Plant Physiol. Drug Metab Dispos
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Plant Physiology 65:1044-1048 (1980)
© 1980 American Society of Plant Biologists

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Articles

Photosynthesis in Isolated Chloroplasts of the Crassulacean Acid Metabolism Plant Sedum praealtum1

Martin H. Spalding2 and Gerald E. Edwards

Horticulture Department, University of Wisconsin Madison, Wisconsin 53706

Intact chloroplasts were isolated from protoplasts of the Crassulacean acid metabolism plant Sedum praealtum D.C. Typical rates of CO2 fixation or CO2-dependent O2 evolution ranged from 20 to 30 micromoles per milligram chlorophyll per hour and could be stimulated 30 to 50% by several Calvin cycle intermediates. The pH optimum for CO2 fixation was 7.0 to 7.6 with considerable activity as low as pH 6.4. Low concentrations of orthophosphate (Pi) (optimum 0.4 millimolar) stimulated photosynthesis while high concentrations (5 millimolar) caused some inhibition. Both CO2 fixation and CO2-dependent O2 evolution exhibited a relatively long lag phase (4 to 6 minutes) which remained constant between 0.4 to 5 millimolar Pi. The lag phase could be decreased by addition of dihydroxyacetone-phosphate or ribose 5-phosphate. Further results are presented which suggest these chloroplasts have a functional phosphate translocator.

A long lag period at optimum Pi concentration, no effect of high Pi levels on the lag phase, lack of severe inhibition of photosynthesis by high Pi concentrations, and the relatively low pH optimum for photosynthesis are characteristics unlike those previously reported with chloroplasts of C3 plants.

2 Current address: Department of Agronomy, University of Illinois, Urbana, Illinois 61801.

1 This work was supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and National Science Foundation Grant PCM 77-09384 to G. E. E.






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Copyright © 1980 by the American Society of Plant Biologists