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Mechanism of the inhibition of phloem loading by sodium sulfite: Effect of the pollutant on the transmembrane potential difference
Author(s) -
Maurousset Laurence,
Bonnemain LeanLouis
Publication year - 1990
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.1399-3054.1990.tb04401.x
Subject(s) - sulfite , chemistry , sodium sulfite , depolarization , biophysics , sodium , sucrose , biochemistry , nuclear chemistry , biology , organic chemistry
Sodium sulfite (Na 2 SO 3 ) decreased uptake from 1 m M sucrose by the parenchyma and by the veins of leaves of broadbean ( Vicia faba L. cv. Aguadulce). The decrease depended on the concentration of the pollutant and the duration of pretreatment. The inhibition was non‐competitive. Sulfite affected the transmembrane potential difference (PD) of the leaf tissues. The short‐term response obeyed an ‘all or nothing’ law. At 0.1 m M and above, sulfite led to a quick depolarization of one‐third of the initial potential after a lag phase of about 5 min; for concentrations lower than 0.1 m M , sulfite did not affect the potential. By contrast, the long‐term effect of Na 2 SO 3 on the transmembrane PD strongly depended on its concentration. After 2–12 h of pretreatmemt there was no effect at 10 μ M , a weak effect at 0.1 m M , and then increasing depolarization as the pollutant concentration increased. The inhibitory effect of Na 2 SO 3 on sucrose uptake is thus, at least partly, due to its effect on a component of the proton‐motive force. ΔΨ. However, the lack of correlation noticed with 0.1 m M Na 2 SO 3 between the effect on sucrose uptake and the long‐term effect on transmembrane PD suggests numerous sites of sulfite action.