Three-dimensional analysis of Kranz anatomy in finger millet ( Eleusine coracana ), an NAD-ME-type C 4 crop

Kranz anatomy in C4 leaves is characterized by the arrangement of mesophyll cells (MC) and bundle sheath cells (BSC) around the vascular bundle. Although this organization has been described in 2D cross-sections, 3D analysis provides quantitative information on cell geometry and organization at the whole-cell level. In this study, we reconstructed the 3D representations of MC and BSC in mature leaves of finger millet (Eleusine coracana (L.) Gaertn.), which is an NAD-ME-type crop, using serial-section light microscopy. These reconstructions showed clear structural differentiation between the two cell types. MC exhibited a highly lobed structure with expanded surface area, whereas BSC formed a less convexo-concave sheath tightly surrounding the vascular bundle and showed chloroplasts localized toward the vascular bundle in a centripetal arrangement. Quantitative analysis revealed differences between MC and BSC in cell volume, surface area, shape, and chloroplast volume per cell. Positional analysis along the adaxial-abaxial axis revealed variation in both cell types. Specifically, abaxial BSC showed greater starch accumulation and a slightly higher chloroplast volume fraction than adaxial BSC. These results provide a comprehensive 3D structural description of Kranz anatomy in finger millet leaves, offering new insights into the spatial organization of photosynthesis.