Effects Of NaHSO₃ And Environmental Stress On Photosynthesis And Chlorophyll Fluorescence Of Stem Mustard (Brassica Juncea Var. Juncea)

The study was conducted to investigate gas exchanges and chlorophyll fluorescence parameters in stem mustard (Brassica juncea var. juncea cv. Suotou) plants grown in pots after spraying of different concentrations of NaHSO3. Photoinhibition of photosynthesis and its recovery were also studied in TuMV-infected stem mustard leaves by exposing them to various light intensities at two temperatures, 23 and 35℃. The main results of this study are as follows:1. Pn increased in plants after treated by 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0mM NaHSO₃, and greatest increase was observed in plants with spraying of 0.5mM NaHSO₃. There was no greatment difference in Gs Ci Tr amongst all treatments. However, Fo tended to increase when the concentration of NaHSO3 was higher than 2mM.2. During the first 3 days after spraying 0.5mM NaHSO₃, Pn had an apparent increase. But it decreased to the level of pre-treating at day 6, whereas there were no difference in Gs, Ci, Tr between control and treated plants. In the first 3⁴ days, Fm, Fv/Fm, ΦPS II qP ETR and P all increased compared with control plants. They all reverted to the level as control after 5 days.3. The content of Chla, total content of Ch1, height, leaf area, fresh weight of stem and leaf increased by application of 0.5mM NaHSO3 every six days for two months.4. After exposing to a light intensity of 1600μmol m^-2s^-1 for 4h at 23 ℃, Fo, qN, NPQ increased sharply in both TuMV-infected and control plants, in which TuMV-infected increased greater than control. However, Fm Fv/Fm qP Φ PS II all decreased, in which TuMV-infected decreased greater than control.The recovery rate of photoinhibited photosystem II (PSII) under various light intensities was slower in TuMV-infected than control plants, as was indicated by chrolophyll fluorescence parameters. The SDS-PAGE and western-bloting of thylakoid membranes showed that the content of Dl protein decreased after high-light exposure, but the TuMV-infected plants were more severely affected. After 4h recovery, the content of Dl protein increased. The recovery rate of photosynthesis from photoinhibition was largely depedent on the light intensity, the illumination intensity was higher, the recovery was worse.5. After exposing to a light intensity of 1600nmol?n"2? s'1 for 4h at 35 °C, Fo,qN, NPQ of TuMV-infectecd and control plants increased sharply, and the infected plants increased greater than the control. Fm> Fv/Fm> qP% PS II all decreased, and the TuMV-infected plants increased greater than the control. The extent of decrease in Fo, qN, NPQ and increase in Fm^ Fv/Fm> qP% OPS II were less than those of TuMV-infected plants at 23 °C. The content of Dl protein decreased more than those of TuMV-infected plants at 23 °C,especially the content of D1/D2 protein. After 4h recovery at 35°C, the content of D1/D2 was still tiny of both control and TuMV-infected leaves, the content of Dl protein of TuMV-infected plants increased slightly, the recovery rate was the best when the illumination intensity was SOOiimol'iri^s"1, when in lOOOfJ.mol-m"2^"1, no Dl protein was detected in TuMV-infected leaves.