Effect Of NaCl Stress On The K～+ Uptake And Plasma Membrane H～+-ATPase Activity Of Suaeda Salsa

Significant differences were observed in the responses of K+ and Na+ uptake, K+/Na+ selectivity under salt stress between the halophytes and the nonhalophytes. These differences may be the major reason that causes the different salt tolerance between the halophytes and the nonhalophytes. The present study aimed at investigating the uptake of K+, the effect of the NaCl stress on the uptake of K+ and the effect of K+ uptake inhibitor (NEM and TEA) on the Na+ content first. Then the effect of K+ nutrition on the growth, water, ion, activity and subunit expression of PM H+-ATPase of the halophyte Suaeda salsa under NaCl stress were studied. The main results are shown as follows. 1 Uptake of K+and Na+1.1 Uptake of K+The K+ uptake of Suaeda salsa is biphasic, mediated by a high affinity and a low affinity transport system. Michaelis-Menten parameter values are Km=22.1 umol/L, Vmax=28.67 umol/gDW/h and k=2.77 for the high and low affinity systems respectively.1.2 Effect of NaCl stress on the uptake of K+Two new K+ uptake kinetic curves were obtained under 100 and 400 mmol/L NaCl stress. The former parameter values are Km=14.87 umol/L, Vmax=28.85 umol/gDW/h and k=1.21 for the high and low affinity systems respectively. It proved that NaCI stress could induce the high affinity system of K+ uptake and enhanced the affinity of the high affinity system for K+. And it also inhibited the low affinity system of K+ uptake of Suaeda salsa. The latter parameter values are Km=14.1 umol/L, Vmax=29.27umol/gDW/h and k=1.1 for the high and low affinity systems respectively. This proved that 400 mmol/L NaCl stress did not affect the high affinity system characteristic markedly compared with 100 mmol/L NaCl stress. But it further inhibited the low affinity system.1.3 Effect of K+ channel inhibitor on the Na+ contentNEM (3 mmol/L) is a specific inhibitor of the high affinity K+ uptake system. It had little effect on the Na+ content of Suaeda salsa at low K+ concentration (0, 0.1, 0.4 mmol/L). This may indicate that Na4 entry into the plants was not mediated by the high affinity K+ uptake system under low K+ application.TEA (6 mmol/L) is a specific inhibitor of the low affinity K+ uptake system. It inhibited the Na+ uptake and accumulation significantly at high K+ concentration (6, 8, 10 mmol/L). This suggested that Na+ entry into the plants, at least, was partly mediated by low affinity K+ uptake system under high K+ application.2 Effect of K+ nutrition and NaCl stress on the growth and K+ content of Suaeda salsa plantsThe results showed that the increase in growth of Suaeda salsa plant was mainly due to the increase of shoots. The Suaeda salsa plants were much small, had few offshoots and the young leaves got yellow when they were grown in K+ deficient solution. The Suaeda salsa plants grew better with the increase of K+ concentration. K+ nutrition significantly enhanced the fresh and the dry weight of shoots and roots whether under control (0 mmol/L NaCl) or under NaCl stress (100, 400 mmol/L). This proved that K+ nutrition played an important role in the growth of Suaeda salsa. Moreover, NaCl treatment significantly enhanced the growth of Suaeda salsa because it caused the leaves succulent and more offshoots markedly. This is very different from the nonhalophytes.K+ content in leaves and roots was increased gradually with the increase of K+ concentration in medium. The NaCl stress markedly reduced the K+ content in leaves and roots of plants grown in 0.7, 1, 6 mmol/L K+ medium but hardly affected K+ content in 0, 0.1 mmol/L K+ medium. Moreover, 400 mmol/L NaCl stress did not reduce K+ content markedly compared with 100 mmol/L NaCl stress whether under low K4 concentration or under high K+ concentration. This is very different from the nonhalophytes. This proved that there is an effective mechanism of K+ homeostasis in Suaeda salsa under salt stress, which was important in the salt tolerance of Suaeda salsa.3 Activity and subunit of PM HT-ATPaseNaCl stress (100, 400 mmol/L) markedly stimulated PM H+...