Application of Salt-tolerant and Nitrogen-fixing Blue-green Algae to Agriculture in Sea Water

我们克隆了耐盐植物分子育种所需的外源合成基因、水稻HKT基因和酵母菌ENA1基因。由于这些基因不足以达到最终目标，其他基因被克隆并分析了它们的功能。过量表达水稻钾离子转运蛋白OsHAK5基因的烟草BY2细胞能在低钾离子条件下生长，并表现出耐盐性。BY2细胞过量表达烟草HAL3基因后，提高了烟草的耐盐性，参与了酪氨酸的积累，氮源的供应将是耐盐植物在海水中生长的重要因素。从冲绳附近海水中分离到的单细胞蓝藻聚球藻TU126能够固定大气中的氮，在无碳、氮源的人工海水中生长。在25℃的人工海水中培养14天和45天，聚球藻的胞内总氮分别为19.22 mg/L、41.8 mg/L，分泌的氮分别为3.2 mg/L、4.2 mg/L。耐盐绿藻衣藻W80在聚球藻的条件培养基中的生长速度与在含NH_4Cl的新鲜培养基中的生长速度相同，表明该聚球藻产生的氮化合物可以被植物利用。海藻酸钙固定化聚球藻细胞在培养30d和60d后，培养液中氮的分泌量分别为1.0 mg/L和5.6 mg/L。综上所述，固定化聚球藻TU126可以为耐盐植物在海水农业中提供氮源。

We have cloned essential genes required for molecular breeding of salt-tolerant plants which can grow in sea water, such as ectoine synthetic genes, rice HKT gene and yeast ENA1 gene. Since these genes were not enough for the final goal, other genes were cloned and analyzed their function. Tobacco BY2 cell, which was over-expressed rice potassium ion transporter, OsHAK5 gene, can grow in low potassium ion medium and showed salt-tolerance. BY2 cell increased salt tolerance when it was over-expressed tobacco HAL3 gene which participate to praline accumulation.Supply of nitrogen source will be an important factor when salt-tolerant plants are grown in sea water. Single-cell blue-green algae, Synechococcus sp.TU126, which was isolated from sea water near from Okinawa can fix atmosphere nitrogen and grew in artificial sea water without carbon and nitrogen source. Total intracellular nitrogen in the Synechococcus grown in artificial sea water under light at 25℃ for 14 days and 45 days, was 19.22 mg/l、 41.8mg/l, respectively, and excreted 3.2 mg/l、4.2 mg/l nitrogen, respectively, in the medium.Salt-tolerant green algae, Clamydomonas sp.W80 grew in the conditioned medium of the Synechococcus in the same extent as that in the fresh medium contained NH_4 Cl in the same level of nitrogen in the conditioned medium, suggesting that nitrogen compounds produced by the Synechococcus can be utilized by plants. Immobilized Synechococcus cells in calcium alginate secreted nitrogen of 1.0 mg/l and 5.6 mg/l in culture medium after 30 days and 60 days, respectively. In conclusion, salt-tolerant plants can be supplied nitrogen source from immobilized Synechococcus sp.TU126 in agriculture in sea water.