Development of regulation mechanisms for sulfate influx in spring wheat triticum aestivum cultivar svenno roots

Jensen, P.; Konig, T.

Physiologia Plantarum 55(4): 459-464


ISSN/ISBN: 0031-9317
DOI: 10.1111/j.1399-3054.1982.tb04527.x
Accession: 005135047

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The development of SO42- influx in roots and S transport to shoots was followed in 35S-tracer experiments for S-deficient spring wheat (T. aestivum L. cv. Svenno) seedlings pretreated for various time periods (0-24 h) in nutrient solutions with SO42-. Effects of the metabolic inhibitor 2,4-dinitrophenol (DNP) and the protein synthesis inhibitor cycloheximide (CH) on SO42- influx were evaluated. The SO42- influx appears feedback-regulated by the internal S level of the roots. Regulation may be achieved solely by a rapidly changed SO42- carrier activity through an allosteric effect by the intracellular SO42-concentration of the roots, followed first by induction of carrier synthesis and then regression of carrier synthesis after transfer of the roots from SO42-deficient nutrient solutions to solutions with SO42-. A Hill plot of the partly sigmoidal relationship between SO42- influx and intracellular S concentration in the roots gave a Hill coefficient of -4.2, indicating negative cooperativity between a minimum number of 4 interacting allosteric binding sites for S on each carrier entity. DNP-experiments showed that SO42- influx was mainly metabolic, especially after short pretreatment in SO42- at an external SO42- concentration of 0.1 mM. Pretreatment with CH rapidly prevented new SO42- carriers from being formed. Long CH pretreatment (24 h) and different SO42- pretreatments reduced SO42- influx below the non-metabolic level obtained by uptake experiments with DNP, indicating the existence of SO42- carriers mediating passive SO42- transport across the plasmalemma of the root cells. SO42- influx was further decreased for the CH pretreated (24 h) plants by the presence of both CH and DNP in the experimental nutrient solution. This probably indicates the diffusive part of the non-metabolic SO42- influx in the present experiments. Possibly, there is a feedback signal between root and shoot, regulating S transport upwards.

Development of regulation mechanisms for sulfate influx in spring wheat triticum aestivum cultivar svenno roots