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Cation (Ca2+ and Mn2+) Partitioning Assays with Intact Arabidopsis Chloroplasts

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Original research article

A brief version of this protocol appeared in:
The Plant Cell
Apr 2016

Abstract

Determination of the relative distribution of Ca2+ and Mn2+ is an important tool for analyzing mutants showing altered levels of calcium and/or manganese transporters in the chloroplast envelope or thylakoid membrane. The method described in this protocol allows quantitative analyses of the relative distribution of calcium and manganese ions between chloroplast stroma and thylakoids using the isotopes [45Ca] and [54Mn] as radioactive tracers. To avoid contaminations with non chloroplastidic membrane systems, the method is designed for isolating pure and intact chloroplasts of Arabidopsis thaliana. Intact chloroplasts are isolated via Percoll gradient centrifugation. Chloroplasts are then allowed to take up [45Ca] or [54Mn] during a light incubation step. After incubation, chloroplasts are either kept intact or osmotically/mechanically treated to release thylakoids. The amount of incorporated [45Ca] or [54Mn] can be determined by liquid scintillation counting and the relative distribution calculated.

Keywords: Arabidopsis, Chloroplast, Ion transport, Thylakoid membrane, Envelope membrane, Photosynthesis

Background

Calcium and manganese are structural components of photosystem II and form the inorganic Mn4CaO5 cluster, where water oxidation takes place with the outcome of electrons, protons and molecular oxygen. Ca2+ and Mn2+ fluxes across the chloroplast envelope membrane and the thylakoid membrane are fundamental processes enabling the plant cell to meet the high demand of PSII for these cations. In a previous study, a Ca2+/H+ antiport activity was analyzed using isolated thylakoid membranes from pea plants (Ettinger et al., 1999). In the model plant Arabidopsis thaliana hardly any Ca2+/H+ antiport activity is detectable in isolated thylakoid membranes (Schneider et al., 2016), thus a protocol which allows the thylakoid membrane system to reside in its naturally physiological environment, namely the chloroplast is presented. Furthermore, this protocol permits the relative distribution of Ca2+ and Mn2+ in chloroplasts to be determined. The protocol given here has been tested with Arabidopsis as well as with pea plants.

How to cite: Harms, A., Steinberger, I. and Schneider, A. (2017). Cation (Ca2+ and Mn2+) Partitioning Assays with Intact Arabidopsis Chloroplasts. Bio-protocol 7(1): e2094. DOI: 10.21769/BioProtoc.2094.
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