Na+ and Cl- Transport in the Phloem from Leaves of NaCl-treated Barley

Abstract

Sieve tube sap was collected from fully expanded leaves of NaCl-treated barley plants through aphid stylets. The sap was analysed for Na+, CI-, K+, phosphate, sucrose and osmolality. Na+ and Cl- appeared in the sap within a day of NaCl being added to the nutrient solution. When plants were exposed to various NaCl concentrations for 1-2 weeks, the sap contained about 15 mol m-3 Na+ and 25 mol m-3 Cl+, irrespective of whether the external NaCl concentration was 25, 100 or 200 mol m-3. When plants were kept for more than 2 weeks at 200 mol m-3 NaCl, the Cl- concentration in the sap increased but the Na+ concentration remained the same. Na+ and Cl- in the sap decreased very slowly when NaCl was removed from the nutrient solution. The calculated efflux of Na+ and Cl- in the phloem from the leaves was only 10% of the influx in the xylem, so the phloem can play little part in controlling the NaCl content of the leaves of these plants.