来自以色列的科学家，最近发表了题为“Leaf hydraulic maze; Differential effect of ABA on vascular bundle-sheath, palisade, and spongy mesophyll controlling hydraulic conductance”的文章。

摘要

叶片水力传导（K叶）促进了水分的蒸腾作用，使CO2上升得以持续，同时保持水分状态。然而，径向水流出木质部及其在良好和胁迫条件下的调节仍然不清楚。我们假设束鞘细胞和叶肉细胞在水从木质部径向流出以及在最佳和胁迫条件下对水流的调节中起关键作用。我们生成了转基因拟南芥植物，它们仅在其束鞘（Babi）或叶肉（MCabi）中对脱落酸（ABA）不敏感。在最佳条件下，BSabi植物表现出更大的K叶和蒸腾作用，气孔开度、指数和脉密度与野生型相似。与野生型相比，MCabi表现出更高的K叶和蒸腾作用，以及更大的气孔孔径、更高的气孔指数和更大的维管直径和生物量。为了响应木质部供给的ABA，两个转基因系都表现出K叶和蒸腾作用的减少，而其叶水势保持不变。ABA降低了野生型海绵叶肉的渗透透水性（Pf）；而栅栏叶肉的下部（Pf）不受ABA的影响。基因修饰的ABA不敏感海绵叶肉细胞具有低（Pf）；而ABA不敏感的束鞘细胞具有较高的（Pf）。ABA增加了共质体水通道上的流量，但其对K叶的贡献可忽略不计。高水平的ABA似乎可以调节束鞘和海绵状叶肉细胞的（Pf），以控制Kleaf。在最佳条件下，ABA通过束鞘和叶肉细胞的生理、形态和发育变化来限制蒸腾作用和K叶。在最佳和干旱条件下，束鞘-海绵状叶肉途径控制K叶和叶片水分平衡。

Leaf hydraulic maze; Differential effect of ABA on vascular bundle-sheath, palisade, and spongy mesophyll controlling hydraulic conductance 

Abstract 

Leaf hydraulic conductance (K leaf ) facilitates water for transpiration, enabling the continuation of CO 2 upsurge while maintaining water status. Nevertheless, radial water flow out–of–the–xylem and its regulation under well and stress conditions remain vague. We hypothesized that bundle–sheath and mesophyll cells play key roles in the radial flow of water out of the xylem and the regulation of that flow under optimal and stress conditions. We generated transgenic Arabidopsis plants that were insensitive to abscisic acid (ABA) exclusively in their bundle sheath (BSabi) or mesophyll (MCabi). BSabi plants showed greater K leaf and transpiration under optimal conditions, with stomatal apertures and index and vein density like those of the wild type. MCabi exhibited even higher K leaf and transpiration, as well as larger stomatal apertures, a higher stomatal index and greater vascular diameter and biomass, relative to the wild type. In response to xylem–fed ABA, both transgenic lines exhibited reduced K leaf and transpiration, while their leaf water potentials remained unchanged. The greater osmotic water permeability ( P f ) of the wild types' spongy mesophyll was reduced by ABA; whereas the lower ( P f ) of the palisade mesophyll was not affected by ABA. Genetically modified, ABA–insensitive spongy mesophyll cells had a low ( P f ) ; whereas ABA–insensitive bundle–sheath cells had a higher ( P f ) . The flow over the symplastic water pathway was increased by ABA, but its contribution to K leaf was negligible. High levels of ABA appear to regulate the ( P f ) of bundle–sheath and spongy mesophyll cells, to control Kleaf. Under optimal conditions, ABA limits transpiration and K leaf via physiological, morphological, and developmental modifications of bundle–sheath and mesophyll cells. The bundle sheath–spongy mesophyll pathway controls K leaf and leaf water balance under both optimal and drought conditions.