Accumulation of selenium in different wheat genotypes and its protective role against various abiotic stress factors

Plant-based foods play a critical role in covering daily requirements of human beings for energy and minerals, especially in the developing world. Most of the nutritional compounds existing in cereal grains are the major protective agents against different chronic diseases. One particular compound with high protective effect against different diseases such as cancer and cardiovascular diseases is selenium (Se). It is widely believed that some forms of selenium (Se) are among the most effective anti-carcinogenic compounds. Studies conducted in different countries revealed that wheat is one of the best Se source for human beings. Wheat is, therefore, an important targeted stable food for enrichment (biofortification) with Se. Selenium is also believed to act protective roles in plants against different abiotic stress factors. However, various controversial results are available in literature regarding the protective roles of Se in plants. In the present study, several experiments have been conducted i) to understand better the protective role of Se in plants under different stress factors, ii) to improve Se status of plants by treating seeds with Se (soaking seeds in a Se-containing solution), and iii) to screen various modern and wild wheat genotypes for their Se accumulation capacity in shoot and seed. In the experiment with seed treatment of Se, the results obtained were promising for improving seed Se concentration. In plants derived from the seeds treated with Se by soaking in a Se-containing solution (up to 5 mM), the seed Se concentration increased from 44 μg kg-1 (non-treated seeds) to 216 μg kg-1 seed (Se-treated seeds). Seed Se treatment could be a practical approach for enrichment of wheat seeds with Se. Several Triticum dicoccoides genotypes and modern wheat cultivars were investigated for their capacity in Se uptake and accumulation in shoot following application of sodium selenate to soil. The results indicated that the Triticum dicoccoides genotypes tested did not show a promising genetic variation in shoot Se accumulation, and were not superior when compared to the modern wheat genotypes in terms of shoot Se concentration. A nutrient solution experiment was established to follow the Se uptake and accumulation of modern wheat cultivars and Triticum spelta genotypes. In this experiment, some Triticum spelta genotypes were identified showing high Se uptake capacity. Such new genotypes with high Se uptake capacity might be a valuable genetic resource for breeding programs to transfer high Se uptake trait to high-yielding cultivars. Selenium is an essential nutrient for human beings, but not for higher plants. However, in literature, controversial results exist about its beneficial effects on plant growth. By using both wheat and maize plants, greenhouse and growth chamber experiments have been conducted to collect information about the role of Se in improving growth under different stress factors such as drought, salinity, flooding and low temperature. The results obtained indicated that Se has no beneficial effect on plant growth under the stress conditions mentioned. In the experiment with low temperature stress the level of antioxidative defense enzymes (e.g., superoxide dismutase, ascorbate peroxidase and glutathione reductase) were measured in maize plants with and without Se supply. vii Increasing Se supply did not result in a consistent effect on activity of antioxidative defense enzymes under both normal and low temperature. A similar result was also found in seeds enriched with Se by foliar application of Se. The seeds differing in Se concentrations were not different in their total antioxidative capacity. The result of this thesis indicate that i) treating seeds with Se (soaking seeds in a Se-containing solution up to 5 mM) might be a practical approach to improve shoot and grain Se concentration, ii) modern wheat and tetraploid wild wheat Triticum dicoccoides genotypes tested in the present study were not promising genetic sources for improving shoot Se concentration, iii) Triticum spelta genotypes have been identified showing high Se uptake capacity which might be exploited in breeding programs, and iv) Se has no consistent beneficial effects on plant growth and antioxidative enzyme activity under various abiotic stress factors.