title: Plant cell growth and ion flux responses to the streptomycete phytotoxin thaxtomin A: calcium and hydrogen flux patterns revealed by the non-invasive MIFE technique.
abstract: Thaxtomin A, a key phytotoxin produced by plant pathogenic Streptomyces sp., is implicit in common scab disease expression in potato. Primary targets and modes of action of thaxtomin A toxicity in plant cells are not well understood. In this work, early signalling events associated with thaxtomin A toxicity were studied using the ion-selective microelectrode ion flux estimation (MIFE) technique. Thaxtomin A-induced changes in net ion fluxes were measured across the plasma membrane (PM) of root and pollen tube tissue in Arabidopsis thaliana and tomato. Within a minute after toxin application, a rapid and short-lived Ca2+ influx was observed. Well ahead of the marked inhibition of root growth, a significant shift towards net H+ efflux across the PM occurred in all tissues. Similar to root tissues, thaxtomin A significantly modified ion flux profiles from growing pollen tubes. Thaxtomin A was more effective in young, physiologically active tissues (root elongation zone or pollen tube apex), suggesting a higher density of thaxtomin A-binding sites in these regions. Overall, our data provide the first evidence that thaxtomin A triggers an early signalling cascade, which may be crucial in plant-pathogen interactions. It also suggests a possible interaction between thaxtomin A and PM auxin receptors, as revealed from experiments on the auxin-sensitive ucu2-2/gi2 A. thaliana mutant.
authors.affiliation: Tasmanian Institute of Agricultural Research, New Town Research Laboratories, 13 St John's Avenue, New Town, Tasmania 7008, Australia.
authors.forename: Robert Steven
authors.initials: RS
authors.lastname: Tegg
authors.forename: Lolita
authors.initials: L
authors.lastname: Melian
authors.forename: Calum Rae
authors.initials: CR
authors.lastname: Wilson
authors.forename: Sergey
authors.initials: S
authors.lastname: Shabala
mesh_terms: D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D004594:Electrophysiology / Q000295:instrumentation / Q000379:methods; D035264:Flowers / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D006859:Hydrogen / Q000378:metabolism; D007211:Indoles / Q000633:toxicity*; D018551:Solanum lycopersicum / Q000187:drug effects* / Q000254:growth & development; D008839:Microelectrodes; D009154:Mutation; D010879:Piperazines / Q000633:toxicity*; D010935:Plant Diseases; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D013302:Streptomyces
chemical_list: D007211:Indoles; D010879:Piperazines; C406691:thaxtomine A; D006859:Hydrogen; D002118:Calcium