Membrane fluxes, bypass flows, and sodium stress in rice: The influence of silicon

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Abstract

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 24 Na +, 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 24 Na + 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.

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Flam-Shepherd, R., Huynh, W. Q., Coskun, D., Hamam, A. M., Britto, D. T., & Kronzucker, H. J. (2018). Membrane fluxes, bypass flows, and sodium stress in rice: The influence of silicon. Journal of Experimental Botany, 69(7), 1679–1692. https://doi.org/10.1093/jxb/erx460

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