The Role In Photoprotection And Induction Mechanism Of Anthocyanins Under Low Temperature In Begonia Semperflorens

With the'garden city'concept being accepted, landscape plants with green leaves cannot meet requirments for beautification. Plants with colorful leaves had attracted more attention. Studying the ecologic function of anthocuanins, substance for leaves colorring, would offer theoretical basis for applying plants with colorful leaves. Further, regulation in anthocyanins biosynthesis would make up deficiencies of breeding, such as needing too long period, limited materials. This study used two genotypes of Begonia semperflorens,'Cocktail'(red leaf) and B. semperflorens cv. 'Super Olympia'(green leaf), to function and role of anthocyanins in photoprotection. We also investigate the effect and mechanism of low temperature on anthocyanin accumulation. The results are as follows:1. To determine the effects of leaf coloration on photosynthetic apparatus, two genotypes of Begonia semperflorens with green leaves or red leaves were compared for their differences in anthocyanin accumulations, gas exchange and chlorophyll fluorescence quenching. Extraction solution of the red leaves showed a high accumulation of anthocyanins and high absorption at 282 and 537 nm. In comparison with red leaf genotype, the green leaf genotype exhibited a higher photosynthetic activity and lower proportion of energy dissipation via light-dependent thermal dissipation. It seems likely that anthocyanins in the vacuoles restricted the absorption of green light to the chloroplasts, leading to a decrease in the efficiency of excitation capture by open PSâ…¡centres and photosynthesis and photochemical quenching decreased followed by a lowered photosynthesis.2. Anthocyanins are thought to provide photoprotection under stressful conditions. We used two genotypes of Begonia semperflorens with different pigmentation to study the effects of anthocyanins on tolerance of high light stress. The maximum quantum yield of PSâ…¡(Fv/Fm) in red leaves was significantly higher than that in green leaves during and after high light stress. High light also induced significant increases in anthocyanins in both genotypes. Despite large differences in anthocyanin content, chlorophyll content and Chl a/b ratio did not differ between red and green leaves. After high light stress, xanthophyll pool size and enzymatic antioxidant activity were lower in red leaves than in green leaves. Non-enzymatic antioxidant activity measured by DPPH assay, however, was significantly higher in red leaves than in green leaves. Meanwhile, changes in DPPH activity were closely correlated with changes in anthocyanin content during and after high light stress. Declines in Fv/Fm were significantly greater for green leaves than for red leaves under green light but were comparable between green and red leaves under red and blue light. Changes in ROS under different colors of light were similar to the changes in Fv/Fm. Our results suggest that anthocyanins primarily function as light filters rather than as antioxidant molecules during high light stress in B. semperflorens.3. Low temperature in fall may induce anthocyanins synthesis in leaves and stems of B. semperflorens cv.'Super Olympia'(green leaf). In this course, callose was synthesized by low temperature and then a mass of carbohydrate accumulated. Carbohydrate may induce anthocyanins synthesis in many plants, which maybe the reason of anthocyanins appearance in'Super Olympia'under fall. To verify this hypothesis, we used girdling stem and adding sucrose exogenously to increase carbohydrate in leaves and stems. Results showed that:carbohydrate increased in leaves and stems truly induced anthocyanins synthesis.4. Leaves of many plants would turn red in fall, which is regarded as function of low temperature. Here we proved that light is necessary in anthocyanins biosynthesis induced by low temperature. Low temperature without light failed to induce anthocyanins biosynthesis, however, increased activities of PAL. To investigate where anthocyanins biosynthesis was choked and where the production of secondary metabolism flew, we mensurated activities of CHI, DFR, UFGT and contents of lignin, phenolic acids and flavonoids. Results showed that, low temperature without light increased activity of CHI, but not for DFR and UFGT. Carbohydrates were metabolized under low temperature without light. Compared with low temperature and light, low temperature without light increased more flavonoids and same phenolic acids but not lignin.