Desiccation-tolerance Biological Research Of The Mycobiont And Photobiont Isolated From Desert Lichens

Lichen is symbiotic organism composed of a fungus partner, the mycobiont, and may be either a green alga or a cyanobacterium, the photobiont.Desert lichens, which have excellent desiccation-tolerance, play an important role in biological weathering of rocks, soil formation and biocrust, sand dune fixation and ecological restoration. There are rare reports about the desiccation-tolerance mechanism of the mycobiont and photobiont isolated from desert lichens.The dissertation deals with preliminary study of the isolation and cultrivation of the mycobiont and photobiont from desert lichens and their biological features under the water stress and provides the scientific bases for dessication-tolerance gene isolation and artificial biocrusts.First,11 mycobionts were isolated from 5 lichen genera, and 4 photobionts were isolated from another 4 lichen genera. Also the result includes a mycobiont and a photobiont isolated from the same lichen-Fulgensia fulgens (Sw.)Elenkin.This work enriched the species of resource library which isolated from desert lichens, too.Second, the drought-resistant biocharacters of the mycobiont isolated from Glypholecia scabra(Pers.)Mull.Arg. and both mycobiont and photobiont isolated from F. fulgens were performed under the water stress. The results show that:1.The mycobiont isolated from F. fulgens goes through the drought environment by increasing free proteins, soluble sugars and GSH.In another hand, the photobiont isolated from F. fulgens increased the content of free proteins and total phenols. Both of them had different pathways got themselves through desiccation;2.The mycobiont isolated from G. scabra accumulating soluble sugars and increasing the concentration of total phenols and GSH to protect itself from low water activities. SOD did not play an important role;3.It follows that the genes in the mycobiont concerning the metabolic pathways of GSH likely to be the candidates of drought-tolerance genes for cloning and expression analysis at aw=0.90 and aw=0.85. In order to provide enough biomass for cloning and expression analysis, optimal liquid culture conditions of the mycobiont isolated from G. scabra were studied using Plackett-Burman design and orthogonal arrays.The optimized medium consisted of 15g glucose,2g soy peptone,200μg Vitamin B12 in 1L potato extract,pH6.3,150ml medium filled in 250ml triangular flask which the revolving speed was 100r/min, at 18℃.The growth curve showed that the biomass of mycobiont improved significantly cultured in the optimized conditions.