Abstract
Numerous methods have been employed to ascertain whether Ascophyllum nodosum exhibits the characteristics of photorespiration. Different oxygen concentrations appear to have little effect on the apparent rate of photosynthesis, the alga displays low CO2 compensation points in air and water, postillumination CO2 bursts (and O2 ‘gulps’) were not observed in either environment, and 14CO2 evolution into a CO2-free atmosphere was inhibited in the light compared with that observed in the dark. Suggestions that photosynthetic quotients can be used as an indicator of the photorespiratory state were found to be unsuitable as determinations of the total inorganic carbon concentration from pH measurements were found to be inconsistent which resulted in variable apparent photosynthetic quotient values. Thus photorespiration is suppressed in Ascophyllum nodosum and it is suggested that the mechanism is based on an inorganic carbon transport pump.
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