[Effects of sulphur dioxide on the relationship between symbionts in lichen]

Xanthoparmellia mexicana was successfully isolating and culturing from its two symbionts and, preliminarily re-symbiosising its thalli in vitro performed from pure cultured photobiont and mycobiont. The solution exposure method was applied, confirming the toxic effect of sulfite solution with pH 4.0. The biochemical responses of lichen thalli and cultured symbionts to the short time stress of SO2 were studied. The chlorophyll PQa value of photobiont was correlated with its absorption of SO2. Chlorophyll a was more sensitive than chlorophyll b; chlorophyll was damaged most severely by the exposure of 0.5 mg.L-1 of SO2 fumigation, but was aggravated with the increase in the concentration of SO2 by way of solution exposure. The activity of acid phosphatase in lichen was mainly dependent on the photobiont. Reduced glutathione(GSH) was activated by oxidative stress of SO2. GSH was confirmed to be highly correlated with SO2 stress, and was proposed to be a significant and prospective biomarker of the status of lichen antioxidant system and the oxidative damage in lichen. The mycobiont was proposed to mainly resist the oxidative stress by SO2, while the photobiont was damaged more easily with energy depletion.