胎猪胰腺干细胞体外诱导分化为胰岛素分泌细胞及其移植治疗裸鼠糖尿病的研究

缺乏供体细胞制约着胰岛替代疗法在Ⅰ型糖尿病治疗过程中的应用。本研究对实验室分离保存的胎猪胰腺干细胞(fetal porcine pancreatic stem cells,FPPSCs),体外诱导分化为胰岛素分泌细胞以及移植治疗裸鼠糖尿病的能力进行了深入研究,以探讨该细胞株作为异种供体细胞的潜力。研究结果表明,该细胞体外增殖活力旺盛,其形态及表面抗原表达特征与间充质干细胞极其相似,除表达胰腺干细胞相关标志外,FPPSCs还表达一些胚胎干细胞的相关标志。采用无血清诱导方案诱导2周后,FPPSCs形成DTZ染色阳性的胰岛样细胞团(islet-like cell cluster,ICC),该细胞团表达胰岛素、Glut-2等胰岛素分泌细胞功能相关的蛋白。RT-PCR结果显示,诱导后,胰腺干细胞相关标志表达减弱,而成熟胰岛素分泌细胞相关标志表达增强。葡萄糖刺激实验结果显示,诱导后,FPPSCs合成、分泌胰岛素和C-肽的能力显著增强(P<0.05)。将诱导2周后的细胞移植到糖尿病裸鼠腹腔内,可缓解其高血糖状况。结果提示,FPPSCs具有间充质干细胞的特性,体外能够诱导分化为胰岛素分泌细胞,并具有改善糖尿病裸鼠高血糖症状的...     

牛肌肉卫星细胞向胰岛素分泌细胞的诱导转分化研究

肌肉卫星细胞是源自中胚层的肌源干细胞,具有增殖分化融合成肌管并形成肌细胞的能力.在体内条件下,肌肉卫星细胞不可能跨胚层分化为内胚层来源的胰腺细胞.本研究从牛(Bos taurus)胎儿肌肉中分离培养得到肌肉卫星细胞,并在体外条件下将其诱导成胰岛素分泌细胞.在诱导过程中,分析了与胰腺发育相关的胰十二指肠同源基因盒1基因(pancreatic and duodenal homeobox 1,PDX1)、神经原素3基因(neurogenin 3,NGN3)、淀粉酶基因(Amylase)和胰岛素基因(Insulin,INS)的动态表达情况.结果表明,PDX1作为决定胰腺分化发育和胰岛功能的主要调节基因,在诱导分化的第2天能够检测到其mRNA的表达,在第3天表达量达到了最大,第4天以后维持在较低水平.NGN3是内分泌细胞形成非常重要的转录因子,是能够将胰岛素分泌到胞外的关键基因,其mRNA在分化诱导的第3天开始表达,第4天达到最高水平,之后逐渐下降.Amylase是胰腺发育中细胞外分泌相关的基因,Amylase mRNA在第6天才开始表达,8d后达到最高.INS mRNA表达量在11～12 d最高,酶联免疫吸附分析(enzyme-linked immunosorbent assay,ELISA)发现,诱导形成的胰腺细胞能够正常分泌胰岛素,培养液中胰岛素的浓度在诱导的11～12 d达到最高值.向培养液中添加葡萄糖后,可使细胞的胰岛素分泌量显著提高,说明诱导得到的细胞类似于成体胰岛的功能,其胰岛素分泌受外界葡萄糖浓度的调节.上述结果表明,肌肉卫星细胞可以被诱导转分化为胰岛素分泌细胞,并对培养环境中的葡萄糖刺激做出应答反应.本研究结果为进一步的研究和临床应用提供基础资料.     

胎猪胰腺干细胞的分离与鉴定

从胎猪胰腺分离得到一株细胞，该细胞经免疫组化检测表达PDX-1，GLUT-2，PCNA，Glucagon，somatostatin，polypeptide，弱表达nestin，目前细胞已传至58代。其在体外的生长行为有类似间充质干细胞样生长形态，经诱导后可分化为具有三维立体结构的类胰岛细胞团。成团后细胞强表达insulin、ck-19等标志，放免测定显示诱导成团后细胞胰岛素分泌量增加，显著高于未诱导细胞（P<0.05）。说明胰腺内存在着多潜能干细胞，本方法分离到胎猪胰腺干细胞，经诱导分化可形成有功能的胰岛样细胞团并释放胰岛素,有望为进一步研究异种胰腺干细胞移植治疗糖尿病提供材料。     

猪前体脂肪细胞与肌卫星细胞体外联合培养

利用差速贴壁法分别纯化前体脂肪细胞与肌卫星细胞,按1∶10的浓度比接种混合培养。以单独两类细胞培养作对照,采用油红O染色和Desmin免疫组化染色鉴定,通过形态学观察和MTT比色绘制生长曲线研究细胞生长规律。结果表明,Desmin免疫组化染色观察肌细胞阳性率达97%以上,油红O染色计数诱导分化细胞比率大于60%;形态学观察发现,联合培养细胞接触汇合前形态呈梭形,接触后不规则重叠交织生长;充脂细胞呈现较晚,且数量稀少;HE染色可见多核细胞融合成肌管样结构;测定2～9d细胞生长曲线显示,联合细胞组增殖比率大于对照组,经历2～3d潜伏期、3～7d指数生长期后,并未与对照组同步进入平台期,而呈持续缓慢上升趋势。实验初步实现了体外猪前体脂肪细胞与肌卫星细胞的直接联合培养,并显示其与对照组生长特性存在差异。     

鸡胚精原干细胞定向诱导分化为脂肪细胞

研究体外定向诱导鸡胚精原干细胞(spetmatogonial stem cells,SSCs)向脂肪细胞分化的能力.取孵化16 d的鸡(Gallus gallus)胚睾丸,提取SSCs,体外培养和传代.采用不同的诱导程序和不同组合的诱导剂(地塞米松、胰岛素和3-异丁基-1-甲基黄嘌呤(3-isobutyl-1-methylxanthine,IBMX))诱导SSCs向脂肪细胞分化.结果显示,诱导SSCs7～2l d后,分化成脂肪细胞,其中地塞米松、胰岛素和IBMX联合使用3 d后更换为胰岛素作用l d,经过3次循环后,用胰岛素继续处理至21 d,这一方法的诱导分化效果较好,分化率为85%.高于诱导剂联合协同作用的诱导效果(P<0.01).同时诱导剂联合作用协同作用的诱导效果高于单独作用的诱导效果(P<0.01).诱导的脂肪细胞经特异性的油红O染色为阳性,并高表达脂肪细胞标志基因PPARγ.表明SSCs体外培养传代后仍具有多向分化潜能,在特异性化学物质的诱导下,可被定向诱导分化为脂肪细胞.     

国产丝裂霉素处理的STO细胞作为饲养层培养牛胚胎干细胞

寻找一种适合牛胚胎干细胞生长的饲养层对成功培育牛胚胎干细胞有重要意义.本研究采用不同浓度国产丝裂霉素处理的SIM小鼠(Mus musculus)成纤维细胞耐硫代鸟嘌呤和耐鸟苯苷亚系(STO细胞)作为饲养层培养牛胚胎干细胞,为牛胚胎干细胞培养体系的建立提供实验依据.用10、15、20、30和40 μg/mL国产丝裂霉素分别处理1.5、3.0和4.0 h的STO细胞;形态学观察不同代次STO细胞生长状态,并对生长在以STO细胞为饲养层的牛胚胎干细胞进行碱性磷酸酶染色(AKP)、阶段特异性胚胎细胞表面抗原-4(OCT-4)和阶段特异性胚胎抗原-1(SSEA-1)免疫组化检测、体外分化形成拟胚体等实验.结果显示,当丝裂霉素的浓度为15 μg/mL处理3.0 h可有效的抑制细胞分裂;STO细胞在5～10代作为饲养层细胞形态最好且获得的牛胚胎干细胞AKP染色及OCT-4和SSEA-1抗原表达均成阳性,分别在体外分化培养形成了拟胚体.结果证明使用国产丝裂霉素能有效地处理STO细胞且在以STO细胞作为饲养层培养的牛胚胎干细胞能保持未分化状态,可以作为常规饲养层培养牛胚胎干细胞.     

过量表达热休克蛋白C端相互作用蛋白(CHIP)抑制小鼠前成骨细胞系的分化和矿化

以MC3T3-E1细胞系为材料,体外转染pEFNeu-HA-CHIP质粒,Western blot检测热休克蛋白Hs70(HSP70)C端相互作用蛋白(CHIP)表达,建立了稳定过量表达CHIP蛋白的MC3T3-E1/HA-CHIP细胞系.然后用含10 mol/L甘油磷酸钠和50靏/mL抗坏血酸的条件培养基诱导MC3T3-E1和MC3T3-E1/HA-CHIP细胞系向成骨细胞定向分化,结果表明,诱导期MC3T3-E1/HA-CHIP细胞系中碱性磷酸酶(ALP)的活性比MC3T3-E1细胞中的ALP活性低,ALP染色实验同时证实了这个结果;诱导培养18d后,Von Kossa染色和茜素红染色结果表明,MC3T3-E1/HA-CHIP细胞系中生成的磷酸钙比MC3T3-E1细胞系中生成的磷酸钙少.结果提示,过量表达CHIP蛋白抑制MC3T3-E1细胞的分化和矿化.     

鸡胚精原干细胞定向诱导分化为脂肪细胞的研究

为研究体外定向诱导鸡胚精原干细胞（Spermatogonial stem cells, SSCs）向脂肪细胞分化的能力，取孵化16d的鸡胚睾丸，无菌获取SSCs，体外培养传代。采用不同诱导程序、不同组合的诱导剂（地塞米松、胰岛素、3-异丁基-1-甲基黄嘌呤（IBMX））诱导SSCs向脂肪细胞分化。结果显示SSCs被诱导7～21d后，分化成脂肪细胞，其中诱导程序⑥的诱导分化效果较好，分化率为85%。诱导剂联合协同作用的诱导效果极显著地(P<0.01)高于单独作用的诱导效果。诱导的脂肪细胞经特异性的油红O染色为阳性，并高表达脂肪细胞标志基因PPARγ。表明鸡胚胎精原干细胞（SSCs）体外培养传代后仍具有多向分化潜能，在特异性化学物质的诱导下，可被定向诱导分化为脂肪细胞。     

培养的睾丸间质细胞对hCG刺激的反应性

本文介绍了用酶解法结合差速离心分离仔猪睾丸间质细胞,并研究其对促性腺激素的反应性。结果表明在0～50IUml内,睾酮的分泌量随着hCG剂量的增加而增加,在50IUml～100IUml内,加大hCG剂量并不能增强间质细胞的分泌功能。研究还发现随着培养时间的延长,间质细胞分泌睾酮的功能逐渐减低,培养1d和2d时对hCG(人绒毛膜促性腺激素)刺激的反应能力最强;随着培养时间的进一步延长,间质细胞的反应性下降,4d时与对照无明显差异(P>0.05)。间质细胞对首次刺激的反应敏感,当连续给予刺激时,睾酮的分泌受到抑制,在24h的分泌峰后不再出现分泌高峰。而首次刺激后间隔2d再刺激,间质细胞虽有反应,但反应较弱。     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Einfluss der düngungsmethoden auf die entwicklung von zuckerrübenkrankheiten

Während neunjähriger (1994-2002) Untersuchungen in der Versuchsanstalt Ba?cyny (Fahlerde, Fall-Gleyboden, ausgebildet aus leichtem Lehmboden) wurde der Befall mit Krankheiten an der Zuckerrübe in Abhängigkeit von der Düngungsmethode bewertet. Folgende Methoden wurden angewendet: A - Mineraldünger, B - Stalldung und Mineraldünger, C - Stroh-, Gründung und Mineraldünger, D - Kompostdünger und Biopräparate (ökologische Düngung). Auf den Objekten A, B, C wurden bei konstanter Phosphor-Kalium-Düngung die Stickstoffgaben von 0 bis 180 kg.ha^?1 differenziert. Auf dem ökologischen Objekt D ohne Mineraldünger wurden statt Stickstoff die Biopräparate P₅₀₀ und P₅₀₁ verabreicht. Der geringste Befall von Krankheiten wurde an der Zuckerrübe auf jenem Objekt festgestellt, das mit Kompost und den Biopräparaten gedüngt worden war. Im Rahmen der konventionellen Düngungsmethoden wurde allgemein die höchste Intensität der Krankheiten an der mit Stroh, Gründung und Mineraldünger gedüngten Zuckerrübe beobachtet. Ausnahmen von dieser Regel bildete das Vorkommen von echtem Mehltau und Keimlingsfäule. Auf den Objekten A, B, C nahm die Intensität der Krankheiten mit der Steigerung der Stickstoffgabe zu. Auch die auf Objekt D verabreichten Biopräparate stimulierten die Entwicklung der Krankheiten. The effect of various fertilization methods on the diseases of sugar beet was estimated on the basis of nine-year studies (1994-2002) conducted in the Experimental Production Farm in Ba?cyny on loess-based, sedimentary-gley, light-clay soil. The following fertilization methods were applied: A - mineral fertilization, B - mineral and manure fertilization, C - straw, green manure and mineral fertilization, D - ecological compost and biodynamic preparations fertilization. In the objects A, B and C fertilized with phosphorus and potassium, various doses of nitrogen ranging from 0 to 180 kg/ha^?1 were used. In the ecological object D, where mineral fertilization was not used, biodynamic preparations P₅₀₀ and P₅₀₁ were applied instead of nitrogen. The lowest ratio of the diseases of sugar beet was observed in the object fertilized with the compost and biodynamic preparations. In view of the conventional fertilization methods, generally the highest incidence of diseases was noted in the sugar beet fertilized with straw, green manure and mineral fertilizers. The exception was the occurrence of powdery mildew and the black leg. In objects A, B and C the incidence of the diseases increased with the increase in nitrogen doses. The applied biodynamical preparations in the object D stimulated the development of diseases too.     

Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp.

Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g^-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×10⁵ viable propagules g^-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.     

细菌、真菌及植物氮营养信号研究进展

氮素吸收代谢是所有生物生命活动的核心部分,因此,各种生物对氮的吸收与同化过程都有精细的调节。这种调节依赖于生物对体内氮素状况信号及体外（生长介质中）氮素信号的感受。过去几十年中,在细菌、真菌中已经对氮素营养信号有了较好的研究,而植物中则相对缓慢,但也有了一定的认识。本文重点比较细菌、真菌及植物中氮信号系统的组成,以期为进一步认识植物中的氮信号接受与转导系统提供启示。     

Aircraft operations near concentrations of birds in Antarctica: The development of practical guidelines

Aircraft operations have the potential to disturb and to impact negatively on bird life. A gradient of increasing behavioural response is evident in birds when exposed to increasing aircraft stimulus. The most major disturbance is likely to lead to impacts on the health, breeding performance and survival of individual birds, and perhaps bird colonies. A process of revision to policies on aircraft operations contained in management plans for a number of specially protected areas in Antarctica by the United Kingdom, accompanied by consultations made within the scientific community through the Scientific Committee on Antarctic Research (SCAR) and with operational interests through the Council of Managers of National Antarctic Programmes (COMNAP) resulted in new guidelines being adopted by the Antarctic Treaty Consultative Parties in June 2004. The principal recommendations of the guidelines are that bird colonies should not be overflown below 2000 ft (∼610 m) above ground level and landings within 1/2 nautical mile (∼930 m) of bird colonies should be avoided wherever possible. These guidelines are less stringent and less specific than those that were recommended by the SCAR specialist group on birds, and represent a compromise to accommodate operational needs. While the adoption of clear and consistent guidelines for the operation of aircraft in Antarctica is welcome in that this provides practical advice that is likely to reduce incidences of close aircraft/bird encounters, there remains insufficient knowledge of the interactions between aircraft and birds in Antarctica, and the consequent impacts on individual birds and on bird populations. It is important, therefore, that the guidelines adopted are considered interim, and should be kept under scrutiny with revisions made as new and improved research results appear.     

The abundance of heterocystous blue-green algae in rice soils and inocula used for application in rice fields

Summary Algal populations were quantified (as colony-forming units [CFU] per square centimetre) in 102 samples of rice soils from the Philippines, India, Malaysia and Portugal, and in 22 samples of soil-based inocula from four countries. Heterocystous blue-green algae (BGA) were present in all samples. Nostoc was the dominant genus in most samples, followed by Anabaena and Calothrix. In soils, heterocystous BGA occurred at densities ranging from 1.0 × 10² to 8.0 × 10⁶ CFU/cm² (median 6.4 × 10⁴) and comprised, on average, 9% of the total CFU of algae. Their abundance was positively correlated with the pH and the available P content of the soils. In soil-based inocula, heterocystous BGA occurred at densities ranging from 4.6 × 10⁴ to 2.8 × 10⁷ CFU/g dw (dry weight), comprising only a moderate fraction (average 13%) of the total algae. In most soils, the density of indigenous N₂-fixing BGA was usually higher than that attained by applying recommended rates of soil-based inoculum. Whereas research on the practical utilization of BGA has been mostly directed towards inoculation with foreign strains, our results suggest that attention should also be given to agricultural practices that enhance the growth of indigenous strains already adapted to local environmental conditions.Maître de Recherches ORSTOM (France), Visiting Scientist at IRRI