LAUSR

BACKGROUND AND AIMS The surface area of mesophyll cells (Smes) and chloroplasts (Sc) facing the intercellular airspace (IAS) are important parameters for estimating photosynthetic activity from leaf anatomy. Although the Smes and Sc are estimated based on the shape assumption of mesophyll cells (MC), it is questionable if the assumption is correct for rice MC with concave-convex surfaces. Therefore, in this study, we establish the reconstruction method for the 3D representation of the IAS in rice leaf tissue to calculate the actual Smes and Sc with 3D images and to determine the correct shape assumption for the estimation of Smes and Sc based on 2D section images. METHODS Here, we used serial section light microscopy (ssLM) to reconstruct the 3D representations of the IAS, MC, and chloroplasts in rice leaf tissue. Actual Smes and Sc values obtained from the 3D representation were compared with those estimated from the 2D images to find out the correct shape-specific assumption (oblate or prolate spheroid) on different orientations (longitudinal and transversal sections) using the same leaf sample. KEY RESULTS The 3D representation method revealed that volumes of the IAS and MC accounted for 30% and 70% of rice leaf tissue excluding epidermis, respectively, and volume of chloroplasts accounted for 44% of MC. The shape-specific assumption on the sectioning orientation affected the estimation of Smes and Sc using 2D section images with discrepancies of 10‒38%. CONCLUSIONS The 3D representation of rice leaf tissue was successfully reconstructed using ssLM and suggested that estimation of Smes and Sc of the rice leaf is more accurate using longitudinal sections with MC assumed as oblate spheroid than transversal sections with MC as prolate spheroid.