Department of Plant Biology, Institute of Biology, University of Campinas, 13083-970 Campinas, Sao Paulo, Brazil.
Ulm University, Institute of Systematic Botany and Ecology, 89081 Ulm, Germany.
Plant Physiol. 2018 Aug;177(4):1629-1638. doi: 10.1104/pp.18.00138. Epub 2018 Jun 5.
In the xylem of angiosperm plants, microscopic pits through the secondary cell walls connect the water-conducting vessels. Cellulosic meshes originated from primary walls, and middle lamella between adjacent vessels, called the pit membrane, separates one conduit from another. The intricate structure of the nano-sized pores in pit membranes enables the passage of water under negative pressure without hydraulic failure due to obstruction by gas bubbles (i.e. embolism) under normal conditions or mild drought stress. Since the chemical composition of pit membranes affects embolism formation and bubble behavior, we directly measured pit membrane composition in wood. Here, we characterized the chemical composition of cell wall structures by synchrotron infrared nanospectroscopy and atomic force microscopy-infrared nanospectroscopy with high spatial resolution. Characteristic peaks of cellulose, phenolic compounds, and proteins were found in the intervessel pit membranes of wood. In addition, the vessel to parenchyma pit membranes and developing cell walls of the vascular cambium showed clear signals of cellulose, proteins, and pectin. We did not find a distinct peak of lignin and other compounds in these structures. Our investigation of the complex chemical composition of intervessel pit membranes furthers our understanding of the flow of water and bubbles between neighboring conduits. The advances presented here pave the way for further label-free studies related to the nanochemistry of plant cell components.
在被子植物的木质部中，通过次生细胞壁的微观凹陷将输水容器连接起来。纤维素网格起源于初生壁，而相邻导管之间的中层称为凹陷膜，将一个导管与另一个导管隔开。凹陷膜纳米级孔隙的复杂结构使得在负压下可以通过水而不会因正常条件下或轻度干旱胁迫下气泡（即栓塞）阻塞而导致水力失效。由于凹陷膜的化学成分会影响栓塞形成和气泡行为，因此我们直接测量了木材中的凹陷膜成分。在这里，我们通过同步加速器红外纳米光谱和原子力显微镜-红外纳米光谱以高空间分辨率对细胞壁结构的化学成分进行了表征。在木材的导管间凹陷膜中发现了纤维素、酚类化合物和蛋白质的特征峰。此外，导管到木质部薄壁组织的凹陷膜和维管形成层的发育细胞壁显示出纤维素、蛋白质和果胶的清晰信号。在这些结构中，我们没有发现木质素和其他化合物的明显峰。我们对导管间凹陷膜复杂化学成分的研究增进了我们对相邻导管之间水流和气泡流动的理解。这里提出的进展为与植物细胞成分纳米化学相关的进一步无标记研究铺平了道路。
