Ação do etileno e de intermediários reativos de oxigênio sobre o crescimento de ápices radiculares em dois genótipos de milho, na presença de alumínio

• Main Author: Fonseca Júnior, élcio Meira da
• Publication Date: 2011
• Format: Doctoral thesis
• Language: por
• Source: LOCUS Repositório Institucional da UFV
• Download full: http://locus.ufv.br/handle/123456789/985
• topic: Alumínio; Etileno; Intermediários reativos de oxigênio; Estresse oxidativo; Milho; Aluminum; Ethylene; Reactive oxygen intermediates; Oxidative stress; Maize; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

The main objective of this study was to evaluate the action of ethylene and reactive oxygen intermediates (ROIs) in the inhibition of root tips growth caused by Al in two genotypes of maize. Seedlings of two maize genotypes, UFVM 100 (sensitive) and UFVM 200 (tolerant) were subjected to treatments with Al 0 and 100 μM in 0.5 mM CaCl2 solution for 24 hours. Al treatment inhibited root elongation and increased ethylene production in two maize genotypes with greater intensity in the UFVM 100. The correlation coefficients between root elongation and ethylene levels in the presence of Al, were -0.97 and -0.90, for genotypes UFVM 200 and 100, respectively. Al treatment also increased the enzymes activities of ethylene synthesis, aminocyclopropane carboxylic acid synthase (ACS) and aminocyclopropane carboxylic acid oxidase (ACO), in both maize genotypes with ever greater intensity in the sensitive genotype. The treatment of seedlings with precursors of ethylene biosynthesis, aminocyclopropane carboxylic acid (ACC) and ethrel inhibited root elongation in the same intensity as that caused by Al applied alone, in both genotypes. On the other hand, application of inhibitors of ethylene synthesis: aminooxiacetic acid (inhibitor of ACS), cobalt chloride (inhibitor of ACO) and silver thiosulfate (inhibitor of ethylene perception) eliminated the inhibition of root elongation caused by the Al in both genotypes. Al treatment increased the levels of superoxide anion and the activities of the enzymes superoxide dismutase and peroxidase, reduced hydrogen peroxide content, but did not influence the activities of catalase and ascorbate peroxidase. None of these variables was modified by Al treatment in the tolerant genotype. Al also increased the activities of enzymes NADPH oxidase (NOX), diamine oxidase (DAO) and NADH peroxidase (NADH-POX) in fractions of plasma membrane and cell wall related to the production of ROIs in the root apoplast, only in the sensitive genotype. Among the inhibitors used: diphenylene iodonium, sodium azide and 2-hidroxietilhidrazina only the azide and the combination of three inhibitors partially eliminated the effect of Al in the genotype UFVM 100. The increase in the activity of DAO enzymes, NADH-POX and NOX was taken as indicative of an increase in the level of ROIs in the apoplast of plants of the genotype UFVM 100 treated with Al. Although no increase in lipid peroxidation in root tips has been observed, we believe that the accumulation of ROIs in the apoplast was high enough to activate peroxidases linked to the cell wall causing cell wall stiffening and, therefore, inhibiting root elongation. The genotype UFVM 200 suffered no damage oxidative in the conditions of this experiment. The sum of these responses of maize genotypes studied suggests that the inhibition of root elongation induced by toxic levels of Al is mediated by signaling mechanisms involving the synthesis and perception of ethylene and the production and removal of reactive oxygen intermediates in the apoplast root.