Carbon Isotope Ratios of Epidermal and Mesophyll Tissues from Leaves of C3 and CAM Plants

The δ13C values for epidermal and mesophyll tissues of two C3 plants, Commelina communis and Tulipa gesneriana, and a CAM plant, Kalanchoē daigremontiana, were measured. The values for the tissues of both C3 plants were similar. In young leaves of Kalanchoē, the epidermis and the mesophyll showed S13C values which were nearly identical, and similar to those found in C3 plants. However, markedly more negative values for epidermal compared to mesophyll tissue, were obtained in the mature Kalanchoē leaf. This is consistent with the facts that the epidermis in a CAM leaf is formed when leaves engage in C3 photosynthesis and that subsequent dark CO2 fixation in guard cells or mesophyll cells makes only a small contribution to total epidermal carbon.