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 photosynthe tic systems in anaerobic atmospheres under flow conditions. Time-depen dent photosynthetic quotients (PSQ) have been obtained. A detailed des cription of the instrument, including how it was constructed, calibrat ed and used for photosynthesis measurements, is presented. An importan t factor in the measurements was a clear understanding of the response time of the instrument. As with any flow system, flow rate, forward v oid 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 us ing an in-line electrolysis cell driven by a programmable constant cur rent source. Carbon dioxide assimilation was mimicked with the use of a programmable electronic gas blending system. Simultaneous step funct ions of these two key photosynthetic parameters fully characterized th e response time and sensitivity of the instrument. In this report, tim e-dependent PSQ for spinach leaf disks and the microalga Scenedesmus D -3 are reported. It is explicitly demonstrated that the transient appr oach to steady state is different for the two systems. Whereas the tim e-dependent PSQ for spinach depended on illumination history and reach ed a steady-state value less than 1, this was not the case for Scenede smus.