Jansen Steven, Choat Brendan, Pletsers Annelies
Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, TW9 3DS, Surrey, UK.
Am J Bot. 2009 Feb;96(2):409-19. doi: 10.3732/ajb.0800248.
Pit membranes between xylem vessels have been suggested to have functional adaptive traits because of their influence on hydraulic resistance and vulnerability to embolism in plants. Observations of intervessel pit membranes in 26 hardwood species using electron microscopy showed significant variation in their structure, with a more than 25-fold difference in thickness (70-1892 nm) and observed maximum pore diameter (10-225 nm). In some SEM images, pit membrane porosity was affected by sample preparation, although pores were resolvable in intact pit membranes of many species. A significant relationship (r(2) = 0.7, P = 0.002) was found between pit membrane thickness and maximum pore diameter, indicating that the thinner membranes are usually more porous. In a subset of nine species, maximum pore diameter determined from SEM was correlated with pore diameter calculated from air-seeding thresholds (r(2) = 0.8, P < 0.001). Our data suggest that SEM images of intact pit membranes underestimate the porosity of pit membranes in situ. Pit membrane porosity based on SEM offers a relative estimate of air-seeding thresholds, but absolute pore diameters must be treated with caution. The implications of variation in pit membrane thickness and porosity to plant function are discussed.
由于木质部导管之间的纹孔膜对植物水力阻力和栓塞脆弱性有影响，因此有人认为其具有功能适应性特征。利用电子显微镜对26种阔叶树种的导管间纹孔膜进行观察，结果表明其结构存在显著差异，厚度（70 - 1892纳米）相差超过25倍，观察到的最大孔径（10 - 225纳米）也有差异。在一些扫描电子显微镜图像中，纹孔膜孔隙率受样品制备的影响，不过在许多物种的完整纹孔膜中孔隙是可分辨的。发现纹孔膜厚度与最大孔径之间存在显著关系（r² = 0.7，P = 0.002），这表明较薄的膜通常孔隙率更高。在九个物种的子集中，由扫描电子显微镜确定的最大孔径与根据气穴阈值计算出的孔径相关（r² = 0.8，P < 0.001）。我们的数据表明，完整纹孔膜的扫描电子显微镜图像低估了原位纹孔膜的孔隙率。基于扫描电子显微镜的纹孔膜孔隙率提供了气穴阈值的相对估计，但绝对孔径必须谨慎对待。文中讨论了纹孔膜厚度和孔隙率变化对植物功能的影响。
