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
He may be contacted at the following address:
Dr. Tony R. Larson
Centre for Novel Agricultural Products
University of York, U.K.
Central Science Laboratory
York YO41 1LZ
tel: 44 1904 462 372
mobile: 44 403 492 867
fax: 44 1904 462 374
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.
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
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.