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Mechanisms behind pH changes by plant roots and shoots caused by elevated concentration of toxic elements
Stockholm University, Faculty of Science, Department of Botany. (Plant Physiology)
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 [en]
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: urn:nbn:se:su:diva-64324ISBN: 978-91-7447-413-8 (print)OAI: oai:DiVA.org:su-64324DiVA: diva2:457095
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
List of papers
1. Cadmium triggers Elodea canadensis to change the surrounding water pH and thereby Cd uptake
Open this publication in new window or tab >>Cadmium triggers Elodea canadensis to change the surrounding water pH and thereby Cd uptake
2011 (English)In: International journal of phytoremediation, ISSN 1522-6514, E-ISSN 1549-7879, Vol. 13, no 1, 95-106 p.Article in journal (Refereed) Published
Abstract [en]

This study was aimed to investigate the influence of Elodea canadensis shoots on surrounding water pH in the presence of cadmium and the effect of plant-induced pH on cadmium uptake. The pH change in the surrounding nutrient solution and Cd uptake by Elodea shoots were investigated after cultivation of various plant densities (1, 3, 6 plants per 500 ml) in hydroponics at a starting pH of 4.0 and in the presence of different concentrations of cadmium (0, 0.1, 0.5 µM). Cadmium uptake was also investigated at different constant pH (4.0, 4.5, 5.5 and 6.5). To investigate if the pH change arose from photosynthetic activities, plants were grown under light, darkness or in the presence of a photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and 0.5 µM cadmium in the solution. Elodea had an ability to increase the surrounding water pH, when the initial pH was low, which resulted in increased accumulation of Cd. The higher the plant density, the more pronounced was the pH change. The pH increase was not due to the photosynthetic activity since the pH rise was more pronounced under darkness and in the presence of DCMU. The pH increase by Elodea was triggered by cadmium.

Keyword
Cadmium uptake, Elodea canadensis, pH increase, photosynthesis, phytofiltration
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-64325 (URN)10.1080/15226511003753987 (DOI)000292159200025 ()
Available from: 2011-11-16 Created: 2011-11-16 Last updated: 2017-12-08Bibliographically approved
2. Cadmium induces cellular pH changes in Elodea canadensis and causes external basification
Open this publication in new window or tab >>Cadmium induces cellular pH changes in Elodea canadensis and causes external basification
(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
Cadmium, Cytosolic pH, Cytosolic Ca2+, Vacuolar pH, Apoplastic pH, Protoplasts, Elodea canadensis
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-64326 (URN)
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
3. pH changes and organic acids exudation by Eriophorum angustifolium roots exposed to elevated concentration of toxic elements
Open this publication in new window or tab >>pH changes and organic acids exudation by Eriophorum angustifolium roots exposed to elevated concentration of toxic elements
(English)Article in journal (Refereed) Submitted
Abstract [en]

This study was aimed to investigate the influence of Eriophorum angustifolium roots on surrounding water pH in the presence of heavy metals and As, and the possible mechanism behind. We monitored the pH in the surrounding nutrient solution by E. angustifolium roots at a starting pH 3.5 and in the presence of a combination of As, Pb, Cu, Cd and Zn at different concentrations. The metal and As contents in the plant shoots and roots were analyzed as well as organic acids in the root exudates. Fluorescence microscopy and a pH-specific fluorescent dye were used to investigate the influence of different elements on apoplastic pH of E. angustifolium roots. The results showed that the roots have the ability to increase the rhizosphere pH even in the presence of different free metal ions and As. The plant root metal and As contents were significantly higher as compared with shoots. Metal and As treatment at higher concentrations significantly caused the apoplastic pH to increase in this species. Of the acids analyzed, the exudation of the oxalic, formic and succinic acids was significantly enhanced after metal and As exposure, as compared with control, giving the maximum concentration of these acids after 25 µM As, Cu, Zn, Pb and 2.5 µM Cd treatment. The roots of E. angustifolium respond to toxic ions by releasing organic acids, which transiently induce rhizosphere basification.

Keyword
Eriophorum angustifolium, Heavy metals and As, pH changes, Organic acids, Phytostabilization
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-64327 (URN)
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
4. Cytosolic uptake of cadmium causes an extra- and intra-cellular basification in Elodea canadensis
Open this publication in new window or tab >>Cytosolic uptake of cadmium causes an extra- and intra-cellular basification in Elodea canadensis
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The current study was aimed to investigate the pH changes by Elodea canadensis shoots under different photosynthetic conditions in the presence and absence of cadmium (Cd) and its influence on Cd uptake. Plants were grown under light, dark and in the presence of the photosynthetic inhibitor (3-(3,4-dichlorophenyl)-1,1-dimethylurea) with and without 0.5 µM Cd in the solution at a starting pH of 5.0. The Cd uptake into the cytosol of leaf protoplasts was investigated by using a Cd-specific fluorescent dye, LeadmiumTM Green AM. Cadmium and proton dynamics were monitored in leaf protoplasts after plant exposure to 0.5 µM CdCl2 for 3 and 7 d, respectively. The pH sensitive dye BCECF-AM was used to detect cytosolic pH changes. The shoots increased the surrounding water pH, which enhanced Cd uptake. Beside pH increase by photosynthetic activity, E. canadensis possessed additional mechanisms to raise the surrounding water pH in the presence of Cd. The cytosolic cadmium (Cd2+cyt) fluorescence of leaf protoplasts increased upon addition of CdCl2 to the external medium, reflecting (Cd2+cyt) uptake. Plant exposure to 0.5 µM CdCl2 for 3 d did not induce significant changes in (Cd2+cyt)and [pH]cyt. However, the (Cd2+cyt) and pHcyt were significantly increased after plant exposure to 0.5 µM CdCl2 for 7d. This suggests that E. canadensis initially sequester Cd in its apoplasmic region depending upon the presence of acidic polysaccharides in its cell wall and external medium basification. With time Cd translocates into the cytosol and subsequently causes its basification.

Keyword
Elodea canadensis, cadmium uptake, pH increase, photosynthesis, protoplast, cytosolic Cd2+/H+ dynamics, fluorescence microscopy
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-64328 (URN)
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

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