Imaging calcium dynamics in living plants using semi-synthetic recombinant aequorins

• Published in: The Journal of cell biology 1993-04, Vol.121 (1), p.83-90
• Main Authors: Knight, M.R. (University of Edinburgh, Edinburgh, UK), Read, N.D, Campbell, A.K, Trewavas, A.J
• Format: Article
• Language: English
• Subjects: ADN RECOMBINADO; ADN RECOMBINE; Aequorin - analogs & derivatives; Aequorin - chemical synthesis; Aequorin - genetics; Aequorin - pharmacology; Biological and medical sciences; CALCIO; CALCIUM; Calcium - metabolism; Calibration; CATION; CATIONES; Cell physiology; Cells; CITOPLASMA; COELENTERATA; Cold Temperature; Cotyledons; CYTOPLASME; Effects of physical and chemical agents; Fundamental and applied biological sciences. Psychology; GENE; GENES; Hypocotyls; Image Processing, Computer-Assisted; Imaging; Imidazoles; Kinetics; LIPOPROTEINAS; LIPOPROTEINE; Luminescence; Luminescent Measurements; MEDICION; MESURE; Molecular and cellular biology; Molecular Structure; NICOTIANA; Nicotiana - metabolism; Photons; Plant cells; Plants, Toxic; PROPIEDADES OPTICAS; PROPRIETE OPTIQUE; Pyrazines; Recombinant Proteins - genetics; Seedlings; TRANSFORMACION GENETICA; TRANSFORMATION GENETIQUE
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.121.1.83

The genetic transformation of the higher plant Nicotiana plumbaginifolia to express the protein apoaequorin has recently been used as a method to measure cytosolic free calcium ([Ca(2+)]i) changes within intact living plants (Knight, M. R., A. K. Campbell, S. M. Smith, and A. J. Trewavas. 1991. Nature (Lond.). 352:524-526; Knight, M. R., S. M. Smith, and A. J. Trewavas. 1992. Proc. Natl. Acad. Sci. USA. 89:4967-4971). After treatment with the luminophore coelenterazine the calcium-activated photoprotein aequorin is formed within the cytosol of the cells of the transformed plants. Aequorin emits blue light in a dose-dependent manner upon binding free calcium (Ca(2+)). Thus the quantification of light emission from coelenterazine-treated transgenic plant cells provides a direct measurement of [Ca(2+)]i. In this paper, by using a highly sensitive photon-counting camera connected to a light microscope, we have for the first time imaged changes in [Ca(2+]i in response to cold-shock, touch and wounding in different tissues of transgenic Nicotiana plants. Using this approach we have been able to observe tissue-specific [Ca(2+)]i responses. We also demonstrate how this method can be tailored by the use of different coelenterazine analogues which endow the resultant aequorin (termed semi-synthetic recombinant aequorin) with different properties. By using h-coelenterazine, which renders the recombinant aequorin reporter more sensitive to Ca(2+), we have been able to image relatively small changes in [Ca(2+)]i in response to touch and wounding: changes not detectable when standard coelenterazine is used. Reconstitution of recombinant aequorin with another coelenterazine analogue (ecoelenterazine) produces a semi-synthetic recombinant aequorin with a bimodal spectrum of luminescence emission. The ratio of luminescence at two wavelengths (421 and 477 nm) provides a simpler method for quantification of [Ca(2+)]i in vivo than was previously available. This approach has the benefit that no information is needed on the amount of expression, reconstitution or consumption of aequorin which is normally required for calibration with aequorin