Sulfate uptake and utilization by two varieties of Brassica oleracea with different sulfur need as affected by atmospheric H2S

In order to get more insight into the interaction between atmospheric and pedospheric sulfur nutrition, the impact of H2S on sulfur metabolism was investigated in two varieties of Brassica oleracea L., viz. curly kale and Chinese cabbage. Measurements on the total sulfur content and relative growth rate of the two varieties showed that Chinese cabbage had a lower need for sulfur and correspondingly a lower sulfate uptake rate than curly kale. Both in curly kale and Chinese cabbage a large proportion of total sulfur was present as sulfate. However, the sulfate content of the roots and shoot was hardly affected at pedospheric sulfate concentration levels ranging from 0.25 up to 10 mM, reflecting a carefully regulated sulfate uptake by the roots. Upon exposure to 0.25 mul l(-1) H2S, an atmospheric level sufficient to meet the sulfur need of the plants, the sulfate uptake by the roots was reduced in curly kale and Chinese cabbage by 54 and 30 %, respectively. H2S exposure resulted in an increase in thiol level in the shoots, whereas that in the roots was hardly affected, demonstrating that thiols have limited significance in the shoot to root signaling of the regulation of the sulfate uptake. The contents of total sulfur, sulfate and glucosinolates remained unaffected upon H2S exposure. Evidently there is a good coordination between the metabolism of atmospheric H2S and pedospheric sulfate in both varieties of Brassica oleracea.