engleski

Defence response of Degenia velebitica (Brassicaceae) to solar UV radiation

Degenia velebitica (Degen) Hayek, a steno-endemic perennial plant which inhabits limestone crevices and screes exposed to intense solar in the Mediterranean mountains of Croatia was used as a model plant. The study was designed to distinguish the effects of solar UV from those of excessive PAR and to investigate acclimation responses of D. velebitica to solar UV radiation. Plants were separated into three experimental groups ; plants grown under constant UV exclusion (UV-), plants grown under UV exclusion and then exposed to UV stress (UVs) and plants continuously exposed to the sun (UV+). The effects on oxidative stress parameters, activities of antioxidative enzymes, chlorophyll and carotenoid concentrations and the expression of proteins involved in the photosynthetic process as well as changes in flavonoids, possible UV filters and antioxidants, were investigated. to evaluate their role. No significant changes in hydrogen peroxide concentrations or damages to lipids and proteins were observed in UVs plants compared to UV- plants. Activities of ascorbate peroxidase, catalase, superoxide dismutase and peroxidases were mostly similar in investigated plants. Also, changes in D1 and RuBisCO protein content were were not observed suggesting that exposure to solar UV radiation did not cause structural or functional damage to the photosynthetic apparatus. Still, increased accumulation of LHCII protein, chlorophyll a, chlorophyll b and carotenoids was detected in UV-exposed plants compared to UV- plants. Furthermore, the concentration of quercetin, kaempferol and isorhamnetin was significantly higher in UVs plants compared to UV- plants after 173 hours of exposure. Fluorescence microscopy showed that flavonoids were localised in epidermal trichomes, vacuoles and cell walls of epidermal cells, and in the palisade parenchyma on both the abaxial and adaxial sides of the leaves. Finally, we suggest that chlorophyll a, chlorophyll b, carotenoids and flavonoids constitute part of a response system in D. velebitica intended to serve as a defence from oxidants and excessive light energy. This mechanism could be a general acclimation mechanism for most Mediterranean plants exposed to intense solar UV radiation.

Degenia; stress; UV; pigments; flavonoids

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