Cr Contents In Roots Research Articles

Zinc oxide nanoparticles alleviate chromium-induced oxidative stress by modulating physio-biochemical aspects and organic acids in chickpea (Cicer arietinum L.)

Extensive chromium (Cr) release into water and soil severely impairs crop productivity worldwide. Nanoparticle (NP) technology has shown potential for reducing heavy metal toxicity and improving plant physicochemical profiles. Herein, we investigated the effects of exogenous zinc oxide NPs (ZnO-NPs) on alleviating Cr stress in Cr-sensitive and tolerant chickpea genotypes. Hydroponically grown chickpea plants were exposed to Cr stress (0 and 120 μM) and ZnO-NPs (25 μM, 20 nm size) twice at a 7-day interval. Cr exposure reduced physiochemical profiles, ion content, cell viability, and gas exchange parameters, and it increased organic acid exudate accumulation in roots and the Cr content in the roots and leaves of the plants. However, ZnO-NP application significantly increased plant growth, enzymatic activities, proline, total soluble sugar, and protein and gas exchange parameters and reduced malondialdehyde and hydrogen peroxide levels, Cr content in roots, and organic acid presence to improve root cell viability. This study provides new insights into the role of ZnO-NPs in reducing oxidative stress along with Cr accumulation and mobility due to low levels of organic acids in chickpea roots. Notably, the Cr-tolerant genotype exhibited more pronounced alleviation of Cr stress by ZnO-NPs. These findings highlight the potential of ZnO-NP in regulating plant growth, reducing Cr accumulation, and promoting sustainable agricultural development.

Effects of Domestic Sewage on the Photosynthesis and Chromium Migration of Coix lacryma-jobi L. in Chromium-Contaminated Constructed Wetlands

To investigate the effects of domestic sewage on the photosynthesis and chromium migration of plants in chromium-contaminated constructed wetlands, small vertical flow constructed wetlands of Coix lacryma-jobi L. were set up. These wetlands were used to treat wastewater containing 0, 20, and 40 mg/L of hexavalent chromium (Cr (VI)), prepared with domestic sewage (DS), 1/2 Hoagland nutrient solution (NS), and 1/2 Hoagland nutrient solution prepared with domestic wastewater (DN), respectively. The aim was to investigate the effects of domestic sewage on indicators, such as plant growth and chromium accumulation. The results were as follows: (1) Plant heights were significantly inhibited under 20 mg/L and 40 mg/L Cr (VI) treatments, and stem diameters were not significantly affected. The use of domestic sewage in treatment alleviated the inhibition of Cr (VI) on the growth of Coix lacryma-jobi L. (2) Indicators such as root activity, photosynthetic gas exchange, and chlorophyll fluorescence properties significantly decreased with the increase in Cr (VI) concentration. The values of these photosynthetic gas exchange parameters under the DN treatment were the greatest, followed by NS and DS. On the 70th day of Cr (VI) treatment, the net photosynthetic rate (Pn) under the DN treatment was significantly higher than that under NS and DS treatments. (3) Glutathione (GSH) content in roots, stems, and leaves of Coix lacryma-jobi L. significantly increased with the increase in Cr concentration, and it increased more significantly under the DN and DS treatments than under the NS treatment. (4) With the same Cr treatment, the Cr content in roots, stems, and leaves of Coix lacryma-jobi L. under the NS treatment was the highest, followed by DS and DN. The total Cr content in the substrate under the DN treatment was the highest, followed by DS and NS. (5) The addition of domestic sewage reduced the Cr (VI) content in the water sample and increased the organic matter content. The Cr (VI) content in the water sample under the NS treatment was the highest, followed by DS and DN. The addition of domestic sewage increased the accumulation of chromium in the substrate, decreased the absorption of chromium by plants, increased GSH content in roots, stems, and leaves, alleviated the damage of Cr (VI) to plants, and thus benefited the growth of Coix lacryma-jobi L. in the constructed wetlands and ensured the sustainable and stable operation of the wetlands.

Anthocyanin synthesis is critical for melatonin-induced chromium stress tolerance in tomato

Chromium (Cr) is a toxic heavy metal for both animals and plants. The multifunctional signaling molecule melatonin can confer plant tolerance to heavy metal stress, but the mechanisms remain largely unknown. Here, we unveiled the critical role of the secondary metabolite anthocyanin in melatonin-induced Cr stress tolerance. Excess Cr caused severe phytotoxicity, which was manifested by leaf yellowing, stunted growth, reduced Fv/Fm, and increased accumulation of reactive oxygen species and malondialdehyde in a dose-dependent manner. Interestingly, leaf anthocyanin content increased under Cr stress and was the highest under 100 µM Cr (7.67-fold), while exogenous melatonin further increased anthocyanin accumulation with the highest being with 100 µM melatonin (by 90.72 %). In addition, exogenous melatonin increased endogenous melatonin content and alleviated Cr stress; however, suppression of melatonin accumulation aggravated Cr phytotoxicity and inhibited anthocyanin accumulation by downregulating the transcript levels of key structural genes. Melatonin also reduced the Cr content in roots and leaves. Crucially, suppression of anthocyanin biosynthesis by silencing an anthocyanin biosynthetic gene ANTHOCYANIDIN SYNTHASE (ANS) significantly compromised melatonin-induced anthocyanin accumulation and alleviation of Cr phytotoxicity, suggesting that anthocyanin potentially acts downstream of melatonin and its accumulation is essential for melatonin-induced Cr stress tolerance in tomato plants.

Do sulfur addition and rhizoplane iron plaque affect chromium uptake by rice (Oryza sativa L.) seedlings in solution culture?

Heavy metal uptake is confined by other elements, namely iron (Fe) and sulfur (S). There are yet no reports on the contribution of S supply to the attenuation of chromium (Cr) uptake when different species of Cr are employed. The bioaccumulation of Cr in two cultivars of rice seedlings subjected to 1.0 mg L−1 Cr (III and VI) stress under S deprived or non-deprived conditions were examined in a hydroponic experiment. Sulfur nutrition promoted the root and shoot growth of rice cultivars under Cr stress. For both + S/ − S seedlings, the concentration of both Cr species followed the sequence ACA (ascorbic citrate acetic) extract > root > shoot, with less Cr accumulated in shoots of + S seedlings to that of − S seedlings. The concentrations of Cr and Fe in ACA extracts were found to be significantly correlated. Compared to + S treatment, Cr and Fe contents in iron plaque without S treatment were markedly reduced, especially for Cr (VI). Cr content in roots and shoots was indicated to be at par between cultivars; however, it significantly differed for S and Cr treatments. The Cr translocation between different parts of plaque-harboring seedlings was more pronounced in Cr (VI) treatment relative to Cr (III) treatment. Increased immobilization of Cr in iron plaque of + S seedlings and its subsequent reduction in aerial tissues may likely shed some light on the barrier function of iron plaques in the uptake of both Cr species by rice seedlings.

Zinc-lysine prevents chromium-induced morphological, photosynthetic, and oxidative alterations in spinach irrigated with tannery wastewater.

Anthropogenic activities have resulted in severe environmental degradation. Untreated wastewater from tanneries is hazardous to all kinds of life on earth. Effluent from tanning industries, containing large amount of Cr, is used to irrigate the crops in Pakistan. The current experiment was carried out to study the effects of tannery wastewater on spinach and the role of lysine-Zn in mitigating the severity of stress. The plants were grown in soil and the following treatments were used: irrigation with 0%, 33%, 66%, and 100% wastewater (ww) along with two doses (0 mM, 10 mM) of Zn-lysine. Foliar application of zinc-lysine enhanced the plant growth, biomass, Zn contents, photosynthesis, and enzyme activities in different tissues of plant. Zinc-lysine (10 mM) considerably decreased the Cr content in roots and shoots, along with ameliorating the oxidative stress by enhancing the activities of antioxidant enzymes in plants. Addition of Zn-lys (10 mM) improved the plant height by 19%, root length by 57%, leaf dry weight by 19%, and root dry weight by33% under 100% Cr treatment. Zn-lys significantly reduces the oxidative stress and concentration of Cr as compared with the Cr treatments alone. Application of Zn-lys (10 mM) reduced the Cr contents in roots by 27 and 22 under 33 and 66% Cr treatment, respectively. Taken together, Zn-lys chelates efficiently ameliorated the toxic effects of chromium. Zn-lysine has the extravagant potential of mitigating the heavy metal toxicity without harming the normal growth and development of the plants.

Role of Zinc–Lysine on Growth and Chromium Uptake in Rice Plants under Cr Stress

Chromium (Cr) is a very toxic heavy metal present in agricultural soils. Soils contaminated with Cr are the major source of Cr entrance into the food chain. The present experiment was designed to determine the effects of different levels of lysine chelated with zinc (Zn–lys) (0, 10, 20, 30 mg L−1) upon photosynthesis, biomass, anti-oxidant enzyme activities, oxidative stress, and the uptake of Cr by rice under various applied levels of Cr (0, 100, 500 mg kg−1). Cr stress decreased the physiological and morphological parameters as well as the activities of anti-oxidants enzymes; and caused oxidative stress by enhancing the Cr concentration in plants over that of controls. Zn–lys foliar treatment enhanced photosynthesis, biomass, Zn contents, and enzyme activities. The application of Zn–lys (30 mg L−1) under 500 mg kg−1 of Cr increased plant height by 50% and shoot dry weight by 74% but also the root dry weight by 129% over the control treatment. In addition, Zn–lys reduced oxidative stress and Cr concentration compared to that of Cr treatments alone. The application of Zn–lys (30 mg L−1) also reduced Cr contents in roots by 26 and 31% in 100 and 500 mg kg−1 Cr treatments, respectively. The results of our study revealed that Zn–lys foliar treatment enhanced rice growth and decreased oxidative stress and Cr concentration by stimulating the anti-oxidant defense system as well as by promoting photosynthesis and Zn uptake in rice plants. Overall, the Zn–lys foliar treatment was helpful in increasing plant growth and Zn concentration while reducing the Cr contents in rice. However, further studies at field levels are required to explore the mechanisms of Zn–lys mediated reduction of Cr and possibly other heavy metal toxicity in plants.

Potential of Arundo donax to treat chromium contamination

The ability of Arundo donax against chromium pollution was tested. A. donax plants were grown under greenhouse conditions in nutrient solution having Cr (0, 50, 100, 200, 400, 600, and 900μgL−1) for three weeks. Shoots and roots dry matter production, growth parameters, plant physiological and morphological characters were measured. The maximum Cr content in roots was 206.33μgg−1. Likewise, Cr concentration in stem was 262.6μgg−1 at 900μgL−1 supplied Cr. In case of leaves, the maximum Cr concentration was 206.33μgg−1 at 900μgL−1 supplied Cr. The IC50 values of antioxidants using ABTS and DPHH standards showed that both time and increasing Cr concentrations affected the production of antioxidants indicated by lower IC50 value on 21st day. A. donax may be used in remediation of Cr contaminated wastewaters.

Inoculation with mycorrhizal fungi modifies proline metabolism and increases chromium tolerance in pepper plants (Capsicum annuum L.)

In general, heavy metals interfere with several physiological processes and reduce plant growth. Plants naturally establish symbiotic associations with soil microorganisms, such as mycorrhizal fungi. The aim of this research was to determine if inoculation with mycorrhizal fungi increases tolerance to Cr, evidenced by growth and biochemical parameters and the effect on roots membranes in Capsicum annum. Plants were either non-inoculated or inoculated with Glomus mosseae or Glomus intraradices, and grown in the presence of different concentration of Cr (K2Cr2O4) in soil. Pepper plants grown without Cr behaved as mycotrophic species. At the highest concentration (200 μM K2Cr2O4), Cr reduced root colonization by G. mosseae or G. intraradices (to 23 and 20% respectively). Moderate and high concentrations of Cr reduced all growth parameters. The interaction of inoculation and Cr increased leaf chlorophyll and proline content while reduced the leaf protein and root proline content. Carotenoid content was not affected by treatments. High Cr concentrations increased significantly electrolytes leakage in roots, either non-inoculated or inoculated plants. At the highest Cr concentration, inoculated plants had double the biomass of non-inoculated plants. Cr content in roots of inoculated plants was significantly higher than in non-inoculated plants. Chromium accumulation was low in leaves and showed no differences between treatments. Mycorrhization increased pepper plant tolerance to Cr in the soil, modifying proline metabolism to assure a more efficient response.

Changes of organic acid exudation and rhizosphere pH in rice plants under chromium stress

The effect of chromium (Cr) stress on the changes of rhizosphere pH, organic acid exudation, and Cr accumulation in plants was studied using two rice genotypes differing in grain Cr accumulation. The results showed that rhizosphere pH increased with increasing level of Cr in the culture solution and with an extended time of Cr exposure. Among the six organic acids examined in this experiment, oxalic and malic acid contents were relatively higher, and had a significant positive correlation with the rhizosphere pH, indicating that they play an important role in changing rhizosphere pH. The Cr content in roots was significantly higher than that in stems and leaves. Cr accumulation in plants was significantly and positively correlated with rhizosphere pH, and the exudation of oxalic, malic and citric acids, suggesting that an increase in rhizosphere pH, and exudation of oxalic, malic and citric acid enhances Cr accumulation in rice plants.