title: Stringent control of cytoplasmic Ca2+ in guard cells of intact plants compared to their counterparts in epidermal strips or guard cell protoplasts.
abstract: Cytoplasmic calcium elevations, transients, and oscillations are thought to encode information that triggers a variety of physiological responses in plant cells. Yet Ca(2+) signals induced by a single stimulus vary, depending on the physiological state of the cell and experimental conditions. We compared Ca(2+) homeostasis and stimulus-induced Ca(2+) signals in guard cells of intact plants, epidermal strips, and isolated protoplasts. Single-cell ratiometric imaging with the Ca(2+)-sensitive dye Fura 2 was applied in combination with electrophysiological recordings. Guard cell protoplasts were loaded with Fura 2 via a patch pipette, revealing a cytoplasmic free Ca(2+) concentration of around 80 nM at -47 mV. Upon hyperpolarization of the plasma membrane to -107 mV, the Ca(2+) concentration increased to levels exceeding 400 nM. Intact guard cells were able to maintain much lower cytoplasmic free Ca(2+) concentrations at hyperpolarized potentials, the average concentration at -100 mV was 183 and 90 nM in epidermal strips and intact plants, respectively. Further hyperpolarization of the plasma membrane to -160 mV induced a sustained rise of the guard cell cytoplasmic Ca(2+) concentration, which slowly returned to the prestimulus level in intact plants but not in epidermal strips. Our results show that cytoplasmic Ca(2+) concentrations are stringently controlled in guard cells of intact plants but become increasingly more sensitive to changes in the plasma membrane potential in epidermal strips and isolated protoplasts.
authors.affiliation: Molecular Plant Physiology and Biophysics, Julius von Sachs Institute for Biosciences, Würzburg University, Würzburg.
authors.forename: V
authors.initials: V
authors.lastname: Levchenko
authors.forename: D R
authors.initials: DR
authors.lastname: Guinot
authors.forename: M
authors.initials: M
authors.lastname: Klein
authors.forename: M R G
authors.initials: MR
authors.lastname: Roelfsema
authors.forename: R
authors.initials: R
authors.lastname: Hedrich
authors.forename: P
authors.initials: P
authors.lastname: Dietrich
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002138:Calibration; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism*; D016257:Fura-2 / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D054046:Plant Stomata / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D011523:Protoplasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D031307:Vicia faba / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
chemical_list: D000255:Adenosine Triphosphate; D002118:Calcium; D016257:Fura-2