Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Bratislava, Slovak Republic.
Ann Bot. 2012 Jul;110(2):361-71. doi: 10.1093/aob/mcs110. Epub 2012 May 28.
Apoplasmic barriers in plants fulfil important roles such as the control of apoplasmic movement of substances and the protection against invasion of pathogens. The aim of this study was to describe the development of apoplasmic barriers (Casparian bands and suberin lamellae) in endodermal cells of Arabidopsis thaliana primary root and during lateral root initiation.
Modifications of the endodermal cell walls in roots of wild-type Landsberg erecta (Ler) and mutants with defective endodermal development - scarecrow-3 (scr-3) and shortroot (shr) - of A. thaliana plants were characterized by light, fluorescent, confocal laser scanning, transmission and cryo-scanning electron microscopy.
In wild-type plant roots Casparian bands initiate at approx. 1600 µm from the root cap junction and suberin lamellae first appear on the inner primary cell walls at approx. 7000-8000 µm from the root apex in the region of developing lateral root primordia. When a single cell replaces a pair of endodermal and cortical cells in the scr-3 mutant, Casparian band-like material is deposited ectopically at the junction between this 'cortical' cell and adjacent pericycle cells. Shr mutant roots with an undeveloped endodermis deposit Casparian band-like material in patches in the middle lamellae of cells of the vascular cylinder. Endodermal cells in the vicinity of developing lateral root primordia develop suberin lamellae earlier, and these are thicker, compared wih the neighbouring endodermal cells. Protruding primordia are protected by an endodermal pocket covered by suberin lamellae.
The data suggest that endodermal cell-cell contact is required for the spatial control of Casparian band development. Additionally, the endodermal cells form a collet (collar) of short cells covered by a thick suberin layer at the base of lateral root, which may serve as a barrier constituting a 'safety zone' protecting the vascular cylinder against uncontrolled movement of water, solutes or various pathogens.
植物中的质外体屏障发挥着重要作用，如控制物质的质外体运动和抵御病原体的入侵。本研究旨在描述拟南芥初生根和侧根起始过程中，内皮层细胞质外体屏障（凯氏带和栓质层）的发育。
利用光镜、荧光共聚焦激光扫描显微镜、透射电镜和冷冻扫描电镜观察野生型 Landsberg erecta（Ler）和内皮层发育缺陷突变体 scarecrow-3（scr-3）、shortroot（shr）拟南芥植株根中的内皮层细胞壁的变化。
在野生型植物根中，凯氏带大约在距根冠交界处 1600 µm 处开始形成，栓质层首先在距根尖 7000-8000 µm 的侧根原基发育区的内皮层初生细胞壁上出现。当 scr-3 突变体中的单个细胞取代一对内皮层和皮层细胞时，凯氏带样物质异位沉积在这个“皮层”细胞与相邻中柱鞘细胞的交界处。内皮层未发育的 shr 突变体根在维管束细胞的中层中形成凯氏带样物质的斑片。在侧根原基发育的近邻内皮层细胞中，栓质层更早形成，且比相邻的内皮层细胞更厚。发育中的侧根原基被一个由栓质层覆盖的内皮层口袋保护。
数据表明，内皮层细胞-细胞接触对于凯氏带发育的空间控制是必需的。此外，内皮层细胞在侧根的基部形成一个短细胞的鞘（collar），被一层厚厚的栓质层覆盖，这可能作为一个屏障，构成一个“安全区”，防止维管束不受控制地移动水分、溶质或各种病原体。
