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Uptake kinetics and assimilation of inorganic nitrogen by Catenella nipae and Ulva lactuca
Runcie, J.W.; Ritchie, R.J.; Larkum, A.W.D. (2003). Uptake kinetics and assimilation of inorganic nitrogen by Catenella nipae and Ulva lactuca. Aquat. Bot. 76(2): 155-174. dx.doi.org/10.1016/s0304-3770(03)00037-8
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770, more
Peer reviewed article  

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Keywords
    Ammonia; Indicator species; Kinetics; Nitrogen compounds; Uptake; Catenella nipae Zanardini, 1872 [WoRMS]; Ulva lactuca Linnaeus, 1753 [WoRMS]; PSE, Australia, New South Wales, Sydney Harbour; Marine

Authors  Top 
  • Runcie, J.W.
  • Ritchie, R.J., correspondent
  • Larkum, A.W.D.

Abstract
    The kinetics of NH4+, the assimilation of NH4+ and nitrate uptake by Catenella nipae (Rhodophyta) were compared with Ulva lactuca (Chlorophyta). Both algal species demonstrated saturable NH4+ and nitrate uptake kinetics. Uptake of NH3 by simple diffusion across the plasmalemma could not account for the observed saturation uptake kinetics of ammonia-N (NH3+ NH4+), so NH4+ was the chemical form being taken up by the transport systems of the cells. Although the Vmax of NH4+ uptake by C. nipae and U. lactuca was high (550 and 450 µmol g-1 DW h-1, respectively), the Km for U. lactuca (85 µM) was much lower than that for C. nipae (692 µM). The Km and Vmax values for nitrate uptake were much lower than for NH4+ for both C. nipae (Km about 5 µM; Vmax about 8.3 µmol g-1 DW h-1) and U. lactuca (Km about 34 µM; Vmax about 116 µmol g-1 DW h-1). Over the incubation times used (up to 28 min) there was no apparent induction of nitrate transport in either species. There was no evidence for induction of NH4+ transport in C. nipae but incubation time did affect the kinetics of NH4+ uptake in U. lactuca. At high concentrations of NH4+, U. lactuca rapidly assimilated it into organic N with limited build-up of intracellular NH4+ whereas C. nipae accumulated large amounts of NH4+ because uptake of NH4+ overtook the rate of assimilation. The effects of species-specific differences and experimental design on uptake-kinetic estimates are discussed in the light of the results of this other comparable studies. C. nipae is promising as a bioindicator species of the N-status of estuaries but U. lactuca changes its N-status too quickly for it to be a useful bioindicator of environmental conditions.

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