Title : Exogenous application of nitric oxide and hydrogen sulfide confers tolerance to chromium (VI) by metabolic rewiring in maize (Zea mays L.) seedlings
The effectiveness of exogenous signalling molecules such as nitric oxide (NO) or hydrogen sulfide (H2S) to mitigate Cr toxicity was investigated on 9-day-old maize seedlings. Application of 500 µM of sodium nitroprusside (SNP; NO donor) or sodium hydrosulfide (NaHS; H2S donor), suppressed Cr elicited embryonic axis growth inhibition and endogenous NO and H2S overproduction. In untreated plants, glutathione and ascorbic acid redox ratios suggested slightly oxidizing status in the radicles and inversely in the epicotyls. Ascorbate-glutathione antioxidant cycle was up-regulated after application of Cr+SNP and Cr+NaHS. Metabolomics data were profiled using flow infusion electrospray high-resolution mass spectrometry (FIE-HRMS) fingerprinting analysis. Carotenoids, tocopherols, and polyamines were discussed as stress regulators, which involved signalling cascade linked to defensive system. Exposure to Cr+SNP and Cr+NaHS increased tocopherols content but decreased spermidine and spermine ones in both radicles and epicotyls. Thus, the protective role of NaHS could be the consequence of high H2S dose by a significant up-build of carotenoids level that is not the case for SNP. The amino-acid metabolic pathways were also modulated as responses to heavy metal stress and application of NO or H2S. Taken together, the results suggested that NO and H2S are multifunctional signalling molecules that lead to activation of defensive responses and regulate different metabolic pathways under adverse conditions.