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To evaluate under controlled temperature conditions, nutrition and water supply, the influence of glyphosate on nitrogen fixation capacity in Roundup Ready (RR) soybean, BRS Valiosa Roundup Ready. Commercially available seeds were sown in pots containing vermiculite and washed sand (1:1) and after germination, the seeds were inoculated with Bradyrhizobium sp. and kept in nutrient solution without nitrogen, in greenhouse, with temperature control to 27 ºC without photoperiod control, at UNESP, Ilha Solteira, SP. At the vegetative stage, glyphosate was applied at a concentration of 1.8 mg glyphosate/plant once a week. There were two harvests: after 15-21 days after herbicide application, and at reproductive stage. The chlorophyll content in leaves was analyzed and the organs were separated (leaves, roots and nodules) for extraction and quantitation of nitrogenous compounds, in addition to the enzyme allantoinase activity analysis (in vitro) and nitrogenase activity (in vivo). Nodules were counted and weighted. Means were compared by 5% Tukey's test. It was observed that the application of glyphosate in RR soybeans moderately affected N fixation and assimilation. There were no drastic metabolic changes for the aminoacids, proteins, chlorophylls and ureides in RR soybean treated with glyphosate.

Is it transgenic soy, resistant to glyphosate, does not suffer any injury or stress in contact with this herbicide? Anatomic studies of plant tissue are necessary to answer this question. This study investigated the influence of glyphosate in glyphosate-resistant soybean plants by analysis of leaf ultrastructure and histochemistry in a morphophysiological context. The experiment was carried out in a greenhouse, using RR soybean seeds (Glycine max (L.) Merrill, cultivar BRS Valiosa) in pots containing vermiculite and washed sand (1:1). Between the phenological stages V2 and V4, two treatments with glyphosate [N-(fosfonometil) glicina] were sprayed once a week: recommended dose (5.0 mg ae plant-1) and control (0.0 mg ae plant-1), with four repetitions each. Samples of midrib and internervural area of the leaves were fixed, dehydrated in ethyl series and blocks were sectioned at a 5-10 μm thickness. The material was stained with toluidine blue 0.05% and blades mounted on “Entellan”. Glyphosate decreased the thickness of the adaxial epidermis, palisade parenchyma, spongy parenchyma and total thickness of the leaf. Although, the diameter of companion cell was decreased with herbicide treatment, the diameter of the vase element increased, also increasing the size of the vascular bundle. Ultrastructural and histochemical changes caused by glyphosate can extend dysfunctions in the metabolic apparatus and plant relationship with the environment, given the inter-relation between tissue structure and its functions.

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