Response of chlorophyll fluorescence characteristics and antioxidant enzyme activities in peach leaves to sulfur dioxide stress

Abstract: 【Objective】Sulfur dioxide is a global pollutant and has a great influence on the growth of peach, but there is little information about this.‘Chunmi'peach is an early maturing variety bred by the Zhengzhou Fruit Research Institute of Chinese Academy of Agricultural Sciences. In this experiment, 1-year-old potted grafted nursery plants of‘Chunmi'peach were used to study the changes in physiological and biochemical parameters under treatments with different concentrations of sulfur dioxide. The chlorophyll fluorescence parameters, fast phase and slow phase fluorescence changes in the plants treated with sulfur dioxide were studied in order to clarify the effects of sulfur dioxide stress on the photochemical and physiological characteristics of PSⅡ, understand the response of peach leaves to sulfur dioxide stress and the physiological mechanism involved in stress resistance and provide a theoretical basis for cultivation of peach under stresses.【Methods】Materials were planted in plastic pots with a diameter of 21 cm and height of 28 cm in the spring of 2016. Sulfur dioxide fumigation was made by a static fumigation device. No-sulfur dioxide was treated as control. Three concentrations of sulfur dioxide (0.14 mg · m-3, 1.43 mg · m-3 and 14.3 mg · m-3) were separately treated on 1-year-old‘Chunmi'plants. Fumigation was implemented 2 hours per day from 9:00 am for 20 days. The plants were removed from the fumigation room after fumigation. The physiological and biochemical indexes were measured at 4 d, 8 d, 12 d, 16 d and 20 d. Each treatment had three replications. Chlorophyll fluorescence kinetics parameters were determined with a PAM-2500 portable pulse modulated chlorophyll fluorescence instrument after dark adaptation. Leaves were collected at the same time every day and randomly from the middle periphery of the plant. The samples were frozen with liquid nitrogen and stored at-80 ℃ for determination of the antioxidant enzyme activity and malondialdehyde content.【Results】The results showed that maximal fluorescence (Fm) , PS Ⅱ maximum photochemical conversion efficiency (Fv/Fm) and PSⅡ potential activity (Fv/F0) significantly decreased with increasing of sulfur dioxide concentration and the prolonging of treatment time. 0.14 mg· m-3 treatment had no significant difference with the control, while 1.43 mg· m-3 and 14.3 mg· m-3 significantly decreased these parameters, the reduction by 14.3 mg· m-3 treatment being more remarkable. The photochemical quenching coefficient (qP) decreased with the increase of sulfur dioxide concentration and the prolonging of treatment time, while the non-photochemical quenching coefficient (qN) showed an opposite pattern. Treatment at dose of 14.3 mg· m-3 had significant difference with the control. The quantum yield of the nonregulated energy dissipation [Y (NO) ] maintained at a lower level compared with the control. The PSⅡ actual quantum efficiency [Y (Ⅱ) ] decreased with the increase of sulfur dioxide concentration and the prolonging of treatment time, while the quantum yield and regulated energy dissipation [Y (NPQ) ]increased gradually. In the O-J-I-P curve, the fluorescence intensity of the JIP point from the fluorescence induced kinetic curve decreased at different degrees by 1.43 mg· m-3 and 14.3 mg· m-3 treatments.The minimal fluorescence (F0) , the fluorescence at the P point (Fp) , the relative variable fluorescence intensity at the J-step (VJ) and the approximated initial slope of the fluorescence transient of O-J-I-P curve (Mo) in the treatments at 0.14 mg· m-3, 1.43 mg· m-3 and 14.3 mg· m-3 were not significant compared with the control. The values of the maximum quantum yield for primary photochemistry (FPo) , quantum yield for electron transport (FEo) , probability that a trapped exciton moves an electron into the electron transport chain beyond QA- (ψo) and photosynthetic mechanism performance index (PIABS, PICSo and PICSm) in the treatments at 1.43 mg· m-3 and 14.3 mg· m-3 at 20 days were decreased, and 14.3 mg· m-3 treatment decreased more. The antioxidant enzyme activities and MDA content in peach leaves in 0.14 mg· m-3 treatment had no significant change compared with the control. The activities of superoxide dismutase (SOD) , peroxidase (POD) , catalase (CAT) and malondialdehyde (MDA) content in 1.43 mg· m-3 treatment reached the maximum at 20 days and increased respectively by 55.31%, 33.42%, 41.69% and58.63% compared with the control. The activities of SOD, POD and CAT in 14.3 mg· m-3 treatment increased and then decreased, and reached the highest value at 12, 16 and 12 days, and increased by83.75%, 51.11% and 48.16% respectively, compared with the control. The MDA content in 14.3 mg· m-3 treatment increased gradually, was 1.8 times higher than the control at 20 days. Based on the results, the physiological responses of peach to sulfur dioxide stress could be rapid detected by fluorescence induction kinetic curve of OJIP and JIP-test analysis.【Conclusion】0.14 mg· m-3 sulfur dioxide treatment had no significant effect on photosynthetic mechanism of peach leaf. The PS Ⅱ reaction center of peach leaf under the treatments of 1.43 mg· m-3 and 14.3 mg· m-3 of sulfur dioxide was closed or irreversibly inactivated with severe photoinhibition.