Structural organization of the spongy mesophyll.

Abstract

Many plant leaves have two layers of photosynthetic tissue: the palisade and spongy mesophyll. Whereas palisade mesophyll consists of tightly packed columnar cells, the structure of spongy mesophyll is not well characterized and often treated as a random assemblage of irregularly shaped cells. Using micro-computed tomography imaging, topological analysis, and a comparative physiological framework, we examined the structure of the spongy mesophyll in 40 species from 30 genera with laminar leaves and reticulate venation. A spectrum of spongy mesophyll diversity encompassed two dominant phenotypes: first, an ordered, honeycomblike tissue structure that emerged from the spatial coordination of multilobed cells, conforming to the physical principles of Euler's law; and second, a less-ordered, isotropic network of cells. Phenotypic variation was associated with transitions in cell size, cell packing density, mesophyll surface-area-to-volume ratio, vein density, and maximum photosynthetic rate. These results show that simple principles may govern the organization and scaling of the spongy mesophyll in many plants and demonstrate the presence of structural patterns associated with leaf function. This improved understanding of mesophyll anatomy provides new opportunities for spatially explicit analyses of leaf development, physiology, and biomechanics.

Plant phenotyping relevance

マイクロCT画像とトポロジー解析を用いて葉肉組織の構造・細胞形態・密度などの植物形質を定量化しており、画像取得・解析が比較研究の中心的手法である。

Code and data availability

The article describes microCT imaging of 40 species and trait analyses, but no public deposit of the microCT image data, trait tables, or analysis code is stated. All URLs in the text are either the license, or generic software/citation links (brranching, nlme, R project) unrelated to this paper's phenotyping data or a

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