Nitric oxide and hydrogen sulfide protect plasma membrane integrity and mitigate chromium-induced methylglyoxal toxicity in maize seedlings.

The present study aims to analyse the potential crosstalk between nitric oxide (NO) and hydrogen sulfide (H2S) in triggering resilience of maize (Zea mays L.) seedlings to hexavalent chromium (Cr VI). Exogenous application of 500 µM sodium nitroprusside (SNP, as a NO donor) or sodium hydrosulfide (NaHS, as a H2S donor) to 9-day-old maize seedlings, countered a Cr (200 µM) -elicited reduction in embryonic axis biomass. Cr caused cellular membrane injury by enhancing the levels of superoxide and hydroxyl radicals as well as methylglyoxal, and 4-hydroxy-2-nonenal. The application of SNP or NaHS considerably improved the endogenous NO and H2S pool, decreased oxidative stress and lipid peroxidation by suppressing lipoxygenase activity and improving some antioxidant enzymes activities in radicles and epicotyls. Radicles were more affected than epicotyls by Cr-stress with enhanced electrolyte leakage and decreased proton extrusion as indicated by lesser H+-ATPase activity. H2S appeared to mitigate Cr toxicity through up-regulated H+-ATPase and glyoxalase pathways and by maintaining optimal GSH levels as downstream effects of ROS and MG suppression. Hence, H2S-mediated the regeneration of GSH pool is associated with the attenuation of MG toxicity by enhancing S-lactoglutathione and D-lactate production. Taken together, our results indicate complementary roles for H2S and GSH to strengthen membrane integrity against Cr stress in maize seedlings.

Selenium alleviates cadmium toxicity by preventing oxidative stress in sunflower (Helianthus annuus) seedlings.

The present study investigated the possible mediatory role of selenium (Se) in protecting plants from cadmium (Cd) toxicity. The exposure of sunflower seedlings to 20µM Cd inhibited biomass production, decreased chlorophyll and carotenoid concentrations and strongly increased accumulation of Cd in both roots and shoots. Similarly, Cd enhanced hydrogen peroxides content and lipid peroxidation as indicated by malondialdehyde accumulation. Pre-soaking seeds with Se (5, 10 and 20µM) alleviated the negative effect of Cd on growth and led to a decrease in oxidative injuries caused by Cd. Furthermore, Se enhanced the activities of catalase, ascorbate peroxidase and glutathione reductase, but lowered that of superoxide dismutase and guaiacol peroxidase. As important antioxidants, ascorbate and glutathione contents in sunflower leaves exposed to Cd were significantly decreased by Se treatment. The data suggest that the beneficial effect of Se during an earlier growth period could be related to avoidance of cumulative damage upon exposure to Cd, thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity.

Salt impact on photosynthesis and leaf ultrastructure of Aeluropus littoralis.

The effects of salinity (400 mM NaCl) on growth, biomass partitioning, photosynthesis, and leaf ultrastructure were studied in hydroponically grown plants of Aeluropus littoralis (Willd) Parl. NaCl produced a significant inhibition of the main growth parameters and a reduction in leaf gas exchange (e.g. decreased rates of photosynthesis and stomatal conductance). However, NaCl salinity affected neither the composition of photosynthesis pigments nor leaf water content. The reduction in leaf gas exchange seemed to correlate with a decrease in mesophyll thickness as well as a severe disorganisation of chloroplast structure, with misshapen chloroplasts and dilated thylakoid membranes. Conspicuously, mesophyll chloroplasts were more sensitive to salt treatment than those of bundle sheath cells. The effects of NaCl toxicity on leaf structure and ultrastructure and the associated physiological implications are discussed in relation to the degree of salt resistance of A. littoralis.