title: The carboxylase activity of Rubisco and the photosynthetic performance in aquatic plants.
abstract: Activated carboxylase activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), as well as photosynthetic rates were measured for 42 species of freshwater and marine macrophytes. While the carboxylase activity varied greatly among the species investigated (0.2-12.5 μmol CO2mg-1chlorophyll min-1), the submersed freshwater plants showed significantly lower activities than emergent, floating leaved or secondary submersed forms. The variability in photosynthetic rates correlated with the carboxylase activity only for the marine macroalgae, and their photosynthesis to carboxylase activity ratios were close to 1. These plants also had a consistently high inorganic carbon transport capability, and it is suggested that ribulose-1,5-bisphosphate carboxylase/oxygenase activity is an important internal factor regulating the photosynthetic capacity within this plant group where, apparently, the internal CO2concentration is high and photorespiration is suppressed. Among the freshwater forms, it appears that their much lower inorganic carbon transport ability, rather than their carboxylase activity, limits the photosynthetic process.
authors.affiliation: Botanical Institute, University of Aarhus, 68 Nordlandsvej, DK-8240, Risskov, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Beer
authors.affiliation: Botanical Institute, University of Aarhus, 68 Nordlandsvej, DK-8240, Risskov, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Sand-Jensen
authors.affiliation: Botanical Institute, University of Aarhus, 68 Nordlandsvej, DK-8240, Risskov, Denmark.
authors.forename: T Vindbaek
authors.initials: TV
authors.lastname: Madsen
authors.affiliation: Botanical Institute, University of Aarhus, 68 Nordlandsvej, DK-8240, Risskov, Denmark.
authors.forename: S L
authors.initials: SL
authors.lastname: Nielsen
keywords: Aquatic; Macrophytes; Marine; Photosynthesis; Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)