Susceptibility of pollen to UV-B radiation: an assay of 34 taxa

Much of the ultraviolet-B radiation (UV-B) research on plants has concentrated on vegetative plant parts, and only a small fraction has dealt with the reproductive system. The present study analyzed pollen grains of 34 taxa germinated and grown under two levels of UV-B radiation (187 and 460 mW/m²) or no UV-B (control group). Visible radiation at 260 micromoles m^-2s^-1 was present in all treatments. Taxa included those with binucleate and trinucleate pollen types. We detected differences among species. A significant reduction in pollen germination occurred in only five species. Pollen tubes of 50% of the species showed significant reduction in length. Trinucleate pollen types were more likely to exhibit tube length reduction than the binucleate types. Proportionately more monocotyledonous species were sensitive to UV-B treatment than dicotyledonous species, and proportionately more wild species were sensitive than cultivated species and pollen collected from plants growing in the field were somewhat more sensitive than pollen collected from plants grown in the greenhouse. Species in which pollination occurred earlier in the season were more likely to be susceptible to UV-B radiation than those for which anthesis took place later in the season, suggesting a possible adaptation to UV-B radiation. (author)