CARBONIC-ANHYDRASE IN RANUNCULUS-PENICILLATUS SPP PSEUDOFLUITANS - ACTIVITY, LOCATION AND IMPLICATIONS FOR CARBON ASSIMILATION

Levels of carbonic anhydrase activity were determined on a total (60 E (U)mg-1 protein), external (7-36 E(U)), internal (50.14 E(U)) and prot oplast (15.63 E(U)) basis for Ranunculus penicillatus (Dumort.) Bab ss p. pseudofluitans (Syme) S. Webster, a freshwater aquatic macrophyte, by conventional electrometric methods. The site of activity of 'extern al' carbonic anhydrase (CA) has been visualized using 5-Dimethylaminon apthalene-1-sulphonamide (DNSA)-CA fluorescent complex formation, and is postulated to be closely associated with the epidermal cell wall. T he photosynthetic rate of R. penicillatus ssp. pseudofluitans at pH 9. 0 is in excess of the uncatalysed rate of production of CO2 from HCO3- , and this plant is therefore using HCO3- for photosynthesis. The poss ible contribution of CA activity to inorganic carbon assimilation, and specifically to transport of HCO3-, in submerged aquatic plants is di scussed.