UV-B and UV-A radiation are natural components of solar radiation that can cause plant stress, as well as induce a range of acclimatory responses mediated by photoreceptors. UV-mediated accumulation of flavonoids and glucosinolates is well documented, but much less is known about UV effects on carotenoid content. Carotenoids are involved in a range of plant physiological processes, including photoprotection of the photosynthetic machinery. UV-induced changes in carotenoid profile were quantified in plants (Arabidopsis thaliana) exposed for up to ten days to supplemental UV radiation under growth chamber conditions. UV induces specific changes in carotenoid profile, including increases in antheraxanthin, neoxanthin, violaxanthin and lutein contents in leaves. The extent of induction was dependent on exposure duration. No individual UV-B (UVR8) or UV-A (Cryptochrome or Phototropin) photoreceptor was found to mediate this induction. Remarkably, UV-induced accumulation of violaxanthin could not be linked to protection of the photosynthetic machinery from UV damage, questioning the functional relevance of this UV response. Here, it is argued that plants exploit UV radiation as a proxy for other stressors. Thus, it is speculated that the function of UV-induced alterations in carotenoid profile is not UV protection, but rather protection against other environmental stressors such as high intensity visible light that will normally accompany UV radiation.

• Keywords
• UV-B, arabidopsis, carotenoid, photoreceptor, photosynthesis, xanthophyll,
• MeSH
• Arabidopsis * metabolism   MeSH
• Chromosomal Proteins, Non-Histone metabolism   MeSH
• Photosynthesis MeSH
• Carotenoids metabolism   MeSH
• Arabidopsis Proteins * metabolism   MeSH
• Ultraviolet Rays adverse effects   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chromosomal Proteins, Non-Histone MeSH
• Carotenoids MeSH
• Arabidopsis Proteins * MeSH
• Uvr8 protein, Arabidopsis MeSH Browser
• violaxanthin MeSH Browser

Photosynthetically active radiation (PAR) is an important environmental cue inducing the production of many secondary metabolites involved in plant oxidative stress avoidance and tolerance. To examine the complex role of PAR irradiance and specific spectral components on the accumulation of phenolic compounds (PheCs), we acclimated spring barley (Hordeum vulgare) to different spectral qualities (white, blue, green, red) at three irradiances (100, 200, 400 µmol m-2 s-1). We confirmed that blue light irradiance is essential for the accumulation of PheCs in secondary barley leaves (in UV-lacking conditions), which underpins the importance of photoreceptor signals (especially cryptochrome). Increasing blue light irradiance most effectively induced the accumulation of B-dihydroxylated flavonoids, probably due to the significantly enhanced expression of the F3'H gene. These changes in PheC metabolism led to a steeper increase in antioxidant activity than epidermal UV-A shielding in leaf extracts containing PheCs. In addition, we examined the possible role of miRNAs in the complex regulation of gene expression related to PheC biosynthesis.

• Keywords
• HPLC, UV tolerance, antioxidants, flavonoids, miRNA, photoprotection, secondary metabolism, spectral quality of light, spring barley (Hordeum vulgare), transcriptomics,
• MeSH
• Phenols metabolism   MeSH
• Flavonoids metabolism   MeSH
• Hordeum * genetics   metabolism   MeSH
• Plant Leaves genetics   metabolism   MeSH
• Light MeSH
• Ultraviolet Rays * MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Phenols MeSH
• Flavonoids MeSH