Cell wall thickness spectrum of photosynthetic cells in herbaceous C, C, and crassulacean acid metabolism plants.

Higher plants are divided into three major photosynthetic groups known as C, C, and crassulacean acid metabolism (CAM) plants. It is considered that cell wall thickness (T) affects diffusion and leakiness of CO within leaves, but it is unclear whether T of photosynthetic cells differs among these groups. This study investigated T of photosynthetic cells in herbaceous C, C, and CAM species under an electron microscope. Among 75 species of monocots and eudicots grown in a growth chamber in the same environment, the T of mesophyll cells (MCs) was much higher in CAM species than in C and C species. However, when T was compared between C and C species of grasses and eudicots, T of MCs tended to be lower in C species than in C species; the opposite trend was observed for T of bundle sheath cells (BSCs). T of MCs and BSCs almost did not differ among the C decarboxylation types (NADP-ME, NAD-ME, and PCK). In plants grown outdoors (51 species), similar trends of T were also found among photosynthetic groups, but their T was generally higher than that of growth-chamber plants. This study provides the T spectrum of photosynthetic cells in herbaceous C, C, and CAM species. The results obtained would be valuable for our understanding of the diffusion and leakage of CO in the leaves of different photosynthetic groups.