Efeitos do glyphosate e do fósforo em eucalipto
Carregando...
Data
2016-06-10
Autores
Pereira, Fernanda Campos Mastrotti [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
A cultura do eucalipto apresenta uma grande importância no cenário econômico nacional e mundial, oferecendo uma vasta gama de produtos florestais. No entanto, a disponibilidade de fósforo nos solos raramente é adequada para o crescimento, desenvolvimento e produtividade das plantas de eucalipto, bem como para diversas outras culturas. A presença de plantas daninhas em eucaliptais é outro fator limitante, e para o manejo da comunidade infestante, glyphosate é o herbicida mais utilizado. As plantas de eucalipto, quando cultivadas em diferentes concentrações de fósforo, podem alterar a expressão gênica de transportadores de fosfato. Em algumas condições, a síntese de transportadores de fosfato de alta afinidade pode ser incrementada. Esses transportadores podem ter afinidade pelo grupo fosfonato do glyphosate, transportando esse herbicida via membrana plasmática. Assim, podem ocorrer alterações no comportamento do glyphosate em função das concentrações de fósforo. Estudos do efeito diferencial de glyphosate em função de concentrações de fósforo e do transporte de glyphosate mediado por transportadores de fosfato ainda são escassos, principalmente em uma espécie perene, como o eucalipto. Com essa pesquisa objetivou-se (1) avaliar, em clones de Eucalyptus urophylla (GG100 e I144) a cinética de absorção de fósforo, as eficiências nutricionais de macronutrientes e seus reflexos no crescimento das plantas; (2) verificar as alterações fotossintéticas, metabólicas e nutricionais de clones de E. urophylla (GG100 e I144) cultivados em concentrações de fósforo e submetidos à aplicação de glyphosate; e (3) estudar, em E. grandis, a coordenação da expressão gênica de transportadores de fosfato, a absorção e a translocação de 14C-glyphosate, e o transporte de 14C-glyphosate através da membrana plasmática em protoplastos. Os experimentos com E. urophylla foram realizados na Universidade Estadual Paulista, Câmpus de Jaboticabal, SP, enquanto aqueles com E. grandis foram desenvolvidos na University of Maryland, Maryland, EUA. Após a avaliação dos parâmetros cinéticos de absorção de fósforo, o clone I144 foi superior, apresentando menores Cmín e Km (concentração limite abaixo da qual a planta é incapaz de absorver um elemento na solução e concentração do nutriente na solução onde foi atingida metade da Vmáx, respectivamente) e maior Vmáx (velocidade máxima de absorção). As eficiências de absorção, translocação e utilização de macronutrientes também foram maiores no clone I144, com exceção da eficiência de utilização de potássio, superior no clone GG100. Não houve diferenças na eficiência nutricional dos clones em relação ao boro. Para a avaliação das alterações fotossintéticas, metabólicas e nutricionais ocasionadas por glyphosate em função de concentrações de fósforo, experimentos foram conduzidos em casa de vegetação utilizando areia como substrato (pulverização foliar de glyphosate) e em câmara de crescimento utilizando sistema hidropônico (aplicação radicular de glyphosate). Para ambos os experimentos, os nutrientes foram oferecidos por meio da solução nutritiva, que foi ajustada para as doses de fósforo 0,5X; 1X e 1,5X de fósforo (em que X correspondeu à concentração de fósforo recomendada para o preparo da solução nutritiva). Interações entre as concentrações de fósforo e as doses de glyphosate ocorreram nas características que avaliaram o processo fotossintético (teores de clorofila e eficiência quântica do fotossistema II), nos teores de glyphosate, AMPA e ácido chiquímico, nos teores nutricionais e massas secas. Essas características ou teores foram menores ou mais intensamente reduzidos, após glyphosate, nas plantas cultivadas com menores concentrações de fósforo (0,5X e, em alguns casos, 1X). Por fim, experimentos foram conduzidos em E. grandis, e a expressão gênica dos transportadores de fosfato (mensurada por meio de RT-qPCR) nas folhas e nas raízes dessas plantas foram alteradas em resposta a deficiência de fosfato. A expressão de transportadores de alta afinidade foi incrementada pela deficiência de fosfato. A absorção de 14C-glyphosate aplicado via foliar ou radicular foi maior nas plantas submetidas à deficiência de fosfato, e a translocação deste herbicida também foi mais rápida nessas plantas. Nos protoplastos, o transporte de 14C-glyphosate via membrana plasmática ocorreu rapidamente na ausência de fosfato, e de modo mais lento quando NaH2PO4 foi adicionado ao meio. Possivelmente, o transporte de fosfato através da membrana plasmática foi realizado em um primeiro momento, e com a redução do fosfato disponível no meio, o transporte de glyphosate foi iniciado, provavelmente, por transportadores de fosfato de alta afinidade.
Eucalypt plantation have great importance in the national and global economic environment, offering a wide range of forest products. However, the phosphorus availability in soils is rarely appropriate for growth, development and yield of eucalypt plants, as well as several other crops. The presence of weeds in eucalypt plantations is another limiting factor, and for weed management glyphosate is the most used herbicide. Eucalypt plants grown under different phosphorus concentrations can change phosphate transporters gene expression. Under specific conditions, high-affinity phosphate transporter synthesis can be increased. Such transporters can have affinity for glyphosate phosphonate group, transporting this herbicide through plasma membrane. So, changes may occur in glyphosate behavior depending on phosphorus concentrations. Studies of glyphosate effect as a function of phosphorus concentrations and glyphosate transport mediated by phosphate transporters are still scarce, especially in a perennial species, such as eucalypt. This study aimed (1) to evaluate, in Eucalyptus urophylla clones (GG100 and I144), the phosphorus absorption kinetics, the nutritional efficiency of macronutrients and their effects on plant growth; (2) verify the photosynthetic, nutritional and metabolic changes in E. urophylla clones (GG100 and I144) grown under phosphorus concentrations and submitted to glyphosate application; and (3) study in E. grandis the phosphate transporters gene expression coordination, the 14C-glyphosate uptake and translocation, and the 14C-glyphosate transport through the plasma membrane in protoplasts. The experiments with E. urophylla were carried out at São Paulo State University, Campus of Jaboticabal, SP, while the experiment with E. grandis were developed at University of Maryland, Maryland, USA. After the evaluation of phosphorus absorption kinetic parameters, I144 clone was considered superior, presenting lower Cmin and Km (respectively, the limiting concentration for absorbing an element in solution and the nutrient concentration in solution which was reached half of Vmax,) and higher Vmax (maximum rate of absorption). The efficiency of absorption, translocation and utilization of macronutrients were also higher in I144 clone, with the exception of potassium utilization efficiency, higher in GG100 clone. No differences in boron nutritional efficiency were found. For the evaluation of photosynthetic, nutritional and metabolic changes caused by glyphosate according phosphorus concentrations, experiments were performed in a greenhouse using sand (glyphosate sprayed in leaves) and in a growth chamber using hydroponic system (glyphosate applied in roots). For both experiments, nutrients were provided by nutrient solution, which was adjusted to phosphorus levels 0.5X, 1X and 1.5X (where X corresponded to the phosphorus concentration recommended for nutrient solution preparation). Interactions between phosphorus concentration and glyphosate doses occurred in the characteristics that evaluated the photosynthetic process (chlorophyll content and quantum efficiency of photosystem II), in the glyphosate, AMPA and shikimic acid content, and in the nutritional content and dry mass. These characteristics or contents were smaller or more strongly reduced after glyphosate in plants grown with lower phosphorus concentration (0.5X, and in some cases, 1X). Finally, experiments were conducted in E. grandis, and the gene expression of phosphate transporters (measured by RT-qPCR) in leaves and roots of these plants have been modified as a phosphate deficiency response. High-affinity transporters expression was increased by phosphate deficiency. The absorption of 14C-glyphosate applied in leaves or roots was higher in plants subjected to phosphate deficiency, and glyphosate translocation was also faster in these plants. In protoplasts, 14Cglyphosate transport via plasma membrane was fast in phosphate absence and slower when NaH2PO4 was added to the medium. Possibly, the phosphate transport through the plasma membrane was performed initially, and with the phosphate reduction in the medium, the glyphosate transport was started probably for highaffinity phosphate transporters.
Eucalypt plantation have great importance in the national and global economic environment, offering a wide range of forest products. However, the phosphorus availability in soils is rarely appropriate for growth, development and yield of eucalypt plants, as well as several other crops. The presence of weeds in eucalypt plantations is another limiting factor, and for weed management glyphosate is the most used herbicide. Eucalypt plants grown under different phosphorus concentrations can change phosphate transporters gene expression. Under specific conditions, high-affinity phosphate transporter synthesis can be increased. Such transporters can have affinity for glyphosate phosphonate group, transporting this herbicide through plasma membrane. So, changes may occur in glyphosate behavior depending on phosphorus concentrations. Studies of glyphosate effect as a function of phosphorus concentrations and glyphosate transport mediated by phosphate transporters are still scarce, especially in a perennial species, such as eucalypt. This study aimed (1) to evaluate, in Eucalyptus urophylla clones (GG100 and I144), the phosphorus absorption kinetics, the nutritional efficiency of macronutrients and their effects on plant growth; (2) verify the photosynthetic, nutritional and metabolic changes in E. urophylla clones (GG100 and I144) grown under phosphorus concentrations and submitted to glyphosate application; and (3) study in E. grandis the phosphate transporters gene expression coordination, the 14C-glyphosate uptake and translocation, and the 14C-glyphosate transport through the plasma membrane in protoplasts. The experiments with E. urophylla were carried out at São Paulo State University, Campus of Jaboticabal, SP, while the experiment with E. grandis were developed at University of Maryland, Maryland, USA. After the evaluation of phosphorus absorption kinetic parameters, I144 clone was considered superior, presenting lower Cmin and Km (respectively, the limiting concentration for absorbing an element in solution and the nutrient concentration in solution which was reached half of Vmax,) and higher Vmax (maximum rate of absorption). The efficiency of absorption, translocation and utilization of macronutrients were also higher in I144 clone, with the exception of potassium utilization efficiency, higher in GG100 clone. No differences in boron nutritional efficiency were found. For the evaluation of photosynthetic, nutritional and metabolic changes caused by glyphosate according phosphorus concentrations, experiments were performed in a greenhouse using sand (glyphosate sprayed in leaves) and in a growth chamber using hydroponic system (glyphosate applied in roots). For both experiments, nutrients were provided by nutrient solution, which was adjusted to phosphorus levels 0.5X, 1X and 1.5X (where X corresponded to the phosphorus concentration recommended for nutrient solution preparation). Interactions between phosphorus concentration and glyphosate doses occurred in the characteristics that evaluated the photosynthetic process (chlorophyll content and quantum efficiency of photosystem II), in the glyphosate, AMPA and shikimic acid content, and in the nutritional content and dry mass. These characteristics or contents were smaller or more strongly reduced after glyphosate in plants grown with lower phosphorus concentration (0.5X, and in some cases, 1X). Finally, experiments were conducted in E. grandis, and the gene expression of phosphate transporters (measured by RT-qPCR) in leaves and roots of these plants have been modified as a phosphate deficiency response. High-affinity transporters expression was increased by phosphate deficiency. The absorption of 14C-glyphosate applied in leaves or roots was higher in plants subjected to phosphate deficiency, and glyphosate translocation was also faster in these plants. In protoplasts, 14Cglyphosate transport via plasma membrane was fast in phosphate absence and slower when NaH2PO4 was added to the medium. Possibly, the phosphate transport through the plasma membrane was performed initially, and with the phosphate reduction in the medium, the glyphosate transport was started probably for highaffinity phosphate transporters.
Descrição
Palavras-chave
Eucalyptus grandis, Membrana plasmática, Proteínas, Transportadores de fosfato, Eucalyptus grandis, Cell membrane, Proteins, Phosphate transporters