Evidence of a Novel Cell Signaling Role for Extracellular Adenosine Triphosphates and Diphosphates in Arabidopsis

Abstract

Extracellular ATP is a known receptor agonist in animals and was previously shown to alter plant growth, and so we investigated whether ATP derivatives could function outside plant cells as signaling agents. Signaling responses induced by exogenous nucleotides in animal cells typically include increases in free cytoplasmic calcium concentration ([Ca 2þ ] cyt ). We have evaluated the ability of exogenously applied adenosine 59-[g-thio]triphosphate (ATPgS), adenosine 59-[b-thio]diphosphate (ADPbS), and adenosine 59-O-thiomonophosphate to alter [Ca 2þ ] cyt in intact apoaequorin transgenic Arabidopsis thaliana seedlings. ATPgS and ADPbS increase [Ca 2þ ] cyt , and this increase is enhanced further when the nucleotides are added with the elicitor oligogalacturonic acid. Exogenous treatment with ATP also increases the level of transcripts encoding mitogen-activated protein kinases and proteins involved in ethylene biosynthesis and signal transduction. The increase in [Ca 2þ ] cyt induced by nucleotide derivatives can be ablated by Ca 2þ -channel blocking agents and by the calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N9,N9-tetraacetic acid (BAPTA), and the changes in gene expression can be partially blocked by these agents. These observations suggest that extracellular ATP can activate calcium-mediated cell-signaling pathways in plants, potentially playing a physiological role in transducing stress and wound responses.

Fluorescence Resonance Energy Transfer-Sensitized Emission of Yellow Cameleon 3.60 Reveals Root Zone-Specific Calcium Signatures in Arabidopsis in Response to Aluminum and Other Trivalent Cations

“…1). In contrast to previous studies with Glu and ATP, which relied mostly on luminescence-based [Ca 2+ ] cyt measurements with aequorin-expressing plant cells (Dennison and Spalding, 2000;Demidchik et al, 2003;Jeter et al, 2004;Qi et al, 2006), the improved spatial resolution of FRETbased confocal imaging of YC3.60 allowed us to define regions of the root from which a particular [Ca 2+ ] cyt response originated. In doing so, we showed that all developmental regions of the root exhibited a [Ca 2+ ] cyt response to Glu and ATP.…”

“…Since ATP has been shown to induce [Ca 2+ ] cyt increases in plants using methods such as aequorin (Demidchik et al, 2003;Jeter et al, 2004) (Fig. 1B), the ATP-induced increase in [Ca 2+ ]cyt was generally followed by a more gradual decline that spanned a period of approximately 3 to 5 min (Fig.…”

Apyrases (Nucleoside Triphosphate-Diphosphohydrolases) Play a Key Role in Growth Control in Arabidopsis

“…For experiments measuring the [ATP] of the PGM, aliquots (30 mL) of medium were removed at 1 and 15 min after the treatments were applied, immediately placed in 1.5-mL graduated plastic vials, labeled, sealed, and frozen in liquid nitrogen until they were analyzed for ATP concentration as described by Jeter et al (2004).…”

“…For pollen growth experiments in which the volume of growth medium applied was 150 mL, the [eATP] in the medium was measured by luciferin-luciferase assay (Jeter et al, 2004) at 1 min after it was placed over the germinated grains and then again at 15 min after being applied. In all trials, the [eATP] of the medium rose between the first and second measurements and these increases were normalized for all experiments by expressing them as fold increases between the first and second time points assayed.…”

“…Of the apyrases characterized in plants, some are plasma membrane associated (Thomas et al, 1999;Day et al, 2000), but the subcellular locale of most of them has not been determined. Plasma membrane-associated apyrases in plants could, in principle, function as ectoapyrases because plant cells, like animal cells, release significant quantities of ATP into their ECM when they are mechanically stimulated (Jeter et al, 2004), when they are wounded , and when they are engaged in activities that involve active secretion, such as growth (Kim et al, 2006). Moreover, control of this eATP could be important because plant cells have significant signaling responses to submicromolar ATP (Demidchik et al, 2003;Song et al, 2006) and extensive depletion of eATP can result in loss of cell viability (Chivasa et al, 2005).…”