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Physiological responses of Daphnia pulex to acid stress
BACKGROUND: Acidity exerts a determining influence on the composition and diversity of freshwater faunas. While the physiological implications of freshwater acidification have been intensively studied in teleost fish and crayfish, much less is known about the acid-stress physiology of ecologically i...
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Formato: | Texto |
Lenguaje: | English |
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BioMed Central
2009
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2689847/ https://www.ncbi.nlm.nih.gov/pubmed/19383148 http://dx.doi.org/10.1186/1472-6793-9-9 |
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author | Weber, Anna K Pirow, Ralph |
author_facet | Weber, Anna K Pirow, Ralph |
author_sort | Weber, Anna K |
collection | PubMed |
description | BACKGROUND: Acidity exerts a determining influence on the composition and diversity of freshwater faunas. While the physiological implications of freshwater acidification have been intensively studied in teleost fish and crayfish, much less is known about the acid-stress physiology of ecologically important groups such as cladoceran zooplankton. This study analyzed the extracellular acid-base state and CO(2 )partial pressure (P(CO2)), circulation and ventilation, as well as the respiration rate of Daphnia pulex acclimated to acidic (pH 5.5 and 6.0) and circumneutral (pH 7.8) conditions. RESULTS: D. pulex had a remarkably high extracellular pH of 8.33 and extracellular P(CO2 )of 0.56 kPa under normal ambient conditions (pH 7.8 and normocapnia). The hemolymph had a high bicarbonate concentration of 20.9 mM and a total buffer value of 51.5 meq L(-1 )pH(-1). Bicarbonate covered 93% of the total buffer value. Acidic conditions induced a slight acidosis (ΔpH = 0.16–0.23), a 30–65% bicarbonate loss, and elevated systemic activities (tachycardia, hyperventilation, hypermetabolism). pH 6.0 animals partly compensated the bicarbonate loss by increasing the non-bicarbonate buffer value from 2.0 to 5.1 meq L(-1 )pH(-1). The extracellular P(CO2 )of pH 5.5 animals was significantly reduced to 0.33 kPa, and these animals showed the highest tolerance to a short-term exposure to severe acid stress. CONCLUSION: Chronic exposure to acidic conditions had a pervasive impact on Daphnia's physiology including acid-base balance, extracellular P(CO2), circulation and ventilation, and energy metabolism. Compensatory changes in extracellular non-bicarbonate buffering capacity and the improved tolerance to severe acid stress indicated the activation of defense mechanisms which may result from gene-expression mediated adjustments in hemolymph buffer proteins and in epithelial properties. Mechanistic analyses of the interdependence between extracellular acid-base balance and CO(2 )transport raised the question of whether a carbonic anhydrase (CA) is involved in the catalysis of the [Image: see text] reaction, which led to the discovery of 31 CA-genes in the genome of D. pulex. |
format | Text |
id | pubmed-2689847 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2009 |
publisher | BioMed Central |
record_format | MEDLINE/PubMed |
spelling | pubmed-26898472009-06-03 Physiological responses of Daphnia pulex to acid stress Weber, Anna K Pirow, Ralph BMC Physiol Research Article BACKGROUND: Acidity exerts a determining influence on the composition and diversity of freshwater faunas. While the physiological implications of freshwater acidification have been intensively studied in teleost fish and crayfish, much less is known about the acid-stress physiology of ecologically important groups such as cladoceran zooplankton. This study analyzed the extracellular acid-base state and CO(2 )partial pressure (P(CO2)), circulation and ventilation, as well as the respiration rate of Daphnia pulex acclimated to acidic (pH 5.5 and 6.0) and circumneutral (pH 7.8) conditions. RESULTS: D. pulex had a remarkably high extracellular pH of 8.33 and extracellular P(CO2 )of 0.56 kPa under normal ambient conditions (pH 7.8 and normocapnia). The hemolymph had a high bicarbonate concentration of 20.9 mM and a total buffer value of 51.5 meq L(-1 )pH(-1). Bicarbonate covered 93% of the total buffer value. Acidic conditions induced a slight acidosis (ΔpH = 0.16–0.23), a 30–65% bicarbonate loss, and elevated systemic activities (tachycardia, hyperventilation, hypermetabolism). pH 6.0 animals partly compensated the bicarbonate loss by increasing the non-bicarbonate buffer value from 2.0 to 5.1 meq L(-1 )pH(-1). The extracellular P(CO2 )of pH 5.5 animals was significantly reduced to 0.33 kPa, and these animals showed the highest tolerance to a short-term exposure to severe acid stress. CONCLUSION: Chronic exposure to acidic conditions had a pervasive impact on Daphnia's physiology including acid-base balance, extracellular P(CO2), circulation and ventilation, and energy metabolism. Compensatory changes in extracellular non-bicarbonate buffering capacity and the improved tolerance to severe acid stress indicated the activation of defense mechanisms which may result from gene-expression mediated adjustments in hemolymph buffer proteins and in epithelial properties. Mechanistic analyses of the interdependence between extracellular acid-base balance and CO(2 )transport raised the question of whether a carbonic anhydrase (CA) is involved in the catalysis of the [Image: see text] reaction, which led to the discovery of 31 CA-genes in the genome of D. pulex. BioMed Central 2009-04-21 /pmc/articles/PMC2689847/ /pubmed/19383148 http://dx.doi.org/10.1186/1472-6793-9-9 Text en Copyright © 2009 Weber and Pirow; licensee BioMed Central Ltd. http://creativecommons.org/licenses/by/2.0 This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( (http://creativecommons.org/licenses/by/2.0) ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. |
spellingShingle | Research Article Weber, Anna K Pirow, Ralph Physiological responses of Daphnia pulex to acid stress |
title | Physiological responses of Daphnia pulex to acid stress |
title_full | Physiological responses of Daphnia pulex to acid stress |
title_fullStr | Physiological responses of Daphnia pulex to acid stress |
title_full_unstemmed | Physiological responses of Daphnia pulex to acid stress |
title_short | Physiological responses of Daphnia pulex to acid stress |
title_sort | physiological responses of daphnia pulex to acid stress |
topic | Research Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2689847/ https://www.ncbi.nlm.nih.gov/pubmed/19383148 http://dx.doi.org/10.1186/1472-6793-9-9 |
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