Receptor-Like Activity Evoked by Extracellular ADP in Arabidopsis Root Epidermal Plasma Membrane

Abstract

Extracellular purine nucleotides are implicated in the control of plant development and stress responses. While extracellular ATP is known to activate transcriptional pathways via plasma membrane (PM) NADPH oxidase and calcium channel activation, very little is known about signal transduction by extracellular ADP. Here, extracellular ADP was found to activate net Ca 2+ influx in roots of Arabidopsis (Arabidopsis thaliana) and transiently elevate cytosolic free Ca 2+ in root epidermal protoplasts. An inward Ca 2+ -permeable conductance in root epidermal PM was activated within 1 s of ADP application and repeated application evoked a smaller current. Such response speed and densitization are consistent with operation of equivalents to animal ionotropic purine receptors, although to date no equivalent genes for such receptors have been identified in higher plants. In contrast to ATP, extracellular ADP did not evoke accumulation of intracellular reactive oxygen species. While high concentrations of ATP caused net Ca 2+ efflux from roots, equivalent concentrations of ADP caused net influx. Overall the results point to a discrete ADP signaling pathway, reliant on receptor-like activity at the PM. Extracellular purine nucleotides have been shown to be involved in the regulation of plant cell viability, membrane permeability, immunity, symbiosis, stress responses, and growth

Rhizobial and Mycorrhizal Symbioses in Lotus japonicus Require Lectin Nucleotide Phosphohydrolase, Which Acts Upstream of Calcium Signaling

“…First, induction of the calcium influx requires a much higher level of Nod factor than does the induction of calcium spiking (Shaw andLong, 2003, Miwa et al, 2006a), so if GS52 silencing were to cause a change in sensitivity to Nod factor, it is possible that nodule morphogenesis could be induced but infection could mostly be blocked. Second, it is possible that Nod factor activation of LNP could increase extracellular ADP levels, and extracellular ADP has been shown to induce an inwardly directed calcium flux across the plasma membrane of root epidermal cells (Demidchik et al, 2011). This fits well with the proposal that a calcium influx may promote infection by rhizobia (Miwa et al, 2006a), but it does not fit so well with the observation that the soybean GS52 apyrase shows significantly higher activity with CTP, CDP, and ADP than it does with ATP (Tanaka et al, 2011).…”

Extracellular ATP signaling and homeostasis in plant cells

“…32 In addition, low doses of eATP (3 to 100 mM) induced an obvious Ca 2+ influx in elongation zone of Arabidopsis roots while higher doses of eATP (1,000 mM) caused a significant increase of Ca 2+ efflux. 24 In Populus euphratica cells, ATP-induced cell death was seen when the applied dose of eATP greater than 500 mM, while low doses (10-200 mM) did not cause PCD over the observation period. 13 These contrasting responses suggest that plant ATP sensors were discriminatively activated in response to different strength of ATP stimulus.…”

“…6,[18][19][20][21][22][23][24] The inhibition effects of ATP l S (a non-hydrolysable ATP homolog) on pollen germination and root hair growth were absent in Arabidopsis mutants with diminished NO and H 2 O 2 production, e.g., nia1/nia2 and atrbohD/F. 26,28 Similarly, genetic evidence also suggests that NO and H 2 O 2 contributed to the eATP-induced stomatal closure (.…”

“…19 In a more recent report, high concentrations (300 and 1,000 mM) of ATP caused a net Ca 2+ efflux from Arabidopsis roots. 24 This is likely a defense response since overloading of Ca 2+ in the cytosol would trigger programmed cell death in plant cells. 13 ATP application into intact root vacuoles of beet plants was found to induce an obvious Ca 2+ release, which is possibly mediated by the activation of depolarization-activated slow vacuolar (SV) channels.…”

“…16 Exogenous application of ATP to plant cells caused numerous physiological responses, including alteration of membrane potential, 17 14,15 and modulation of ion fluxes across the plasma membrane and tonoplast. 13,19,24 In addition to artificially increasing eATP concentrations in the ECM, a few studies focused on the effects of eATP depletion on plant and cellular responses. Slabas and colleagues reported that the removal of eATP caused expression of pathogenesis-related (PR) genes and cell death.…”