Ultrastructural and Histochemical Changes in Glyphosate-Tolerant Soybean Leaves Exposed to Glyphosate

Abstract

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.

Glyphosate residues in soil can modify plant resistance to herbivores through changes in leaf quality.

“…Herbivores rarely consume plants randomly but tend to prefer large and vigorous individuals of high nutritional quality (the plant vigour hypothesis; Price, 1991). In a study of glyphosate‐tolerant soybean, direct glyphosate application reduced leaf thickness (Bomfim et al ., 2019), making individuals more palatable to folivores. Glyphosate has also been found to reduce nodulation (Reddy & Zablotowicz, 2003; Zobiole et al ., 2010), which can be critical for a plant's nitrogen availability and nutrient balance.…”