Increased UV intensity reduces pollen viability in Brassica rapa

Ultraviolet (UV) radiation is known to be an important environmental stressor of plants. Evidence of its effects on plant reproduction is mixed, with studies usually showing that short doses of UV lead to a reduction in pollen viability, but that longer exposure can improve viability. Here, we tested the effect of UV intensity (control, low-UV, high-UV) and the duration in which the plants were exposed for different time periods prior to flowering (long: from seed; short: exposed after 7 days of growth) on pollen viability of Brassica rapa. We also tested how changes in floral morphology (UV-absorbing area) related to pollen viability, before carrying out a meta-analysis on the effects of UV on pollen performance. We found that high UV intensity reduced pollen viability, but there was no effect of UV exposure prior to anthesis on pollen viability. Unexpectedly, we found a negative relationship between UV-absorbing area and pollen viability. Our meta-analysis showed a significant negative effect of UV on pollen viability, tube growth and germination. In summary, our results show that high UV generally negatively impacts pollen viability.