In vascular plants, the root endodermis surrounds the central vasculature as a protective sheath that is analogous to the polarized epithelium in animals, and contains ring-shaped Casparian strips that restrict diffusion. After an initial lag phase, individual endodermal cells suberize in an apparently random fashion to produce ‘patchy’ suberization that eventually generates a zone of continuous suberin deposition. Casparian strips and suberin lamellae affect paracellular and transcellular transport, respectively. Most angiosperms maintain some isolated cells in an unsuberized state as so-called ‘passage cells’, which have previously been suggested to enable uptake across an otherwise-impermeable endodermal barrier. Here we demonstrate that these passage cells are late emanations of a meristematic patterning process that reads out the underlying non-radial symmetry of the vasculature. This process is mediated by the non-cell-autonomous repression of cytokinin signalling in the root meristem, and leads to distinct phloem- and xylem-pole-associated endodermal cells. The latter cells can resist abscisic acid-dependent suberization to produce passage cells. Our data further demonstrate that, during meristematic patterning, xylem-pole-associated endodermal cells can dynamically alter passage-cell numbers in response to nutrient status, and that passage cells express transporters and locally affect the expression of transporters in adjacent cortical cells.

中文翻译：

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细胞分裂素信号的弥散抑制产生内胚层对称性和传代细胞

在维管植物中，根内皮层围绕中央脉管系统作为保护鞘，类似于动物的极化上皮，并包含限制扩散的环形凯斯帕带。在最初的滞后期之后，单个内胚层细胞以明显随机的方式木栓化以产生“片状”木栓化，最终产生连续的木栓质沉积区。里海带和木栓质薄片分别影响细胞旁和跨细胞运输。大多数被子植物将一些分离的细胞保持在未分化的状态，即所谓的“传代细胞”，此前曾有人建议这些细胞能够穿过原本不可渗透的内胚层屏障吸收。在这里，我们证明这些传代细胞是分生组织图案形成过程的晚期散发，该过程读​​出脉管系统的潜在非径向对称性。该过程由根分生组织中细胞分裂素信号传导的非细胞自主抑制介导，并导致不同的韧皮部和木质部相关的内胚层细胞。后一种细胞可以抵抗脱落酸依赖的栓化作用以产生传代细胞。我们的数据进一步表明，在分生组织形成过程中，木质部相关的内胚层细胞可以根据营养状态动态改变传代细胞数量，传代细胞表达转运蛋白并局部影响相邻皮层细胞转运蛋白的表达。该过程由根分生组织中细胞分裂素信号传导的非细胞自主抑制介导，并导致不同的韧皮部和木质部相关的内胚层细胞。后一种细胞可以抵抗脱落酸依赖的栓化作用以产生传代细胞。我们的数据进一步表明，在分生组织形成过程中，木质部相关的内胚层细胞可以根据营养状态动态改变传代细胞数量，传代细胞表达转运蛋白并局部影响相邻皮层细胞转运蛋白的表达。该过程由根分生组织中细胞分裂素信号传导的非细胞自主抑制介导，并导致不同的韧皮部和木质部相关的内胚层细胞。后一种细胞可以抵抗脱落酸依赖的栓化作用产生传代细胞。我们的数据进一步表明，在分生组织形成过程中，木质部相关的内胚层细胞可以根据营养状态动态改变传代细胞数量，传代细胞表达转运蛋白并局部影响相邻皮层细胞转运蛋白的表达。