The K⁺/Na⁺ Selectivity of a Cation Channel in the Plasma Membrane of Root Cells Does Not Differ in Salt-Tolerant and Salt-Sensitive Wheat Species

Abstract

The characteristics of cation outward rectifier channels were studied in protoplasts from wheat root (Triticum aestivum L. and Triticum turgidum L.) cells using the patch clamp technique. The cation outward rectifier channels were voltage-dependent with a single channel conductance of 32 ± I picosiemens in 100 millimolar KCI. Whole-cell currents were dominated by the activity of the cation outward rectifiers. The time-and voltage-dependence of these currents was accounted for by the summed behavior of individual channels recorded from outside-out detached patches. The K+/Na+ permeability ratio of these channels was measured in a salt-sensitive and salt-tolerant genotype of wheat that differ in rates of Na+ accumulation, using a voltage ramp protocol on protoplasts in the whole-cell configuration. Permeability ratios were calculated from shifts in reversal potentials following ion substitutions. There were no significant differences in the K+/Na+ permeability ratios of these channels in root cells from either of the two genotypes tested. The permeability ratio for K+/Cl-was greater than 50:1. The K+/Na+ permeability ratio averaged 30:1, which is two to four times more selective than the same type of channel in guard cells and suspension culture cells. Lowering the Ca2+ concentration in the bath solution to 0.1 millimolar in the presence of 100 millimolar Na+ had no significant effect on the K+/Na+ permeability ratios of the channel. It seems unlikely that the mechanism of salt tolerance in wheat is based on differences in the K+/Na+ selectivity of these channels.In saline conditions, most salt-tolerant monocotyledonous plants accumulate lower amounts of sodium in their leaves than salt-sensitive monocotyledonous plants (1). Salt-tolerant genotypes of wheat have been shown to transport less sodium from roots to shoots than do salt-sensitive genotypes, both in the long term (24) and in the short term (5). There is only indirect evidence for a sodium-specific effect on growth in the long term; wheat plants grown in high sodium chloride solutions have lower growth rates than those grown in high

Evaluation of Growth Parameters for Jatropha curcas L. (Biofuel Plant) under Salinity and Water Stress Using Tensiometer for Irrigation Guiding

“…Also, they suggested that alteration of mineral uptake from SA applications may be one mechanism for alleviation of salt stress, and positively affected K+/Na+. Similar explanation was reported by Schachtman et al (1991) who found that SA application may resulted in restore the ionic homeostasis and to keep the cytoplasm of actively growing or photosynthesizing cells of free of Na+ as possible.…”

Aluminum activates an anion channel in the apical cells of wheat roots

“…Although these currents were not examined in detail they were similar to those already described for mature root cells. These include a time-dependent outward and a time-dependent inward current, characteristic of the K ϩ -outward and K ϩ -inward rectifiers (15,21,22) and a fast, outwardly rectifying anion current (6).…”

“…Seeds were surface sterilized with 0.5% NaOCl and grown for 5 to 7 days in 0.2 mM CaCl 2 , pH 4.5, in a growth cabinet (12 h, 20°C and light͞12 h, 22°C and dark, photosynthetic flux density 250 mol⅐m Ϫ2 ⅐s Ϫ1 ). Protoplasts were prepared from the terminal 2-3 mm of root (root apices) or from the nonapical root tissue, using the procedure described by Schachtman et al (15).…”

Roles of Higher Plant K+ Channels

“…Thus, some K+ channels conduct Na+ to a finite extent, and this could have an impact on the degree to which plants can withstand salinity (e.g. Schachtman et al, 1991).…”