| Summary: | Excessive ultraviolet B (UV-B) irradiation is one of the most serious threats leading to severe crop production losses. It is known that secondary metabolite biosynthesis plays an important role in plant defense and forms a protective shield against excessive UV-B irradiation. The contents of stilbenes and other plant phenolics are known to sharply increase after UV-B irradiation, but there is little direct evidence for the involvement of stilbenes and other plant phenolics in plant UV-B protection. This study showed that foliar application of <i>trans</i>-resveratrol (1 and 5 mM) and <i>trans</i>-piceid (5 mM) considerably increased tolerance to a shock of UV-B (10 min at 1800 µW cm<sup>−2</sup> of irradiation intensity) of four-week-old <i>Arabidopsis thaliana</i> plants that are naturally incapable of stilbene production. Application of <i>trans</i>-resveratrol and <i>trans</i>-piceid increased the leaf survival rates by 1–2%. This stilbene-induced improvement in UV-B tolerance was higher than after foliar application of the stilbene precursors, <i>p-</i>coumaric and <i>trans</i>-cinnamic acids (only 1–3%), but less than that after treatment with octocrylene (19–24%), a widely used UV-B absorber. Plant treatment with <i>trans</i>-resveratrol increased expression of antioxidant and stress-inducible genes in <i>A.</i><i>thaliana</i> plants and decreased expression of DNA repair genes. This study directly demonstrates an important positive role of stilbenes in plant tolerance to excessive UV-B irradiation, and offers a new approach for plant UV-B protection.
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