Department of Renewable Resources, University of Alberta, Edmonton, AB, Canada.
Am J Bot. 2012 Jul;99(7):1249-54. doi: 10.3732/ajb.1200088. Epub 2012 Jul 4.
Aquaporins (AQPs) are channel proteins, and their function is mostly associated with transmembrane water transport. While aquaporin genes are known to be expressed in woody poplar stems, little is known about AQP expression at the cellular level. Localization of AQP expression to particular cell and tissue types is a necessary prerequisite in understanding the biological role of these genes.
Subsets of plants were subjected to 6 wk of high nitrogen fertilization (high N plants) or to a controlled drought. Experimental treatments affected cambial activity and wood anatomy. RNA in situ hybridization was used to characterize spatial expression of three AQP genes in stem cross sections.
The strongest labeling consistently occurred in the cambial region and in adjacent xylem and phloem cells. Expression was also detected in rays. Contact cells exhibited high expression, while expression in other ray cells was more variable. High N plants exhibited a broader band of expression in the cambial region than plants receiving only adequate N fertilization (control plants) and plants subjected to drought.
Water channels in stems were expressed in a manner that allows hydraulic coupling between xylem and other tissues that may serve as water reservoirs, including phloem and pith parenchyma. Expression of AQPs in rays may increase radial flow of water from xylem and phloem to the cambial region where AQPs may help sustain rapid cell division and expansion of developing vessel elements.
水通道蛋白（AQP）是通道蛋白，其功能主要与跨膜水运输有关。虽然木本杨树茎中已知表达水通道蛋白基因，但对细胞水平上水通道蛋白的表达知之甚少。在了解这些基因的生物学功能之前，必须首先确定 AQP 表达在特定的细胞和组织类型中的位置。
将植物的亚组进行 6 周的高氮施肥（高氮植物）或受控干旱处理。实验处理会影响形成层的活性和木材解剖结构。使用 RNA 原位杂交技术来描述三个 AQP 基因在茎横切面上的空间表达。
最强的标记始终出现在形成层区域以及相邻的木质部和韧皮部细胞中。在射线中也检测到了表达。接触细胞表现出高表达，而其他射线细胞中的表达则更加多变。高氮植物在形成层区域的表达带比仅接受足够氮施肥的植物（对照植物）和受干旱处理的植物更宽。
茎中的水通道以允许木质部和其他可能作为水库的组织（包括韧皮部和髓部薄壁组织）之间水力偶联的方式表达。AQP 在射线中的表达可能会增加木质部和韧皮部到形成层区域的径向水流，AQP 可能有助于维持快速的细胞分裂和发育中的导管分子的扩展。
