Separating the contribution of the upper and lower mesophyll to photosynthesis in Zea mays L. leaves.

摘要: The appearance of transverse sections maize leaves indicates the existence two airspace systems serving mesophyll, one connected to stomata upper epidermis and other lower surface, with few or no connections between two. This study tests hypothesis that air-space mesophyll are separated by a defined barrier measurable conductance. A mathematical procedure, based on this hypothesis, is developed for quantitative separation contributions made halves carbon assimilation using gasexchange data. Serial paradermal three-dimensional scanning-electron-microscope images confirmed there were air-systems. Simultaneous measurements nitrous-oxide diffusion across leaf transpiration from surfaces showed internal conductance was about 15% maximum observed stomatal demonstrates poor connections, indicated microscopy, represent substantial gas diffusion. By measuring CO2 water-vapour fluxes each surface independently, intercellular concentration (ci) system determined flux them calculated. allowed correction apparent uptake at derive true cells leaf. approach used analyse contribution as whole in response varying light levels incident surface. light-saturated photon approx. 1000 μmol·m-2·s-1 (i.e. one-half full sunlight). not fully saturated nearly double sunlight. At low ci significantly less than generating significant upward CO2. equivalent sunlight, above, did differ air space systems. physiological importance exchange discussed.