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Quantification of the rate of CO 2 formation in the periplasmic space of microalgae during photosynthesis. A comparison of whole‐cell rate constants for CO 2 and HCO 3 – uptake among three species of the green alga Chlorella
Author(s) -
MATSUDA Y.,
WILLIAMS T. G.,
COLMAN B.
Publication year - 1999
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.1999.00399.x
Subject(s) - photosynthesis , reaction rate constant , chemistry , analytical chemistry (journal) , kinetics , environmental chemistry , biochemistry , physics , quantum mechanics
As previously described, the absolute rate of photosynthesis due to a limited concentration of dissolved inorganic carbon at alkaline pH, where the rate of CO 2 formation is strictly limited, plotted as a function of chlorophyll (Chl) concentration, will take the form of a rectangular hyperbola combined with a linear rate directly proportional to [Chl], which are, respectively, due to the contribution of CO 2 and HCO 3 – to photosynthesis. This model represents that the mathematical asymptote of absolute rate of photosynthesis versus cell density is described by the whole‐cell rate constant for HCO 3 – uptake and the maximum rate of CO 2 formation in the extracellular space. This means that any trace modification of the CO 2 formation rate outside the cell will alter the photosynthetic rate and should be detectable experimentally. In air‐grown Chlorella ellipsoidea and C. kessleri and in high CO 2 ‐grown C. saccharophila , the graph of the absolute rate of photosynthesis against [Chl] clearly followed the mathematical model described above and the actual CO 2 formation rates outside the cells were not significantly different from the calculated rates. It also indicated that the whole‐cell rate constants for CO 2 and HCO 3 – uptake in air‐grown C. ellipsoidea and C. saccharophila were similar at ≈ 300 and 2·0 mm 3 μ g –1 Chl min –1 , respectively, whereas those in air‐grown C. kessleri were ≈ 550 and 15 mm 3 μ g –1 Chl min –1 . These results indicate that no acidification of the periplasmic space occurs, and there is no trace activity of external carbonic anhydrase in these microalgae.