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Plant Physiology 72:488-491 (1983) © 1983 American Society of Plant Biologists Photosynthetic Properties of Chloroplasts from Chlamydomonas reinhardii1Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts 02254
Chloroplasts isolated from synchronous cultures of the unicellular green alga Chlamydomonas reinhardii, SAG 11-32/b (), fix CO2 at rates between 25 and 50 micromoles per milligram chlorophyll per hour. The upper value is approximately half of the rate of the intact cell. During storage in the dark on ice, the chloroplast preparation loses 30 to 50% of its CO2 fixing capability per hour. Under reducing conditions (+ 1 millimolar dithiothreitol), this loss of activity is about twice as fast. The same reducing conditions stimulate CO2 fixation in the light. High concentrations of inorganic phosphate (>2 millimolar) inhibit CO2 fixation. This inhibition is overcome by the addition of glycerate 3-phosphate. It is concluded that chloroplasts from C. reinhardii possess a higher plant type phosphate translocator. With respect to dependency upon light intensity, pH and Mg2+ concentration, the results were similar to that reported for chloroplasts from higher plants. However, in contrast to higher plant chloroplasts, maximum CO2 fixation is observed at the relatively low osmotic concentration of 0.12 molar mannitol in the reaction buffer.
2 Supported by a fellowship from the Deutsche Forschungsgemeinschaft. Present address: Botanisches Institut der Universität, Kirschallee 1, 5300 Bonn 1, Federal Republic of Germany. 3 Supported by a grant from the Ministry of Education, People's Republic of China. Permanent address: Department of Biology, Hunan Teachers College Changsha, People's Republic of China. 1 Supported by Department of Energy DE-AC02-76-ER03231 and National Science Foundation PCM 79-22612.
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