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Cadmium induces cellular pH changes in Elodea canadensis and causes external basification
Stockholm University, Faculty of Science, Department of Botany.
Stockholm University, Faculty of Science, Department of Botany.
Stockholm University, Faculty of Science, Department of Botany.
(English)Article in journal (Refereed) Submitted
Abstract [en]

Earlier investigations showed that Elodea canadensis causes a basification of the surrounding medium in the presence of cadmium. This study was aimed to investigate the mechanism by which Cd causes this plant to increase the surrounding water pH. Cd-induced pH changes in cytosol, vacuole and apoplastic regions of E. canadensis were monitored by fluorescence microscopy and pH-specific fluorescent dyes. Since cytosolic Ca2+ and pH homeostasis are closely linked, the cytosolic calcium [Ca2+]cytwas also investigated after Cd treatment. Cd binding to the cell walls of E. canadensis was investigated after cultivation of plants at different fixed pH. We developed a new enzymatic method for the isolation of protoplasts from E. canadensis leaves. Cd exposure resulted in a subsequent increase in both cytosolic and vacuolar pH of leaf protoplasts and concomitant rise in the [Ca2+]cyt. Changes in [Ca2+]cyt and [pH]cyt followed the same dynamics upon Cd addition, but the changes in [pH]cyt seemed to be prior to the [Ca2+]cyt changes. Cd treatment decreased the apoplastic pH by 0.85 units and Cd contents of cell walls were enhanced at low pH. In conclusion, Cd exposure decreased the apoplastic pH of E. canadensis and resulted in Cd binding to the cell walls which may prevent Cd influx to the cytosol. The results suggest that the Cd-induced apoplastic acidification can be one of the mechanisms to increase the surrounding medium pH by E. canadensis shoots.

Keyword [en]
Cadmium, Cytosolic pH, Cytosolic Ca2+, Vacuolar pH, Apoplastic pH, Protoplasts, Elodea canadensis
National Category
Botany
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-64326OAI: oai:DiVA.org:su-64326DiVA: diva2:457077
Note
In thesis, Mechanisms behind pH changes by plant roots and shoots caused by elevated concentration of toxic elementsAvailable from: 2011-11-16 Created: 2011-11-16 Last updated: 2011-11-17Bibliographically approved
In thesis
1. Mechanisms behind pH changes by plant roots and shoots caused by elevated concentration of toxic elements
Open this publication in new window or tab >>Mechanisms behind pH changes by plant roots and shoots caused by elevated concentration of toxic elements
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Toxic elements are present in polluted water from mines, industrial outlets, storm water etc. Wetland plants take up toxic elements and increase the pH of the medium. In this thesis was investigated how the shoots of submerged plants and roots of emergent plants affected the pH of the surrounding water in the presence of free toxic ions. The aim was to clarify the mechanisms by which these plants change the surrounding water pH in the presence of toxic ions.

The influence of Elodea canadensis shoots on the pH of the surrounding water was studied in the presence of cadmium (Cd) at low initial pH (4-5). The involvement of photosynthetic activity in the pH changes was investigated in the presence and absence of Cd. The cytosolic, vacuolar and apoplasmic pH changes as well as cytosolic Cd changes in E. canadensis were monitored. The influence of Eriophorum angustifolium roots on the pH of the surrounding water was investigated in the presence of a combination of Cd, copper, lead, zinc and arsenic at low initial pH (3.5). Eriophorum angustifolium root exudates were analyzed for organic acids.

Elodea canadensis shoots increased the pH of the surrounding water, an effect more pronounced with increasing Cd levels and/or increasing plant biomass and increased plant Cd uptake. The pH increase in the presence of free Cd ions was not due to photosynthesis or proton uptake across the plasmalemma or tonoplast. Cadmium was initially sequestered in the apoplasm of E. canadensis and caused its acidosis. Eriophorum angustifolium roots increased the surrounding water pH and this effect was enhanced in the presence of arsenic and metals. This pH increase was found to depend partly on the release of oxalic acid, formic acid and succinic acid by the plants.

In conclusion, E. canadensis shoots and E. angustifolium roots were found to increase the low initial pH of the surrounding water. The pH modulation by these species was enhanced by low levels of free toxic ions in the surrounding water.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University, 2011. 40 p.
Keyword
Elodea canadensis, Eriophorum angustifolium, fluorescence microscopy, mechanisms, metals and metalloid, pH changes, protoplasts, phytofiltration, phytostabilization, root exudates
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-64324 (URN)978-91-7447-413-8 (ISBN)
Public defence
2011-12-20, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: Manuscript.Available from: 2011-11-28 Created: 2011-11-16 Last updated: 2011-11-28Bibliographically approved

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