Selenium-biofortified pollen from Olea europaea L. retains germination capacity under heat stress and oxidative imbalance

Hydrogen peroxide-induced oxidative stress disrupts cytosolic Ca²⁺ homeostasis, a critical indicator of pollen fertility. Thus, measuring Ca²⁺ levels provides valuable insights into the role of antioxidants in protecting plant reproductive processes. Given the established link between high temperatures and oxidative stress, this study evaluates the response of selenium (Se)-biofortified pollen from Olea europaea L. (Leccino cultivar) to combined thermal and oxidative challenges. Pollen from untreated and Se-sprayed trees was incubated for 48 h at 20 °C, 30 °C, and 40 °C, with or without 10 mM hydrogen peroxide. The results show that disruptions to Ca²⁺ homeostasis across these temperatures reflect an additive effect beyond that of hydrogen peroxide alone. Se-biofortified pollen significantly mitigated these disruptions, suggesting protective mechanisms that were particularly evident in germination assessments. At 40 °C without hydrogen peroxide, Se-biofortified pollen achieved 22% germination, compared to 9% in untreated samples. Under oxidative stress, Se-biofortified pollen exhibited a 15% germination rate, whereas untreated samples showed less than 2%. In contrast, pollen maintained at 20 °C without stress displayed a 51% germination rate. While Se biofortification is known to enhance plant resilience, seed quality, and fertility, its effects under combined high-temperature and oxidative stress have not been explored until now. Notably, these findings underscore a greater protective capacity than previously reported. Furthermore, Se speciation data that align with prior studies affirm the robustness of the biofortification protocol, positioning it as a viable strategy to mitigate the adverse effects of rising temperatures on plants, either independently or in combination with other stress-mitigating agents.