Thompson Matthew V
Department of Cell Biology and Molecular Genetics, H.J. Patterson Hall, University of Maryland, College Park, MD 20742, USA.
Trends Plant Sci. 2006 Jan;11(1):26-32. doi: 10.1016/j.tplants.2005.11.009. Epub 2005 Dec 13.
The structure of phloem sieve-element-companion-cell complexes reflects a duality of function: to conduct photoassimilates throughout the plant, and to exchange solutes between the phloem and surrounding tissues. The conceptual integration of these long- and short-distance functions requires the abandonment of a long-cherished concept in phloem physicochemistry, that source-sink turgor differentials control flow. The manifest inability of decentralized organisms such as plants to control phloem translocation centrally disqualifies such differentials as control variables; besides, the phloem is maximally efficient if the pressure differentials are small. Testing this hypothesis and whether turgor differentials are small will require a significant recommitment to studying the quantitative anatomy of phloem.
韧皮部筛管分子-伴胞复合体的结构反映了功能的双重性：在整个植物体内传导光合产物，并在韧皮部与周围组织之间交换溶质。这些长距离和短距离功能的概念整合需要摒弃韧皮部物理化学中一个长期以来的概念，即源-库膨压差控制物质流动。像植物这样的分散型生物体显然无法集中控制韧皮部的物质运输，这就排除了将这种压差作为控制变量的可能性；此外，如果压力差较小，韧皮部的效率最高。检验这一假设以及膨压差是否较小，将需要重新大力研究韧皮部的定量解剖学。
