• vegetables
• biofortification
• quality
• ethylene
• rosmarinic acid

The ability of some crops to accumulate selenium (Se) is crucial for human nutrition and health. Selenium has been identified as a cofactor of the enzyme glutathione peroxidase, which is involved in the reduction of peroxides that can damage cells and tissues, and can act as an antioxidant. Plants are the first link in the food chain, which ends with humans. Increasing the Se amount in plant products, without exceeding the toxic threshold, is thus a good way to increase animal and human Se intake, with positive effects on long-term health. In many Se-enriched plants, most Se is in its organic form. Given that this form is more available to humans and more efficient in increasing the selenium status than inorganic forms, the consumption of Se-enriched plants appears to be beneficial. An antioxidant effect of Se has been detected in Se-enriched vegetables and fruit crops. In addition, Se appears to be effective in delay fruit ripening and plant senescence. This thus highlights the possible positive effect of Se in preserving a longer shelf-life and longer-lasting quality.
The main goal of the present thesis was to investigate the effects of selenium on plant metabolism in order to use the potential beneficial effects of Se to improve the quality and the shelf-life of leafy and fruity vegetables.
The mechanism of Se uptake, distribution, accumulation, and the effects of Se concentration on plant growth, quality and post-harvest shelf-life in sweet basil (Ocimum basilicum L.) were investigated.
The first two experiments aimed to study the ability of sweet basil to accumulate selenium, and to evaluate the possibility to obtain Se-enriched basil as a Se supplement resource for humans. Different Se concentrations (0.5, 1, 2 and 4 mg Se L-1) were tested in order to determine the optimal Se concentration in leaves that may induce benefits to human health without phytotoxic effects. Floating system was tested as a possible cultivation system for the production of Se biofortified basil plants. The results showed that the addition of selenium as sodium selenate in the nutrient solution significantly increased the Se content in basil, and could be an efficient system for providing enriched basil plants.
On the basis of the results of the first two experiments, a third trial was conducted in order to understand the processes of Se uptake and accumulation in basil plants. Since the amount of Se accumulated in leaves in the previous experiments was far from the Se toxic threshold for humans, higher Se concentrations (4, 8 and 12 mg Se L-1) were tested. The Se concentration in all plant organs was measured during the growth cycle, and the relationship among Se uptake rate, Se concentration in the nutrient solution and plant growth was evaluated. Selenium was absorbed by the roots, translocated to the above-ground organs and accumulated particularly in the leaves, without affecting the plant biomass. Se concentration increased during seedling growth, was highest in the younger leaves and then declined before or upon flowering. The growing trend detected in the total Se was more dependent on the biomass, which increased throughout the experiment, than on the Se concentration, which reached the maximum values during the first part of the experiment and then decreased.
The fourth experiment aimed at studying the allocation of selenium absorbed by roots in the different plants organs. The remobilization of Se accumulated in the seeds to the seedlings, and the effects of Se on the quality of sprouts were investigated. Basil plants accumulated Se mostly in leaves and roots. High amounts of Se were also accumulated in seeds and then remobilized to sprouts. The sprouts, produced by the seeds of Se-enriched plants, showed higher germination index and antioxidant capacity compared to seeds of control plants.
Given the potential action of Se in ameliorating the oxidative stress and delaying senescence, the effects of Se on basil leaf quality and shelf-life were studied in the fifth experiment. The different climate conditions during the two experiments reported in the fifth chapter may have affected the amount of Se taken up by plants. Lower values of cumulative solar radiation during the second experiment may have determined a lower plants growth and transpiration rate, inducing a lower Se accumulation in basil leaves, compared to the first experiment reported in the same chapter. Se-treated plants showed increased phenolic content and antioxidant activity, thus contrasting the reduction of biomass due to the high Se concentrations added to the nutrient solution. This resulted in an improved quality of basil leaves.
As final issue, the effects of Se in tomato fruit were investigated. Tomato plants were grown in solution enriched with selenium to study the effects of Se treatments on fruit ripening and shelf-life. The results obtained in this experiment confirmed the effect of Se in delaying fruit ripening, and the possibility to use Se-treatments to improve the postharvest shelf-life of fruits.