Arabidopsis Flavonoid Mutants Are Hypersensitive to UV-B Irradiation.

Abstract

Increases in the terrestrial levels of ultraviolet-B (UV-B) radiation (280 to 320 nm) due to diminished stratospheric ozone have prompted an investigation of the protective mechanisms that contribute to UV-B tolerance in plants. In response to UV-B stress, flowering plants produce a variety of UV-absorptive secondary products derived from phenylalanine. Arabidopsis mutants with defects in the synthesis of these compounds were tested for UV-B sensitivity. The transparent testa-4 (tt4) mutant, which has reduced flavonoids and normal levels of sinapate esters, is more sensitive to UV-B than the wild type when grown under high UV-B irradiance. The tt5 and tt6 mutants, which have reduced levels of UV-absorptive leaf flavonoids and the monocyclic sinapic acid ester phenolic compounds, are highly sensitive to the damaging effects of UV-B radiation. These results demonstrate that both flavonoids and other phenolic compounds play important roles in vivo in plant UV-B protection.

Retracted: Nitric oxide enhances plant ultraviolet‐B protection up‐regulating gene expression of the phenylpropanoid biosynthetic pathway

“…ROS cause damage to proteins, lipids and DNA, affecting cell integrity, morphology and physiology of plants (Frohnmeyer & Staiger 2003). The molecular plant response to UV-B involves mechanisms of DNA repair (Pang & Hays 1991), up-regulation of non-enzymatic antioxidants as glutathione and ascorbate, increasing activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) (Jansen, Gaba & Greenberg 1998), and accumulation of compounds that absorb UV-B (Hahlbrock & Scheel 1989;Tevini & Teramura 1989;Li et al 1993).…”

UV-B-Induced PR-1 Accumulation Is Mediated by Active Oxygen Species.

“…Flavonoids and anthocyanins have been shown to accumulate in the epidermis and absorb UV-B radiation, preventing damage to the underlying cells (Beggs et al, 1986;Li et al, 1993). However, the protection from UV-B irradiation afforded by flavonoids is often incomplete, and UV-B is able to penetrate the epidermis to the underlying tissue (Tevini et al, 1991;Day et al, 1993), where it may induce further protective responses.…”

“…One important defense mechanism appears to be the accumulation of UV-6-absorbing flavonoids and sinapate esters in leaf epidermal cells (Beggs et al, 1986;Li et al, 1993). Genes encoding key enzymes involved in the biosynthesis of flavonoids are induced by UV irradiation (Chappell and Hahlbrock, 1984;Dangl et al, 1987;Douglas et al, 1987).…”

Flavonoid Profiling and Biosynthetic Gene Expression in Flesh and Peel of Two Tomato Genotypes Grown under UV-B-Depleted Conditions during Ripening

“…Nonetheless, UV-B has proven to be an important stimulating factor of two flavonoid biosynthetic enzymes, chalcone synthase (CHS) and chalcone isomerase (CHI) (15). Finally, flavonoid-deficient mutants from Arabidopsis thaliana displayed more sensitivity to excessive UV-B irradiation (16), whereas other mutants characterized by high flavonoid content were shown to be less sensitive than wild type (17). Flavonoids are not the only components involved in the plant response to UV-B radiation; other phenolics, such as hydroxycinnamic acids, are also thought to contribute to the plant natural shielding (18).…”