title: Time of day modulates low-temperature Ca signals in Arabidopsis.
abstract: We tested the hypothesis that the circadian clock modulates Ca(2+)-based signalling pathways, using low-temperature (LT)-induced Ca(2+) signals. We investigated the relationship between diurnal and circadian modulation of LT-induced increases in cytosolic-free calcium ([Ca(2+)](cyt)), and regulation of [Ca(2+)](cyt)-dependent outputs of the LT-signalling network (RD29A transcript abundance and stomatal closure). We measured [Ca(2+)](cyt) non-invasively using aequorin, and targeted aequorin to the guard cell using a guard cell-specific GAL4-green fluorescent protein enhancer trap line. LT caused transient increases in whole plant and guard cell [Ca(2+)](cyt). In guard cells, the LT-induced [Ca(2+)](cyt) elevation preceded stomatal closure. In whole plants, the magnitude of LT-induced [Ca(2+)](cyt) transients, measured from the entire plant or specifically the guard cell, varied with the time of day: LT-induced [Ca(2+)](cyt) transients were significantly higher during the mid-photoperiod than at the beginning or end. Diurnal variation in LT-induced guard cell [Ca(2+)](cyt) increases was not correlated to diurnal variation in LT-induced stomatal closure. There was circadian modulation of LT-induced whole plant [Ca(2+)](cyt) increases, which were correlated to the circadian pattern of RD29A induction. In order to understand the significance of LT-induced [Ca(2+)](cyt) increases, we used a computer simulation to demonstrate that, in guard cells, LT-induced [Ca(2+)](cyt) increases measured from a population of cells are likely to represent the summation of cold-induced single-cell [Ca(2+)](cyt) oscillations.
authors.affiliation: Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
authors.forename: Antony N
authors.initials: AN
authors.lastname: Dodd
authors.forename: Mia Kyed
authors.initials: MK
authors.lastname: Jakobsen
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Baker
authors.forename: Anja
authors.initials: A
authors.lastname: Telzerow
authors.forename: Sui-Wen
authors.initials: SW
authors.lastname: Hou
authors.forename: Laurent
authors.initials: L
authors.lastname: Laplaze
authors.forename: Laure
authors.initials: L
authors.lastname: Barrot
authors.forename: R Scott
authors.initials: RS
authors.lastname: Poethig
authors.forename: Jim
authors.initials: J
authors.lastname: Haseloff
authors.forename: Alex A R
authors.initials: AA
authors.lastname: Webb
mesh_terms: D000331:Aequorin / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling; D002940:Circadian Rhythm; D003080:Cold Temperature; D020869:Gene Expression Profiling; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism
chemical_list: D049452:Green Fluorescent Proteins; D000331:Aequorin