Influence of Glutathione (GSH) on Sulphate Influx, Xylem Loading and Exudation in Excised Tobacco Roots |
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Authors: | HERSCHBACH, CORNELIA RENNENBERG, HEINZ |
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Abstract: | In short-term experiments sulphate influx of excised tobaccoroots {Nicotiana tabacum L. var. 'Samsun') followed monophasicMichaelis-Menten kinetics with an approximate Km of 12 ±4 µM and vmax of 657 ± 211 nmol g1 FW h1.An inhibition of sulphate influx, xylem loading and exudationof more than 70% was achieved with 01 mM GSH within 1 h. Cysteinewas two orders of magnitude more effective as an inhibitor thanGSH. An inhibition of more than 75% was already obtained with1.0µM cysteine. It may, therefore, be assumed that GSHis decomposed to yield cysteine concentrations that may inhibitsulphate influx, xylem loading and exudation. When BSO, a specificinhibitor of the initial step of GSH synthesis, was added, cysteine-mediatedinhibition on sulphate influx, xylem loading and exudation wasstrongly diminished. Apparently, GSH synthesis is required toobtain inhibition of these processes by cysteine. The physiologicalmechanisms that may cause the inhibition of sulphate influx,xylem loading and exudation by glutathione are discussed. Key words: Sulphate transport, Nicotiana, Solanaceae, glutathione, cysteine, buthionine sulphoximine |
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