High blue light improves acclimation and photosynthetic recovery of pepper plants exposed to UV stress

• We studied the impact of light on acclimation of pepper plants to UV.
• Higher amount of blue light in the PAR spectrum reduced UV sensitivity.
• Higher PAR and blue light alleviate the UV impact on photosynthetic performance.
• Adaptations at chloroplast and leaf level influenced stress tolerance to UV.
• Changes in pigment composition pattern supported the physiological adaptations.

Intensity of photosynthetic active radiation (PAR) plays an important role in the acclimation of plants to UV radiation. Thereby, specific morphological and physiological characteristics influenced by high irradiance are also affected by blue light. With this background we conducted two experiments to evaluate the impact of light intensity and the relevance of blue light for the acclimation of pepper plants to UV. In this context we hypothesized that higher amount of blue light in the PAR spectrum significantly improves the plant acclimation and recovery to UV radiation. Our results demonstrate that UV stressed plants cultivated either under the higher light intensity (PAR 300 μmol m−2 s−1) or under higher amount of blue light (62%) show better photosynthetic performance (i.e., higher photosynthetic rate (Pn), higher maximal photochemical efficiency of PSII (Fv/Fm) and lower non-photochemical quenching (NPQ)) than UV stressed plants grown under lower light intensity (PAR 100 μmol m−2 s−1) or lower amount of blue light (30%). Contents of chlorophyll a and b, as well as carotenoids, had a stronger decrease due to UV in those plants cultivated either under the lower light intensity or under the lower amount of blue light. In contrast, plants grown either under 300 μmol m−2 s−1 or 62% blue light accumulated more epidermal flavonols. Analogous to the well described effects of high PAR intensity, we demonstrate here that high amount of blue light triggers specific biochemical and physiological processes resulting in better acclimation and recovery of plants to UV stress.