CO₂ concentration and vertical profile of photosynthetic activity in a CAM leaf

Abstract

In CAM plants, intercellular CO₂ concentration (C_i) increases during daytime. This is due to CO₂ released by malate decarboxylation. In leaves of Kalanchoe daigremontiana, the rates of CO₂ uptake and malate accumulation differ between the adaxial and abaxial parts (Winter, 1987, 1989). Then, C_i would differ considerably within leaf. We measured C_i for each surface and the photosynthetic products in successive three horizontal layers cut from leaf discs. In daytime, C_i was greater in the side that showed a greater CO₂ uptake rate at night. Moreover, in some occasions, the two surfaces showed uptake and efflux of CO₂. Therefore, C_i was not constant inside the leaf, implying a large CO₂ resistance to diffusion. We are now examining localization of Rubisco, PEPCase and chlorophyll to understand vertical heterogeneity in CAM photosynthesis.