Phenotyping of basil (Ocimum basilicum L.) illuminated with UV-A light of different wavelengths and intensities

The effects of light on plants depend on the energy dose and spectral characteristics. We investigated how UV-A radiation with two different wavelengths, 365 and 385 nm, combined at different intensities as supplemental light to red-blue baseline illumination affects growth and selected physiological and biochemical traits of green leaf basil (Ocimum basilicum L.). Conventional physiological measurements and biochemical analyses of photosynthetic pigments and phenolics were combined with high-throughput phenotyping. We did not detect any negative effects of UV-A on plant growth and photosynthetic functions, even at high doses of short-wave UV-A. Furthermore, thylakoid processes were enhanced under UV-A, as evidenced by higher electron transport rates and increased photochemical efficiency. The increase in anthocyanin index (ARI) indicates the UV-screening response. However, no anthocyanins were detected in the leaves, and the only phenolic compounds that responded to UV-A were hydroxycinnamic acid derivatives, which have a dual function in responding to UV-A (UV protection and antioxidants). UV-A increased the pool of xanthophyll cycle pigments and their ratio to chlorophylls. All this prevents photoinhibition and contributes to a high plasticity/efficiency of the basil's response to light environment.