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Title: Nitrate uptake by Phaeodactylum
Author: Cresswell, R. C.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1982
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The marine diatom Phaeodactylum tricornutum was shown to accumulate nitrate against a concentration gradient. This made it possible to study the process of uptake of nitrate as distinct from further nitrate metabolism because the appearance of nitrate within the cells could be followed as well as its disappearance from the medium. Two aspects of the uptake of nitrate by Phaeodactylum were studied in detail: 1) Development of ability to take up nitrate: It was found that, after growth on ammonium, cells had no ability to take up nitrate but that the ability developed during a period of N-starvation. This development process was shown to be inhibited by cycloheximide and ammonium and to have a requirement for concurrent photosynthesis. 2) Characteristics of the nitrate uptake system: Using cells with a well developed uptake system it was shown that both uptake and assimilation of nitrate were stimulated by light and inhibited by DCMU and CCCP. The presence of ammonium inhibited nitrate uptake, but not nitrate reduction, in the short term, and the ammonium analogue, methylanmonium, inhibited both nitrate uptake and utilization of accumulated nitrate. Other amines also inhibited nitrate uptake. Experiments were also carried out in order to study nitrite uptake by following nitrite disappearance from the medium, and it was found that the nitrite uptake process appeared to be very similar to that of nitrate uptake. Kinetic studies were made on both nitrate and nitrite uptake and Ks values of ca 7pM and ca 6pM were obtained respectively. Nitrite uptake was strongly inhibited by the presence of nitrate in the medium but nitrite only weakly inhibited nitrate uptake. It was concluded that nitrite was taken up either by the same uptake system as nitrate or by a very similar system. Nitrate uptake was found to have a requirement for sodium which was very specific and could not be satisfied by the presence of other cations such as lithium and potassium. High concentrations of either lithium or potassium were found to inhibit nitrate uptake. Sodium may either be required directly for nitrate uptake, e.g. by a co-transport mechanism, or may have other roles not yet understood.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available