Selênio em Oliveiras: tolerância ao estresse hídrico e biofortificação do azeite de oliva extravirgem

Abstract

The application of selenium (Se) in plants can enhance their tolerance to abiotic stresses by reducing reactive oxygen species (ROS) and increasing antioxidant compounds. Furthermore, it brings significant benefits for human nutrition and health, as it is an essential element for mammals. However, there is a knowledge gap regarding the effects of Se on olive trees subjected to drought and soil flooding conditions, considering the current context of global climate change with extreme temperature fluctuations and changes in rainfall patterns. Additionally, there is a lack of studies related to the biofortification of olive products with Se. Therefore, the aim of this dissertation was to evaluate the effect of foliar selenium fertilization on olive trees concerning the alleviation of plant water stress and the biofortification and quality of olive oil. For this purpose, two independent studies were conducted. The first evaluated the effect of foliar fertilization with different doses of Se on the total Se content, ROS activity, antioxidant compounds, and productivity of adult olive trees in two cities in Rio Grande do Sul. This study also focused on characterizing the biofortification of extra virgin olive oils extracted from two adult orchards of the Arbequina cultivar. The second study addressed the effect of the presence and absence of Se on responses to water stress induced by ROS and antioxidant activity of leaf and root tissues of young Frantoio olive trees grown in a greenhouse. These plants were exposed to conditions of water scarcity and excess in the soil during post-water stress and recovery periods. In the first study, different doses of Se increased the total Se content in leaves and olive oil, reaching up to 2.056 mg Se kg-1 of oil. However, Se application did not induce significantly changes in fruit productivity or the physicochemical quality of the oil. Se fertilization led to lower levels of ROS in the leaves of the orchard in the city of Caçapava do Sul, where higher Se levels were detected in the oil. After the first Se application, lower levels of ROS were quantified in leaf tissue with doses of 150 and 200 mg Se dm-3 , while after the second Se application, the lowest level was observed in the treatment of 100 mg Se dm-3 , with an increase in ROS observed with higher Se concentrations. In the second study, Se levels in leaf and root tissues in all treatments were below the quantification limit by ICP-OES. However, an increase in GSH levels and a decrease in lipid peroxidation were observed in leaves, as well a decrease in ROS in leaf and root tissues of plants treated with Se. Selenium did not significantly alter fruit yield or olive oil quality but demonstrated both antioxidant and pro-oxidant actions dependent on the dose in adult olive trees. Although Se was not detected in the leaves and roots of young olive trees, its application showed beneficial results for the plants, regardless of water treatment.