Integral of Sporopollenin Autofluorescence Intensity (ISAI), a novel marker for UV adaptation in spores/pollen

Sporopollenin, a key adaptation enabling plants' transition to terrestrial environments, shields spores and pollen from UV damage, ensuring their survival and dispersal on land. The concentration of UV-absorbing <italic>p</italic>-CA and ferulic acids within sporopollenin correlates with UV levels, offering a proxy for reconstructing UV irradiance. However, the composition of UV-absorbing compounds varies across species, and a universal marker linking sporopollenin chemistry to UV resistance has yet to be identified. Given that UV-absorbing components may convert UV radiation into visible light, we developed a method to quantify the Integral of Sporopollenin Autofluorescence Intensity (ISAI), a novel parameter hypothesized to reflect pollen UV resistance. We analyzed ISAI in spores/pollen from 55 plant species and 18 <italic>Arabidopsis</italic> <italic>thaliana</italic> ecotypes. Our results reveal significant ISAI variation, which associates with solar-irradiance gradients. Species exposed to sunlight exhibited higher ISAI values than those adapted to shaded environments. Plants flowering during periods of elevated solar radiation displayed increased ISAI. Notably, analysis of <italic>A</italic>. <italic>thaliana</italic> ecotypes demonstrated that ISAI is heritable and correlated with pollen UV resistance. This study indicates ISAI as a metric in spore and pollen research, linking sporopollenin autofluorescence to UV adaptation. ISAI provides a novel tool for investigating plant responses to UV environments.