Morphological, biochemical and physiological responses of Indian cress (Tropaeolum majus) to elevated UV-B radiation

Background and Purpose: UV-B radiation is an important environmental factor for many plants with remarkable influence on defence-related secondary metabolite biosynthesis. Possible consequences of UV-B radiation on plants have been widely reported, but its effect on secondary plant metabolites in ornamental and medicinal plants is poorly understood. The aim of the present research was to establish whether it is feasible to cultivate Tropaeolum majus under conditions of enhanced UV-B radiation to alter the content of total phenolic compounds in leaves and flowers and whether UV-B treatment affect plant physiological response. Material and Method: An outdoor study was conducted to examine the effect of different levels of UV-B radiation on the morphological (specific leaf area and length of internodes and petiole), biochemical (photosynthetic pigments, UV absorbing compounds) and physiological characteristics (photosynthesis, photochemical yield of PSII, transpiration rate, water use efficiency) of the widely cultivated annual herb Indian cress (T. majus L). Results and Conclusions: Enhanced UV-B radiation induced increased synthesis of total phenolic compounds in leaves, but not in flowers. Photosynthesis and photochemical yield of PHI were mostly unaffected by UV-B. Transpiration rate was higher at elevated UV-B levels in the beginning and peak of the season. Specific leaf area and length of internodes and petiole were unaffected. UV-B treated specimens of T. majus possessed enhanced amounts of total phenolic compounds, which are important for utilisation of T. majus herbs for human health. Enhanced UV-B treatment affected flowering of T majus at the end of the growing season, which may have an important negative implication for success of this species in elevated UV-B radiation environments.