人工诱导根瘤菌与非豆科植物结瘤共生的研究

生物固氮方式中以豆科植物和根瘤菌的共生固氮体系最为有效,目前仍以此作为主要研究模型。     

根瘤菌结瘤基因研究的新突破

根瘤菌是能侵入合适寄主植物根部并形成根瘤的一类细菌。由于在根瘤中,根瘤菌可以大量固定大气中的氮,因而在生物固氮研究中具有重要地位。过去十年中,由于分子生物学技术的进展使我们对根瘤菌遗传的各个方面有了许多了解。在一些根瘤菌中,成功地识别、分离了与共生固氮有关的基因。这些基因中有一类是与根瘤菌固氮能力有关的,统称为固氮基因(Fix基因)其中偏码固氮酶的结构基因nif HDK在所有已检查过的固氮微生物中具     

根瘤菌-豆科植物共生体系在重金属污染环境修复中的地位、应用及潜力

土壤重金属污染严重影响了人类健康和生态系统稳定,已成为亟待解决的现实问题。在重金属污染地,氮素的极端不足是植被恢复主要限制因子之一。根瘤菌-豆科植物共生体系是固氮能力最强的生物固氮体系,在促进重金属污染地氮素循化和营养元素积累中具有重要作用。本文阐述土壤重金属污染的修复方法及其特点,微生物抗重金属的机理及促植物生长和重金属积累的特性,根瘤菌-豆科植物共生体系在土壤重金属污染修复中的优越性,研究现状及应用潜力。提出应用"豆科植物-根瘤菌共生体系"修复重金属污染土壤的新思路和新任务。     

根瘤菌的现代分类及其系统发育

根瘤菌是一类与农业生产关系甚为密切的细菌,它们与豆科植物共生具有很高的固氮效率。根瘤菌的分类因而成为生物固氮和细菌分类学两个领域的结合点,它的发展与这两个领域的发展有着直接的联系。近年来,随着根瘤菌资源的不断挖掘和发现以及新技术的不断发展和应用,根瘤菌的分类也经历了很大的变化和发展。特别是多相分类方法与d（N测序技术的发展和应用,使得根瘤菌的分类及其系统发育研究有了突破性进展。在这些多相分类研究的方法中,数值分类为大量菌株提供了生理学、形态学、血清学等各个表型方面的综合信息;分子技术的应用,如DN…     

根瘤菌菌剂的研究与开发现状

根瘤菌与豆科植物共生成为豆科植物固氮的重要方式,它可以为豆科植物提供所需氮量的1/2～1/3。因此,土壤中有效根瘤菌的数量是决定豆科植物产量的重要因素,而根瘤菌菌剂的使用可以有效地提高土壤中根瘤菌数量。本文从根瘤菌菌剂制备中高效菌种的选育及匹配、高密度菌剂的制备、菌剂保存方法等方面进行综述。比较了自然选育、杂交选育和诱变选育等各类选育方法及琼脂试管配对法和水培配对法的优缺点;总结了菌剂制备的一般过程和方法;论述了菌剂保藏过程中冷冻干燥法和各种保护剂的使用对菌剂保藏效果的影响。本文阐述了根瘤菌菌剂的制备工艺和发展方向,为根瘤菌剂的研制提供重要参考。     

一株分离自裸子植物罗汉松根瘤的根瘤菌

根瘤菌与豆科植物共生结瘤固氮被认为是地球上最重要的生物固氮体系. 裸子植物罗汉松与根瘤菌共生结瘤至今未见报道. 采用常规根瘤菌分离技术从罗汉松及其变种小叶罗汉松根瘤中分离获得11株内生细菌, 将它们回接宿主可导致结瘤, 乙炔还原法测出微弱的固氮酶活性. 传统的生理生化鉴定方法和16S rDNA全序列分析证明该内生细菌代表菌株GXLO 02隶属于根瘤菌.     

豆料植物—根瘤菌共生固氮体系中的根瘤菌结瘤基因组(nod和hsn基因)和固氮基因组(nif和fix基因)及其功能

豆科植物一根瘤菌共生固氮在自然界中占有极其重要的地位.据估计,全球生物固氮量约为17500万吨,而现今工业上采用的Haber-Bosch法固定大气氮的无机氮量约为4500万吨,不及生物固氮量的三分之一.其中豆科植物一根瘤菌的共生固氮量为3500万吨,几乎可以与工业的无机氮相媲美(Burns和Hardy,1975).根瘤菌侵染豆科植物根而形成根瘤,由此产生了一种互通有无、共存共荣的固定空     

载有苜蓿根瘤菌巨型质粒的豇豆根瘤菌侵染苜蓿根瘟的形态

生物固氮的过程是把大气氮素还原为氨,为植物生长提供有效的氮素营养。在共生固氮过程中,根瘤菌与豆科植物共生有着较为严格的宿主专性关系,如苜蓿根瘤菌只诱导苜蓿植物结瘤固氮,豌豆根瘤菌只诱导豌豆植物结瘤固氮。     

1991年度生命科学重点项目简介

项目编号:39130201 项目名称:中国豆科植物根瘤菌资源、分类及应用基础研究在各类生物固氮体系中,根瘤菌与豆科植物共生固氮能力居于首位,我国豆科植物种类占世界3/4,根瘤菌种类繁多,特异性强。充分挖掘丰富的根瘤菌资源,选择固氮能力和抗逆性强的优良菌株,组建高效菌株与寄主的最佳组合,可更高地发挥根瘤菌的固氮作用,并为自然选种和遗传工程研究提供广茂的种质资源和基因材料。根瘤菌的分类系统很不完善,包括种类也有限。我国根瘤菌分类工作有较好的基础。在     

根瘤菌与豆科植物共生固氮的生化基础

根瘤菌在与其主植物共生过程中,具有形成根瘤和固定大气中游离氮的能力。全世界每年通过生物固氮大约可固定一亿七千五百万吨氮,而根瘤菌与豆科植物共生固氮的总量就达三千五百万吨。     

Mutation breeding of grain legumes

Genetic variation among existing cultivars and in germplasm collections is the outcome of selection during evolution and plant breeding. Mutagenesis offers the plant breeder a chance to tackle unconventional objectives, particularly those that were at a selection disadvantage in the past. Effective mutagens are available, but the bottleneck is the effective selection of rare desired variants from large mutagenized populations. Selection methods must be non-destructive. Grain legume mutation breeding has already led to improved cultivars with higher yield, better grain quality, or stronger resistance to pathogenens. Many mutations affecting nitrogen fixation related traits have also been reported. Some could be useful in breeding better cultivars, but the majority are being used to study the factors interacting in the complex process of symbiotic nitrogen fixation and to improve the strategy for producing cultivars with better fixation capacity.     

Soybean genotypic differences in sensitivity of symbiotic nitrogen fixation to soil dehydration

Nitrogen fixation activity by soybean (Glycine max (L.) Merr.) nodules has been shown to be especially sensitive to soil dehydration. Specifically, nitrogen fixation rates have been found to decrease in response to soil dehydration preceding alterations in plant gas exchange rates. The objective of this research was to investigate possible genetic variation in the sensitivity of soybean cultivars for nitrogen fixation rates in response to soil drying. Field tests showed substantial variation among cultivars with Jackson and CNS showing the least sensitivity in nitrogen accumulation to soil drying. Glasshouse experiments confirmed a large divergence among cultivars in the nitrogen fixation response to drought. Nitrogen fixation in Jackson was again found to be tolerant of soil drying, but the other five cultivars tested, including CNS, were found to be intolerant. Experiments with CNS which induced localized soil drying around the nodules did not result in decreases in nitrogen fixation rates, but rather nitrogen fixation responded to drying of the entire rooting volume. The osmotic potential of nodules was found to decrease markedly upon soil drying. However, the decrease in nodule osmotic potential occurred after significant decreases in nitrogen fixation rates had already been observed. Overall, the results of this study indicate that important genetic variations for sensitivity of nitrogen fixation to soil drying exist in soybean, and that the variation may be useful in physiology and breeding studies.     

Genotypic variation in biological nitrogen fixation by common bean

Field experiments were performed in Austria, Brazil, Chile, Colombia, Guatemala, Mexico and Peru as part of an FAO/IAEA Co-ordinated Research Programme to investigate the nitrogen fixing potential of cultivars and breeding lines of common bean (Phaseolus vulgaris L.). Each experiment included approximately 20 bean genotypes which were compared using the ¹⁵N isotope dilution method. Great differences in nitrogen fixation were observed between and within experiments, with average values of 35% N derived from atmosphere (% Ndfa) and highest values of 70% Ndfa being observed. These values which were larger than had been reported previously for common bean, were observed only when environmental factors were favorable. Therefore, common bean lines are available, which can support high biological nitrogen fixation. These can be used either directly as cultivars for production or in breeding programmes to enhance nitrogen fixation in other cultivars.     

Mutation breeding of grain legumes

Summary Grain legumes are an important group of crop plants. They provide an essential source of protein food for many developing countries, but their production has gone down in favour of more profitable crops like cereals. Therefore, genetic improvement of grain legumes is urgently needed. The primary aim of grain legume breeding must be the increase of production through adaptation to more advanced cropping schemes and reduction of crop losses. Symbiotic nitrogen fixation as developed by natural evolution does not always seem to be compatible with the needed substantial increase in yield: It is not supplying sufficient nitrogen and supplementation by fertilizer is rather uneconomic. By genetic manipulation of the plant's regulatory system nitrogen fixation may become more effective and tolerant to high soil nitrogen levels. Through a number of mutation breeding projects in different countries involving all important grain legume species it has been proven that mutation induction is a good tool for supplementing the genetic variation available from natural evolution and from selection by man. High-yielding cultivars have been developed from induced mutants, which eventually also possess a more efficient nitrogen fixation capacity.     

The effect of seed weight on the early growth and nodulation of white clover

The results of growing, in agar culture, nodulated and un-nodulated white clover seedlings from three seed-weight categories, and the subsequent growth of selected plants in soil in pots, are reported. Seed-weight variations greatly influenced plant growth, made substantial differences in nodulation parameters and nitrogen fixation, and contributed appreciably to the observed variability. The relationship of such effects to nitrogen fixation and the relevance to breeding for superior symbiosis are discussed. The growth of plants, as determined by agar culture technique, was not predictive of their subsequent performance in the soil in pots, and restricting seed weight variations did not improve the prediction. The importance of such effects and the relevance of tube culture to breeding work are discussed.     

Yield and biological nitrogen fixation of common bean (Phaseolus vulgaris L.) in Peru

Two field experiments were performed to evaluate the nitrogen fixation potential of twenty common bean cultivars and breeding lines during summer and winter seasons of 1986 and 1988, respectively. The ¹⁵N isotope dilution method was used to quantify N₂ fixation. The cultivars and breeding lines were variable in terms of their N₂ fixation. The cv. Caballero was very efficient, with more than 50% N derived from the atmosphere and 60–80 kg N ha^–1 fixed in both seasons. Other cultivars were less efficient, since the poorest ones derived less than 30% of their nitrogen from the atmosphere and fixed less than 20 kg N ha^–1. After additional testing the best cultivars may be used directly by the farmers for cultivation. The experiments have provided information about which genotypes may be used to breed for enhanced fixation in common bean.     

COMPARATIVE STUDIES OF NITROGEN FIXATION AND PHOTOSYNTHESIS IN ANABAENA CYLINDRICA

Manometric methods were developed to allow short-time measurements on relatively small amounts of cell material. The methods provided measurement of the nitrogen uptake and oxygen evolution attributable to nitrogen fixation either in the presence or absence of carbon dioxide. The methods were applied to observe effects of cell history, light intensity, temperature, pH, and ammonia on nitrogen fixation and photosynthesis with 2 new and significant findings. Nitrogen fixation is markedly accelerated by a preceding period of cellular nitrogen depletion. Nitrogen fixation is depressed by light intensities greater than those required to saturate photosynthesis.     

Contribution of nitrogen fixation to first year Miscanthus × giganteus

Many characteristics make Miscanthus × giganteus an appealing bioenergy feedstock in temperate North America, but the degree to which this plant species interacts with nitrogen‐fixing bacteria remains understudied. Demonstration of associative nitrogen fixation in Miscanthus would support management with minimal fertilizer inputs that is demanded of long‐term biofuel sustainability. As a first step, we investigate the role of biological nitrogen fixation in nutrition of immature Miscanthus and temporal dynamics of plant‐associated nitrogen fixers. The contribution of biological nitrogen fixation to plant nitrogen acquisition in first year Miscanthus × giganteus was estimated using a yield‐dependent ¹⁵N isotope dilution model. Temporal changes in plant‐associated diazotroph relative abundance and community composition were analyzed with quantitative PCR and terminal restriction fragment length polymorphism of the nifH gene in rhizome and rhizosphere DNA extracts. We estimate 16% of new plant nitrogen was derived by nitrogen fixation during the growing season, despite non‐limiting soil nitrogen. Diazotroph communities from rhizome and rhizosphere changed with plant development and endophytic nitrogen fixers had significantly higher relative abundance and altered community composition at sampling dates in July and August. This study provides evidence for a small, but measurable, benefit of associative nitrogen fixation to first year Miscanthus × giganteus that underscores the potential and need for selection of breeding lines that maximize this trait.     

Comparison of common bean (Phaseolus vulgaris L.) genotypes for nitrogen fixation tolerance to soil drying

Aims

Common bean is a major source of protein for many people worldwide. However, the crop is often subjected to drought conditions and its advantage in undertaking symbiotic nitrogen fixation can be severely decreased. The primary objective of this study was to compare the resistance of nitrogen fixation of 12 selected genotypes to soil drying.

Methods

Twelve common bean genotypes of diverse genetic background were compared. Plants were grown in pots and subjected to soil drying over about 2 weeks. Nitrogen fixation was measured daily using a flow-through acetylene reduction technique. The plants were exposed to acetylene for only a short time period allowing repeated measures. The acetylene reduction rate of plants on drying soil was normalized against the rates measured for well-watered plants.

Results

Substantial variability was identified among genotypes in the threshold soil water content at which nitrogen fixation was observed to decrease. Genotypes SER 16, SXB 412, NCB 226, and Calima were found to have the greatest delay in their decrease in nitrogen fixation rates based on soil water content. These four genotypes expressed substantial tolerance of nitrogen fixation to soil drying. These experiments also resulted in data on the threshold soil water contents at which transpiration rates decreased. A decrease in transpiration rates at high soil water contents is potentially advantageous since it allows soil water conservation for use as the severity of the drought increases. There was a general trend of those genotypes with sustained nitrogen fixation rates to low soil water contents also expressing decreased transpiration rates at high soil water contents.

Conclusions

This study identified genetic variation among common bean genotypes in their response of nitrogen fixation and transpiration to soil drying. Five genotypes (SER 16, SXB 412, NCB 226, Calima, and SEA 5) expressed the desired traits for water-limited conditions, which might be exploited in breeding efforts.