Osmotic and saline effects of different solutes on chloride fluxes and accumulation in excised maize roots

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Abstract
The effect of different saline or non saline solutes (i.e. K2SO4, Na2SO4, MgSO4 and mannitol) on fluxes and accumulation of chloride occurring in excised maize roots were studied adopting the method of compartmental analysis. A stimulation of chloride fluxes outer medium-cytoplasm and symplasm-xylem was induced by solutions of K2SO4 and Na2SO4 at osmotic potential between –1.5 and –3.0 bars. A sharp decrease of the same fluxes was noted with solutions of K2SO4 at –5.7 bars, while the effect was lower when Na+ ions were substituted for the K+ ions. The flux cytoplasm-outer medium was generally stimulated by the decrease of osmotic potential in solutions of electrolytes, but not in solutions of mannitol. The effect on fluxes occurring at tonoplast was clearly lower than the effect on fluxes occurring at plasmalemma. Chloride retention in apparent free space was not significantly modified by a decrease of osmotic potential in every case. Chloride accumulation in cytoplasm was stimulated by solutions of Na2SO4 at osmotic potential values between –1.5 and –3.0 bars and notably depressed by K2SO4 solutions at –5.7 bars. Vacuolar accumulation was increased by media containing Na2SO4 at –5.7 bars and mannitol at –3.0 bars, while it was strongly depressed by K2SO4 solutions at –5.7 bars and not significantly modified by solutions of MgSO4 Increasing concentrations of potassium and sodium sulphate stimulated chloride exchange, whereas equivalent concentrations of mannitol retarded it. Probable explanations of these effects and correlations between chloride transport and outer osmotica are discussed.