Chernobyl flax takes the flak

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  • Published: Sep 15, 2010
  • Author: Steve Down
  • Channels: Proteomics
thumbnail image: Chernobyl flax takes the flak

The worst nuclear disaster in history occurred at the Chernobyl nuclear power plant on April 26th, 1986, when a steam explosion and the subsequent fires over 10 days threw about 5% of the radioactive core into the atmosphere. About nine tons of radioactive material, 90 times as much as the Hiroshima bomb, were released. Situated in northern Ukraine, then part of the USSR, the radioactive cloud spread over most of Europe, spreading iodine-131 initially, with caesium-137 taking over as the main hazard.

In the immediate impact of the explosion, about 116,000 people living within a 30-km radius were evacuated and this later grew by a further 220,000 as the exclusion zone was expanded. The local wildlife was not so fortunate but, surprisingly, later studies have revealed that both fauna and flora have been able to adapt to living in the presence of permanent ionising radiation.

For instance, wheat and soybean plants grown in contaminated plots near Chernobyl were found to adapt by incorporating changes in their DNA and protein profiles, although the basis for plant survival remains unclear. In order to try and expand knowledge of the survival mechanism, a team of scientists has broadened the range of crops by examining the growth of a local variety of flax in radio-contaminated soil 5 km from the Chernobyl site.

Martin Hajduch and co-researchers from the Slovakian Institute of Plant Genetics and Biotechnology, Nitra, and the Institute of Virology and Center of Molecular Medicine, Bratislava, worked with scientists from the ARS/USDA and the University of Missouri, Columbia, and the Institute of Cell Biology and Genetic Engineering of the National Academy of Sciences of Ukraine, Kiev. They compared the proteome of flax grown in the contaminated soil with that grown in clean control soil 100 km from the site.

Mature flax seeds accumulated about 10-fold less radioactivity from caesium-137 than reported for the soybean data, so the results from the two species will complement each other. The flax seeds looked and weighed the same as those from the control site but the degree of germination was slightly reduced.

The proteins were extracted from the seeds and subjected to two-dimensional gel electrophoresis using isoelectric focusing with immobilised pH gradient strips covering pH 3-10 and 4-7. The spots showing different abundances between the contaminated and control sites were identified following digestion with trypsin and liquid chromatography-tandem mass spectrometry.

The ultra-performance LC system was used in conjunction with high mobile phase pressure and a column containing small particles to give improved analyte resolution and increased analyte peak concentration, which improved mass spectrometric detection. The mass spectrometer was operated with alternating low and high collision energies in the same run to obtain precursor ion information then full-scan accurate mass spectra, respectively.

The spectra were searched against combined UniProt databases for Arabidopsis thaliana and flax, then unidentified spectra were searched against the UniProt Viridiplantae database.

A total of 720 2-DE spots were separated, 267 using the pH 3-10 strips and 453 using the pH 4-7 strips. Of these, 35 spots displayed different abundances between the contaminated and control samples.

This small number is similar to the 64 out of 698 spots that the same research team reported for soybean seeds from plants grown in radio-contaminated soil. So, although only two plant species have been studied, the combined results do suggest that the effects of ionising radiation on the seed proteome are relatively small.

Once the differentially regulated proteins were identified, it was clear that a number of them belonged to several signalling pathways, such as the omega form of 14-3-3, which was reduced in the seeds from the contaminated site.

Two glycolytic enzymes were more abundant in contaminated seeds, in line with the reported increased rates of respiration and glycolytic flux induced by environmental stress in plants.

A further eight of the affected proteins were involved with transcription or translation, consistent with a small adjustment in overall protein synthesis as opposed to a genome-wide change.

Choline monooxygenase was also differentially expressed. This protein catalyses the first step of the glycine betaine biosynthetic pathway, which was also implicated in the soybean studies. Glycine betaine has been shown to protect blood cells from ionising radiation, so it may play a similar role in plants.

These observations were incorporated into a working model to account for the radiation-induced changes, in which network signalling, the stress response and glycine betaine metabolism were considered to be primary events.

The effects of ionising radiation in flax, where the signalling pathways were mostly affected, were different to those found for soybean, in which seed storage proteins were to the fore. The reasons for this are uncertain, although the differences may be linked to the different amounts of radiation that each plant accumulated.

The team proposed that incorporation of the data from the soybean study would allow this flax model to be refined. In addition, they are currently performing further tests on second and third generation plants grown in the Chernobyl fields to produce complementary data.

Taken together, the flax and soybean results suggest that the seed proteomes of plants grown in soil contaminated with ionising radiation induce relatively minor changes to the proteome.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.



chernobylThe Chernobyl No.4 reactor following the explosion


flaxFlax is thriving in the shadow of the mothballed nuclear power plant

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