Tolerance mechanisms to UV-B in olive pollen demonstrate cultivar-dependent biochemical responses

Ultraviolet-B radiation is a major abiotic stress factor that can impair pollen performance and limit plant reproductive success. It primarily targets the architecture of pollen tube cell walls and induces cultivar-specific sensitivity patterns. However, the way in which these structural effects are coordinated with biochemical and molecular responses remains unclear. We examined the responses of pollen grains from three Italian olive cultivars to ultraviolet-B radiation by integrating analyses of reactive oxygen species dynamics, antioxidant capacity and stress-related proteins. Different tolerance strategies were observed among the cultivars. The 'Leccino' cultivar maintained a redox balance through enhanced antioxidant capacity but showed alterations in cytoskeletal and membrane-associated proteins that were likely to affect turgor and pollen tube growth. The 'Olivastra Seggianese' cultivar exhibited a coordinated tolerance strategy involving stable regulation of reactive oxygen species, high levels of polyphenols, sustained induction of heat shock protein 70, and preserved aquaporin and actin, which support tube elongation. By contrast, the 'Pendolino' cultivar exhibited increased levels of reactive oxygen species and significant variability in metabolic and structural parameters, suggesting poor integration of stress responses. Taken together with previous cell wall analyses, these findings show that the ability of olive pollen to tolerate ultraviolet-B radiation depends on the cultivar and is not solely due to individual defensive components, but rather to the coordinated regulation of biochemical, molecular and structural mechanisms.