Regulation of body dimethylsulfoniopropionate (DMSP) content by the copepod Temora longicornis: a test of four mechanisms |
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Authors: | K W Tang T D Fenn P T Visscher H G Dam |
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Institution: | (1) Department of Marine Sciences, University of Connecticut, Groton, Connecticut 06340, USA e-mail: k.w.tang@uconn.edu Fax: +1-860-4059153, US;(2) Biochemistry Department, Brandeis University, Waltham, Massachusetts 02254, USA, US |
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Abstract: | Copepods contain dimethylsulfoniopropionate (DMSP) in their tissues in addition to the DMSP in their gut contents and therefore
constitute an additional pool of DMSP in the ocean. In the estuarine copepod Temora longicornis Müller, this dynamic pool of DMSP is reduced when external salinity decreases. In the present study the mechanism(s) used
by T. longicornis to adjust its DMSP content were examined. Four possible mechanisms were tested in experiments conducted between July 1997
and May 1999: (1) DMSP cleavage, (2) demethylation, (3) conversion to methionine, and (4) release from the body. Tissue extracts
of T. longicornis did not exhibit the ability to cleave or demethylate DMSP. In incubation experiments, when external salinity decreased, T. longicornis individuals reduced their DMSP content without increasing their methionine content. The total amount of DMSP in the incubation
vials was conserved regardless of salinity. The copepods retained most of the DMSP in their tissues in 30‰ water, but when
salinity was reduced to 20‰, the copepods released 41 to 55% of their body DMSP to the surrounding medium; 89 to 91% of the
total DMSP was recovered. This suggests that estuarine copepods represent a reservoir of DMSP, which is released as dissolved
DMSP upon salinity decline. Therefore, while osmoregulation by these copepods may have little impact on the chemical properties
of DMSP, it will affect the partitioning of DMSP between particulate and dissolved phases in the water column.
Received: 20 August 1999 / Accepted: 28 March 2000 |
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