Abstract: | During the first 7 d of sulphate-deprivation stored SO42- wasredistributed and assimilated into organic forms in the tropicallegume Macroptilium atropurpu-reum cv. Siratro. However, whilstthe sulphate content of all tissues declined after removingthe external SO42- supply this was slowest in mature leaves.By contrast, the total S content of mature leaves declined markedlyin the absence of external sulphate whilst that of both youngleaves and roots increased. Furthermore, when radiolabelledSO42- was applied to abraded surfaces of mature leaves, mostof the translocated label was recovered in the root following2 d SO42- deprivation. By contrast, radiolabelled SO42-appliedto young leaves was mostly retained in these tissues and nottranslocated. Within 3 d of removing the SO42- supply there was a large increasein extractable APS-sulphotransferase activity in roots accompaniedby a decline in nitrate reductase activity, but these effectswere not seen in leaves. Five days after the removal of SO42-there was a large increase in the content of asparagine in roots. The results are discussed in relation to the co-ordination ofNO3- and SO42- uptake and assimilation and the partitioningof sulphur during S-stress. Key words: Sulphate supply, stomatal conductance, ATP-sulphurylase, APS-sulphotransferase, nitrate reductase |