Study On Algal Partners Associated With The Lichen-forming Fungus Porpidia Crustulata From The Guancen Mountains

Lichens are obligate symbiotic associations consisting of a fungus (mycobiont) and an algal or cyanobacterial photosynthetic partner. Morphological and phylogenetic analyses are conducted on algal partners associated with the lichen-forming fungus Porpidia crustulata from the Guancen Mountains. In addition, relationship between the algal partners and the growth of lichen-forming fungus Porpidia crustulata and resistibility of the algal partners were studied too.More than 200 specimens are collected form Guancen Mountains and forty-one species are identified. Among them,7 species are first reported in Guancen Mountains,1 family,4 genera and 6 species are newly recorded from Shanxi Province.The newly recorded species are listed as follows:Rimelia reticulate, Melanelia huei, Flavopunctelia soredica, Lecanora caesiocinerea, Porpidia crustulata and Physcia aipolia. The dominant families are Parmeliaceae, Physciaceae, Lecanoraceae, Cladoniaceae and Lecanoraceae.The macro and micro morphological features are thallus (crustose), surface (yellowish white, white, greenish gray or pale gray, rarely tinged orange), apothecia (round, sometimes clustered, sessile, constricted at the base,0.3-1.5 mm in diam). The chemical characteristics are thallus (K- and C-), medulla (I-) and secondary metabolite (+stictic acid and +norstictic acid). According to the phylogenetic study, the genus of Porpidia is not monophyletic group.The algal photobiont of the lichen Porpidia crustulata from the Guancen Mountains was successfully cultivated under axenic conditions and tentatively designated as Chlorella sp. GC. Phylogenetic analysis of ribulose bisphosphate carboxylase (rbcL) and internal transcribed spacer (ITS) nucleotide sequence data revealed that this alga is closely related to Chlorella sorokiniana. There are clear morphological differences between Chlorella sp. GC associated with Porpidia crustulata and the free-living Chlorella sorokiniana. A larger central pyrenoid was observed in Chlorella sp. GC. Based on our genetic and morphological characterization, the Chlorella photobiont of Porpidia crustulata is distinct from closely related Chlorella species.In this study, we investigated the photobiont Chlorella sp. GC (Trebouxiophyceae), a partner of Porpidia crustulata from the Guancen Mountains, China. We examined the relationship between photobiont layer thickness and Porpidia crustulata growth over a six-year period (2007-2012). Althouglh Porpidia crustulata exhibited moderate growth rates (0.4-0.62 mm year-1), photobiont layer became increasingly thinner over the six-year period. We speculate that prolonged exposure to sunlight and desiccation may deleteriously alter photobiont morphology and physiology. Porpidia crustulata may be forced into a state of physiological dormancy.Initially, carotenoid content of Chlorella sp. GC was higher than Chlorella vulgaris and then decreased to less than Chlorella vulgaris after they were cultured 12d at 5 ℃. Initially, SOD activity and soluble sugar content of Chlorella sp. GC were much higher than Chlorella vulgaris. MDA content of Chlorella sp. GC was less than Chlorella vulgaris after they were cultured 3d at 5 ℃ and 10 ℃. The amount of soluble protein of Chlorella sp. GC was less than Chlorella vulgaris after cultured 12d. Low temperature adaptation mechanisms of Chlorella sp. GC was established in a long-term symbiotic relationship. Chlorella sp. GC had better stress tolerance than Chlorella vulgaris.