Atmospheric H(2)S: Impact on Plant Functioning

Hydrogen sulfide (H(2)S) is an air pollutant present at high levels in various regions. Plants actively take up H(2)S via the foliage, though the impact of the gas on the physiological functioning of plants is paradoxical. Whereas elevated H(2)S levels may be phytotoxic, H(2)S levels realistic for polluted areas can also significantly contribute to the sulfur requirement of the vegetation. Plants can even grow with H(2)S as sole sulfur source. There is no relation between the rate of H(2)S metabolism and the H(2)S susceptibility of a plant, which suggests that the metabolism of H(2)S does not contribute to the detoxification of absorbed sulfide. By contrast, there may be a strong relation between the rate of H(2)S metabolism and the rate of sulfate metabolism: foliar H(2)S absorbance may downregulate the metabolism of sulfate, taken up by the root. Studies with plants from the Brassica genus clarified the background of this downregulation. Simultaneously, these studies illustrated that H(2)S fumigation may be a useful tool for obtaining insight in the regulation of sulfur homeostasis and the (signal) functions of sulfur-containing compounds in plants.