as a control. However, applied biochar significantly decreased the electrolyte leakage (EL), antioxidant enzymes, lipid peroxidation, proline content, soluble sugars, and available fraction of Cr in soil as well as Cr (VI and III) concentration in root and shoot tissues of maize plant. In addition to this, maize cultivar differences were also found in relation to their tolerance to Cr toxicity and cultivar P-1543 performed better over other cultivars in both soils. In conclusion, biochar application in tannery polluted soils could be an efficient ecofriendly approach to reduce the Cr toxicity and to promote plant health and growth.

Title: The Cumulative Dose of AMF and GB is More Effective in The Amelioration of Cr(VI) Toxicity in Sorghum (Sorghum Bicolor L.) Than Individually

Industrial and anthropogenic activities are the major source of heavy metal toxicants in agricultural soils. Among, heavy metal toxicants, hexavalent chromium is the most toxic toxicant that negatively affects plant’s metabolic activities and yield. It reduces the plant growth and development by influencing the antioxidant defence system’s activities. In the present experiment, two different soil applied dozes of GB viz. 50 and 100mM, and AMF, both individually and in combination were tested for their capability to ameliorate Cr toxicity in sorghum. The promotive behaviour of these treatments for antioxidant defence system was analysed at vegetative (35 DAS) and grain filling stage (95 DAS) in three varieties of sorghum viz. SSG 59-3, HJ 513 (multi-cut) and HJ 541 (single-cut) under 2 and 4 ppm Cr toxicity. At the same time resultant effects of this behaviour on Cr accumulation, grain yield and indices of oxidative stress was also studied. In this experiment antioxidant defence system includes enzymes viz. SOD, APX, CAT, GR, POD and metabolites viz. glutathione, ascorbate, proline, β-carotene and indices of oxidative stress includes parameters viz. PPO, H2O2 and MDA. The results delineated that Cr accumulation and indices of oxidative stress were increased with increasing concentration of Cr stress in all the varieties at both growth stages. Chromium stress at high concentration (4 ppm), decreased the grain yield (71.69 %) as compared with control. Due to 4 ppm Cr stress, PPO activity, MDA and H2O2 accumulation increased significantly (72.29 %, 73.15 %, 79 % respectively, at 35 DAS and 70.36 %, 74.78 %, 79.83 % respectively, at 95 DAS). GB and AMF individually increased antioxidant activity but in combination, further significantly increased antioxidant defence system’s activity which in turn decreased indices of oxidative stress and reduced the Cr toxicity and increased grain yield of sorghum in all varieties at both the growth stages. However, treatment of 100mM GB with AMF was observed most significant in decreasing oxidative stress and improved antioxidant system’s activities and grain yield as compared with all other treatments at both growth stages in all the varieties. SSG 59-3 cultivar showed lowest chromium content (1.60 and 8.61 ppm), indices of oxidative stress and highest antioxidant system’s activity as compared to HJ 513 followed by HJ 541 variety, at 35 and 95 DAS respectively. Thus, among the varieties SSG 59-3 was found most tolerant as compared to HJ 513 followed by HJ 541 variety. These findings suggest that both GB and AMF, either individually or combined can play a positive role to reduce oxidative stress and increased yield attributes under Cr toxicity in sorghum.

Exogenous AMF with Glycine Betaine Reduces Cr (VI) Uptake and Alleviates Chromium Toxicity by Supressing the Oxidative Stress in Three Genetically Different Sorghum (Sorghum bicolor L.) Cultivars

Background: Chromium is most toxic pollutant that negatively affects plant’s metabolic activities and yield. It reduces plant growth by influencing the antioxidant defense system’s activities. The aim of the present research was to examine the ameliorative capability of exogenous GB and AMF spiked in soil, either individually or in combination against Cr toxicity. The ameliorative effects were studied in terms of Cr uptake, grain yield, antioxidative defense system parameters (viz. enzymes – SOD, APX, CAT, GR, POX and metabolites – proline, glutathione, ascorbate, β-carotene) and indices of oxidative stress parameters (viz. PPO, H2O2, and MDA). Results:The results delineated that Cr uptake and indices of oxidative stress were increased with increasing concentration of Cr stress in all the varieties (HJ 541, HJ513 & SSG 59-3) at both the growth stages (35 & 95 DAS). At higher concentration (4 ppm), Cr stress decreased the grain yield (45-50%) as compared with controls. PPO activity, MDA and H2O2 content increased at both growth stages in all the varieties. However, antioxidative enzymes and metabolite activities increased due to Cr stress but this increase was not sufficient to counteract with ROS generated under Cr stress which was enhanced on the application of AMF and GB either individually or in combination (spiked in soil). It decreased the indices of oxidative stress and ameliorated the Cr toxicity and increased grain yield (65-70%) in all the varieties. Conclusions:Both GB and AMF, improved the plant growth and stress tolerance capacity of the plant. GB at both 50 and 100 mM level, significantly ameliorated Cr (VI) toxicity. However, AMF concomitantly with GB further boost up the amelioration behavior of the plant against Cr toxicity, at both growth stages in all the varieties. The combination of 100 mM GB with 10 g AMF was observed most effective among all the treatments. Among the varieties SSG 59-3 had the lowest chromium uptake, indices of oxidative stress, and highest antioxidative system’s activity as compared to HJ 513 followed by HJ 541 variety. Thus AMF and GB either individually or in combination may be used to maintain plant yield attributes under Cr toxicity.

Influence of Metal-Resistant Staphylococcus aureus Strain K1 on the Alleviation of Chromium Stress in Wheat

Chromium (Cr) is recognized as a toxic metal that has detrimental effects on living organisms; notably, it is discharged into soil by various industries as a result of anthropogenic activities. Microbe-assisted phytoremediation is one of the most emergent and environmentally friendly methods used for the detoxification of pollutants. In this study, the alleviative role of Staphylococcus aureus strain K1 was evaluated in wheat (Triticum aestivum L.) under Cr stress. For this, various Cr concentrations (0, 25, 50 and 100 mg·kg−1) with and without peat-moss-based bacterial inoculum were applied in the soil. Results depicted that Cr stress reduced the plants’ growth by causing oxidative stress in the absence of S. aureus K1 inoculation. However, the application of S. aureus K1 regulated the plants’ growth and antioxidant enzymatic activities by reducing oxidative stress and Cr toxicity through conversion of Cr6+ to Cr3+. The Cr6+ uptake by wheat was significantly reduced in the S. aureus K1 inoculated plants. It can be concluded that the application of S. aureus K1 could be an effective approach to alleviate the Cr toxicity in wheat and probably in other cereals grown under Cr stress.