Department of Plant Sciences, University of California Davis, Davis, CA, 95616, USA.
School of Forestry & Environmental Studies, Yale University, New Haven, CT, 06511, USA.
New Phytol. 2017 Sep;215(4):1609-1622. doi: 10.1111/nph.14687. Epub 2017 Jul 10.
The mesophyll surface area exposed to intercellular air space per leaf area (S ) is closely associated with CO diffusion and photosynthetic rates. S is typically estimated from two-dimensional (2D) leaf sections and corrected for the three-dimensional (3D) geometry of mesophyll cells, leading to potential differences between the estimated and actual cell surface area. Here, we examined how 2D methods used for estimating S compare with 3D values obtained from high-resolution X-ray microcomputed tomography (microCT) for 23 plant species, with broad phylogenetic and anatomical coverage. Relative to 3D, uncorrected 2D S estimates were, on average, 15-30% lower. Two of the four 2D S methods typically fell within 10% of 3D values. For most species, only a few 2D slices were needed to accurately estimate S within 10% of the whole leaf sample median. However, leaves with reticulate vein networks required more sections because of a more heterogeneous vein coverage across slices. These results provide the first comparison of the accuracy of 2D methods in estimating the complex 3D geometry of internal leaf surfaces. Because microCT is not readily available, we provide guidance for using standard light microscopy techniques, as well as recommending standardization of reporting S values.
叶肉单位面积暴露于细胞间隙空气的面积（S）与 CO2 扩散和光合速率密切相关。S 通常通过二维（2D）叶片切片来估算，并针对三维（3D）叶肉细胞的几何形状进行修正，这可能导致估算的细胞表面积与实际表面积之间存在差异。在这里，我们研究了用于估算 S 的 2D 方法与来自高分辨率 X 射线微计算机断层扫描（microCT）的 3D 值之间的差异，涵盖了广泛的系统发育和解剖学范围。与 3D 相比，未经修正的 2D S 估算值平均低 15-30%。通常，4 种 2D S 估算方法中的 2 种方法与 3D 值相差在 10%以内。对于大多数物种，只需要少数几个 2D 切片就能准确地估算出整个叶片样本中位数的 10%以内的 S 值。然而，对于具有网状叶脉网络的叶片，由于切片之间的叶脉覆盖率存在更大的异质性，因此需要更多的切片。这些结果首次比较了 2D 方法在估算复杂的内部叶片表面 3D 几何形状方面的准确性。由于 microCT 不易获得，我们提供了使用标准的光学显微镜技术的指导，并建议对 S 值的报告进行标准化。
