Studies on the distribution of Na and CI in two species of lupin (Lupinus luteus and Lupinus angustifolius) differing in salt tolerance

Abstract

The distribution of K, Na and CI in various tissues was studied in two species of lupin, Lupinus luteus L. (ex. Portugal) and L. angustifolius L. (cv. Kubesa) under conditions of NaCl‐induced salinity stress. L. luteus appeared more tolerant to salt and less effective in excluding Na and Cl from its above‐ground parts than L. angustifolius. Electron probe X‐ray microanalysis of vacuolar contents of individual root cells of salt‐treated L. luteus showed a decreasing gradient of Na and CI contents from the epidermis inwards, but in the inner cortical cells adjacent to the pericycle/endodermis, Na levels were again high while Cl remained low. L. luteus may be inefficient in restricting entry of Na into the shoot because of a limited capacity for Na storage in the vacuoles of root cells. In addition, this species appears to exclude Cl from the vacuoles of inner cortical root cells but not from its symplastic pathway. In the leaves of L. luteus, Cl levels were particularly high towards the lower surface (abaxial side), while Na accumulated in the adaxial side of the leaf. Likewise, different cells of the petiole appeared to place unequal demands on Na and Cl for osmotic adjustment. It is suggested that excess Na in the adaxial side of the leaf and the generally high levels of Na and CI in the foliage may explain the 50% fresh weight stimulation which was observed in L. luteus but not in L. angustifolius at 50 mM NaCl. However, the halophytic response of L. luteus is limited to moderate concentrations of NaCl since 100 mM NaCl caused severe necrosis and leaf abscission.