Creation On Artificial Associations Between N₂-fixing Cyanobacteria And Wheat And Screening Of Compatible Algae Strains

In order to create the artificial combination between Ni-fixing cyanobacteria and wheat, this paper were mainly studied and explored on molecular identification and screening on free-living cyanobacteria Synechococcus 805 and 22 symbiosis N2-fixing cyanobacteria strains, including 12 Nostoc strains and 10 Anabaena strains, and physiological effect of co-cultivation for cyanobacteria and wheat seedling. First, system analysis of 23 cyanobacteria strains by 16SrRNA-RFLP, ITS-RFLP showed that 23 strains of cyanobacteria could be separated into two clusters basically corresponding to Anabaena and Nostoc genus on the basis of morphological classification, excluding synechococcus 805. However, the 8981 strain, identified as Nostoc genus on the basis of morphological classification, was classified into Anabaena genus on the level of molecular and amino acid. Second, the comparison on the effect on co-cultivation of cyanobacteria and wheat seedling showed that the effect of Nostoc was better than that of Anabaena, and Nostoc 9101 : 1 was the best among which. The height, dry weight, root length, root dry weight of wheat seedlings inoculated with the 9101 : 1 strain increased by 113.7%, 110.3%, 20.21%, 28.16% respectively. Which may relate to the content and composition of amino acid, especially Cysteine, Tyrptophan and Phenylalanine. Third, the further study on the attaching ability showed the A665 of co-cultivation of Nostoc and wheat was higher than that of co-cultivation of Anabaena and wheat, which indicated Nostoc could attach tightly with wheat roots, and suggested that Nostoc was better than Anabaena. Fourth, the research results of the cells differentiation and morphology of cyanobacteria demonstrated that BG11 medium with nitrogen restricted the differentiation of cyanobacteria cells, but the nitrogen starvation could induce heterocyst development. However, only was the heterocyst frequency of the 9101 .' 1 strain in the treatment of wheat and BG11(-N) medium more obviously different than that in BG11 (-N) medium. The heterocyst frequency ranged from 9.45% to 16.55%. Moreover, the 9101 .' 1 strain was induced to differentiate hormogonia after 10 days when inoculated into the treatment, which suggested the Nostoc 9101 : 1 may be a good candidate on the creation of symbiosis system.