Physiological responses of Scenedesmus quadricauda (Chlorophyceae) to UV-A and UV-C light

Despite intensive research focused on the effects of UV-B, deeper metabolic responses to UV-A and UV-C are still scarce. Besides, especially microalgal species had to develop efficient protective features in comparison with tissue structure of vascular plants. We exposed axenic cultures of Scenedesmus quadricauda (Chlorophyceae) to UV-A (366 nm) and UV-C (254 nm) light over 1 h. Both wavelengths stimulated increase in soluble proteins, superoxide radical and hydrogen peroxide, but had a nonsignificant effect on cell viability. Within 17 detected free amino acids, five (including proline) increased in response to UV-A while only aspartic acid and histidine increased in UV-C treatment. Total soluble phenols and flavonoids were influenced neither by UV-A nor by UV-C while selected flavonols (quercetin and kaempferol) decreased in UV-A and were not detected in UV-C treatment. Benzoic acid derivatives increased preferentially after UV-A illumination (vanillic acid and vanillin) while cinnamic derivatives (caffeic, chlorogenic and p-coumaric acids) decreased in both UV-A and UV-C. It is concluded that UV light stimulated oxidative stress while exposure time was not sufficient to stimulate larger changes in phenolic metabolites. Present findings in the context of available data and with emphasis on phenolics in algae are discussed.