Central Research and Development Department, Experimental Station, E.I. du Pont de Nemours and Company, 19801, Wilmington, DE, USA.
Planta. 1983 Apr;157(5):411-21. doi: 10.1007/BF00397198.
The paraveinal mesophyll (PVM) is a unique and specialized, one-cell-thick tissue spanning the vascular bundles at the level of the phloem in soybean (Glycine max) (L.) Merr.) leaves. Its position within the leaf dictates that all photosynthate produced in the palisade and spongy mesophyll must pass through this specialized layer enroute to the phloem. Symplastic continuity, via plasmodesmata, exists between the PVM and bundle sheath, palisade parenchyma and spongy mesophyll. During leaf ontogeny the PVM is the first tissue to differentiate and at maturity these cells are six to eight times larger than other mesophyll cells, are highly vacuolate, and are interconnected by tubular arms. The PVM undergoes several unique structural and metabolic modifications during leaf development. The PVM cytoplasm, in vegetative plants, is dense, enriched in rough endoplasmic reticulum and dictyosomes, but contains few, small starch-free chloroplasts and few microbodies. Unlike the tonoplast of mesophyll cells, the tonoplast of the PVM is unusually thick and dense-staining. During leaf development the vacuoles of PVM cells accumulate a glycoprotein derived from the dictyosomes which reacts with the protein staining reagents, mercuric bromophenol blue and sulfaflavine, and is degraded by Pronase. Both the vacuolar material and tonoplast are also stained by phosphotungstic acid, which at low pH is relatively selective for glycoprotein. A unique role of the PVM in the transport and compartmentation of nitrogen reserves in soybeans is discussed.
叶肉旁区（PVM）是大豆（Glycine max）（L.）Merr.）叶片中位于韧皮部水平的维管束之间的独特而特化的单层组织。它在叶片中的位置决定了在栅栏组织和海绵组织中产生的所有光合作用产物都必须通过这个特化层才能到达韧皮部。通过胞间连丝，PVM 与束鞘、栅栏薄壁组织和海绵组织之间存在共质体连续性。在叶片发生过程中，PVM 是第一个分化的组织，在成熟时，这些细胞比其他叶肉细胞大 6 到 8 倍，高度液泡化，并通过管状臂相互连接。PVM 在叶片发育过程中经历了几个独特的结构和代谢修饰。在营养植物中，PVM 细胞质密集，富含粗糙内质网和高尔基体，但含有少量小的无淀粉叶绿体和少量微体。与叶肉细胞的液泡膜不同，PVM 的液泡膜异常厚且染色深。在叶片发育过程中，PVM 细胞的液泡积累了一种来源于高尔基体的糖蛋白，该糖蛋白与蛋白染色试剂汞溴酚蓝和磺基荧光素反应，并被蛋白酶降解。液泡物质和液泡膜都被磷钨酸染色，在低 pH 值下，磷钨酸对糖蛋白具有相对选择性。讨论了 PVM 在大豆氮素储备运输和区隔化中的独特作用。
