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9. Jan. 2023
Results suggest the need for customized approaches for safe and sustainable plant cultivation
Contamination of agricultural soils with heavy metals such as cadmium is a long-term problem despite efforts to move towards sustainable agricultural production. An important factor contributing to the increasing content of cadmium in agricultural soils is the use of mineral phosphate fertilizers. Cadmium is a toxic heavy metal that, even at low concentrations, poses a significant health risk to animals, including humans, mainly due to its accumulation in the food chain. However, contamination is not the only adverse factor reducing soil quality. The amount of nutrients in the soil also plays an important role. One of the nutrients currently deficient in the soil is sulphur, paradoxically due to the reduction of industrial emissions of sulphur dioxide. PhD student Martin Lycka, under the supervision of Miloslava Fojtova CEITEC Masaryk University, focused on these two problems. Their results showed common as well as specific features of the response of the two different model plants to the toxic cadmium exposure. These data suggest the need for customized approaches for safe and sustainable plant cultivation. The manuscript was published in the prestigious international peer-reviewed Journal of Hazardous Materials.
The aim of the research team from the laboratory of Jiri Fajkus was to investigate the response of plants to exposure to heavy metals. Although there are hundreds of scientific articles on this topic, most of them deal with short-term exposure of plants to high concentrations of metals. This approach is adequate for describing the mechanism of the stress response, but these conditions are not commonly found in the environment. "We chose a concentration of cadmium salt that is realistic in the environment and corresponds to the Czech Republic’s preventive limits for agricultural soils, and we combined it with a limited supply of sulphur in the form of sulphates. Sulphur is essential for an effective plant defence against the detrimental effects of heavy metals. In our study, we analysed the problem from many different perspectives, studying plant morphology, physiological, photosynthetic and biochemical parameters," explains Miloslava Fojtova, senior author of the study.
The research focused on two common model plants, thale cress (Arabidopsis thaliana) and tobacco (Nicotiana tabacum). "Nicotiana tabacum is not only a model plant but also an economically important crop. It is also interesting because it has been characterised as a heavy metal hyperaccumulator, which means that it is able to accumulate heavy metals in its organs and thus tolerate higher levels of soil contamination. Compared to Arabidopsis thaliana, tobacco is also less studied and our results can serve as a basis for further studies to elucidate the molecular mechanisms of this plant’s response to cadmium exposure," says Miloslava Fojtova. The hyperaccumulation properties of tobacco make it potentially suitable for phytoremediation, in other words for the removal of pollutants from the environment using plants, but also poses a problem for the tobacco industry, where the high cadmium content of the plant further exacerbates its negative impact on human health.
"Cadmium negatively affected the growth of both plants, induced changes in the content of the green pigment chlorophyll and reduced photosynthesis, which was associated with yellowing of the leaves. These effects were amplified by the limited sulphate supply, which even led to necrosis - cell and tissue death, in tobacco leaves," explains the lead author of the study Martin Lycka. Despite the similar external manifestations, thale cress and tobacco often responded differently to the presence of cadmium salts in combination with a limited supply of sulphate, e.g., in the accumulation of cadmium in the leaf and root, changes in the levels of other metal ions or macronutrient salts. Considering those findings, it can be said that just as modern health care is moving towards personalised medicine, modern agriculture should reflect the needs of specific crops to limit the effects of undesirable factors and design specific cultivation conditions accordingly.
This work was an example of an interdisciplinary collaboration involving the National Centre for Biomolecular Research and the Laboratory of Photosynthetic Processes of the Institute of Experimental Biology (Faculty of Science of the Masaryk University), the Institute of Analytical Chemistry of the Czech Academy of Sciences (CAS), the Institute of Biophysics of the Czech Academy of Sciences (CAS) and the group of Prof. Stanislav Kopriva from the University of Cologne. The work was supported by the SINGING PLANT project funded by the European Regional Development Fund and the INTER-COST project funded by the Ministry of Education, Youth and Sports of the Czech Republic. Thanks to the Erasmus+ programme, Martin Lycka's internship at the University of Cologne was possible.