title: Molecular and physiological analysis of Al³⁺ and H⁺ rhizotoxicities at moderately acidic conditions.
abstract: Al³⁺ and H⁺ toxicities predicted to occur at moderately acidic conditions (pH [water] = 5-5.5) in low-Ca soils were characterized by the combined approaches of computational modeling of electrostatic interactions of ions at the root plasma membrane (PM) surface and molecular/physiological analyses in Arabidopsis (Arabidopsis thaliana). Root growth inhibition in known hypersensitive mutants was correlated with computed {Al³⁺} at the PM surface ({Al³⁺}(PM)); inhibition was alleviated by increased Ca, which also reduced {Al³⁺}(PM) and correlated with cellular Al responses based on expression analysis of genes that are markers for Al stress. The Al-inducible Al tolerance genes ALUMINUM-ACTIVATED MALATE TRANSPORTER1 and ALUMINUM SENSITIVE3 were induced by levels of {Al³⁺}(PM) too low to inhibit root growth in tolerant genotypes, indicating that protective responses are triggered when {Al³⁺}(PM) was below levels that can initiate injury. Modeling of the H⁺ sensitivity of the SENSITIVE TO PROTON RHIZOTOXICITY1 knockout mutant identified a Ca alleviation mechanism of H⁺ rhizotoxicity, possibly involving stabilization of the cell wall. The phosphatidate phosphohydrolase1 (pah1) pah2 double mutant showed enhanced Al susceptibility under low-P conditions, where greater levels of negatively charged phospholipids in the PM occur, which increases {Al³⁺}(PM) through increased PM surface negativity compared with wild-type plants. Finally, we found that the nonalkalinizing Ca fertilizer gypsum improved the tolerance of the sensitive genotypes in moderately acidic soils. These findings fit our modeling predictions that root toxicity to Al³⁺ and H⁺ in moderately acidic soils involves interactions between both toxic ions in relation to Ca alleviation.
authors.affiliation: Faculty of Applied Biological Sciences, Gifu University, Gifu 501-1193, Japan.
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Watanabe
authors.forename: Jon E
authors.initials: JE
authors.lastname: Shaff
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
authors.forename: Leon V
authors.initials: LV
authors.lastname: Kochian
authors.forename: Tadao
authors.initials: T
authors.lastname: Wagatsuma
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Kinraide
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Koyama
mesh_terms: D000535:Aluminum / Q000633:toxicity*; D017360:Arabidopsis / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D055786:Gene Knockout Techniques; D006859:Hydrogen / Q000633:toxicity*; D006863:Hydrogen-Ion Concentration; D008957:Models, Genetic; D018517:Plant Roots / Q000254:growth & development / Q000502:physiology; D012987:Soil / Q000737:chemistry; D013312:Stress, Physiological
chemical_list: D029681:Arabidopsis Proteins; D012987:Soil; D006859:Hydrogen; D000535:Aluminum; D002118:Calcium