Mitigation effects of exogenous melatonin-selenium nanoparticles on arsenic-induced stress in Brassica napus.

Melatonin (MT) and selenium (Se) application known to decrease heavy metal uptake and toxicity in plants. By mixing the Se in MT medium a new complex MT-Se nanoparticles (MT-Se NPs) was synthesized and we investigated the role of MT-Se NPs on B. napus growth and tolerance against As stress. The MT-Se particles significantly enhanced the plant growth and other associated physiological attributes under As stress. The As treatment at 80 µM was more phytotoxic, however MT-Se NPs application resulted in a substantial increase in leaf chlorophyll fluorescence, biomass accumulation, and decreased ROS relative to As stressed plants. The use of MT-Se NPs to As stressed plants reduced photosynthetic inhibition and oxidative stress and attenuated the increase in MDA and H2O2 contents. The application of MT-Se NPs also boosted the antioxidant enzymes activities such as SOD, POD and CAT as well as the APX, GR and GSH activates under As stress. The results also showed MT-Se NPs treatments alleviated the growth inhibition induced by As and reduced the accumulation of As in leaves and roots of B. napus seedlings. Moreover, treatment with MT-Se NPs improved the plant growth more successfully than treatment of MT and Se alone. This study explored the mechanism of melatonin and selenium efficiency in the composition can be jointly encouraged to exert synergistic effects and boost plant enzymatic activities.

Comprehensive proteomic analysis of arsenic induced toxicity reveals the mechanism of multilevel coordination of efficient defense and energy metabolism in two Brassica napus cultivars.

Arsenic (As) a non-essential element is of particular concern with respect to harmful effects on plant metabolism. While extensive studies have been conducted on the physiological responses of plants to increase As concentrations, however, molecular differences elucidating species-specific changes remain largely unknown. In the present experiment, two oilseed Brassica napus (B. napus) cultivars, ZS758 and ZD622, were treated by elevated As concentration. Their responses to the As stress have been investigated through pulse amplitude modulated fluorometer and isobaric tags based proteomic (iTRAQ) analysis. The chlorophyll fluorescence attributes showed that As stress significantly decrease the photochemical efficiency of photosystem II (PSII) and photosystem I (PSI) as well as the comparatively closed stomata observed under scanning electron microscopy (SEM). In this study, 65 proteins displayed increased abundance and 52 down-regulated were found in the control vs As comparison in cultivar ZS758, while 44 up and 67 down-regulated proteins were found in the control vs As comparison in ZD622. Metabolic pathways, followed by ribosome and biosynthesis of secondary metabolites were the dominant functional annotation categories among the differentially expressed protein (DEPs). Many genes involved in primary metabolism, stress and defense were found to be As-responsive DEPs and/or DEPs between these two cultivars. Based on these results, a schematic description of key processes involved in As tolerance in ZS758 and ZD622 is proposed, which suggests that higher tolerance in ZS758 depends on a multilevel coordination of efficient defense and energy metabolism. Real-time quantitative PCR supported the expression patterns of several genes encoding a protein similar to their corresponding DEPs. In addition, these findings could shed light in unraveling the molecular mechanisms of B. napus exposed to As stress and provide or improve essential understandings in the development of advanced B. napus cultivars against As resistance.

Melatonin induced changes in photosynthetic efficiency as probed by OJIP associated with improved chromium stress tolerance in canola (Brassica napus L.).

Chromium toxicity is considered as a major problem for agricultural soil that reduced crop productivity by affecting photosynthetic tissues. Exogenous application of melatonin can alleviate the adverse effects of chromium toxicity on plant growth. However, little is known about its effect on thylakoidal protein complexes responsible for conversion of solar energy to biochemical energy. Chlorophyll fluorescence a transients considered one of the best non-invasive and rapid method for the evaluation of photosynthetic (Photosystem II) efficiency of plants and plant health under environmental stress conditions. In the present study, three-week old plants of two canola cultivars AC-Excel and DGL were applied to melatonin (0, 1, 5, 10 µM) when grown under chromium stress (0, 50 and 100 µM) for further two weeks. Chromium stress reduced the growth (fresh and dry weights of shoots and roots) of both canola cultivars and exogenous application of 5 and 10 µM melatonin improved the growth of canola at 50 or 100 µM chromium stress. This improvement was greater in cv DGL than in AC-Excel. Increasing chromium decreased the photosynthetic pigments (chlorophyll a and chlorophyll b). However, 5 and 10 µM melatonin application improved chlorophyll a at 50 µM chromium stress. Structural stability and efficiency of photosystem II (PSII) measured as performance index (PIABS) and ratios of fluorescence (Fv/Fm, Fv/Fo) Fv decreased due to chromium stress. JIP-test parameters showed that chromium stress increased the absorption and trapping fluxes with decrease in electron transport fluxes which caused the damage to reaction centers (RC), detachment of oxygen evolving complex (OEC) from RC or inefficiency of electron transfer from OEC to RC. Such adverse effects were greater in cv AC-Excel. However exogenous application of melatonin improved PIABS, electron transport per reaction center (ET/RC), reduced variable fluorescence at J step (VJ) reflecting melatonin protected PSII from chromium stress induced damage by protecting OEC. Thus, OJIP fluorescence transients are quite helpful for understanding the intersystem electron transport beyond photosystem II in canola cultivars due to melatonin application under chromium stress. FINDINGS: Exogenous application of melatonin alleviated toxic effects of chromium on plant growth of canola by modulating photosynthesis, enhanced photosystem II efficiency and regulation of electron transport flux to protect photo-inhibition of PSII from oxidative damage.