Membrane Biophysics Group, National Centre for Biological Sciences, University of Agricultural Sciences-G.K.V.K Campus, Bellary Road, Bangalore, India.
J Exp Bot. 2012 May;63(8):3289-96. doi: 10.1093/jxb/ers052. Epub 2012 Feb 17.
Salinity poses a major threat for agriculture worldwide. Rice is one of the major crops where most of the high-yielding cultivars are highly sensitive to salinity. Several studies on the genetic variability across rice cultivars suggest that the activity and composition of root plasma membrane transporters could underlie the observed cultivar-specific salinity tolerance in rice. In the current study, it was found that the salt-tolerant cultivar Pokkali maintains a higher K+/Na+ ratio compared with the salt-sensitive IR20 in roots as well as in shoots. Using Na+ reporter dyes, IR20 root protoplasts showed a much faster Na+ accumulation than Pokkali protoplasts. Membrane potential measurements showed that root cells exposed to Na+ in IR20 depolarized considerably further than those of Pokkali. These results suggest that IR20 has a larger plasma membrane Na+ conductance. To assess whether this could be due to different ion channel properties, root protoplasts from both Pokkali and IR20 rice cultivars were patch-clamped. Voltage-dependent K+ inward rectifiers, K+ outward rectifiers, and voltage-independent, non-selective channels with unitary conductances of around 35, 40, and 10 pS, respectively, were identified. Only the non-selective channel showed significant Na+ permeability. Intriguingly, in both cultivars, the activity of the K+ inward rectifier was drastically down-regulated after plant growth in salt but gating, conductance, and activity of all channel types were very similar for the two cultivars.
盐度对全球农业构成重大威胁。水稻是主要作物之一，其中大多数高产品种对盐度高度敏感。多项关于水稻品种间遗传变异性的研究表明，根质膜转运体的活性和组成可能是水稻品种特异性耐盐性的基础。在本研究中，发现耐盐品种 Pokkali 在根和地上部保持比盐敏感品种 IR20 更高的 K+/Na+ 比值。使用 Na+ 报告染料，IR20 根原生质体显示出比 Pokkali 原生质体更快的 Na+ 积累。膜电位测量表明，暴露在 Na+ 中的 IR20 根细胞比 Pokkali 根细胞去极化程度更大。这些结果表明 IR20 具有更大的质膜 Na+ 电导。为了评估这是否可能是由于不同的离子通道特性，从 Pokkali 和 IR20 水稻品种中分离出根原生质体进行了膜片钳研究。鉴定出电压依赖性 K+内向整流器、K+外向整流器和电压非依赖性、非选择性通道，其单位电导分别约为 35、40 和 10 pS。只有非选择性通道显示出显著的 Na+ 通透性。有趣的是，在两个品种中，K+内向整流器的活性在盐中生长后急剧下调，但所有通道类型的门控、电导和活性在两个品种中非常相似。
