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In vivo analysis of calcium dynamics in plant cells: a holistic view
In vivo calcium dynamics in plant cells: a holistic view
In plants, increases in cytosolic Ca2+ concentration ([Ca2+]cyt), occuring in response to both biotic and abiotic stimuli, work as a key components of different signal transduction pathways. Depending on the stimulus, Ca2+ rises can display the form of a single transient or repetitive Ca2+ oscillations and are commonly designated as “Ca2+ signatures”. Generation and shaping of Ca2+ signatures depends on fine-tuning of Ca2+ influxes and effluxes occurring at both the plasma membrane (PM) and membranes of the different subcellular compartments. The opening of PM Ca2+-permeable influx channels (e.g. GLRs, CNGCs, OSCAs….) in response to different stimuli will release Ca2+ into the cytosol and cause the generation of a Ca2+ spike, while activity of active Ca2+ efflux transporters (e.g H+-Ca2+ antiporters, Ca2+-ATPases…) will return the [Ca2+]cyt to resting concentrations. Not only cytosol but also organelles and other subcellular compartments (e.g. chloroplasts, mitochondria, endoplasmic reticulum…) experience Ca2+transients, hence putatively participating in the cellular Ca2+ homeostasis and potentially in the Ca2+signature shaping process. Moreover, as explained above, after a stimulus-induced [Ca2+]cyt rise, it is generally accepted that Ca2+-ATPases and Calcium Exchangers (CAXs) work synergistically to restore the pre-stimulus [Ca2+]cyt. Interestingly, such Ca2+ transporters have been shown to not only transport Ca2+ but also H+, leading to the hypothesis that Ca2+ and pH homeostasis are intimately linked. We have therefore investigated this possibility by means of in vivo molecular imaging of Arabidopsis plants expressing the genetically encoded Ca2+ probe Cameleon YC3.6 and the pH probes (pH-GFP and cpYFP) targeted to the cytosol, plastids and mitochondria to compare Ca2+ and pH dynamics triggered by different stimuli.
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