Effect of NaCI Salinity on Growth, Development, Ion Distribution, and Ion Translocation in Castor Bean (Ricinus communis L.)

Abstract

Summary Castor bean ( Ricinus communis L.) was grown over a wide range of external salinities (up to 160 mol m -3 NaCl) and effects on growth, ion distribution, and composition of xylem and phloem sap were studied. NaCl above 40 mol m -3 caused severe changes in plant development with reduction in growth, suppressed branching, and reduced size and epinasty of leaves, but even at 160 mol m -3 NaCl Ricinus survived and produced viable seeds. In presence of external salt internal concentrations of Na + and Cl - increased, but Na + concentration in stem and petiole tissues were substantially higher than in leaf blades. Conversely, K + concentrations in petioles or stems decreased while those of leaf blades remained high. Na + concentrations in xylem and phloem saps increased with external NaCl salinity but very slightly so, while K + concentrations in both long distance transport fluids were maintained at high levels. Na + concentrations in phloem sap collected from young petioles were 2-5 times lower than in those obtained from petioles of older leaves or from the stem base. Apparently Na + was removed from xylem and phloem sap by stem and petiolar tissues. The resulting non-uniform distribution of K + and Na + within the shoot as a whole and the leaf was maintained over extended exposures to high external salinity. The importance of these processes for salinity tolerance of Ricinus are discussed.