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Millisecond UV‐B irradiation evokes prolonged elevation of cytosolic‐free Ca 2+ and stimulates gene expression in transgenic parsley cell cultures
Author(s) -
Frohnmeyer Hanns,
Loyall Linda,
Blatt Michael R.,
Grabov Alexander
Publication year - 1999
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1999.00584.x
Subject(s) - chalcone synthase , gene expression , luciferase , microbiology and biotechnology , biology , biophysics , cell culture , cytosol , gene , chemistry , biochemistry , enzyme , transfection , genetics
Summary Chalcone synthase (CHS) is a key enzyme leading to the generation of protective flavonoids in plants under environmental stress. Expression of the CHS gene is strongly upregulated by exposures to UV light, a response also observed in heterotrophic parsley cell cultures. Although there are hints that the stimulus for CHS expression may be coupled to UV‐B irradiation through a rise in cytosolic‐free Ca 2+ ([Ca 2+ ] i ), the temporal relationship of these events has never been investigated critically. To explore this question, we have used a CHS promoter/luciferase ( CHS/LUC ) reporter gene fusion and recorded its expression and [Ca 2+ ] i elevation in a transgenic parsley cell culture following millisecond light pulses. Luciferase expression was enhanced maximally seven‐ ( ± 2) fold by 30 10 ms flashes of UV‐B light. The response was specific to wavelengths of 300–330 nm and could be inhibited in the presence of the Ca 2+ channel blocker nifedipine. In parallel measurements, using Fura‐2 fluorescence ratio microphotometry, we found that 10 ms UV‐B flashes also evoked a gradual and prolonged rise of [Ca 2+ ] i in the parsley cells which was irreversible within the timescale of these experiments, but could be prevented by prior treatment with nifedipine. These, and additional results, indicate a remarkably high temporal sensitivity to, and specificity for, UV‐B light in CHS gene expression independent of UV‐mediated DNA damage by thymine dimerization. The ability of transient UV‐B stimulation to evoke prolonged elevations of [Ca 2+ ] i suggests a functional coupling between the initial light stimulus and subsequent gene expression that takes place many tens of minutes later.