Effects Of UV-B And Periodic Desiccation On The Morphogenesis Of Cyanobacterium Nostoc Flagelliforme

Nostoc flagelliforme (Berk.& Curtis) Bornet & Flahault, named Fat Choi in China, is a terrestrial macroscopic filamentous cyanobacterium that is widely distributed on arid or semiarid areas. It has been used as a food and herbal ingredient for hundreds of years, and has important values on the improvement of soil from desertification and the propagating of soil microbes, is classified the first-grade state protection wild plant. In the present study, I introduced the ecological characteristics, the physiological and biochemical properties, and the artificial cultivation of N. flagelliforme, and the effect of UV-B on cyanobacterium in order to highlight the roles of UV-B and wetting-dry in the habitat of N. flagelliforme. Then, effects of UV-B and periodic desiccation on the morphogenesis of N. flagelliforme were investigated to develop the cultivation techniques of N.flagelliforme from cells.With low fluence rates of UV-B treatment (0.094 W m-2), single trichomes developed into filamentous thalli more than 1 cm length after 28 days of cultivation, which were the longest filamentous thalli cultured in liquid suspension at present. UV-B affected the morphogenesis of thallus by increasing the synthesis of sheaths and reducing the aggregation of colonies. Low fluence rates of UV-B induced the synthesis of MAAs with an increasing of 60%, which might exist in sheath but did not act as the secondary metabolite to cope with UV-B stress for no negative effects on the increase of biomass was observed.With periodic desiccation, single trichomes cultivated on solid medium developed into filamentous, banded or flat thalli. Periodic desiccation not only increased the synthesis of extracellular polysaccharides (EPS) and the thickness of sheaths, but also promoted the parallel arrangement of filaments within the thallus. With the assistance of UV-B, the effects of desiccation were more significant. Filamentous thalli cultured in liquid suspension for 14 days were transferred to solid medium, treated with UV-B and periodic desiccation simultaneously, and grew into almost 3 cm in length 40 days latter. Their filamentous morphology was similar to natural colonies. The rebuilding of thalli indicated that the formation of sheaths and the morphogenesis of N. flagelliforme were directly related to periodic desiccation, and sheaths were an important strategy to resistdrought. Thalli were cultivated on BG11 and N-free BG11 solid medium, and nitrogen sources affected the color of thalli. They presented yellow-green on solid N-free BG11 medium, while deep green on standard BG11. Nitrogen starvation also increased the synthesis of EPS, and affected the morphologic characteristics of thalli. Thalli on BG11 plates formed irregular folds on the surface, while the surfaces of thalli were smooth on N-free BG11 plates.Our findings suggest that both UV-B and periodic desiccation affect the morphogenesis of N. flagelliforme, which directly illustrates the correlation between morphologic charactersistics and the environment factors. Three models of cultivation provided in the present study have important values for large-scale artificial cultivation both in liquid and solid media.