Effects of UV-B radiation on the morphology, UV-B absorbing compounds and photosynthetic pigment content of Plantago lanceolata and Rheum rhabarbarum

In recent decades the fluence of ultraviolet-B (UV-B) radiation striking the ground has increased as a consequence of ozone depletion at southern latitudes. This phenomenon has sparked much interest in unravelling how plants acclimate to this condition. UV-B radiation triggers several responses that affect plant physiology, morphology and biochemistry. In this study, the effects of supplemental UV-B radiation on plant architecture, UV-B absorbing compounds and photosynthetic pigments were analyzed in two cosmopolitan species. A different range of responsiveness was found in the morphological parameters (leaf area, length and width; plant height) of species. The effects on photosynthetic pigment content and the UV-B absorbing compounds were studied through absorbance measurements. The obtained data showed that only carotenoids increased in irradiated plants of R. rhabarabarum. Likewise, an increase in the UV-B absorbing compounds content was found in irradiated plants from the same species. This effect may be regarded as a chemical protection against the damaging effects of light in photosynthesis and against oxidative cell damage. UV-B radiation induced photomorphogenic responses. In fact, all the morphological parameters of P. lanceolata were increased. The clear increase shown in leaf size and plant height suggest that cell division and stem elongation and/or differentiation processes are stimulated by UV-B radiation. These changes can be seen as an eustress effect and may indicate that plants are physiologically adapted to this level of UV-B radiation.