Effects of anthocyanin accumulation on photosynthesis in leaves of asparagus lettuce under low temperature

【Objective】To investigate the effects of anthocyanin accumulation on photosynthesis and its mechanism in the asparagus lettuce leaves at low temperature in winter, and provide reference basis for asparagus lettuce cultivation and breeding.【Method】The seedlings grown in the experimental field in Guangxi University were taken as test materials, and the chlorophyll fluorescence, photosynthetic gas exchange characteristics were measured on the living plants in the field at the normal temperature season(middle October), the early chill season(late November-early December), middle chill season(middle January in next year) and late chill season(early February in next year) in winter respectively, and then, the sample leaves were taken back to laboratory.Hydrogen peroxide(H₂O₂) concentration, superoxide dismutase(SOD), peroxidase(POD) and catalase(CAT) activities and anthocyanin contents were determined by spectrophotometry in those leaves.【Result】Compared with the normal temperature season, predawn maximal photochemical efficiency of PSⅡ(F_v/F_m) value in asparagus lettuce leaves decreased, and the ground fluorescence(F_o) value increased slightly at the earlychill season.At the same time, the apparent photosynthetic electron transport rate(ETR) value decreased by 8.9%, and the photochemical quenching coefficient(qP), actual PSII photochemical efficiencyY(Ⅱ), stable net photosynthetic rate(P_n) values were decreased slightly, and the maxim photosynthesis rate(P_max) decreased by 3.59 µmol/(m²·s).SOD and POD activity increased by 5 times and once respectively, yet CAT activity decreased by 31%.H₂O₂ and anthocyanin contents increased by 81% and 9 times respectively at this period.During the middle chill season, F_v/F_m value increased to 0.85, F_o, ETR, Y(II), P_n and P_max values also increased to be slightly higher than that at the normal temperature season.SOD and CAT activities increased by one time, and H₂O₂ content was slightly decreased, however, anthocyanin contents raised by 7 times compared with early stage.At the end of the chill season, with the warming up of the weather, F_v/F_m value decreased to 0.77.Both F_o(0.1) and the non-regulatory energy dissipation Y(NO) (34%) value raised to the highest level.The values of ETR, P_n and P_max decreased by 22%, 28% and 33%.Although SOD, POD and CAT activity increased by 178%, 28% and 36%, H₂O₂ concentration increased by 1.36 times of that at the middle chill season.Anthocyanin concentration also increased by 3 times of that at the middle chill season.Across the normal and the chill season, anthocyanin contents had significant positive correlation with H₂O₂ concentrations, and H₂O₂ concentrations had positive correlation with SOD activities(P< 0.05).Moreover, there were no significant positive correlations between P_n values and anthocyanin contents and H₂O₂ concentrations(P> 0.05). P_n was affected by multiple factors.【Conclusion】The combined effects of low temperature with strong light synthetize more anthocyanin in asparagus lettuce leaves compared with low temperature alone.It maintains the photosynthetic apparatus running in its right track through increasing leaf temperature, regulating energy balance and increasing antioxidant ability under the chilling stress, which provides support for maintenance and functio-ning of photosynthetic apparatus under low temperature.