Science - April 19, 2012

Gene expression reveals how potatoes are cultivated

Organically grown potatoes have a higher gene expression for starch production than conventional ones. So says Rikilt researcher Jeroen van Dijk, who can tell organically grown potatoes from conventional ones by measuring the RNA in the plant cells. But he cannot say if organic potatoes are any healthier because of this.

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Unlike in traditional potato cultivation, no artificial fertilizers or chemical pesticides are used in the cultivation of organic potatoes. Van Dijk discovered that the different cultivation conditions can influence gene expression in the potato plant when he was establishing the gene expression - or the RNA - of both types of potatoes. 'When we were doing some measuring - which genes were switched on and to what extent - we found significant differences between conventional and organically grown Santé potatoes.'
It wasn't that simple really, because Van Dijk had to examine about 40,000 genes. 'Of these, half may be switched on; that would give you very many variables. Although it's possible to measure the gene expression for each gene, that won't tell you much. Fortunately, we know the types of proteins and ingredients produced by some of the genes. That enabled us to cluster these genes and assign properties to them.' In so doing, Van Dijk succeeded in measuring the differences between organic and conventional potatoes.
He found that some of the RNA are related to proteins responsible for the production of starch in the potatoes. Organic potatoes have more of such RNA than conventional potatoes, Van Dijk says. But he cannot tell if the organic potato is more nutritious as a result, because he did not examine the starch composition.
He also measured the production of lipoxygenases, genes involved in the plant's defence mechanism, and a group of genes which protect the plant from harmful bugs. Both groups of genes are expressed better under organic fertilization, while pesticides have either no effect or stimulate in fact the gene expression. Based on these results, it would not be right to say that organic potatoes can cope better with diseases, says Van Dijk.
In any case, that was not the aim of his study, published last month in the Journal of Agricultural and Food Chemistry. Van Dijk wanted to find out if differences in cultivation methods are measurable in the potato. The answer is: yes. Therefore, a test like this can be used in safety assessments of GMOs because small differences in gene expression can be traced in this way. 'Currently, a 90-day test using mice is often used to gauge the safety of transgenic plants, but nothing ever comes out of that,' says Van Dijk. 'It's better to analyze the gene expression in the lab. You'll achieve two objectives in this way: have more information and do away with the need for test animals to assess the safety of new crops.'

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