Department of Biological Sciences and Canadian Centre for World Hunger Research (CCWHR), University of Toronto, Toronto, Canada.
School of BioSciences, The University of Melbourne, Parkville, Victoria, Australia.
J Exp Bot. 2018 Mar 24;69(7):1679-1692. doi: 10.1093/jxb/erx460.
Provision of silicon (Si) to roots of rice (Oryza sativa L.) can alleviate salt stress by blocking apoplastic, transpirational bypass flow of Na+ from root to shoot. However, little is known about how Si affects Na+ fluxes across cell membranes. Here, we measured radiotracer fluxes of 24Na+, plasma membrane depolarization, tissue ion accumulation, and transpirational bypass flow, to examine the influence of Si on Na+ transport patterns in hydroponically grown, salt-sensitive (cv. IR29) and salt-tolerant (cv. Pokkali) rice. Si increased growth and lowered [Na+] in shoots of both cultivars, with minor effects in roots; neither root nor shoot [K+] were affected. In IR29, Si lowered shoot [Na+] via a large reduction in bypass flow, while in Pokkali, where bypass flow was small and not affected by Si, this was achieved mainly via a growth dilution of shoot Na+. Si had no effect on unidirectional 24Na+ fluxes (influx and efflux), or on Na+-stimulated plasma-membrane depolarization, in either IR29 or Pokkali. We conclude that, while Si can reduce Na+ translocation via bypass flow in some (but not all) rice cultivars, it does not affect unidirectional Na+ transport or Na+ cycling in roots, either across root cell membranes or within the bulk root apoplast.
向水稻（Oryza sativa L.）根部供应硅（Si）可以通过阻断从根部到地上部的质外体、蒸腾性旁路流来缓解盐胁迫。然而，人们对 Si 如何影响跨细胞膜的 Na+通量知之甚少。在这里，我们测量了放射性示踪剂 24Na+的通量、质膜去极化、组织离子积累和蒸腾性旁路流，以研究 Si 对水培生长的盐敏感（cv.IR29）和盐耐受（cv. Pokkali）水稻中 Na+运输模式的影响。Si 增加了两个品种的生长并降低了地上部的[Na+]，对根部的影响较小；根和地上部的[K+]均不受影响。在 IR29 中，Si 通过大大降低旁路流来降低地上部[Na+]，而在 Pokkali 中，旁路流很小且不受 Si 影响，这主要是通过地上部 Na+的生长稀释来实现的。Si 对 IR29 或 Pokkali 中的单向 24Na+通量（流入和流出）或 Na+刺激的质膜去极化没有影响。我们得出结论，虽然 Si 可以在某些（但不是所有）水稻品种中通过旁路流减少 Na+转运，但它不会影响单向 Na+运输或根中的 Na+循环，无论是在根细胞膜上还是在根质外体内部。
