External and Internal CO2 Transport in Lemanea: Interactions with the Kinetics of Ribulose Bisphosphate Carboxylase |
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Authors: | MACFARLANE, J. J. RAVEN, J. A. |
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Abstract: | The rate of photosynthesis by the freshwater alga Lemanea mamillosais proportional to CO2 concentration, virtually to the pointof saturation, and inversely proportional to the radius of thethallus. By contrast, the CO2 response curve of very thin slicesof the thallus is a rectangular hyperbola with a (lower) halfsaturation concentration of 10 mmol m3. For the intactplant, the kinetics of CO2 fixation are strongly masked by internalCO2 transport limitations, although the maximum rate of photosynthesisis probably determined by the rate of supply of ribulose bisphosphate(RuBP). The flow of water over the alga becomes turbulent atwater velocities greater than about 90 mm s1 and thethallus stretches significantly at higher water velocities.In its natural habitat, therefore, the external unstirred layerwill be thin (< 10 µm) and the thallus will be stretched,leading to rapid external and increased internal rates of CO2transport from the bulk solution. The estimated maximum rateof CO2 transport is commensurate with the maximum rate of photosynthesis(i.e. the rate of supply of RuBP). Key words: Transport limitations, Kinetics of CO2 fixation |
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