Cysteine sulfate transport

The most active sulfate uptake was observed in the range of pH 5.5-7.0 it rapidly decreased above pH 7.0 (Fig. 4.7). This may be due to the high affinity of protons to the system, of S04 transport in yeasts it was shown (Borst-Powels, 1981) that the sulfate transport occurs in a symport with protons. Sulfate, and especially thiosulfate, considerably inhibited the transport of the labeled sulfate, in contrast to cysteine, which showed no significant effect on sulfate uptake, so that the cells grown with cysteine utilized S04 to the same extent as those grown with sulfate. It means that... 

Most of the sulfate obtained through the root system is transported in the xylem (Pate, 1965 Tolbert and Wiebe, 1955) to leaf tissue where it is reduced and assimilated into cysteine in light-dependent reactions (Schmidt and Trebst, 1969 Schwenn and Trebst, 1976 Trebst and Schmidt, 1969). Some sulfate reduction occurs in nonphotosynthetic tissue (Ellis, 1%3 Ferrari and Renosto, 1972) but this is of minor importance. In the field pea for example Pate (1965) found that only 0.2-0.4% of the S label of plants supplied with p S]sulfate via their root systems was present in xylem sap as organic sulfur. 

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