Kj. Flynn et al., MODELING THE INTERACTIONS BETWEEN AMMONIUM AND NITRATE UPTAKE IN MARINE-PHYTOPLANKTON, Philosophical transactions-Royal Society of London. Biological sciences, 352(1361), 1997, pp. 1625-1645
An empirically based mathematical model is presented which can simulat
e the major features of the interactions between ammonium and nitrate
transport and assimilation in phytoplankton. The model (ammonium-nitra
te interaction model), which is configured to simulate a generic micro
alga rather than a specified species, is constructed on simplified bio
chemical bases. A major requirement for parametrization is that the N:
C ratio of the algae must be known and that transport and internal poo
l sizes need to be expressed per unit of cell C. The model uses the si
ze of an internal pool of an early organic product of N assimilation (
glutamine) to regulate rapid responses in ammonium-nitrate interaction
s. The synthesis of enzymes for the reduction of nitrate through to am
monium is induced by the size of the internal nitrate pool and repress
ed by the size of the glutamine pool. The assimilation of intracellula
r ammonium (into glutamine) is considered to be a constitutive process
subjected to regulation by the size of the glutamine pool. Longer ter
m responses have been linked to the nutrient history of the cell using
the N:C cell quota. N assimilation in darkness is made a function of
the amount of surplus C present and thus only occurs at low values of
N:C. The model can simulate both qualitative and quantitative temporal
shifts in the ammonium-nitrate interaction, while inclusion of a deri
vation of the standard quota model enables a concurrent simulation of
cell growth and changes in nutrient status.