Both the stimulation and inhibition of root hair growth induced by extracellular nucleotides in Arabidopsis are mediated by nitric oxide and reactive oxygen species

Abstract

Root hairs secrete ATP as they grow, and extracellular ATP and ADP can trigger signaling pathways that regulate plant cell growth. In several plant tissues the level of extracellular nucleotides is limited in part by ectoapyrases (ecto-NTPDases), and the growth of these tissues is strongly influenced by their level of ectoapyrase expression. Both chemical inhibition of ectoapyrase activity and suppression of the expression of two ectoapyrase enzymes by RNAi in Arabidopsis resulted in inhibition of root hair growth. As assayed by a dose-response curve, different concentrations of the poorly hydrolysable nucleotides, ATPγS and ADPβS, could either stimulate (at 7.5-25 μM) or inhibit (at ≥ 150 μM) the growth rate of root hairs in less than an hour. Equal amounts of AMPS, used as a control, had no effect on root hair growth. Root hairs of nia1nia2 mutants, which are suppressed in nitric oxide (NO) production, and of atrbohD/F mutants, which are suppressed in the production of H(2)O(2), did not show growth responses to applied nucleotides, indicating that the growth changes induced by these nucleotides in wild-type plants were likely transduced via NO and H(2)O(2) signals. Consistent with this interpretation, treatment of root hairs with different concentrations of ATPγS induced different accumulations of NO and H(2)O(2) in root hair tips. Two mammalian purinoceptor antagonists also blocked the growth responses induced by extracellular nucleotides, suggesting that they were initiated by a receptor-based mechanism.

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

“…Extracellular purine nucleotides have been shown to be involved in the regulation of plant cell viability, membrane permeability, immunity, symbiosis, stress responses, and growth (Lew and Dearnaley, 2000;Tang et al, 2003;Chivasa et al, 2005Chivasa et al, , 2009Kim et al, 2006Kim et al, , 2009Roux and Steinebrunner, 2007;Wu et al, 2007;Riewe et al, 2008a;Wu and Wu, 2008;Yi et al, 2008;Demidchik et al, 2009;Govindarajulu et al, 2009;Kim et al, 2009;Clark et al, 2010aClark et al, , 2010bTanaka et al, 2010aTanaka et al, , 2010bTerrile et al, 2010;Tonó n et al, 2010). Purine nucleotide release from plant cells may occur through wounding, exocytosis, or through the activity of plasma membrane (PM) ATP-binding cassette transporters (Thomas et al, 2000;Kim et al, 2006).…”

“…Growth points are hotspots of extracellular ATP (Kim et al, 2006) while touch-stimulated ATP release is mediated by heterotrimeric G-protein activity (Weerasinghe et al, 2009). Levels of extracellular ATP and ADP can be regulated by the concerted action of ecto-apyrases, phosphatases, and adenosine nucleosidases with retrieval of adenine (the ultimate hydrolytic product) by PM purine permeases (Komoszyń ski, 1996;Steinebrunner et al, 2003;Wu et al, 2007;Riewe et al, 2008aRiewe et al, , 2008bGovindarajulu et al, 2009;Clark et al, 2010b;Liang et al, 2010). Manipulation of ecto-apyrase levels results in abnormal growth in Arabidopsis (Arabidopsis thaliana), cotton (Gossypium hirsutum), and potato (Solanum tuberosum; Wu et al, 2007;Riewe et al, 2008a;Clark et al, 2010aClark et al, , 2010b while nodulation by Bradyrhizobium japonicum is impaired in ecto-apyrase-deficient soybean (Glycine max; Govindarajulu et al, 2009).…”

“…Levels of extracellular ATP and ADP can be regulated by the concerted action of ecto-apyrases, phosphatases, and adenosine nucleosidases with retrieval of adenine (the ultimate hydrolytic product) by PM purine permeases (Komoszyń ski, 1996;Steinebrunner et al, 2003;Wu et al, 2007;Riewe et al, 2008aRiewe et al, , 2008bGovindarajulu et al, 2009;Clark et al, 2010b;Liang et al, 2010). Manipulation of ecto-apyrase levels results in abnormal growth in Arabidopsis (Arabidopsis thaliana), cotton (Gossypium hirsutum), and potato (Solanum tuberosum; Wu et al, 2007;Riewe et al, 2008a;Clark et al, 2010aClark et al, , 2010b while nodulation by Bradyrhizobium japonicum is impaired in ecto-apyrase-deficient soybean (Glycine max; Govindarajulu et al, 2009). Current models suggest that poise of the cell's state between death, stress adaptation, and growth involves signaling governed by the level of extracellular ATP (Chivasa et al, 2005Roux and Steinebrunner, 2007;Wu et al, 2007;Wu and Wu, 2008;Kim et al, 2009;Clark et al, 2010aClark et al, , 2010bTerrile et al, 2010;Tonó n et al, 2010).…”

“…Manipulation of ecto-apyrase levels results in abnormal growth in Arabidopsis (Arabidopsis thaliana), cotton (Gossypium hirsutum), and potato (Solanum tuberosum; Wu et al, 2007;Riewe et al, 2008a;Clark et al, 2010aClark et al, , 2010b while nodulation by Bradyrhizobium japonicum is impaired in ecto-apyrase-deficient soybean (Glycine max; Govindarajulu et al, 2009). Current models suggest that poise of the cell's state between death, stress adaptation, and growth involves signaling governed by the level of extracellular ATP (Chivasa et al, 2005Roux and Steinebrunner, 2007;Wu et al, 2007;Wu and Wu, 2008;Kim et al, 2009;Clark et al, 2010aClark et al, , 2010bTerrile et al, 2010;Tonó n et al, 2010).…”

“…The resultant reactive oxygen species (ROS) activate a PM Ca 2+ influx pathway that governs a transcriptional response. In Arabidopsis root hairs, extracellular ATP also causes intracellular ROS accumulation by activating NADPH oxidases (Clark et al, 2010b). Leaves also support extracellular ATP-induced transcription via PM NADPH oxidases (Song et al, 2006).…”