Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan.
Ann Bot. 2011 Jan;107(1):89-99. doi: 10.1093/aob/mcq221. Epub 2010 Nov 22.
Many wetland species form aerenchyma and a barrier to radial O(2) loss (ROL) in roots. These features enhance internal O(2) diffusion to the root apex. Barrier formation in rice is induced by growth in stagnant solution, but knowledge of the dynamics of barrier induction and early anatomical changes was lacking.
ROL barrier induction in short and long roots of rice (Oryza sativa L. 'Nipponbare') was assessed using cylindrical root-sleeving O(2) electrodes and methylene blue indicator dye for O(2) leakage. Aerenchyma formation was also monitored in root cross-sections. Microstructure of hypodermal/exodermal layers was observed by transmission electron microscopy (TEM).
In stagnant medium, barrier to ROL formation commenced in long adventitious roots within a few hours and the barrier was well formed within 24 h. By contrast, barrier formation took longer than 48 h in short roots. The timing of enhancement of aerenchyma formation was the same in short and long roots. Comparison of ROL data and subsequent methylene blue staining determined the apparent ROL threshold for the dye method, and the dye method confirmed that barrier induction was faster for long roots than for short roots. Barrier formation might be related to deposition of new electron-dense materials in the cell walls at the peripheral side of the exodermis. Histochemical staining indicated suberin depositions were enhanced prior to increases in lignin.
As root length affected formation of the barrier to ROL, but not aerenchyma, these two acclimations are differentially regulated in roots of rice. Moreover, ROL barrier induction occurred before histochemically detectable changes in putative suberin and lignin deposits could be seen, whereas TEM showed deposition of new electron-dense materials in exodermal cell walls, so structural changes required for barrier functioning appear to be more subtle than previously described.
许多湿地物种在根中形成通气组织和阻止径向 O(2) 损失（ROL）的屏障。这些特征增强了内部 O(2) 向根尖端的扩散。在水稻中，屏障的形成是由在停滞溶液中的生长引起的，但对屏障诱导和早期解剖变化的动力学知之甚少。
使用圆柱形根套管 O(2) 电极和亚甲基蓝指示剂染料评估短根和长根水稻（Oryza sativa L. 'Nipponbare'）中 ROL 屏障的诱导。还通过根横切片监测通气组织的形成。通过透射电子显微镜（TEM）观察下皮层/外表皮层的微观结构。
在停滞的培养基中，长不定根中的 ROL 屏障形成在数小时内开始，并且在 24 小时内形成良好。相比之下，短根中的屏障形成需要超过 48 小时。通气组织形成的增强时间在短根和长根中是相同的。ROL 数据和随后的亚甲基蓝染色的比较确定了染料法的表观 ROL 阈值，并且染料法证实长根的屏障诱导速度快于短根。屏障的形成可能与在外表皮层的外周侧细胞壁中新的电子致密物质的沉积有关。组织化学染色表明，在木质素增加之前，先增强了蜡质的沉积。
由于根长影响 ROL 屏障的形成，但不影响通气组织的形成，因此水稻根中的这两种适应是不同调节的。此外，ROL 屏障的诱导发生在组织化学上可检测到潜在的蜡质和木质素沉积变化之前，而 TEM 显示出外表皮层细胞壁中新的电子致密物质的沉积，因此屏障功能所需的结构变化似乎比以前描述的更微妙。
