title: Accumulation of 1,3-beta-D-glucans, in response to aluminum and cytosolic calcium in Triticum aestivum.
abstract: One of the most rapid responses to aluminum (Al) stress in plants is enhanced synthesis and deposition of 1,3-beta-D-glucans (callose) in root tips. Ironically, Al-induced synthesis and deposition of callose occurs in vivo, despite evidence from in vitro systems that suggests that Al is a powerful inhibitor of 1,3-beta-D-glucan synthase. We set out to test the hypothesis that an Al-induced increase in the activity of free calcium in the cytoplasm ([Ca(2+)](cyt)) is the trigger for enhanced synthesis of callose in in vivo systems, an effect that would not be observed in in vitro systems. Root tips of an Al-sensitive cultivar of Triticum aestivum were treated with Al (0-100 microM) or the Ca ionophore A23187 (0-3 micro M) for 3-24 h, and the effects on [Ca(2+)](cyt) and synthesis of callose were measured using confocal laser scanning microscopy. Treatment with Al induced a rapid increase in both [Ca(2+)](cyt) (4.7-fold) and synthesis of callose (30-fold). Treatment with the Ca ionophore, A23187, also elicited an increase in [Ca(2+)](cyt) (6.6-fold). Despite a greater increase in [Ca(2+)](cyt) in the presence of A23187, this increase was accompanied by a smaller increase in callose deposition (11-fold) than was observed in the presence of Al. These data suggest that an increase in [Ca(2+)](cyt) is not the only factor modulating increases in callose synthesis and deposition in the presence of Al.
authors.affiliation: University of Alberta, Department of Biological Sciences, CW405 Biological Sciences Building, Edmonton, Alberta, T6G 2E9 Canada.
authors.forename: Paulus
authors.initials: P
authors.lastname: Bhuja
authors.forename: Kristi
authors.initials: K
authors.lastname: McLachlan
authors.forename: Julie
authors.initials: J
authors.lastname: Stephens
authors.forename: Gregory
authors.initials: G
authors.lastname: Taylor
mesh_terms: D000535:Aluminum / Q000378:metabolism* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005936:Glucans / Q000096:biosynthesis / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D018613:Microscopy, Confocal; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D014908:Triticum / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D047071:beta-Glucans
chemical_list: D005936:Glucans; D007476:Ionophores; D047071:beta-Glucans; C033363:beta-1,3-glucan; C048306:callose; D000535:Aluminum; D002118:Calcium