ISSN:
1432-2048
Keywords:
Chlamydomonas
;
Inorganic-carbonconcentrating mechanism
;
Mehler reaction
;
Oxygen photoreduction
;
Pseudocyclic photophosphorylation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Mass-spectrometric measurements of 16O2 and 18O2 were made to compare the rates of light-dependent O2 evolution and uptake by Chlamydomonas reinhardtii Dang. grown in air (0.035% CO2; low-Ci cells) or CO2-enriched air (5% CO2; high-Ci cells) at pH 5.5 and 8.0. While at pH 5.5, no differences were observed in the isotopic O2-gas exchange of high- and low-Ci cells, at pH 8.0 the rates of true O2 evolution and uptake were considerably higher in low-Ci than in high-Ci cells. The enhanced rates of O2 uptake and evolution by low-Ci cells were completely inducible within 6 h after transferring high-Ci cells to ambient air. At pH 8.0, O2 uptake in the light was inhibited by 2 μM 3-(3,4-dichlorophenyl)-1,1 dimethylurea in both types of alga, but this effect was more pronounced in low-Ci than in high-Ci cells. When the cells were grown at pH 5.5 the activities of the superoxide-radical-degrading enzymes, superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase, were similar regardless of the CO2 concentration provided during growth. At pH 8.0, however, the activities of these enzymes were 4 to 20 times higher in low-Ci than in high-Ci cells. When high-Ci cells were allowed to acclimate to ambient air for 6 h at pH 8.0, the activities of superoxide dismutase, ascorbate peroxidase and monodehydroascorbate dehydrogenase increased to more than 50% of the level observed with low-Ci cells. These results are consistent with an enhanced operation of O2 photoreduction which could provide energy to the inorganic-carbon-concentrating mechanism via pseudo-cyclic photophosphorylation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00195082
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