SIMULTANEOUS MEASUREMENT OF PHOTOSYNTHETIC OXYGEN EVOLUTION AND CARBON-DIOXIDE ASSIMILATION UNDER ANAEROBIOSIS

Instrumentation has been developed for measuring absolute simultaneous assimilation of carbon dioxide and evolution of oxygen by photosynthetic systems in anaerobic atmospheres under flow conditions. Time-dependent photosynthetic quotients (PSQ) have been obtained. A detailed description of the instrument, including how it was constructed, calibrated and used for photosynthesis measurements, is presented. An important factor in the measurements was a clear understanding of the response time of the instrument. As with any flow system, flow rate, forward void volume and relative position of the O-2 and CO2 sensors in the gas train were crucial to performance. Response time was measured by step-function calibrations mimicking PSQ of unity. Oxygen was generated using an in-line electrolysis cell driven by a programmable constant current source. Carbon dioxide assimilation was mimicked with the use of a programmable electronic gas blending system. Simultaneous step functions of these two key photosynthetic parameters fully characterized the response time and sensitivity of the instrument. In this report, time-dependent PSQ for spinach leaf disks and the microalga Scenedesmus D-3 are reported. It is explicitly demonstrated that the transient approach to steady state is different for the two systems. Whereas the time-dependent PSQ for spinach depended on illumination history and reached a steady-state value less than 1, this was not the case for Scenedesmus.