恶劣条件下浮萍中淀粉含量激增的机理研究

The food vs fuel debate reached a global scale as a result of the international community's concerns regarding the steep increase in food prices. In order to alleviate this problem, it is necessary to explore novel starch sources to supplement corn starch to make the development of ethanol industry more sustainable and environmentally friendly. The information of starch content, granule size, and derivation of starch granules is critical to duckweed as a kind of feedstock for bioethanol. But there is almost no research about this respect. In this study, duckweed, that was found to have a great potential for starch production, was used for starch production, in order to understand the mechanism of the starch accumulation. The methods of batch test in a small growth chamber and box test in greenhouse are used to study the duckweed's starch content changing granule size, and derivation of starch granules as the physical and chemical environmental conditions are changed. At the same time, the contents and compositions of pigments, the chloroplast ATP synthase activities, and the activities of antioxidant enzymes in duckweed are analyzed to examine the metabolic regulation of these features. This study seeks to identify key enzymes, whose manipulation at the molecular level could optimize the timing and level of starch production. Considering the currently predominant energy sources, fossil fuels, are limited and the feedstock of bioethanol are complexed, the carry out of this project will not only help to promote bio-energy technology development, but also can removal of nitrogen and phosphorus in water body providing important data for water pollution restoration. Hence, this project has important theoretical and practical significance.

为缓解燃料乙醇与人"争粮"问题，国内外科学家都在努力寻找一种环境友好，经济便宜的生物乙醇原料。浮萍中淀粉的含量，淀粉颗粒的大小和演变决定着浮萍能否作为生物乙醇原料，但是目前对这方面的研究目前很少。本项目以常见的水生飘浮植物－浮萍为研究对象，着重研究恶劣环境下浮萍中淀粉含量突然增加的原因和机理。采用光照恒温培养箱内批实验和温室内箱实验的方法，研究物理环境变化和化学环境变化下浮萍内淀粉含量变化，淀粉颗粒的大小和演变情况，同时分析细胞内叶绿体色素组分与含量变化和ATP合成酶以及抗氧化酶系的变化，实现从分子生物学角度解释浮萍中淀粉含量激增的机理。 鉴于石油能源紧缺的普遍性和目前生物燃料乙醇原料的复杂性，本项目的开展不仅有助于推动生物能源技术向前发展，而且可以去除污水的营养组分，为水体污染恢复治理提供重要的基础资料和科学依据，因此，本项目研究具有重要的理论意义和现实意义。

鉴于石油能源紧缺的普遍性和目前生物燃料乙醇原料的复杂性，特定条件下能快速积累淀粉浮萍作为发酵产乙醇的生物质原料成为研究热点。而浮萍中淀粉含量变化机理决定着浮萍能否作为生物乙醇原料。脱落酸（ABA）是一种生物激素，控制植物的生长发育和应激反应。本研究以紫背浮萍和稀脉浮萍为研究对象，加入植物生长调节剂：脱落酸，测定叶绿素和类胡萝卜素含量、超氧化物歧化酶（SOD）、过氧化物酶（POD）活性、可溶性淀粉合成酶的活性（SSS）和淀粉分支酶（SBE），淀粉降解酶（α-淀粉酶、β-淀粉酶）活性以及浮萍内淀粉含量，此外我们还测定了ADP-葡萄糖焦磷酸化酶（AGPase）活性和ADP-葡萄糖焦磷酸化酶三大亚基（APL1, APL2 和APL3）的表达，通过淀粉合成途径和降解途径分析浮萍内淀粉含量变化机理。.对于紫背浮萍，ABA的浓度小于1×10−3 mg/L时，可以促进生物生长和二氧化碳的固定，而ABA的浓度大于1×10−3 mg/L时抑制生物生长和二氧化碳固定。在ABA浓度小于1×10−2 mg/L时SSS和SBE的活性增加，叶绿素a，叶绿素b和类胡萝卜素的含量增加，从而导致淀粉含量的提高。培养10天后，在1×10−2 mg/L ABA中得到35.3%的干重的淀粉含量，这是本研究的最高值。基因表达显示ABA主要通过诱导APL2表达促进葡萄糖焦磷酸化活性的升高，从而有助于淀粉的合成。ABA的浓度为1×10−3 mg/L时，培养天数控制在10天，淀粉积累含量相比于对照可增加78.6%。.对于稀脉浮萍，在低浓度ABA作用下，前6天对浮萍生长有促进作用，高浓度ABA对于浮萍生长有较强的抑制作用。在不同浓度脱落酸作用下，叶绿素a及叶绿素b含量缓慢下降；类胡萝卜素含量有不同程度的增加。SOD及POD活性先逐渐升高后逐渐降低。α-淀粉酶及β-淀粉酶活性不断降低，导致浮萍内部淀粉的降解过程受阻，淀粉含量不断积累，培养14天后，淀粉含量百分比范围为20%~24%。浮萍在10-9 ~10-7 mol/L脱落酸浓度范围内生长良好，培养天数控制在6天内，淀粉积累含量相比于对照分别增加了209%、250%、264%。.这意味着两种浮萍都有积累淀粉的巨大潜力，或者说浮萍可以替代玉米，甘蔗等粮食作物作为一种淀粉来源。