Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA.
Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA.
Plant Physiol. 2024 Mar 29;194(4):2288-2300. doi: 10.1093/plphys/kiad679.
The water status of the living tissue in leaves between the xylem and stomata (outside xylem zone (OXZ) plays a critical role in plant function and global mass and energy balance but has remained largely inaccessible. We resolve the local water relations of OXZ tissue using a nanogel reporter of water potential (ψ), AquaDust, that enables an in situ, nondestructive measurement of both ψ of xylem and highly localized ψ at the terminus of transpiration in the OXZ. Working in maize (Zea mays L.), these localized measurements reveal gradients in the OXZ that are several folds larger than those based on conventional methods and values of ψ in the mesophyll apoplast well below the macroscopic turgor loss potential. We find a strong loss of hydraulic conductance in both the bundle sheath and the mesophyll with decreasing xylem potential but not with evaporative demand. Our measurements suggest the OXZ plays an active role in regulating the transpiration path, and our methods provide the means to study this phenomenon.
叶片中木质部和气孔之间的活组织的水分状态（外侧木质部区域 (OXZ)）对植物功能和全球质量和能量平衡起着至关重要的作用，但基本上仍无法触及。我们使用水势 (ψ) 的纳米凝胶报告器 AquaDust 来解决 OXZ 组织的局部水分关系，该报告器可原位、非破坏性地测量木质部的 ψ 和 OXZ 中蒸腾末端的高度本地化的 ψ。在玉米 (Zea mays L.) 中进行的这项工作中，这些局部测量揭示了 OXZ 中的梯度比基于传统方法的梯度大几个数量级，并且在宏观膨压损失潜力以下，质外体中的 ψ 值也远低于宏观膨压损失潜力。我们发现，随着木质部势的降低，在束鞘和叶肉中水力传导率都有很强的损失，但与蒸发需求无关。我们的测量表明 OXZ 在调节蒸腾路径方面发挥着积极作用，我们的方法为研究这一现象提供了手段。
