Transgenic soybeans present nutritional and biochemical changes

Brazilian university research compared the genetically modified variety most produced in Brazil with a natural equivalent and found higher levels of iron, copper and cobalt.

By Karina Toledo

Agência FAPESP – When comparing the variety of transgenic soybeans most often grown in Brazil with a natural equivalent, researchers from the Chemistry Institute of the University of Campinas (Unicamp) found that genetically modified seeds present higher copper and iron contents as well as increased bioavailability of these micronutrients.

Analyses also indicated a difference in protein concentration and the levels of antioxidant enzymes, such as catalase, superoxide dismutase, ascorbate peroxidase and glutathione reductase. The findings were presented in December 2013 at FAPESP headquarters during the Workshop on Interdisciplinary Plant Science.

“The data suggest that transgenesis induces a state of oxidative stress in plants. They then begin to produce more antioxidant enzymes in an attempt to find a new equilibrium, and this seems to accelerate their entire metabolism,” said Marco Aurelio Zezzi Arruda, a professor at the Chemistry Institute of Unicamp and the coordinator of the study funded by FAPESP. Zezzi is also a researcher on the project "Oxidative stress induced by metals: new approaches," coordinated by Ricardo Antunes de Azevedo of the Luiz de Queiroz College of Agriculture (Esalq) at the University of São Paulo (USP).

Zezzi emphasizes that the impact that these alterations have on the environment and the health of those whose diet includes transgenic soybeans were not part of the study and should be the subject of further research. However, with regard to plant development, oxidative stress and the resulting biochemical effects appear to be beneficial.

“Transgenic soybeans have a higher rate of success in germination, develop a higher organic matter content and grow more quickly. The plant responds in a more magnified way to any external stimulus it is given, such as an increase in temperature or in the amount of water. If there is any negative response that is also increased, we are not aware of it,” said Zezzi.

The researchers compared the seeds of the native plant MSOY 7501 with the genetically modified version MSOY 7575 RR, which is known as “Roundup Ready” (RR) and was developed by Monsanto in the mid-1980s.

This transgenic variety was introduced for planting in the United States for the first time in 1994. In 2003, it was introduced in Brazil, where it currently corresponds to over 90% of the grains produced there.

The genetic modification involved in the present study was designed to increase the plant’s resistance to glyphosate herbicides – those sold most frequently throughout the world because they are easy to use and offer economic advantages to farmers. To achieve this, the gene cp4EPSPS, extracted from Agrobacterium, was added to the plant’s DNA.

In natural soybeans, glyphosate blocks the production of the EPSPS enzyme and thus blocks the entire production of aromatic amino acids, such as phenylalanine, tyrosine and tryptophan, which are essential to the plant’s survival. Through genetic engineering, soybeans produce a slightly modified enzyme on which glyphosate has no effect.

“In some way that still needs to be clarified, the insertion of the gene alters secondary biochemical mechanisms related to the production of aromatic amino acids and this causes an increased production of reactive oxygen species, such as superoxide radicals, hydrogen peroxide, hydroxyl radicals and singlet oxygen. When there is an excess of these substances, what we call ‘oxidative stress’ occurs. The plant then begins to produce higher amounts of antioxidant enzymes,” Zezzi explained.

Analyses using spectrophotometry (which allows the identification of substances by the absorption or transmission of light) indicated that the antioxidant levels in the transgenic seeds were 35% higher compared with the natural variety. The difference was found to be 70% higher in the leaves of the transgenic plant.

In the case of proteomic analysis – the objective of which is to identify the entire set of plant proteins – the difference was much larger in the leaves after cultivation than in the seeds from which the plants were grown.

In total, the group identified dozens of different proteins in the seeds or leaves of the two varieties of soybeans. With the help of a particular software program, the scientists looked for so-called ‘differential proteins,’ the abundance of which differed by at least 90% (both increases and decreases) from one variety to another.

“When comparing the seeds, we found only four differential proteins. After we cultivated these seeds and analyzed the leaves, the number jumped to 77. Oxidative stress was also higher in the leaves after cultivation than in the seeds. Now, we intend to study the next generations of the plant to determine whether this escalation of biochemical alterations continues to increase and at any time becomes detrimental to the plant or whether it ceases,” said Zezzi.

According to the researcher, some of the differential proteins found in the leaves are related to photosystem II – one of the multiprotein complexes involved in the process of photosynthesis.

“The activity of the reactions involved in photosystem II, as well as in the entire transgenic plant, seem to have increased. The way light is captured from the sun had changed, but we do not have sufficient data to conclude whether this is good or bad,” explained Zezzi.

The accelerated metabolism also causes the plant to capture higher amounts of nutrients from the soil. Nutritional analyses indicated that the transgenic seeds had 39% more cobalt, 40% more copper and 20% more iron than the natural seeds. The natural variety was higher only in the level of strontium, which was 34% greater than in the genetically modified version.

“With the help of chemical reagents, we are able to simulate a gastric digestion process and an intestinal digestive process in the laboratory, and we determined that these micronutrients are more bioavailable in the transgenic soybeans. In the natural variety, these metals usually bind to a variety of compounds, which makes their absorption difficult,” said Zezzi.

According to the researcher, all the analyses were conducted with plants grown under the same soil, temperature and irrigation conditions. “I cannot say with certainty that all the differences manifested are the result of genetic modification, but I believe a good many of them are,” estimated Zezzi.

The findings obtained in the enzymatic and proteomic analyses were published in an article that appeared in the journal Analytical and Bioanalytical Chemistry and in articles published in the Journal of Proteomics in 2010 and 2013.

The findings related to the concentration of metals in the seeds were published in articles in the journal Metallomics and in the Journal of Analytical Atomic Spectrometry.

The project “Metallomics studies applied to genetically modified species of soybean [Glycine max (L.) Merrill] and Arabidopsis thaliana” began in April 2013 and will continue until March 2015.