Exogenously applied calcium regulates antioxidative system and reduces cadmium-uptake in Fagopyrum esculentum.

Calcium (Ca) being macronutrient plays a prominent role in signal transduction during various abiotic stresses. However, their involvements to alleviate heavy metal stress in plants remain evasive. In the present investigation, we found that application of exogenous Ca to Cd-stressed common buckwheat plants reversed the toxic effects of Cd by enhancing root and shoot length, biomass accumulation and reduced Cd-uptake as revealed by the translocation factor (<1), indicating more Cd is restrained in the roots. Moreover, present data also revealed that exogenous Ca significantly alleviated the Cd-induced oxidative damage by enhancing proline by 66.12% and 47.20% respectively in roots and shoots than control. The decline in the total chlorophyll content upon Ca application in Cd-treated plants was found less (38.96%) compared to buckwheat plants treated with Cd-stress alone (80.2%). APX and POD activities increased by 1.97 and 1.44 times in shoots, respectively, and increased by 2.81and 1.33 times in roots, respectively compared to the Cd-treated plants alone. The mineral content (Ca, K, Mg, Fe, P and S) that were suppressed in Cd-treated plants in both root and shoot were restored upon exogenous Ca application. Further, the correlation analysis showed significant positive correlation among proline and GSH synthesis in the Ca + Cd treatment. The correlations of Ca revealed to be positive with enhanced levels of APX and POD activity. Our data showed that exogenous application of Ca minimizes the Cd-toxicity and modulates the physiological and biochemical pathway in common buckwheat to withstand Cd-induced oxidative stress.

Biochar promotes arsenic (As) immobilization in contaminated soils and alleviates the As-toxicity in soybean (Glycine max (L.) Merr.).

Pot experiments were carried out to examine the biochar application and its alleviating effect on arsenic (As) toxicity in soybean plants. The data showed that As inhibits the growth indices and it increased with enhanced As-concentration in the substrate. The growth indices declined by more than 40% and the osmolyte concentration, photosynthetic pigments and antioxidant enzymes were decreased significantly among As-stressed plants. However, biochar application effectively mitigated the inhibitory effects of As on the soybean growth and the mitigation effect of treatment is more prevalent to the plants subjected to higher As-treatment. Biochar significantly reduced the As-uptake as revealed by the translocation factor (<1), indicating more As is restrained in the roots. The reduction in the total chlorophyll and carotenoid content was found less in the As-treated soybean plants upon biochar application. Similarly, the osmolytes comprising proline, sugar and protein increased upon application of biochar. The biomarkers viz., membrane stability index (MSI), hydrogen peroxide and malondialdehyde (MDA) content significantly decreased at higher As-levels upon biochar application as was also supported by the heatmap analysis. Moreover, the antioxidative enzymes also showed a significant increase upon addition of biochar. Our data showed that biochar amendment effectively alleviates the As-stress by enhancing the sorption of As in the substrate thus, significantly declining the As concentration in plant leaves, and thus the results of the current study depicting the role of biochar as a promising, cost-effective and eco-friendly amendment to decontaminate the As-polluted soils.

Comparative Study on Phytochemical Profile and Antioxidant Activity of an Epiphyte, Viscum album L. (White Berry Mistletoe), Derived from Different Host Trees.

The study aimed at evaluating the antioxidant profile of a medicinal epiphyte Viscum album L. harvested from three tree species, namely, Populus ciliata L, Ulmus villosa L., and Juglans regia L. The crude extracts were obtained with ethanol, methanol, and water and were evaluated for the total phenol content (TPC), total flavonoid content (TFC), and antioxidant activities using total reducing power (TRP), ferric reducing antioxidant power (FRAP), 1, 1-diphenyl 1-2-picryl-hydrazyl (DPPH), superoxide radical scavenging (SOR), and hydroxyl radical scavenging (•OH) assays. Our results showed that crude leaf extracts of plants harvested from the host Juglans regia L. exhibited higher yields of phytochemical constituents and noticeable antioxidative properties. The ethanolic leaf samples reported the highest phenols (13.46 ± 0.87 mg/g), flavonoids (2.38 ± 0.04 mg/g), FRAP (500.63 ± 12.58 µM Fe II/g DW), and DPPH (87.26% ± 0.30 mg/mL). Moreover, the highest values for TRP (4.24 ± 0.26 µg/mL), SOR (89.79% ± 0.73 mg/mL), and OH (67.16% ± 1.15 mg/mL) were obtained from aqueous leaf extracts. Further, Pearson correlation was used for quantifying the relationship between TPC, TFC, and antioxidant (FRAP, DPPH, SOR, OH) activities in Viscum album L. compared to their hosts. It was revealed that the epiphyte showed variation with the type of host plant and extracting solvent.

γ-Aminobutyric acid (GABA) mitigates drought and heat stress in sunflower (Helianthus annuus L.) by regulating its physiological, biochemical and molecular pathways.

Drought and heat stress are two dominant abiotic stress factors that often occur simultaneously in nature causing oxidative damage in plants and thus decline in yield. The present study was conducted to examine the γ-aminobutyric acid (GABA)-induced heat and drought tolerance in sunflower through physiological, biochemical and molecular analysis. The results showed that drought and heat stress triggered oxidative stress as revealed by enhanced level in hydrogen peroxide, malondialdehyde and electrolyte leakage. Moreover, the photosynthetic attributes such as photosynthetic rate, stomatal conductance and quantum efficiency declined when subjected to drought and heat stress. In this study, GABA treatment effectively alleviated the drought and heat-induced stress as reflected by significantly higher levels of proline, soluble sugar and total protein content. Besides, the data also revealed the direct relationship between antioxidant enzyme activities (superoxide dismutase, peroxidase, glutathione reductase, monodehydroascorbate peroxidase, ascorbate peroxidase) and the relative expression of genes (Heat Shock Proteins, Dehydrin, Osmotin, Aquaporin, Leaf Embryogenesis Protein), under drought and heat stress. Moreover, a significant increase in gene expression was observed upon GABA treatment with respect to control. This data suggest that GABA-induced drought and heat tolerance in sunflower could involve the improvement in osmolyte metabolism, gene expression and antioxidant enzyme activities and thus a rise in the GABA shunt which in turn provides intermediates during long-term drought and heat stress, thus maintaining homeostasis.

Aluminium stress modulates the osmolytes and enzyme defense system in Fagopyrum species.

The present investigation describes aluminum-induced changes in the leaves of two buckwheat species using both physiological and biochemical indices. With increasing levels of Al (viz. 100, 200 and 300 µM), the mean length of root, shoot as well as their biomass accumulation decreased linearly with respect to control. Tolerance test of F. kashmirianum revealed that it was more tolerant to Al-stress than F. tataricum as revealed by higher accumulation of Al in its roots without any significant damage. Translocation factor (TF) values of both species were found to be < 1, indicating more Al is restrained in roots. Total chlorophyll showed a non-significant increase in F. tataricum while as decreased in F. kashmirianum at 300 µM concentration besides, the carotenoid content exhibited inclined trend in F. tataricum and showed a concomitant decrease in F. kashmirianum. The anthocyanin level showed a non-significant decline in F. kashmirianum. Exposure to different Al-treatments enhances malondialdehyde (MDA), H2O2 and membrane stability index (MSI) in both species, with increases being greater in F. kashmirianum than F. tataricum as also revealed by DAB-mediated in vivo histo-chemical detection method. The osmolyte level in general were elevated in both buckwheat species however, enhancement was more in F. tataricum than F. kashmirianum. The activities of antioxidant enzymes viz. superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (POD), glutathione reductase (GR), glutathione-S-transferase (GST) were positively correlated with Al-treatment except catalase (CAT) which exhibits a reverse outcome in F. kashmirianum. The present investigation could play an essential role to better understand the detoxification mechanisms of Al in plants.

Characterization of mercury-induced stress biomarkers in Fagopyrum tataricum plants.

The effect of mercury stress on antioxidant enzymes, lipid peroxidation, photosynthetic pigments, hydrogen peroxide content, osmolytes, and growth parameters in Tartary buckwheat were investigated. The effect of Hg-exposure was found to be time (15 and 30 days) and concentration (0, 25, 50, and 75 µM) dependent. Hg was readily absorbed by seedlings with higher content in roots and it resulted in reduction of root and shoot length. The root and shoot Hg uptakes were significantly and directly correlated with each other. However, the fresh mass and biomass increased up to 50 µM Hg-treatment at both time periods. A significant positive correlation was observed between biomass accumulation with relative water content. Hg levels were positively correlated with the production of hydrogen peroxide in leaves as evidenced by 3, 3-diaminobenzidine (DAB)-mediated tissue fingerprinting. The osmolyte levels in general were elevated except for proline and protein which showed a decline at 75 µM Hg-treatment at 30-days. Amongst the photosynthetic pigments, chlorophyll showed a decline while as carotenoid and anthocyanin levels were elevated. The activity of antioxidant enzymes such as ascorbate peroxidase (APX), guaiacol peroxidase (POD), glutathione reductase (GR), Glutathione-s-transferase (GST) and superoxide dismutase (SOD) were positively correlated with Hg-treatment except SOD, which declined at 75 µM Hg-treatment in 30-days old seedlings. Catalase (CAT) activity showed a positive correlation up to 50 µM Hg-treatment but at 75 µM Hg-stress it decreases at both 15 and 30 days.