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Effects of hyper‐osmotic stress on K + fluxes, H + extrusion, transmembrane electric potential difference and comparison with the effects of fusicoccin
Author(s) -
Zingarelli Luisa,
Teresa Marrè Maria,
Massardi Ferdinando,
Lado Piera
Publication year - 1999
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 - 10.1034/j.1399-3054.1999.106305.x
Subject(s) - fusicoccin , hyperpolarization (physics) , osmotic shock , mannitol , chemistry , biophysics , ion transporter , osmotic pressure , tetraethylammonium , efflux , membrane potential , membrane transport , atpase , biochemistry , stereochemistry , membrane , potassium , biology , enzyme , organic chemistry , gene , nuclear magnetic resonance spectroscopy
The stimulation of H + extrusion by hyper‐osmotic stress (0.2–0.3 M mannitol) in cultured cells of Arabidopsis thaliana (L.) Heynh. was shown to be associated with an inhibition of Cl − efflux, whereas hypo‐osmotic stress, inhibiting H + extrusion, early and strongly stimulated Cl − efflux. In this paper, we investigate the contribution of other factors [K + transport and transmembrane electric potential difference (E m )] to the hyper‐osmotic‐induced activation of the plasma membrane (PM) H + ‐ATPase. The effects of mannitol (MA) on K + transport and on E m were compared with those of fusicoccin (FC) since the modes of action of osmotica and of the toxin in stimulating H + ‐ATPase activity seem to differ at least in some steps. The changes in H + extrusion induced by hyper‐ or hypo‐osmotic stress were opposite and could be reversed by the application of the respective opposite stress. The effect of MA on H + extrusion was dependent on the presence of K + (or Rb + ) similarly to that of FC, while Na + and Li + , which also stimulated the FC effect, were ineffective on that of MA. The MA effect was independent of the anions (Cl − , SO 4 2− , NO 3 − ) accompanying K + . K + net uptake and K + influx were stimulated by both MA and FC. Tetraethylammonium (TEA + ) and Cs + inhibited both MA‐ and FC‐induced H + extrusion, suggesting the involvement of K + channels. MA (0.2 M ) induced a strong hyperpolarization of E m both in the absence and in the presence of K + . The hyperpolarizing effect of MA was also found when the cells were already hyperpolarized by FC, and was rapidly reversed by removing the osmoticum from the medium. In the presence of the lipophilic cation tributylbenzylammonium (TBBA + ), MA was no longer able to stimulate H + extrusion, while FC still stimulated it. In cells pretreated with TBBA + , which strongly depolarized E m , the subsequent addition of FC repolarized it, while the hyperpolarizing effect of MA was lacking. On the contrary, in cells pretreated with Erythrosine B (EB), E m was strongly depolarized and the following addition of FC did not hyperpolarize it, while the hyperpolarizing effect of MA was still observed. These results suggest that the mechanism of MA in activating H + extrusion and K + uptake is different from that of FC. The rise in net K + uptake seems to be driven by the activation of some hyperpolarizing system that does not seem to depend on a direct activation of PM H + ‐ATPase, but rather on the inhibition of Cl − efflux induced by hyper‐osmotic stress.