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

Nayane C P Bomfim,Liliane S Camargos,Aline R Martins,Márcio S Silva

doi:10.5539/jas.v11n18p243

Nayane C P Bomfim, Liliane S Camargos + Show 2 more

Open Access

https://doi.org/10.5539/jas.v11n18p243

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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 &mu;m thickness. The material was stained with toluidine blue 0.05% and blades mounted on &ldquo;Entellan&rdquo;. 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.

Highlights

Brazil is the second largest producer of soybeans (Glycine max) in the world accounting for more than 30% of world grain production
Regarding characterization of leaves of GR soybean, the mesophyll is dorsiventral with two layers of palisade parenchyma cells and four to five layers of spongy parenchyma cells (Figure 1) and the latter has sizes that vary significantly with intercellular spaces
Glyphosate decreased the thickness of palisade parenchyma (Figure 2D)

Summary

Introduction

Brazil is the second largest producer of soybeans (Glycine max) in the world accounting for more than 30% of world grain production. Brazil takes the 2nd place in the world ranking with 49.1 million ha of GM crops planted, behind the United States (72.92 million ha) with 49.1 million ha of planted GM crops accounting for 27% of the world’s arable land (International Service for the Acquisition of Agri-biotech Applications [ISAAA], 2017). There are 32.69 million hectare of transgenic soybeans, with 12.43 million hectares being cultivated with herbicide resistant cultivars, 36.7% (ISAAA, 2017). The weeds limit soybean growth and development potential, decreasing plant productivity and grain quality (Hock, Knezevic, Martin, & Lindquist, 2005; Knezevic, Evans, & Mainz, 2003). Glyphosate acts by inhibiting enzyme 5-enolpiruvilchiquimate 3-phosphate synthase (EPSPs), which blocks the synthesis of the essential aromatic amino acids, namely phenylalanine, tyrosine and tryptophan (Duke, Rimando, Pace, Reddy, & Smeda, 2003)

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