Teor de lignina e respostas antioxidantes de milho forrageiro sob estresse salino e ácido salicílico exógeno
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Data
2018-03-23
Autores
Ferreira Júnior, Domingos da Costa
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Muitos estudos apontam que o ácido salicílico (AS) está envolvido na adaptação de plantas a estresses abióticos. Entretanto, pouco se sabe sobre a ação deste hormônio na síntese de importantes metabólitos secundários em condições de estresse, como a lignina. Para tanto, foram estudados neste trabalho os efeitos de AS exógeno no crescimento, lignificação, metabolismo antioxidativo, acúmulo de osmólitos compatíveis e acúmulo de Na+ e macronutrientes em folhas de milho sob concentrações crescentes de NaCl. O delineamento experimental utilizado foi o inteiramente casualizado em esquema fatorial 2x4, representado pelas concentrações de AS (0,0 e 0,5 mM) e concentrações de NaCl (0, 50, 100 e 150 mM). As plantas foram submetidas aos tratamentos no estádio fenológico V4 (quatro folhas completamente desenvolvidas), enquanto que as avaliações foram realizadas no estádio V6 (seis folhas completamente desenvolvidas). Foram avaliados os seguintes parâmetros na parte aérea: área foliar, massa seca, teor de lignina, peroxidação lipídica, teor de peróxido de hidrogênio (H2O2), atividade enzimática da superóxido dismutase (SOD) e catalase (CAT), teor de prolina (Pro) e glicina betaína, relação Na+/K+ e teor de macronutrientes (N, P, Ca, Mg, S). O estresse salino reduziu o crescimento da parte aérea da planta, além de induzir maior acúmulo de Pro e GB, peroxidação lipídica, atividade da CAT e lignificação foliar. A adição de AS à solução nutritiva atenuou o efeito da salinidade sobre o crescimento vegetal até a concentração de 100 mM de NaCl, o que pode estar relacionado à maior lignificação, aumento na atividade da SOD e teores de Pro e H2O2, maior teor de N e Ca, além de reduções nos níveis foliares de Na+ e peroxidação de lipídios. Dessa forma, conclui-se que o AS exógeno atenua os efeitos deletérios de estresse salino baixo e moderado por três vias: maior lignificação foliar, o que pode se relacionar à maior produção de H2O2; menor peroxidação lipídica, relacionada à maior atividade de SOD; e menor teor foliar de Na+, aliado a aumento nos teores de Ca2+ e N.
Several studies demonstrate that salicylic acid (AS) is involved in the adaptation responses of plants to abiotic stresses. However, not much is known about the action of this hormone on the synthesis of important secondary metabolites, as lignin. For this purpose, in this work it was assessed the effects of exogenous application of SA on the growth, lignification, antioxidant metabolism, compatible osmolytes content, and concentration of Na+ and in maize leaves under increasingly NaCl concentrations. It was adopted a completely randomized design and a 2x4 factorial layout, representing SA concentrations (0.0 and 0.5 mM) and NaCl concentrations (0, 50, 100 and 150 mM) in hydroponics. Plants were exposed to the treatments at the V4 phenological stage (with four completely developed leaves), and evaluations were performed at V6 stage (six completely developed leaves). The following parameters were assessed on shoots: leaf area, dry weight, lignin content, lipid peroxidation, enzymatic activity of superoxide dismutase (SOD) and catalase (CAT), proline (Pro) and glycinebetaine (GB) contents, Na+ /K+ ratio and macronutrients concentration (N, P, Ca, Mg and S). Salt stress impaired shoot growth, also inducting higher accumulation of Pro and GB, lipid peroxidation, CAT activity, leaf lignification and also lower content of all evaluated nutrients. The application of AS alleviated the deleterious effects of salinity on maize shoot growth until 100 mM of NaCl, what can be related to an enhancement of SOD activity, lignin, proline and H2O2 contents, higher N and Ca contents, as to lower lipid peroxidation and Na+ content. This way, it is concluded that exogenous AS mitigates the negative effects of low and moderate salt stress on maize through three main ways: higher leaf lignification, which can be correlated with higher H2O2; lower lipid peroxidation, explained by higher SOD activity; and lower Na+ content, followed by increased leaf contents of Ca2+ .
Several studies demonstrate that salicylic acid (AS) is involved in the adaptation responses of plants to abiotic stresses. However, not much is known about the action of this hormone on the synthesis of important secondary metabolites, as lignin. For this purpose, in this work it was assessed the effects of exogenous application of SA on the growth, lignification, antioxidant metabolism, compatible osmolytes content, and concentration of Na+ and in maize leaves under increasingly NaCl concentrations. It was adopted a completely randomized design and a 2x4 factorial layout, representing SA concentrations (0.0 and 0.5 mM) and NaCl concentrations (0, 50, 100 and 150 mM) in hydroponics. Plants were exposed to the treatments at the V4 phenological stage (with four completely developed leaves), and evaluations were performed at V6 stage (six completely developed leaves). The following parameters were assessed on shoots: leaf area, dry weight, lignin content, lipid peroxidation, enzymatic activity of superoxide dismutase (SOD) and catalase (CAT), proline (Pro) and glycinebetaine (GB) contents, Na+ /K+ ratio and macronutrients concentration (N, P, Ca, Mg and S). Salt stress impaired shoot growth, also inducting higher accumulation of Pro and GB, lipid peroxidation, CAT activity, leaf lignification and also lower content of all evaluated nutrients. The application of AS alleviated the deleterious effects of salinity on maize shoot growth until 100 mM of NaCl, what can be related to an enhancement of SOD activity, lignin, proline and H2O2 contents, higher N and Ca contents, as to lower lipid peroxidation and Na+ content. This way, it is concluded that exogenous AS mitigates the negative effects of low and moderate salt stress on maize through three main ways: higher leaf lignification, which can be correlated with higher H2O2; lower lipid peroxidation, explained by higher SOD activity; and lower Na+ content, followed by increased leaf contents of Ca2+ .
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Zea mays L.;, Salinidade, Regulador vegetal, Estresse oxidativo, Lignificação, salinity, plant growth regulator, lignification, oxidative stress