Plant responses to H2S and SO2 fumigation. II. Differences in metabolism of H2S and SO2 in spinach

Fumigation of spinach (Spinacia oleracea L. cvs Estivato and Monosa) with H2S or SO, for 1 to 6 days resulted in accumulation of sulfhydryl (SH) compounds in the shoots of both H2S‐ and SO2‐exposed plants. The sulfate concentration in shoots of SO2‐exposed plants increased linearly with time. SH accumulation showed saturation kinetics as a function of time as well as H2S concentration, ascribed to the internal H2S concentration in the plant and the availability of substrates for glutathione synthesis, respectively. SH compounds accumulated more at lower exposure temperatures, whereas sulfate accumulation was more pronounced at higher temperatures. These results are discussed in relation to the possible foliar uptake of H2S and SO2, the temperature dependence of uptake and the water solubility of these gases. The possibility of SO2‐induced H2S emission rather than sulfate accumulation as a source for SH accumulation is also discussed. Cessation of fumigation resulted in a decrease in SH compounds and sulfate content that could be accounted for by sulfur metabolism and growth, respectively.