Biological solar energy conversion approaches to overcome yield stability and product limitations. Progress report no. 6, 1 October 1977-31 March 1978

A series of experiments were performed in which the authors monitored chlorophyll fluorescence in parallel with the mass spectrometer gas exchange measurements. It was observed that the fluorescence yield is not significantly altered when O2, rather than CO2, was the terminal electron acceptor, and it was concluded that the state of the photosynthetic apparatus is not strongly affected by a changeover from CO2 fixation to O2 reduction, or vice-versa. The study of photosynthetic activities in chloroplasts and particles of corn leaves was continued. Improved rates of photosystem I sheath particles were obtained. The feasibility of measuring the relative contents of system I and system II photocenters in spinach and maize chloroplasts has been examined. Measurements at 430nm with detergent-treated material indicate that the bundle sheath chloroplasts have 70 percent more system I than do spinach chloroplasts. To measure system II content, two methods have been used. In one, the flash-induced trans-membrane electrical field is used as a probe. Another method measures 'C-550' to indicate Q, the primary acceptor of system II. The second method appears more reliable than the first and indicates that bundle sheath chloroplasts contain 40% less system II than spinach chloroplasts.