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(ISAAA, 2006). A soja geneticamente modificada resistente ao glifosato (GM RR ) foi obtida pela introdução, juntamente com a região t-DNA e o gene marcador de seleção, de gene correspondente à enzima 5-enolpiruvilchiquimato-3-fosfato sintase (EPSPS, E.C. 2.5.1.19, CP4), enzima da via de chiquimato, resistente ao glifosato, mantendo ativa a via biossintética de aminoácidos aromáticos (BUSSE et al., 2001). O glifosato [N-(fosfonometil) glicina] age sobre a enzima EPSPS inibindo a via de síntese dos aminoácidos aromáticos essenciais, fenilalanina, triptofano e tirosina, os quais são precursores de outros produtos, como lignina, alcalóides, flavonóides e ácidos benzóicos (AMARANTE; SANTOS, 2002). A priori, a soja GM RR é tolerante ao glifosato por possuir uma isoforma da EPSPS resistente a essa molécula. Porém, é sabido que o glifosato será absorvido e metabolizado pela planta podendo alterar o metabolismo secundário, uma vez AbstractThe use of Glyphosate is the best way to control weed growing when cultivating genetically modified soybean (GMRR) BRS 244 RR. However, there have been doubts about the safety of this herbicide use concerning its effects on the quality of grains and on the soil of Albaqualf cultivated GMRR soybean. Glyphosate and the metabolite aminomethylphosphonic acid (AMPA) residues can be present in the grains and affect the isoflavones concentration. Therefore, BRS 244 RR and BRS 154 soybeans with the following cultivated treatments were evaluated: T1 -soybean BRS 244 RR, without herbicide and hand-weeded at 28 days after planting (dap); T2 -soybean BRS 154, without herbicide and hand-weeded at 28 dap; T3 -soybean BRS 244 RR with one application of 960 g ai ha -1 of glyphosate at 28 dap; T4 -soybean BRS 244 RR, with two applications of 960 g ai ha -1 of glyphosate at 28 and 56 dap; T5 -soybean BRS 244 RR, with one application of 100 g ai ha -1 of imazethapyr at 28 dap; and T6 -soybean BRS 154 with one application of 100 g ai ha -1 of imazethapyr at 28 dap. It was verified that the glyphosate application for weed control resulted in high levels of glyphosate and aminomethylphosphonic acid on the soil. The levels of isoflavone in the grains apparently were not affected by the glyphosate application, but the herbicide residues were higher than the current amount allowed by the legislation (10 mg.kg -1 ).

Transformação genética e aplicação de glifosato na microbiota do solo, fixação biológica de nitrogênio, qualidade e segurança de grãos de soja geneticamente modificada

Estudou-se o controle de plantas daninhas, as variações da biomassa e do metabolismo microbiano do solo em áreas cultivadas com soja geneticamente modificada e não modificada, em função da aplicação dos herbicidas glifosato ou imazetapir. Testaram-se cultivares de soja (BRS 244RR, geneticamente modificada e BRS 154, não modificada) e herbicidas (glifosato e imazetapir), e tratamento controle com capina. Como variáveis foram avaliadas a fitotoxicidade à cultura, controle de Raphanus raphanistrum (nabo), Digitaria sp. (milhã) e Brachiaria plantaginea (papuã), teores de carbono orgânico total (COT), carbono da biomassa microbiana (CBM), respiração basal (RB) e quociente metabólico (QCO 2 ). O herbicida glifosato, aplicado em dose única ou seqüencial, controla eficientemente as plantas daninhas nabo, milhã e papuã, e aumenta a atividade microbiana, a taxa de respiração basal e o quociente metabólico. O metabolismo microbiano do solo não foi afetado pelo genótipo, geneticamente modificado ou não, mas sim pelo uso do herbicida glifosato.

Genetically‐modified soybean [Glycine max (L.) Merr.] resistant to glyphosate (N‐phosphono‐methyl‐glycine) herbicide (GR) has turned out to be one of the most highly‐used products of plant engineering. The impacts of the soybean, genetically transformed for glyphosate resistance, on the environment under Brazilian soil and climatic conditions are still unknown. For this purpose, two soybean genotypes, one genetically modified (GR BRS 244 RR) and a conventional isogenic genotype were grown under different weed‐control methods: hand weeding and glyphosate or imazethapyr herbicide application. The study was performed in Rio Grande do Sul State with evaluations of soil microbial biomass and respiration, biological nitrogen fixation, isoflavone content in seed and glyphosate, and aminomethylphosphonic acid (AMPA) residues in seeds and soil. The use of GR did not affect soil microbial population, biological nitrogen fixation, or plant yield or isoflavone contents in seed. However, even though we used the recommended application doses, the glyphosate residues in the seeds were above levels permitted by Brazilian law. Also, AMPA residues were detected in the soil and the seeds.

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The use of Glyphosate herbicide is the best way to control weed growing when cultivating genetically modified soybean [Glycine max (L.) Merr.] resistant to glyphosate (N-phosphono-methylglycine) (GR). However, there have been doubts about the safety of this herbicide use concerning its effects on the plant, quality of grains and on the soil cultivated. Hence, the present study aimed at evaluating the effects of weed management two soybean cultivars (GR) and its conventional isogenic genotype with the use of different doses of glyphosate on soil processes and microorganisms, physiology and metabolism of the plant along with possible contamination of soil and seed by herbicide residues. For this purpose, two soybean genotypes, one GR BRS 243 RR and a conventional (isogenic genotype) were grown under different weed control methods: hand weeding and glyphosate herbicide application. The study was performed in Rio Grande do Sul State, during the crop seasons of 2008 to 2009, 2009 to 2010, 2010 to 2011 and 2011 to 2012, with evaluations of soil microbial biomass and respiration, chlorophyll, nitrogen, ureides, nitrates, carotenoid, isoflavone content in seeds, and glyphosate and aminomethylphosphonic acid (AMPA) residues in seeds and soil. The use of glyphosate positively affected the microbial biomass, basal respiration and seeds yield. On the other hand, the chlorophyll, nitrogen, ureides, nitrates, carotenoid, and isoflavone contents in seeds were unaffected by the treatment. Even though we used the recommended application doses, the glyphosate residues in the seeds were above the levels permitted by the Brazilian law. Also, AMPA residues were detected in the soil and the seeds.