Dynamic of na+, k+ and proline accumulation in salt treated Vigna sinensis

Abstract

The dynamics of Na+, K+, and proline accumulation in various organs of non nodulated Vigna sinensis and Phaseolus aureus was followed during their acclimation to two levels of salinities for a period of 35 days and was correlated to the vegetative growth of the two species. The rate of Na+ and K+ absorption is at a maximum during the first 15 to 20 days of culture. K+ absorption is not completely inhibited even at 100 mM NaCl although the endogenous Na+ largely surpasses that of K+ in certain organs. Low salinity rather accelerates K+ absorption in both species. The relative growth rates (RGR) correlate with the rate of Na+ and K+ accumulation. At low salinity (10 mM NaCl), the RGR of V. sinensis is greater than that of P. aureus. However, at high salinity (100 mM NaCl) the RGR is the same for both species. The growth of the younger parts of the two species is not arrested by salt treatment. Very high accumulation of Na+ is avoided in organs with less vacuolated tissues. At no time does the endogenous K : Na ratio in these organs fall below 1.0. Certain organs, especially the roots, hypocotyls, and the lower parts of the stems are capable of storing large quantities of Na+. In V. sinensis, the accumulated Na+ and K+ are evenly distributed among the various organs while in P. aureus they are rather concentrated in the roots. External salinity creates water deficiency in the younger plant parts and as a consequence, proline accumulates especially in the youngest aerial organs - more in P. aureus than in V. sinensis. The accumulation of this amino acid in both the species is dependent on time and correlates directly, not only with the water deficit, but also with the K+ contents. In contrast, it does not seem to depend directly on the endogenous Na+ content. The relative salt tolerance of the two species and the possible role of K+, Na+ and proline in the osmotic adjustments of the two species under saline conditions are discussed.