title: Root growth restraint can be an acclimatory response to low pH and is associated with reduced cell mortality: a possible role of class III peroxidases and NADPH oxidases.
abstract: Low pH (<5.0) can significantly decrease root growth but whether this is a direct effect of H(+) or an active plant response is examined here. Tomato (Solanum lycopersicum cv Micro-Tom) roots were exposed directly or gradually to low pH through step-wise changes in pH over periods ranging from 4 to 24 h. Roots exposed gradually to pH 4.5 grew even less than those exposed directly, indicating a plant-coordinated response. Direct exposure to pH 4.0 suppressed root growth and caused high cell mortality, in contrast to roots exposed gradually, in which growth remained inhibited but cell viability was maintained. Total class III peroxidase activity increased significantly in all low pH treatments, but was not correlated with the observed differential responses. Use of the enzyme inhibitors salicylhydroxamic acid (SHAM) or diphenyleneiodonium chloride (DPI) suggest that peroxidase and, to a lesser extent, NADPH oxidase were required to prevent or reduce injury in all low pH treatments. However, a role for other enzymes, such as the alternative oxidase is also possible. The results with SHAM, but not DPI, were confirmed in tobacco BY-2 cells. Our results indicate that root growth inhibition from low pH can be part of an active plant response, and suggest that peroxidases may have a critical early role in reducing loss of cell viability and in the observed root growth constraint.
authors.affiliation: Escola Superior de Agricultura 'Luiz de Queiroz', University of São Paulo, Piracicaba, Brazil.
authors.forename: J P
authors.initials: JP
authors.lastname: Graças
authors.affiliation: Centro de Energia Nuclear na Agricultura, University of São Paulo, Piracicaba, Brazil.
authors.forename: R
authors.initials: R
authors.lastname: Ruiz-Romero
authors.affiliation: Escola Superior de Agricultura 'Luiz de Queiroz', University of São Paulo, Piracicaba, Brazil.
authors.forename: L D
authors.initials: LD
authors.lastname: Figueiredo
authors.affiliation: Escola Superior de Agricultura 'Luiz de Queiroz', University of São Paulo, Piracicaba, Brazil.
authors.forename: L
authors.initials: L
authors.lastname: Mattiello
authors.affiliation: Escola Superior de Agricultura 'Luiz de Queiroz', University of São Paulo, Piracicaba, Brazil.
authors.forename: L E P
authors.initials: LE
authors.lastname: Peres
authors.affiliation: Centro de Energia Nuclear na Agricultura, University of São Paulo, Piracicaba, Brazil.
authors.forename: V A
authors.identifier: http://orcid.org/0000-0001-9677-7444
authors.initials: VA
authors.lastname: Vitorello
mesh_terms: D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D018551:Solanum lycopersicum / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development / Q000502:physiology; D024101:Mitochondrial Proteins / Q000378:metabolism; D019255:NADPH Oxidases / Q000378:metabolism*; D009861:Onium Compounds / Q000494:pharmacology; D010088:Oxidoreductases / Q000378:metabolism; D010544:Peroxidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development / Q000502:physiology; D012457:Salicylamides / Q000494:pharmacology; D014026:Nicotiana / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development / Q000502:physiology; D000099188:Alternative Oxidase
chemical_list: D004791:Enzyme Inhibitors; D024101:Mitochondrial Proteins; D019255:NADPH Oxidases; D009861:Onium Compounds; D010088:Oxidoreductases; D010544:Peroxidases; D010940:Plant Proteins; D012457:Salicylamides; D000099188:Alternative Oxidase; C007517:diphenyleneiodonium; C005703:salicylhydroxamic acid
keywords: Cell viability; NADPH oxidase; cell wall; class III peroxidase; low pH; root growth