Cape Town researcher probes nutrition and safety of GM cereals
GENETIC engineering and plant breeding techniques are used in biofortification programmes to improve the nutritional quality of African cereals such as sorghum and pearl millet.
Apart from being important food sources for many poor people around the world, especially in drought-stricken areas, these cereals also contain important plantbased chemicals that can assist in the fight against cardiovascular disease, hypertension, Type 2 diabetes and some cancers.
“Improving the nutritional quality of sorghum and pearl millet is important, but it is equally vital to determine whether altering the composition of these cereals may lead to unforeseen and undesirable consequences that may not be immediately obvious,” says Dr Roya Ndimba, a postdoctoral researcher at iThemba LABS in Cape Town.
A recent PhD graduate in Plant Biotechnology from Stellenbosch University, Ndimba adds that we need extensive testing of biofortified sorghum and pearl millet to ensure that ‘improvements’ are as intended, and do not introduce any unwanted or undesirable changes in the composition of the grains. She points out that biofortification – the process of increasing the nutritional value of crops through agronomic practices, conventional plant breeding, or modern biotechnology – is considered the most cost-effective and sustainable approach for improving the iron and zinc content in staple foods.
In South Africa, about 55% of sorghum grain is consumed as sorghum meal – “Mabele” – which is served as a breakfast cereal or as a soured porridge. The grain is also used for malting and brewing in the production of traditional sorghum beer.
Pearl millet is mainly produced as a subsistence crop in rural areas of Limpopo, KwaZulu-Natal and the Free State. Sorghum and pearl millet are important food security crops in countries like Namibia, Botswana, Malawi and Zimbabwe.
As part of her research, Ndimba set out to determine if there was a difference between the key physical and chemical characteristics as well as the protein profile of genetically modified (GM) sorghum and sorghum that hasn’t been altered. She also tried to find out whether using plant breeding techniques to increase the concentration of two essential minerals, iron and zinc, in pearl millet was evident in the most nutritionally important grain tissues.
Ndimba used various techniques and experiments to compare biofortified sorghum and pearl millet with wild types that had not been altered, to study the distribution and concentration of mineral elements within cereal grain tissues and to assess the effect of biofortification on the composition and other quality characteristics of the grain.
Sorghum
“As far as biofortified sorghum and wild types are concerned, important differences were found in grain weight and density, as well as the texture of the nutritive tissue inside the grains,” says Ndimba.
“There was also a difference in the lysine content of biofortified sorghum and wild types. Lysine is an essential amino acid and building block of protein. The highest increase in grain lysine content was observed biofortified sorghum.
“An increase in lysine content is indicative of an increase in the overall protein quality of the grain. In GM sorghum, the protein, kafirins, which serve as repositories of carbon, nitrogen and sulphur for seed germination, was suppressed.”
Making up 70-80% of the total proteins found in sorghum wholegrain flour, kafirins have a low lysine content and are also hard to digest.
Ndimba says about 1742 genes that exhibited different expression patterns in genetically modified and wild-type sorghum grain samples were also identified. Gene expression is a complex series of processes in which the information encoded in a gene is used to produce a protein that dictates cell function.
“The vast majority of these genes were upregulated or, in other words, displayed higher expression levels in the genetically modified samples as compared to those not modified: the non-transgenic counterpart.
“Of note among the top most up-regulated genes were genes encoding for two types of albumin proteins, which are considered to be more nutritionally valuable in comparison to kafirins,” Ndimba says.
“However, there was also some evidence of an increase in expression for certain proteins that may be allergenic or that may be indicative of increased plant stress. Further research is therefore needed to establish more clearly if the changes in gene expression adversely impact the overall nutritional value of the genetically modified grain.”