The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
Plant Cell Environ. 2013 Feb;36(2):275-87. doi: 10.1111/j.1365-3040.2012.02572.x. Epub 2012 Aug 7.
Boron (B) is known to accumulate in the leaf margins of different plant species, arguably a passive consequence of enhanced transpiration at the ends of the vascular system. However, transpiration rate is not the only factor affecting ion distribution. We examine an alternative hypothesis, suggesting the participation of the leaf bundle sheath in controlling radial water and solute transport from the xylem to the mesophyll in analogy to the root endodermis. In banana, excess B that remains confined to the vascular system is effectively disposed of via dissolution in the guttation fluid; therefore, impairing guttation should aggravate B damage to the leaf margins. Banana plants were subjected to increasing B concentrations. Guttation rates were manipulated by imposing a moderate osmotic stress. Guttation fluid was collected and analysed continuously. The distribution of ions across the lamina was determined. Impairing guttation indeed led to increased B damage to the leaf margins. The kinetics of ion concentration in guttation samples revealed major differences between ion species, corresponding to their distribution in the lamina dry matter. We provide evidence that the distribution pattern of B and other ions across banana leaves depends on active filtration of the transpiration stream and on guttation.
硼（B）被认为会在不同植物物种的叶缘积累，这可以说是增强叶脉系统末端蒸腾作用的被动结果。然而，蒸腾速率并不是影响离子分布的唯一因素。我们提出了另一种假设，即叶鞘可能参与了从木质部到叶肉的径向水分和溶质运输的控制，类似于根内皮层。在香蕉中，过量的 B 被限制在维管束系统中，通过在溢泌液中溶解而有效处理；因此，溢泌作用受损会加重 B 对叶缘的损伤。香蕉植株受到了越来越高的 B 浓度的影响。通过施加适度的渗透胁迫来操纵溢泌速率。连续收集和分析溢泌液。确定了离子在叶片中的分布。溢泌作用确实受损会导致 B 对叶缘的损伤增加。溢泌液样本中离子浓度的动力学揭示了不同离子种类之间的主要差异，这与它们在叶片干物质中的分布相对应。我们提供的证据表明，B 和其他离子在香蕉叶片中的分布模式取决于蒸腾流的主动过滤和溢泌作用。
