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Development of regulation mechanisms for SO 4 2‐ influx in spring wheat roots
Author(s) -
Jensén Paul,
König Tomas
Publication year - 1982
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1982.tb04527.x
Subject(s) - cycloheximide , sulfur , chemistry , intracellular , sulfur metabolism , allosteric regulation , nutrient , biophysics , biochemistry , enzyme , protein biosynthesis , biology , organic chemistry
The development of SO 4 2‐ influx in roots and sulfur transport to shoots was followed in 35 S‐tracer experiments for sulfur‐deficient spring wheat ( Triticum aestivum L. cv. Svenno) seedlings pretreated for various time periods (0–24 h) in nutrient solutions with SO 4 2‐ . Effects of the metabolic inhibitor 2,4‐dinitrophenol (DNP) and the protein synthesis inhibitor cycloheximide (CH) on SO 4 2‐ influx were also evaluated. The SO 4 2‐ influx appears feedback‐regulated by the internal sulfur level of the roots. Regulation may be achieved solely by a rapidly changed SO 4 2‐ carrier activity through an allosteric effect by the intracellular SO 4 2‐ concentration of the roots, followed first by induction of carrier synthesis and then by repression of carrier synthesis after transfer of the roots from SO 4 2‐ ‐deficient nutrient solutions to solutions with SO 4 2‐ . A Hill plot of the partly sigmoidal relationship between SO 4 2‐ influx and intracellular sulfur concentration in the roots gave a Hill coefficient of ‐4.2, indicating negative cooperativity between a minimum number of four interacting allosteric binding sites for sulfur on each carrier entity. DNP‐experiments showed that SO 4 2‐ influx was mainly metabolic, especially after short pretreatment in SO 4 2‐ at an external SO 4 2‐ concentration of 0.1 m M . Pretreatment with CH rapidly prevented new SO 4 2‐ carriers from being formed. Long CH pretreatment (24 h) and different SO 4 2‐ pretreatments reduced SO 4 2‐ influx below the non‐metabolic level obtained by uptake experiments with DNP, indicating the existence of SO 4 2‐ carriers mediating passive SO 4 2‐ transport across the plasmalemma of the root cells. SO 4 2‐ 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 SO 4 2‐ influx in the present experiments. Finally, it is suggested that there is a feedback signal between root and shoot, regulating sulfur transport upwards.