Interaction between metabolism of atmospheric H2S in the shoot and sulfateuptake 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 suff icient 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 nitra te uptake was not affected upon exposure to 0.2-0.8 mu l l(-1) H2S. H2S exp osure 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 conditio ns had a decreased biomass production, very low content of sulfate and decr eased content of thiols in both shoot and roots. Sulfate-deprived plants ha d a two-fold higher sulfate uptake after transfer to a sulfate-containing s olution, while nitrate uptake was decreased by 50%, When sulfate-deprived p lants were exposed to 0.25 mu l l-(1) H2S, plant biomass production and nit rate uptake were restored but the sulfate uptake after transfer to a sulfat e-containing solution remained high. Also here, H2S exposure resulted in an increase in the thiol and cysteine content of both shoot and roots, wherea s the content of sulfate remained low. The presented results clearly demons trate 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 s upply of sulfur in the form of pedospheric or atmospheric sulfur to the sul fur needed for growth appears to be regulated nicely. However, the signific ance of thiols as signal in the shoot/root coordination of sulfate uptake a ppears to be limited. From the data it is evident that there is no direct m utual regulation between the uptake of sulfate and nitrate by the roots.