UV-B shock induces photoprotective flavonoids but not antioxidant activity in Antarctic Colobanthus quitensis (Kunth) Bartl

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Colobanthus quitensis, the only dicot that inhabits Antarctica, is subjected to different abiotic factors such as high UV-B levels in spring-summer. Several authors described the flavonoid biosynthesis as crucial to tolerating UV-B enriched environments. The goal of this work is the study of the relationship between biosynthesis of flavonoids, resistance to high UV-B levels and the maintenance of redox homeostasis. With this objective, C. quitensis plantlets were subjected to low, medium and high levels of UV-B radiation, in the presence and absence of aminooxiacetic acid (AOA), a phenylalanine ammonia-lyase (PAL) inhibitor with the aim to determine the role of flavonoids in the capacity of C. quitensis to survive to UV-B. The results showed that plants subjected to increasing levels of UV-B, in the absence of the inhibitor, did not present oxidative damage; on the other hand, plants that were treated by the inhibitor showed oxidative stress symptoms and photosynthetical damage. Oxidative damage was correlated with flavonoids content; at the molecular level, these results showed an increase in transcript levels related to the phenylpropanoid pathway enzymes and their activity, as well as the expression of the UVR8−COP1-HY5 transduction system. Moreover, in AOA treated plants, the results show significant damage and plant death. Our results suggest that the survival mechanism showed by C. quitensis to UV-B radiation is mediated by biosynthesis of flavonoids.