The influence of inorganic phosphate on photosynthesis in intact chloroplasts fromMesembryanthemum crystallinumL. plants exhibiting C3photosynthesis or crassulacean acid metabolism
✍ Scribed by Russell K. Monson; Mary E. Rumpho; Gerald E. Edwards
- Publisher
- Springer-Verlag
- Year
- 1983
- Tongue
- English
- Weight
- 850 KB
- Volume
- 159
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
Intact chloroplasts were obtained from mesophyll protoplasts isolated from Mesembryanthemum crystallinum in the C 3 or Crassulacean acid metabolism (CAM) photosynthetic mode, and examined for the influence of inorganic phosphate (Pi) on aspects of bicarbonate-dependent 0 2 evolution and CO 2 fixation. While the chloroplasts from both modes responded similarly to varying Pi, some features appear typical of chloroplasts from species capable of CAM, including a relatively high capacity for photosynthesis in the absence of Pi, a short induction period, and resistance to inhibition of photosynthesis by high levels of Pi. In the absence of Pi the chloroplasts retained 75-85% of the 14CO2 fixed and the total export of dihydroxyacetone phosphate was low compared with the rate of photosynthesis. In CAM plants the ability to conduct photosynthesis and retain most of the fixed carbon in the chloroplasts at low external Pi concentrations may enable storage of carbohydrates which are essential for providing a carbon source for the nocturnal synthesis of malic acid. At high external Pi concentrations (e.g. 10 25 mM), the amount of total dihydroxyacetone phosphate exported to the assay medium relative to the rate of photosynthesis was high while the products of 14CO2 fixation were largely retained in the chloroplasts which indicates starch degradation is occurring at high Pi levels. Starch degradation normally occurs in CAM plants in the dark; high levels of Pi may induce starch degradation