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AGU Ocean Sciences Meeting (Feb. 2002) COAST abstracts:


Examining the Occurrence of Phosphate-Stress in Coastal Phytoplankton
Communities Using a Cell-Specific Enzymatic Assay.

Kathleen C. Ruttenberg, Department of Marine Chemistry &
Geochemistry, and Sonya T. Dyhrman, Department of Biology,
Woods Hole Oceanographic Institution, Woods Hole MA 02543, USA,,

As part of the CoOP COAST project, a multi-PI and multi-disciplinary
effort, water column samples from May and August 2001 cruises to
the Oregon shelf are being analyzed for nutrient inventories,
chlorophyll-a, and Alkaline phosphatase (APase) activity.
One objective of our study is to evaluate the physiological state
of the phytoplankton regarding phosphate stress.  The primary
tool we use for evaluating phosphate stress is the APase enzyme.
Production of this enzyme is typically induced in phytoplankton
when they are stressed by low environmental phosphate levels.
As such, the presence of this enzyme can serve as an indicator of
phosphate-stress, or phosphate-limitation.

APase data from the May cruise indicated that some groups of
phytoplankton on the Oregon shelf were experiencing phosphate-stress.
These data were generated using a cell-specific APase assay known as
Enzyme Labeled Fluorescence, or ELF. This method involves tagging
cells with a fluorescent precipitate at sites of APase activity.
Subsequent examination of cells using epifluorescent microscopy
reveals which cells are expressing APase, and thus permits resolution
of differences in phytoplankton physiological condition at the
genus or species level.  For example, in some cases we observed
different species of diatoms, within the same sample, where one
species exhibits extensive ELF-APase activity the other species
does not.  Observations such as this suggest that different species
of phytoplankton may exhibit variable physiological responses to
the same external nutrient environment.