Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijng 100093, China.
J Plant Physiol. 2011 Jul 15;168(11):1249-55. doi: 10.1016/j.jplph.2011.01.017. Epub 2011 Feb 25.
Casparian bands of endodermis and exodermis play crucial roles in blocking apoplastic movement of ions and water into the stele of roots through the cortex. These apoplastic barriers differ considerably in structure and function along the developing root. The present study assessed net Na+ fluxes in anatomically distinct root zones of rice seedlings and analyzed parts of individual roots showing different Na+ uptake. The results indicated that anatomically distinct root zones contributed differently to the overall uptake of Na+. The average Na+ uptake in root zones in which Casparian bands of the endo- and exo-dermis were interrupted by initiating lateral root primordia (root zone III) was significantly greater than that at the root apex, where Casparian bands were not yet formed (root zone I), or in the region where endo- and exo-dermis with Casparian bands were well developed (root zone II). The measurement of net Na+ fluxes using a non-invasive scanning ion-selective electrode technique (SIET) demonstrated that net Na+ flux varied significantly in different positions along developing rice roots, and a net Na+ influx was obvious at the base of young lateral root primordia. Since sodium fluxes changed significantly along developing roots of rice seedlings, we suggest that the significantly distinct net Na+ flux profile may be attributed to different apoplastic permeability due to lateral root primordia development for non-selective apoplastic bypass of ions along the apoplast.
内皮层和外皮层的凯氏带在阻止离子和水分通过皮层进入根柱的质外体运动方面起着至关重要的作用。这些质外体屏障在发育中的根中在结构和功能上有很大的不同。本研究评估了水稻幼苗解剖学上不同根区的净 Na+通量，并分析了显示不同 Na+吸收的个别根的部分。结果表明，解剖学上不同的根区对 Na+的整体吸收有不同的贡献。在侧根原基开始中断内皮层和外皮层凯氏带的根区（根区 III）中，Na+的平均吸收量明显大于尚未形成凯氏带的根尖（根区 I）或内皮层和外皮层凯氏带发育良好的区域（根区 II）。使用非侵入性扫描离子选择性电极技术（SIET）测量净 Na+通量表明，净 Na+通量在发育中的水稻根的不同位置差异显著，在年轻侧根原基的基部有明显的净 Na+内流。由于钠离子通量在水稻幼苗发育的根中变化显著，我们认为，由于侧根原基的发育导致非选择性质外体旁路离子的质外体渗透率不同，因此净 Na+通量的明显差异可能归因于不同的质外体渗透率。
