This article is part of a series on Daphnia: the companion papers for the genome sequence.

Research article

Acclimatory responses of the Daphnia pulex proteome to environmental changes. I. Chronic exposure to hypoxia affects the oxygen transport system and carbohydrate metabolism

Bettina Zeis¹ , Tobias Lamkemeyer² , Rüdiger J Paul¹ , Frank Nunes¹ , Susanne Schwerin¹ , Marita Koch¹ , Wolfgang Schütz² , Johannes Madlung² , Claudia Fladerer² and Ralph Pirow¹

¹Institute of Zoophysiology, University of Münster, Münster, Germany

²Proteom Centrum Tübingen, Interfaculty Institute for Cell Biology, University of Tübingen, Tübingen, Germany

author email corresponding author email

BMC Physiology 2009, 9:7doi:10.1186/1472-6793-9-7

Published:	21 April 2009

Abstract

Background

Freshwater planktonic crustaceans of the genus Daphnia show a remarkable plasticity to cope with environmental changes in oxygen concentration and temperature. One of the key proteins of adaptive gene control in Daphnia pulex under hypoxia is hemoglobin (Hb), which increases in hemolymph concentration by an order of magnitude and shows an enhanced oxygen affinity due to changes in subunit composition. To explore the full spectrum of adaptive protein expression in response to low-oxygen conditions, two-dimensional gel electrophoresis and mass spectrometry were used to analyze the proteome composition of animals acclimated to normoxia (oxygen partial pressure [Po₂]: 20 kPa) and hypoxia (Po₂: 3 kPa), respectively.

Results

The comparative proteome analysis showed an up-regulation of more than 50 protein spots under hypoxia. Identification of a major share of these spots revealed acclimatory changes for Hb, glycolytic enzymes (enolase), and enzymes involved in the degradation of storage and structural carbohydrates (e.g. cellubiohydrolase). Proteolytic enzymes remained constitutively expressed on a high level.

Conclusion

Acclimatory adjustments of the D. pulex proteome to hypoxia included a strong induction of Hb and carbohydrate-degrading enzymes. The scenario of adaptive protein expression under environmental hypoxia can be interpreted as a process to improve oxygen transport and carbohydrate provision for the maintenance of ATP production, even during short episodes of tissue hypoxia requiring support from anaerobic metabolism.