Modelling intra-cellular control of nitrate uptake and long distance transport in plant
2002
Gent, Martin P.N.
A review of the scientific literature shows plant roots have a complex pattern of nitrate uptake behavior. The apparent binding constant for uptake is on the order of 1 - 10 micromolar under limiting nitrate conditions. However, horticultural crops respond to additional nitrate into the mM range. Nitrate uptake and metabolism can take several days to respond to changes in nitrate supply. All of these responses may be due to feedback control to maintain a relatively constant nitrate concentration in the cytoplasm of plant cells. I developed a kinetic model of nitrate transport to simulate this behavior. The plant was simplified to a single cytoplasm, vacuole and xylem compartment in the root or in the leaf. Feedback inhibition of membrane transport was used to maintain an approximately constant concentration in the cytoplasm. The model parameters were chosen so the volume and concentration of nitrate were much lower in the cytoplasm than in the vacuole. The nitrate uptake predicted by this model responded to external concentrations in the range from 0.01 to 1.0 mM, but there was no further increase in uptake between 1.0 and 10 mM. Acclimation to nitrate supply occurred over a day or more. Feedback control for homeostasis should be included in simulations to select an appropriate nitrate supply for horticultural crops.
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