Na+-K+ transport in roots under salt stress（文献编号R2008-001）
Salinity causes billion dollar losses in annual crop production. So far, the main avenue in breeding crops for salt tolerance has been to reduce Na+ uptake and transport from roots to shoots. Recently we have demonstrated that retention of cytosolic K+ could be considered as another key factor in conferring salt tolerance in plants. A subsequent study has shown that Na+-induced K+ efflux in barley root epidermis occurs primarily via outward rectifying K+ channels (KORC). Surprisingly, expression of KORC was similar in salt- tolerant and sensitive genotypes. However, the former were able to better oppose Na+-induced depolarization via enhanced activity of plasma membrane H+-ATPase (thus minimizing K+ leak from the cytosol). In addition to highly K+-selective KORC channels, activities of several types of non-selective cation channels were detected at depolarizing potentials. Here we show that the expression of one of them, NORC, was significantly lower in salt-tolerant genotypes. As NORC is capable of mediating K+ efflux coupled to Na+ influx, we suggest that the restriction of its activity could be beneficial for plants under salt stress.
图注：Plasma membrane transporters controlling cytosolic K+/Na+ in barley root epidermal cell under salt stress. (1) Increase of NaCl in external medium provokes the Na+ influx through NSCC channels causing a depolarization of plasma membrane. (2) Efflux of K+ across suitable K+- permeable channels, NSCC and KORC. (3) Activation of plasma membrane H+-ATPase opposes NaCl-induced membrane depolarization and linked K+ efflux. (4) Proton gradient built by H+-ATPase assists Na+/H+ antiport, further improving cytosolic Na+/K+ ratio.