Effects of Age on Sodium Fluxes in Primary Bean Leaves

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Abstract
The effects of age on sodium fluxes in primary‐leaf sections from control and decapitated bean plants were determined. It was assumed that at high external salt concentrations the measurements represent mainly fluxes through the tonoplast, and that in brief efflux experiment subsequent to free‐space exchange efflux from the cytoplasma is essentially measured. Net‐ and influxes to the vacuoles increase during the period of leaf expansion and net chlorophyll synthesis. Both fluxes and amount of chlorophyll decrease rapidly in senescing leaves. The exchangeability of previously absorbed sodium also increased in senescing leaves. Decapitation delayed senescence and very much reduced the decreases in net flux and influx, and the exchangeability of sodium. The results are discussed in relation to solutes redistribution in the plant.