Interaction between metabolism of atmospheric H2S in the shoot and sulfate uptake by the roots of curly kale (Brassica oleracea)

Exposure of curly kale (Brassica oleracea L.,) to gaseous H2S resulted in a decreased sulfate uptake by the roots. At 0.2 mu l l(-1) H2S, a level sufficient to meet the sulfur need of plants for growth, the sulfate uptake was maximally decreased by 50% after 3 or 4 days of exposure. Higher levels up to 0.8 mu l l(-1) H2S did not further affect the sulfate uptake. The nitrate uptake was not affected upon exposure to 0.2-0.8 mu l l(-1) H2S. H2S exposure did not affect the sulfate content of the plants, but it resulted in an increased content of thiols and cysteine in the shoots, whereas that in the roots was hardly affected. Plants grown under sulfate-deprived conditions had a decreased biomass production, very low content of sulfate and decreased content of thiols in both shoot and roots. Sulfate-deprived plants had a two-fold higher sulfate uptake after transfer to a sulfate-containing solution, while nitrate uptake was decreased by 50%, When sulfate-deprived plants were exposed to 0.25 mu l l-(1) H2S, plant biomass production and nitrate uptake were restored but the sulfate uptake after transfer to a sulfate-containing solution remained high. Also here, H2S exposure resulted in an increase in the thiol and cysteine content of both shoot and roots, whereas the content of sulfate remained low. The presented results clearly demonstrate a direct interaction between the regulation of sulfate uptake by the roots and the metabolism of gaseous H2S by the shoot. Curly kale is able to use both sulfate and H2S as a sulfur source for growth, and matching the supply of sulfur in the form of pedospheric or atmospheric sulfur to the sulfur needed for growth appears to be regulated nicely. However, the significance of thiols as signal in the shoot/root coordination of sulfate uptake appears to be limited. From the data it is evident that there is no direct mutual regulation between the uptake of sulfate and nitrate by the roots.