Metabolic regulation of ammonium uptake by Ulva rigida (Chlorophyta): A compartmental analysis of the rate-limiting step for uptake

Journal Article · Thu Dec 01 00:00:00 EST 1988 · Journal of Phycology; (USA)

DOI:https://doi.org/10.1111/j.1529-8817.1988.tb00106.x· OSTI ID:5051797

Fujita, R M; Wheeler, P A; Edwards, R L ^[1]

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1. Oregon State Univ., Corvallis (USA)

Non-linear time courses of ammonium (NH{sub 4}{sup +}) depletion from the medium and internal accumulation of soluble nitrogen (N) in macroalgae imply that the rate-limiting step for ammonium uptake changes over time. We tested this hypothesis by measuring the time course of N accumulation in N-limited Ulva rigida C. Agardh. Total uptake was measured as removal of NH{sub 4}{sup +} from medium. Rates for the component processes (transport of NH{sub 4}{sup +} across the membrane = R{sub t}, assimilation of tissue NH{sub 4}{sup +} into soluble N compounds = R{sub a}, and incorporation of soluble N compounds into macromolecules = R{sub i}) were determined by measuring the rate of labelling of the major tissue N pools after the addition of {sup 15}N-ammonium. The results indicate that nitrogen-specific rates (mass N taken up/mass N present/unit time) are ranked in the order of R{sub t} > R{sub a} > R{sub i}. Absolute uptake rates ({mu}mol N{center dot}mg dry wt{sup {minus}1}{center dot}h{sup {minus}1}) showed a different relationship. Membrane transport appears to be inhibited when NH{sub 4}{sup +} accumulates in the tissue. Maximum uptake rates occur when assimilation of NH{sub 4}{sup +} into soluble N compounds begins. Assimilation of NH{sub 4}{sup +} into soluble N compounds was initially faster than incorporation of soluble N compounds into macromolecules. Implications of rate limitations caused by differences in maximal rates and maximal pool sizes are discussed.

• OSTI ID: 5051797
• Journal Information: Journal of Phycology; (USA), Vol. 24:4; ISSN 0022-3646
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ALGAE
METABOLISM
AMMONIUM COMPOUNDS
UPTAKE
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL ACCUMULATION
LABELLED COMPOUNDS
MEMBRANE TRANSPORT
NITROGEN
NITROGEN 15
TRACER TECHNIQUES
ELEMENTS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
NITROGEN ISOTOPES
NONMETALS
NUCLEI
ODD-EVEN NUCLEI
PLANTS
REACTION KINETICS
STABLE ISOTOPES
550501* - Metabolism- Tracer Techniques