EFFECTS OF UV-B ON PHOTOSYNTHETIC PARAMETERS, LIPID PEROXIDATION, FLAVONOIDS AND GROWTH TRAITS OF CONOCARPUS LANCIFOLIUS (ENGL.)

Conocarpus lancifolius is a perennial ornamental plant adapted to the semi-arid conditions of Kuwait. It accumulates most of its biomass during the stressful summer conditions which includes UV-B irradiation. The study evaluated equivalent UV-B irradiation intensities that plants would normally experience sometime during the course of a year in Kuwait. Leaf area, plant height, photosynthetic parameters, Lipid Peroxidation (LP) and Phenyl Alanine Lyase (PAL) were measured in C. lancifolius plants exposed to different UV-B treatments. UV-B treatments decreased leaf area and plant height but induced the formation of lateral branches. Chlorophyll content, photosynthesis, chlorophyll fluorescence measured as maximum quantum efficiency of photosystem II (Fv/Fm) and Electron Transport Rate (ETR) decreased in the short term or the first 10-20 days after treatment. Lipid Peroxidation (LP) measured in terms of Malondiadehyde (MDA) content decreased in the long term after a short term increase but Phenyl Alanine Lyase (PAL) activity increased linearly by 41.2, 66.8 and 78.6% after 30 days. There was also Positive Linear Correlation between UV-B dosage and total flavonoid accumulation which was localized in epidermal cell walls, trichomes and cuticular layer. The response of C. lancifolius to ameliorate and/or tolerate UV-B stress involved multiple mechanisms that included increased concentrations of PAL activity, increased flavonoids production; and reduced lipid peroxidation. The net effect of flavonoid accumulation and PAL enzyme activity probably contributed significantly to the protection or tolerance of the species to the effects of UV-B.