Impact of atmospheric H2S, salinity and anoxia on sulfur metabolism in Zea mays

Plants in coastal salt marshes have to deal with salinity, anoxia and excessive reduced sulfur at the same time. Sulfur metabolism is presumed to have significance in plant stress-tolerance. In order to obtain more insight into the physiological significance of sulfur metabolism in plant responses to multiple abiotic stress factors, the glycophyte maize (Zea mays) was exposed to atmospheric H2S, salinity and anoxia. Maize seedlings appeared to be rather unsusceptible for the potentially toxic effects of these stressors. A 7-day exposure to 0.25 µl l-1 H2S and/or anoxia (anoxic root conditions) slightly enhanced biomass production, whereas it was not affected upon exposure to 100 mM NaCl. A simultaneous exposure of plants to salinity with H2S and/or anoxia resulted in a decreased biomass production. The total sulfur content of the shoot and root was hardly affected by H2S exposure, whereas it was strongly decreased upon anoxia. The total sulfur content of the shoot was decreased upon exposure to salinity. The decreases in total sulfur content could be predominantly ascribed to a decrease in the sulfate content. H2S exposure only resulted in an enhanced content of the water-soluble non-protein thiol content in shoots, whereas it was not affected by salinity and anoxia. Only a simultaneous exposure of plants to H2S, salinity and/or anoxia resulted in an enhanced water-soluble non-protein thiol content of the root. Anoxia and salinity exposure induced aerenchyma formation in the root, and the increased root thiol contents might be the result of the direct diffusion of atmospheric H2S via the stomata through the aerenchyma and subsequent metabolism in the root.