Effects of exogenous NO on the growth and photosynthetic fluorescence characteristics of ryegrass seedlings under B[a]P stress Li Yue yuanlinliyue@163.com Ma Junqiang majunqiang_mail@163.com Wang Yu 15617874658@163.com Xu Sunan xusunan1983@126.com Jiang Lei 359958434@qq.com Zhang Lihong lihongzhang132@163.com Hou Wei houwei@lnu.edu.cn School of Environment, Liaoning University, Shenyang, 110036, China China School of Environment, Liaoning University, Shenyang, 110036, China China School of Environment, Liaoning University, Shenyang, 110036, China China School of Environment, Liaoning University, Shenyang, 110036, China China School of Environment, Liaoning University, Shenyang, 110036, China China School of Environment, Liaoning University, Shenyang, 110036, China China School of Environment, Liaoning University, Shenyang, 110036, China China 12 01 2022 31 03 2023 3103202382

Fig. 1. Effect of different concentrations (100, 200, 300 and 400 μmol L-1) of sodium nitroprusside (SNP), a NO donor, on the biomass of ryegrass seedlings under benzoapyrene (B[a]P) stress. (A) Aboveground dry weight, (B) Belowground dry weight, (C) Aboveground fresh weight, (D) Belowground fresh weight, (E) Aboveground plant height, (F) Belowground root length. Data are mean ± standard deviation, n = 3. Different letters indicate significant differences at p < 0.05.

Fig. 2. Effect of different concentrations (100, 200, 300 and 400 μmol L-1) of sodium nitroprusside (SNP), a NO donor, on the photosynthetic pigment content of ryegrass seedlings under benzoapyrene (B[a]P) stress. (A) Chlorophyll a content, (B) Chlorophyll b content, (C) Carotenoid content, (D) Total chlorophyll content. FW – fresh weight. Data are mean ± standard deviation, n = 3. Different letters indicate significant differences at p < 0.05.

Fig. 3. Effect of different concentrations (100, 200, 300 and 400 μmol L-1) of sodium nitroprusside (SNP), a NO donor, on photosynthetic gas exchange parameters of ryegrass seedlings under benzoapyrene (B[a]P) stress. (A) Net photosynthetic rate (Pn), (B) Stomatal conductance (Gs), (C) Intercellular carbon dioxide concentration (Ci), (D) Transpiration rate (Tr), (E) Water use efficiency (WUE). Data are mean ± standard deviation, n = 3. Different letters indicate significant differences at p < 0.05.

Fig. 4. Effect of different concentrations (100, 200, 300 and 400 μmol L-1) of sodium nitroprusside (SNP), a NO donor, on chlorophyll fluorescence parameters of ryegrass seedlings under benzoapyrene (B[a]P) stress. (A) PSII potential activity (Fv/F0), (B) PSII maximum light energy conversion efficiency (Fv/Fm), (C) Actual quantum yield of PSII photochemistry (ФPSII), (D) Steady-state fluorescence (Fs), (E) Photochemical quenching coefficient (qP), (f) Non-photochemical quenching coefficient (qN). Data are mean ± standard deviation, n = 3. Different letters indicate significant differences at p < 0.05.

Fig. 5. Effect of different concentrations (100, 200, 300 and 400 μmol L-1) of sodium nitroprusside (SNP), a NO donor, on antioxidant enzyme activity of ryegrass seedlings under benzoapyrene (B[a]P) stress. (A) Superoxide dismutase (SOD) activity. (B) Catalase (CAT) activity. (C) Peroxidase (POD) activity. Data are mean ± standard deviation, n = 3. U – unit of enzyme activity, FW – fresh weight. Different letters indicate significant differences at p < 0.05.

Fig. 6. Principal component analysis (PCA) plots of growth, photosynthetic characteristics and chlorophyll fluorescence parameters and antioxidant enzyme activity of ryegrass for different concentrations (100, 200, 300 and 400 μmol L-1) of sodium nitroprusside (SNP) in combination with benzoapyrene (B[a]P) as well as control.