Characteristics of Nitrogen- and Iron-Limited Growth in the Diatom Phaeodactylum tricornutum, and in Natural Phytoplankton Populations.
type: CreativeWork
description: The biochemical pathways involved in nitrogen (N) utilisation by marine phytoplankton have received considerable attention over the last forty years, but our understanding of these processes, and how they are affected by environmental change is still far from complete. This study investigates N metabolism in marine phytoplankton in both a controlled laboratory environment (using the coastal marine diatom Phaeodactylum tricomutum), and in the open ocean (e.g. Jellicoe Channel and the Subtropical Convergence Zone, New Zealand). Although the characteristics of ammonium uptake have been extensively studied in marine phytoplankton, comparatively little information exists on rates of assimilation. In this study, a robust method for measuring the rate of ammonium assimilation after a transient addition of ammonium is described. The method relies on the measured ability of the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) to release unassimilated ammonium from the cell and prevent further assimilation. There was little or no correspondence between the rate of ammonium assimilation and rates of ammonium uptake or maximum glutamine synthetase (GS) activity in Phaeodactylum tricomutum. Moreover, in N-limited cells maximum GS activity was a poor measure of N incorporation under steady-state conditions. However, GS activity did provide reliable information on N status (e.g. increased GS activity with increased N-limitation). Comparisons of the effects of varying N-source suggest that nitrate-grown cells are not disadvantaged under conditions of N-limitation due to the extra costs associated with nitrate reductase (NR) and nitrite reductase (NiR) activity. The metabolic costs of growth on nitrate may be significantly increased under iron (Fe)-limitation, as both NR and NiR require Fe. Fe-limited chemostat cultures excreted nitrite and ammonium when grown on nitrate. This release is probably a response to insufficient photoreductant under Fe-limited conditions. Howe…
abstract: The biochemical pathways involved in nitrogen (N) utilisation by marine phytoplankton have received considerable attention over the last forty years, but our understanding of these processes, and how they are affected by environmental change is still far from complete. This study investigates N metabolism in marine phytoplankton in both a controlled laboratory environment (using the coastal marine diatom Phaeodactylum tricomutum), and in the open ocean (e.g. Jellicoe Channel and the Subtropical Convergence Zone, New Zealand). Although the characteristics of ammonium uptake have been extensively studied in marine phytoplankton, comparatively little information exists on rates of assimilation. In this study, a robust method for measuring the rate of ammonium assimilation after a transient addition of ammonium is described. The method relies on the measured ability of the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) to release unassimilated ammonium from the cell and prevent further assimilation. There was little or no correspondence between the rate of ammonium assimilation and rates of ammonium uptake or maximum glutamine synthetase (GS) activity in Phaeodactylum tricomutum. Moreover, in N-limited cells maximum GS activity was a poor measure of N incorporation under steady-state conditions. However, GS activity did provide reliable information on N status (e.g. increased GS activity with increased N-limitation). Comparisons of the effects of varying N-source suggest that nitrate-grown cells are not disadvantaged under conditions of N-limitation due to the extra costs associated with nitrate reductase (NR) and nitrite reductase (NiR) activity. The metabolic costs of growth on nitrate may be significantly increased under iron (Fe)-limitation, as both NR and NiR require Fe. Fe-limited chemostat cultures excreted nitrite and ammonium when grown on nitrate. This release is probably a response to insufficient photoreductant under Fe-limited conditions. Howe…
author: Grant, Coral M.
language: en
license: https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm
date published: 2001
date modified: 2026-07-24T01:07:07Z
provider: University of Auckland
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: ResearchSpace@Auckland

PropertyValue
property ID: Handle
value: https://hdl.handle.net/2292/909