Shapira Or, Khadka Sudha, Israeli Yair, Shani Uri, Schwartz Amnon
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel.
Plant Cell Environ. 2009 May;32(5):476-85. doi: 10.1111/j.1365-3040.2009.01941.x. Epub 2009 Jan 14.
Typical salt stress symptoms appear in banana (Musa sp., cv. 'Grand Nain' AAA) only along the leaf margins. Mineral analysis of the dry matter of plants treated with increasing concentrations of KCl or NaCl revealed significant accumulation of Na+, but not of K+ or Cl(-), in the affected leaf margins. The differential distribution of the three ions suggests that water and ion movement out of the xylem is mostly symplastic and, in contrast to K+ and Cl(-), there exists considerable resistance to the flow of Na+ from the xylem to the adjacent mesophyll and epidermis. The parallel veins of the lamina are enclosed by several layers of bundle sheath parenchyma; in contrast, the large vascular bundle that encircles the entire lamina, and into which the parallel veins merge, lacks a complete bundle sheath. Xylem sap containing a high concentration of Na+ is 'pulled' by water tension from the marginal vein back into the adjacent mesophyll without having to cross a layer of parenchyma tissue. When the marginal vein was dissected from the lamina, the pattern of Na+ distribution in the margins changed markedly. The distinct anatomy of the marginal vein plays a major role in the accumulation of Na+ in the margins, with the latter serving as a 'dumping site' for toxic molecules.
典型的盐胁迫症状仅在香蕉（Musa sp.，品种‘大矮蕉’AAA）的叶缘出现。对用浓度递增的氯化钾或氯化钠处理的植株干物质进行矿物质分析发现，在受影响的叶缘中，钠离子显著积累，而钾离子或氯离子则没有。这三种离子的差异分布表明，水和离子从木质部流出主要是共质体途径，与钾离子和氯离子不同，钠离子从木质部流向相邻叶肉和表皮存在相当大的阻力。叶片的平行叶脉被几层维管束鞘薄壁细胞包围；相反，环绕整个叶片且平行叶脉汇入其中的大维管束没有完整的维管束鞘。含有高浓度钠离子的木质部汁液在水的张力作用下从边缘叶脉‘拉’回到相邻叶肉，而无需穿过一层薄壁组织。当从叶片上分离出边缘叶脉时，边缘部分的钠离子分布模式发生了显著变化。边缘叶脉独特的解剖结构在边缘钠离子积累中起主要作用，边缘部分充当有毒分子的‘倾倒场所’。
