Application of zinc oxide nanoparticles immobilizes the chromium uptake in rice plants by regulating the physiological, biochemical and cellular attributes

Zinc oxide nano particles (ZnO NPs) have been employed as a novel strategy to regulate plant tolerance and alleviate heavy metal stress, but our scanty knowledge regarding the systematic role of ZnO NPs to ameliorate chromium (Cr) stress especially in rice necessitates an in-depth investigation. An experiment was performed to evaluate the effect of different concentrations of ZnO NPs (e.g., 0, 25, 50, 100 mg/L) in ameliorating the Cr toxicity and accumulation in rice seedlings in hydroponic system. Our results demonstrated that Cr (100 µM) severely inhibited the rice seedling growth, whereas exogenous treatment of ZnO NPs significantly alleviated Cr toxicity stress and promoted the plant growth. Moreover, application of ZnO NPs significantly augmented the germination energy, germination percentage, germination index, and vigor index. In addition, biomass accumulation, antioxidants (SOD, CAT, POD), nutrient acquisition (Zn, Fe) was also improved in ZnO NPs-treated plants, while the lipid peroxidation (MDA, H₂O₂), electrolyte leakage as well as Cr uptake and in-planta accumulation was significantly decreased. The burgeoning effects were more apparent at ZnO NPs (100 mg/L) suggesting the optimum treatment to ameliorate Cr induced oxidative stress in rice plants. Furthermore, the treatment of ZnO NPs (100 mg/L) reduced the level of endogenous abscisic acid (ABA) and stimulated the growth regulator hormones such as brassinosteroids (BRs) possibly linked with enhanced phytochelatins (PCs) levels. The ultrastructure analysis at cellular level of rice revealed that the application of 100 mg/L ZnO NPs protected the chloroplast integrity and other cell organells via improvement in plant ionomics, antioxidant activities and down regulating Cr induced oxidative stress in rice plants. Conclusively, observations of the current study will be helpful in developing stratigies to decrease Cr contamination in food chain by employing ZnO NPs and to mitigate the drastic effects of Cr in plants for the sustainable crop growth.

Physio-ultrastructural footprints and iTRAQ-based proteomic approach unravel the role of Piriformospora indica-colonization in counteracting cadmium toxicity in rice

Due to its immense capability to concentrate in rice grain and ultimately in food chain, cadmium (Cd) has become the cause of an elevated concern among agriculturists, scientists and the environmental activists. Symbiotic association of Piriformospora indica (P. indica) has been characterized as a potential aid in combating heavy metal stress in plants for sustainable crop production but our scant knowledge regarding ameliorative tendency of P. indica against Cd, specifically in rice, necessitates an in-depth investigation. This study aimed at elaborating the underlying mechanisms involved in P. indica-mediated tolerance against Cd stress in two rice genotypes, IR8 and ZX1H, varying in Cd accumulation pattern. Either colonized or un-inoculated with P. indica, seedlings of both genotypes were subjected to Cd stress. The results showed that P. indica colonization significantly supported plant biomass, photosynthetic attributes and chlorophyll contents in Cd stressed plants. P. indica colonization sustained chloroplast integrity and reduced Cd translocation (46% and 64%), significantly lowering malondialdehyde (MDA) content (11.3% and 50.4%) compared to uninoculated roots under Cd stress in IR8 and ZX1H, respectively. A genotypic difference was evident when a 2-fold enhancement in root peroxidase (POD) activity was recorded in P. indica colonized IR8 plants as compared to ZX1H. The root proteomic analysis was performed using isobaric tags for relative and absolute quantification (iTRAQ) and the results showed that P. indica alleviates Cd stress in rice via down-regulation of key glycolysis cycle enzymes in a bid to reduce energy consumption by the plants and possibly re-directing it to Cd defense response pathways; and up-regulation of glutamine synthetase, a key enzyme in the L-Arg-dependent pathway for nitric oxide (NO) production, which acts as a stress signaling molecule, thus conferring tolerance by reduction of NO-mediated modification of essential proteins in response to Cd stress. Conclusively, both the tested genotypes benefited from P. indica symbiosis at varying levels by an enhanced detoxification capacity and signaling efficiency in response to stress. Hence, a step forward towards the employment of an environmentally sound and self-renewing approach holding the hope for a healthy future.

Interplaying roles of silicon and proline effectively improve salt and cadmium stress tolerance in Phaseolus vulgaris plant

The interplaying defensive roles of silicon (Si) and proline (Pro) in improving growth and yield attributes, physio-biochemical attributes, and antioxidant defense systems in common bean plant grown under saline (NaCl) and/or cadmium (Cd²⁺) stress were assessed. Seed were sown in plastic pots filled with sand-free ions as a growing medium that watered with a ½-strength Hoagland's nutrient solution. Twenty five days after planting, pots were split into 4 plots; control (no stress), 150 mM NaCl (salt stress), 1.5 mM Cd²⁺ in CdCl₂ (Cd²⁺ stress), and 100 mM NaCl + 1.0 mM Cd²⁺ (salt + Cd²⁺ stress). Four treatments; foliar spray with distilled water, 6 mM Si (in K₂SiO₃.nH₂O) solution, 6 mM Pro solution, and a combination of Si and Pro were allotted under each of the 4 plots. The experimental layout was a completely randomized design with 15 replicates. Compared to control, NaCl or Cd²⁺ stress significantly (P ≤ 0.05) reduced plant growth and yield attributes, leaf contents of chlorophylls, carotenoids, N, P, and K⁺, K⁺/Na⁺ ratio, RWC, MSI, Pn and Tr, while elevated significantly leaf EL, leaf contents of proline, soluble sugar, glutathione, MDA, Na⁺, and root, leaf and pod contents of Cd²⁺. The activities of antioxidant enzymes were also raised. The combined stress (NaCl + Cd²⁺) was more influential. Addition of Si and/or Pro for common bean plants under NaCl and/or Cd²⁺ stress significantly enhanced all investigated attributes of physiology, morphology, and biochemistry, and further increased the activities of antioxidant enzymes. Supplementation of Si + Pro was the best treatment having more positive influential, especially reducing the Cd²⁺ content in Phaseolus vulgaris pods to the limits (0.27 mg kg^-1) for legumes. Therefore, this combined treatment is recommended to use for alleviating environmental stress effects, especially salinity and Cd²⁺ for common bean production.