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Tony Larson

email
trl1@...



Figure 1

Figure 2




Tony Larson | PhD Candidate


Tony successfully defended his thesis in March of 1998. He is presently working on the regulation of fatty acid oxidation in Arabidopsis (with Ian Graham). However, his long-term goal is to characterize this process in diatoms.

He may be contacted at the following address:

Dr. Tony R. Larson
Centre for Novel Agricultural Products
University of York, U.K.

Mailing address:
CNAP
Central Science Laboratory
Sand Hutton
York YO41 1LZ
U.K.

tel: 44 1904 462 372
mobile: 44 403 492 867
fax: 44 1904 462 374

email: trl1@yorkl.ac.uk

Storage Lipid Metabolism in Marine Diatoms

In marine diatoms conditions of extreme nutrient limitation, such as at the end of a bloom, will lead to a reduction in growth rates and an accumulation of storage lipids. These lipids have been assumed to be important in respiratory metabolism, particularly when diatoms require carbon skeletons, energy, and reductant for nitrogen assimilation. A model for lipid accumulation and utilization by a diatom population can be seen in Fig. 1.

High density semi-continuous cultures of the marine diatom Phaeodactylum tricornutum are currently being used to investigate the coordination of nitrate and ammonium assimilation with storage lipid metabolism. Both nitrate or ammonium addition to N-starved cultures stimulated a mobilization of storage lipid in the light or dark. Nitrogen assimilation is typically greatest in the light, hence lipid mobilization in the light was greater than in the dark (Fig. 2). This suggests that storage lipid plays an important role in the nitrogen nutrition of diatoms over and above that of maintenance respiration.

Activity measurements were also made for the enzyme isocitrate lyase, which may have a regulatory role in the glyoxylate pathway. Light mediated isocitrate lyase activity was four times higher during the onset of lipid mobilization in the presence of nitrate than in the presence of ammonium. Thus, while the patterns of lipid mobilization in the presence of nitrate or ammonium may look similar, their metabolic fates are likely to be different. It is my suggestion that the glyoxylate cycle may be activated during nitrate assimilation to provide extra reductant needed for the enzyme nitrate reductase.


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