Endophytic Nitrogen Fixation by European Beachgrass (Ammophila Arenaria)

有些草似乎能够通过与各种细菌的共生关系获得固定的氮。该项目涉及一种新的共生关系，涉及欧洲滩草（砂氨菌）和生活在寄主植物的芽和根茎中的固氮细菌。主要目的是确定这种草的固氮（乙炔还原）活性的程度，以确认其速率是显著的。其他目标是表征与嗜氨菌共生关系有关的微生物，确定这些微生物的自然丰度和分布，并确定类似的共生关系是否可能存在于或引入到其他禾草物种（包括作物物种）中。接种和无菌的幼苗将用于温室和田间试验，以确定嗜氨菌是否从其细菌共生体中受益。田间固氮速率和环境变量的影响将通过乙炔还原试验来测量。内生细菌的精确位置将使用免疫学技术在光学和电子显微镜水平上与现有的抗体确定。这些细菌将被描述为与固氮有关的基因以及氧和固定氮对固氮的影响。其他种类的草也将使用乙炔还原法和光学显微镜的免疫定位来检查类似的共生。嗜氨菌共生是有希望的，因为它涉及具有未知特性和寄主范围的新型细菌共生体，这种共生体以前被认为大部分（如果不是完全）局限于热带草类。这些研究除了提供了对水嗜菌在光秃秃的沙子上的惊人成功的见解之外，还可能为具有农业意义的草的内生固氮提供可能性。

Some grasses appear to be able to obtain fixed nitrogen throughsymbiotic relations with various bacteria. This project deals with a newsymbiosis involving European beachgrass (Ammophila arenaria) andnitrogen-fixing bacteria living within the shoots and rhizomes of the hostplant. The primary objective is to determine the extent of nitrogenfixation (acetylene reduction) activity in this grass in order to confirmif the rates are significant. Additional objectives are to characterizethe microorganisms involved in the Ammophila symbiosis, to determine thenatural abundance and distribution of these microorganisms, and todetermine if a similar symbiosis might be present in or introduced intoother species of grasses (including crop species). Inoculated and axenicseedlings will be used in greenhouse and field trials to determine ifAmmophila benefits from its bacterial symbiont. The rates of nitrogenfixation in the field and the effects of environmental variables will bemeasured by acetylene reduction assays. The precise location ofendophytic bacteria will be determined using immunological techniques atboth the light and electron microscope level with existing antibodies.The bacteria will be characterized with regards to the genes involved withnitrogen fixation and the effects of oxygen and fixed nitrogen on nitrogenfixation. Other species of grasses will also be examined for similarsymbioses using acetylene reduction assays and immunolocalization by lightmicroscopy. The Ammophila symbiosis is promising in that it involvesnovel bacterial symbionts with unknown properties and host ranges in atype of symbiosis previously thought to be largely if not entirelyrestricted to tropical grasses. In addition to providing insight into thephenomenal success of Ammophila on bare sand, these studies might openossibilities for endophytic nitrogen fixation by grasses of agriculturalsignificance.