Circadian and Diurnal Calcium Oscillations Encode Photoperiodic Information in Arabidopsis

Abstract

We have tested the hypothesis that circadian oscillations in the concentration of cytosolic free calcium ([Ca 21 ] cyt ) can encode information. We imaged oscillations of [Ca 21 ] cyt in the cotyledons and leaves of Arabidopsis (Arabidopsis thaliana) that have a 24-h period in light/dark cycles and also constant light. The amplitude, phase, and shape of the oscillations of [Ca 21 ] cyt and [Ca 21 ] cyt at critical daily time points were controlled by the light/dark regimes in which the plants were grown. These data provide evidence that 24-h oscillations in [Ca 21 ] cyt encode information concerning daylength and light intensity, which are two major regulators of plant growth and development.

Cell- and Stimulus Type-Specific Intracellular Free Ca2+ Signals in Arabidopsis

“…The major limitation of the use of aequorin is low light emission, meaning that imaging even at the subtissue level has proved elusive (Zhu et al, 2013), and subcellular imaging in plants is not possible. Aequorin has found high utility and has identified roles for [Ca 2+ ] cyt signaling in mechanical stimulation, cold, salinity, and pathogen stress and in the daily timing of plants (Campbell et al, 1996;Knight et al, 1996Knight et al, , 1997Gong et al, 1998;Kawano et al, 1998;Baum et al, 1999;Love et al, 2004;Kosuta et al, 2008;Monshausen et al, 2009;Zhu et al, 2013). However, in leaves and shoots, it is not known from which tissues the stress-and circadian-regulated [Ca 2+ ] i signals arise.…”

“…Despite the central importance of [Ca 2+ ] i signaling in the regulation of leaf biology, study of the dynamics of stimulus-induced and circadian-regulated [Ca 2+ ] i signals in leaves has usually been limited to the stomatal guard cells, or data have only been gathered on the responses at the whole seedling level or from images of whole leaves, summing the responses of different cell types (Johnson et al, 1995;Wood et al, 2000Wood et al, , 2001Love et al, 2004;Dodd et al, 2006Dodd et al, , 2010Zhu et al, 2013). In this study, we identify cell-and stimulusspecific [Ca 2+ ] i signals in the leaf and other tissues of Arabidopsis, suggesting the presence of cell-specific signaling cassettes in plants.…”

“…We use trichome, spongy mesophyll, epidermal pavement, vascular bundle, and guard cell-specific enhancer trap lines that we described previously (Dodd et al, 2006;Gardner et al, 2009) to investigate the responses of cell types to NaCl, cold, mechanical stimulation, and hydrogen peroxide (H 2 O 2 ) because all cause a rapid increase in [Ca 2+ ] i followed by dynamic alterations of [Ca 2+ ] i when measured in seedlings in which aequorin has been targeted to the whole seedling (Lynch et al, 1989;Price et al, 1994;Knight et al, 1996Knight et al, , 1997Monshausen et al, 2009 ] cyt were first detected in seedlings in which aequorin was constitutively expressed (Johnson et al, 1995) and later demonstrated to be occurring in the leaves (Love et al, 2004). The daily oscillations of [Ca 2+ ] cyt peak at around 300 nM about 8 h after dawn (Love et al, 2004). The circadian clock and PHYTOCHROME A-, CRYPTOCHROME1-, and CRYPTOCHROME2-dependent signaling pathways drive daily rhythms of [Ca 2+ ] cyt (Dalchau et al, 2010) with cyclic ADP ribose (cADPR) acting as an intermediary Xu et al, 2007).…”

Ca2+-dependent GTPase, Extra-large G Protein 2 (XLG2), Promotes Activation of DNA-binding Protein Related to Vernalization 1 (RTV1), Leading to Activation of Floral Integrator Genes and Early Flowering in Arabidopsis

“…It is likely that GTP-bound XLG2 and/or XLG2 cycling between GTP-and GDP-bound states, which occur in the presence of Ca 2ϩ , are required for enhanced RTV1 association with targets such as FT and SOC1. Circadian oscillations in intracellular free calcium ions ([Ca 2ϩ ] i ) occur and encode photoperiodic information (74,75). It is interesting to note that XLG2 and RTV1 transcripts exhibit in-phase circadian oscillation (see the Diurnal Search Tool Web site).…”

The theater management model of plant memory

“…The condensation of calcium onto charged membranes and linear polymers and might also underpin the organization of FDSs and chromatin and their putative action in memory. In many of our experiments, changes in the level of calcium are responsible for triggering what we have termed the recall of stored information and, significantly, calcium variations are central to diurnal rhythms in plants [35][36][37][38][39] and possibly to seasonal ones. [40][41][42] This is consistent with such variations playing a role in the sequential aspect of memory.…”