High Acetylene Reduction Activity Research Articles

Changes in Acetylene Reduction Activities and nifH Genes Associated with Field-Grown Sweet Potatoes with Different Nursery Farmers and Cultivars

Sweet potato cultivars obtained from different nursery farmers were cultivated in an experimental field from seedling-stage to harvest, and the acetylene reduction activity (ARA) of different parts of the plant as well as the nifH genes associated with the sweet potatoes were examined. The relationship between these parameters and the plant weights, nitrogen contents, and natural abundance of 15N was also considered. The highest ARA was detected in the tubers and in September. Fragments of a single type of nitrogenase reductase gene (nifH) were amplified, and most of them had similarities with those of Enterobacteriaceae in γ-Proteobacteria. In sweet potatoes from one nursery farm, Dickeya nifH was predominantly detected in all of the cultivars throughout cultivation. In sweet potatoes from another farm, on the other hand, a transition to Klebsiella and Phytobacter nifH was observed after the seedling stage. The N2-fixing ability contributed to plant growth, and competition occurred between autochthonous and allochthonous bacterial communities in sweet potatoes.

Plant growth promotion by four species of the genus Burkhoderia

The genus Burkholderia is highly diverse and may mediate plant growth via several mechanisms. The current study evaluates the role of strains from four Burkholderia species in maize growth promotion. Twenty three strains of diazotrophic Burkholderia species were applied to two maize genotypes (SHS5050 and BRS4157) under greenhouse and field conditions. Strains were tested for growth promotion in greenhouse during 40 days. Strain 41 from B. silvatlantica was used under field conditions. Parameters evaluated: biomass accumulation, N and root measurements in pots and grain yield, N % and N in the grains under field conditions. Eleven strains were evaluated under soil substrate. The inoculation of the hybrid SHS5050 showed root biomass improvement using three strains, namely M130, M209 and PPe7. The highest acetylene reduction activity was observed in strain 41 from B. silvatlantica. Strain 41 from B. silvatlantica improved plant dry mass on both genotypes. This strain produced 31 % more aerial tissue and 7 % more root dry mass in the BRS4157 variety than it did in the control. Both genotypes planted at Seropedica, RJ, produced 7 % more grains under field conditions and the variety produced 10.9 % more grains in comparison to the non-inoculated control. Strain 41 from B. silvatlantica showed beneficial plant-growth promotion of maize under greenhouse and field experiments specially in a low fertility soil.

뿌리혹 형성능과 질소 고정능이 우수한 헤어리베치 유래 Rhizobium의 분리 및 선발

본 연구에서는 헤어리베치로부터 뿌리혹 형성능과 질소 고정능이 우수한 Rhizobium 균주를 분리하고자 하였다. 전국의 일곱 군데 헤어리베치 재배 지역에서 수집 후 뿌리혹으로부터 균주를 분리하였고, 헤어리베치에 분리 균주를 재접종하여 뿌리혹 형성능과 질소 고정능을 확인하였다. 그 결과, 52개의 Rhizobium 속 균주를 분리하였고, 이 중 0.5% NaCl 농도 이상에서 자라는 Rhizobium은 16균주이었다. 뿌리혹 형성능은 16개 균주 중 Rhizobium sp. RH1, RH3, RH81, RH82, RH84, RH93의 균주를 접종한 시험구에서 우수하였다. 또한, 질소 고정능을 확인한 결과 Rhizobium sp. RH84가 가장 높은 acetylene reduction activity를 보였다. 이러한 결과는 향후 염의 분포가 불균일한 간척지에 적용 시에도 헤어리베치의 생육을 촉진해 녹비 작물로의 활용 가능성을 높여주는 결과로 판단된다. This study was conducted to select rhizobia from hairy vetch (Vicia villosa Roth) with nodulation and excellent nitrogen-fixing ability. Hairy vetch root was collected from 7 of cultivation region of all over the country, rhizobia were isolated from the root nodules. Isolates were re-inoculated into a hairy vetch separately and studied nodulation and nitrogen-fixing ability. As a result, total of 52 Rhizobium isolates were isolated from the hairy vetch root nodules, among these, 16 isolates were Rhizobium which show good growth at more than 0.5% NaCl concentration. These 16 isolates were re-inoculated separately, 8 weeks after, good root nodule formation was observed from Rhizobium sp. RH1, RH3, RH81, RH82, RH84, and RH93 strain treated samples. Six isolates were positive for nitrogen fixing ability, the highest acetylene reduction activity was shown by Rhizobium sp. RH84. Results suggest that the Rhizobium sp. RH84 could be used as the possibility of its application as a green manure crop of hairy vetches in nonuniform salt distribution reclaimed land.

Evaluation of effective Myanmar Bradyrhizobium strains isolated from Myanmar soybean and effects of coinoculation with Streptomyces griseoflavus P4 for nitrogen fixation

In order to substitute the use of chemical fertilizers in legume production, there is a need for the production of rhizobial inoculants which are capable of being used as biofertilizers. To achieve this, an effective symbiotic nitrogen (N) fixation between legumes and root nodule bacteria will be essential. Evaluation of effective Myanmar Bradyrhizobium (Jordan 1982) strains isolated from Myanmar soybean (Glycine max L. Merr.) and effects of coinoculation with Streptomyces griseoflavus Krainsky 1914 P4 for N fixation were studied in pot experiments using sterilized vermiculite and Hoagland solution in the Phytotron (25°C and 70% relative humidity) with completely randomized design and three replicates. N fixation ability of soybean was evaluated by acetylene reduction activity (ARA) by gas chromatography. It was found that MAS23 showed a relatively high degree of stability and a high level of ARA per plant on both Yezin-3 and Yezin-6 soybean varieties. In the symbiotic relationship between Bradyrhizobium strains and P4 experiments, the treatments consisted of six Bradyrhizobium strains (MAS23, MAS33, MAS34, MAS43, MAS48 and USDA110) and Streptomyces griseoflavus P4 were evaluated with four Myanmar soybean varieties (Yezin-3, Yezin-6, Hinthada and Shan Sein). In the Yezin-3 soybean variety, the best treatment for ARA per plant was found in the dual inoculation of P4 and MAS34. In the Yezin-6 soybean variety, the highest nodule dry weight was found in dual inoculation of P4 with MAS34 but the highest ARA per plant was observed in the dual inoculation of P4 and MAS23. On the other hand, single inoculation of MAS43 and coinoculation of P4 with MAS48 were significantly higher in N fixation of Hinthada, and coinoculation of P4 with MAS33 was significant improvement of ARA per plant (P < 0.05) in Shan Sein soybean.

Nitrogen-Fixing and Uricolytic Bacteria Associated with the Gut of Dendroctonus rhizophagus and Dendroctonus valens (Curculionidae: Scolytinae)

The bark beetles of the genus Dendroctonus feed on phloem that is a nitrogen-limited source. Nitrogen fixation and nitrogen recycling may compensate or alleviate such a limitation, and beetle-associated bacteria capable of such processes were identified. Raoultella terrigena, a diazotrophic bacteria present in the gut of Dendroctonus rhizophagus and D. valens, exhibited high acetylene reduction activity in vitro with different carbon sources, and its nifH and nifD genes were sequenced. Bacteria able to recycle uric acid were Pseudomonas fluorescens DVL3A that used it as carbon and nitrogen source, Serratia proteomaculans 2A CDF and Rahnella aquatilis 6-DR that used uric acid as sole nitrogen source. Also, this is the first report about the uric acid content in whole eggs, larvae, and adults (male and female) samples of the red turpentine beetle (Dendroctonus valens). Our results suggest that the gut bacteria of these bark beetles could contribute to insect N balance.

Isolation, molecular characterization and growth-promoting activities of endophytic sugarcane diazotroph Klebsiella sp. GR9

A group of endophytic diazotrophs were isolated from surface-sterilized roots and stems of different sugarcane varieties in the Tamilnadu region of India. From these, four isolates were selected, based on the highest acetylene reduction activity. Gene-specific PCR amplification confirmed the presence of nif-D genes in those isolates. The 16S rRNA sequence of isolates GR4 and GR7 had a 99.5% sequence similarity to the Pseudomonas sp. pDL01 (AF125317) and 16S rDNA sequence of isolate GR3 had a 100% similarity to that of Burkholderia vietnamiensis (AY973820). The 16S rDNA sequence of isolate GR9 was 99.79% similar to that of the Klebsiella pneumoniae type strain (KPY17657). Colonization by the isolates was confirmed using micropropagated sugarcane and sterile rice seedlings. Isolate GR9, identified as Klebsiella pneumoniae, was consistently more active in reducing acetylene as compared with the other isolates. The effects of GR9 and the sugarcane diazotroph Gluconacetobacter diazotrophicus were compared in inoculated micropropagated sugarcane plantlets. The effects of K. pneumoniae GR9, and four other diazotrophs, G. diazotrophicus, Herbaspirillum seropedicae, Azospirillum lipoferum 4B, and Burkholderia vietnamiensis in inoculated rice seedlings were compared. GR9 alone or in combination with the other diazotrophs performed best under pot conditions. The combined effects of nitrogen fixation and endophytic colonization of this diazotroph may be useful for the development of bio-inoculants.

Effects of a Nitrogen‐Fixing Indigenous Bacterium (Klebsiella pneumoniae) on the Growth and Development of the Halophyte Salicornia bigelovii as a New Crop for Saline Environments

Abstract Salicornia bigelovii is a novel crop for salty soils, which can contribute to arid‐zone management where irrigation with salty water, including sea water, is now a necessity. Nitrogen fixation by bacteria associated with the roots of S. bigelovii and similar halophytes is an important source of available nitrogen in salt marsh ecosystems. However, the diversity of the rhizosphere of Salicornia is unknown. Five areas around the Bay of La Paz in Baja California Sur, Mexico were sampled to detect nitrogen‐fixing bacteria associated with this halophyte; from these, 18 colonies were isolated. Only one showed high acetylene reduction activity. This bacterium was identified as Klebsiella pneumoniae. The effects of K. pneumoniae were evaluated at the germination and early seedling growth stages of two genotypes of S. bigelovii (‘wild genotype’ and cultivar SOS‐10), as an alternative crop for semiarid and saline environments. This bacterium, in conjunction with Azospirillum halopraeferens, was tested for growth‐promoting ability when inoculated on S. bigelovii genotypes under various saline concentration conditions. During germination and early seedling growth, K. pneumoniae showed high specificity for the wild S. bigelovii genotype, while A. halopraeferens was more specific for the improved S. bigelovii genotype SOS‐10. This is the first report of K. pneumoniae as a nitrogen‐fixing bacterium associated with the oilseed S. bigelovii, a novel halophyte crop. A reliable biological method, based on beneficial bacteria, is suggested to help maintain or improve the fertility of soils sustaining Salicornia fields.

Cultivable heterotrophic N2-fixing bacterial diversity in rice fields in the Yangtze River Plain

Heterotrophic N2-fixing bacteria are a potentially important source of N2 fixation in rice fields due to the moist soil conditions. This study was conducted at eight sites along a geographic gradient of the Yangtze River Plain in central China. A nitrogen-free solid malate-sucrose medium was used to isolate heterotrophic N2-fixing bacteria. Numbers of the culturable N2-fixing bacteria expressed as CFU (colony forming units) ranged between 1.41±0.42×106 and 1.24±0.23×108 in the sampled paddy field sites along the plain. Thirty strains with high ARA (acetylene reduction activity) were isolated and purified; ARA of the strains varied from 0.9 to 537.8 nmol C2H4 culture-1 h-1, and amounts of 15N fixed ranged between 0.008 and 0.4866 mg·culture-1·day-1. According to morphological and biochemical characteristics, 14 strains were identified as the genus Bacillus, 2 as Burkholderia, 1 as Agrobacterium, 4 as Pseudomonas, 2 as Derxia, 1 as Alcaligenes, 1 as Aeromonas, 2 as Citrobacter, and 3 strains belonged to the corynebacter-form group.

Relationship between bacteroid poly-beta-hydroxybutyrate accumulation and nodule functioning in the Galega orientalis-Rhizobium galegae symbiosis under diamine treatment.

Exposure of Galega orientalis plants to diamines putrescine (Put) and cadaverine (Cad) at concentrations from 0.01 to 2.0 mM significantly altered carbon and nitrogen metabolism in their root nodules. Correlative studies of bacteroid poly-beta-hydroxybutyrate (PHB) content and acetylene-reduction capacity of the nodules revealed a negative relationship between these parameters. Utilisation of PHB deposits by bacteroids and high acetylene reduction activity was observed when applying low diamine concentrations. The increase in PHB accumulation in response to high diamine levels was accompanied by a considerable decline in nodule nitrogenase activity. Supplying isolated Galega bacteroids with various diamine concentrations significantly modified bacteroid oxygen consumption, which might be associated with alterations in carbon flux to the bacteroids. Finally, modulation of the bacteroid content upon Put and Cad treatment was examined. The results are discussed in terms of possible causes of the diamine-induced changes in nodule metabolism.

Seed size effects on growth and N 2 fixation of juvenile sainfoin

Seed size of forage legumes influences seedling establishment and vigor. Two studies were conducted to examine the effects of seed size on growth and N 2 fixation of juvenile sainfoin ( Onobrychis viciifolia Scop.). In two growth chamber experiments, ‘Remont’ sainfoin was evaluated for nodulation, plant height, dry matter yield, N concentration, and acetylene reduction activity (ARA). Seedlings from large seed emerged faster, had more nodules, and had higher N 2 fixation rates at most harvest dates up to 84 d. Across all harvests, seed size accounted for 60, 81, 87, 90, and 98% of the variability in mean ARA, nodule number, total plant N content, plant dry weight, and plant height, respectively. The superiority of seedlings from large seed was not due to increased relative growth rates. Two Remont seed lots that differed in seed weight distributions had similar ARA and shoot dry weight patterns, but varied in their correlations between ARA and seed size. It appears that the factors influencing seed size also affected subsequent seedling behavior of these two seed lots. Divergent individual plant selections for high or low ARA at 56, 70, or 84 d would have arisen from the largest or smallest seed size classes, respectively, if seed size effects had been ignored in a breeding program. Considerable variability for plant dry weight and ARA existed within seedlings from uniformly sized seed. We conclude that for breeding purposes, growth or ARA analyses of juvenile sainfoin should be conducted with sized seed in order to minimize seed-size effects and to better expose genetic variability in N 2 fixation.

Nitrogen fixation in peanut at various concentrations of15N-Urea and slow release15N-fertilizer

Abstract Nitrogen fixation of peanut (Arachis hypogaea L.) was studied using pots (1 kg soil/pot) at various concentrations of 15N-urea and 15N-super-IB (a slow release N fertilizer). The soil used was an Andosol with the following characteristics pH 6.02, CEC 23.4 cmol(+) kg-1, total-C 20.9 g kg-1, total-N 2.5 g kg-1, and a loam texture. The number and weight of the nodules and acetylene reduction activity (ARA) decreased by the addition of 15N-urea but not by the addition of 15N-super-IB even at higher doses. Irrespective of the type of fertilizer or the amount of nitrogen applied, the highest ARA of the crop was observed between 75 and 98 d after sowing (DAS). Nitrogen fixation determined by the A-value method showed that the addition of higher doses of 15N-urea markedly decreased the fixation, unlike that of 15N-super-IB. At 75 DAS the percentage of nitrogen derived from fixation (%Ndfa) at 100, 200, and 400 mg N per pot was 61, 54, and 29 (333, 308, and 171 mg N per plant), respectively when N was ap...

Irradiance and Nitrate Effects on Growth and Symbiotic Parameters of the Supernodulating and Nitrate-tolerant Soybean Mutant En6500 and its Parent Cultivar Enrei

The supernodulating and nitrate-tolerant soybean ( Glycine max [L.] Merr.) mutant «En6500 and its parent cv. «Enrei were compared in their response to combined irradiance and nitrate treatments. The mutant exhibited substantially less overall dry matter (DM) production but had markedly more nodules plant -1 , larger nodule DM, and higher acetylene reduction activity (ARA) plant -1 compared to Enrei at all nitrate (KNO 3 ) concentrations of 0.5, 5.0, and 15.0 mM and irradiance levels of 150 and 850 μmol m -2 s -1 . In both genotypes, high irradiance increased DM of the shoot and root, and leaf apparent photosynthetic rate, while symbiotic activity and nodule mass were increased in the mutant but essentially unaffected in Enrei. Dry matter production increased with nitrate level in the mutant but tended to be reduced by the highest level in Enrei. Reduction in nodule DM in favor of the roots and shoot at high levels of nitrate and irradiance was more pronounced in Enrei. High nitrate levels stimulated nodule formation only in the mutant regardless of irradiance, but it consistently depressed specific nodule activity, indicating that the tolerance of the mutant to nitrate is essentially limited to nodule formation and does not extend to nitrogenase function. The failure of high irradiance to overcome the depressive effect of high nitrate on specific nodule activity suggests that carbon is preferentially used for nodulation rather than nodule function in the mutant. At high nitrate levels, the mutant, in contrast to Enrei, appeared to rely more on symbiotically-fixed N than on mineral N. Nodule N concentrations were surprisingly similar across genotypes, irradiance, and nitrate levels despite substantial differences in specific nodule activity, indicating the presence in both genotypes of a common mechanism(s) regulating nodule N metabolism.

Relative contributions to nitrogenase (acetylene reducing) activity of stem and root nodules in Sesbania rostrata

Six experiments, two each in the phytotron, greenhouse, and field, were conducted to assess the contribution of nitrogenase activity (acetylene reduction) by stem nodules in the presence and absence of root nodules of Sesbania rostrata (Brem &amp; Oberm). In a greenhouse experiment, the effect of detaching already formed aerial stem nodules on the restoration of root nodules and nitrogenase activity was studied. The field experiment compared nodulation and acetylene-reduction activity by dual-nodulating S. rostrata and root-nodulating Sesbania cannabina. Acetylene-reduction activity expressed per gram of nodule dry weight was higher for stem nodules than for root nodules. Root nodule dry weight and acetylene-reduction activity failed to increase after stem inoculation, but root nodule dry weight and acetylene-reduction activity increased several fold within 15 days of detachment of aerial stem nodules. Stem nodulation, which occurred without inoculation under lowland field condition, suppressed root nodulation, thus accounting for more than 75% of total nitrogenase activity. Sesbania rostrata showed higher acetylene-reduction activity than S. cannabina. In dual-nodulating plants, root and stem nodules appeared to strike a balance in competition for energy, which may be controlled by stem nodulation. Key words: Sesbania rostrata, Azorhizobium caulinodans, stem nodule, root nodule, acetylene-reducing activity.

Epicaulous, Nitrogen-Fixing Microepiphytes in a Tropical Mangal Community, Guadeloupe, French West Indies

The mangal community fringing the Grand Cul-de-Sac Marin of Guadeloupe, French West Indies is composed of Rhizophora mangle (red), Avicennia germinans (black), and Laguncularia racemosa (white mangrove). These species form six discrete vegetation zones along a Canal Perrin transect. A. germinans supports dense epicaulous crusts of nitrogen-fixing cyanobacteria which cover the bole and even the finest branchlettes. Crusts on red and white mangrove were less dense. Acetylene reduction activity (ARA) recorded for these previously unreported crusts ranged from 174 to 2012 nmol C2H4 mg Chl.a-1 hr-'. The ARA in the aerial stratum represents a potentially important source of nitrogen to this mangal community. Preliminary data showed that the 42.3 g N m-2 yr-I biologically fixed by cyanobacteria growing epiphytically on Avicennia in zone IV of the Canal Perrin Transect was 3.2 times greater than the total nitrogen budget of an Avicennia community in Southern Australia. The rate-controlling effects of crust hydration and salinity on the ARA and the recovery rate of nitrogenase activity following a period of dehydration are reported. MANGAL COMMUNITIES ARE CIRCUMPOLAR, they occupy approximately 75 percent of the tropical coastlines and often extend inland along the banks of rivers (Zuberer & Silver 1978). The paradox of the high productivity of mangal communities situated in nutrient limited coastal lowlands (Ryther & Dunstan 1971) may be resolved by studies concerning the role of symbiotic cyanobacteria in both the substrate and aerial levels of the community. Although the literature on mangroves in 1981 included over 6000 citations (Rollet 1981), certain aspects of mangrove ecology such as mineral cycling and the contribution of N by nitrogen fixation are poorly understood (Lugo & Snedaker 1974; Walsh 1974; Chapman 1976, 1977; van der Valk & Attiwill 1984; Tomlinson 1986). Investigations of biological nitrogen fixation in mangal communities have been confined to the substrate layer. Rates of nitrogen fixation measured in estuarial muds were low (Brooks et al. 1971, Patriquin & Knowles 1972, Bohlool 1978), while those of mangrove sediments were higher (Zuberer & Silver 1978). Decaying leaves at the substrate surface in New Zealand exhibited a mean acetylene reduction activity (ARA) of 32.4 nmol C2H4 gdw-l hr-I (Hicks & Silvester 1985). These same authors also reported high ARA rates by the cyanobacterium Calothrix (100-500 nmol C2H4 . pneumatophoreI yr'-). N-fixation in leaf litter plus the root and sediment layers contributed 42 percent of the total mangal nitrogen requirement of 13 g N m-2yr-l (van der Valk & Attiwill 1984). Anaerobic fixation in R. mangle litter in Key Biscayne, Florida contributed 11 ,ug N gdw-I hr-I (Gotto & Taylor 1976). Light-independent nitrogenase activities have been detected in the surface sediments of mangrove forests in New Zealand (Hicks & Silvester 1985), Southern Australia (van der Valk & Attiwill 1984) and in decaying leaves of Rhizophora mangle at Key Biscayne, Florida (Gotto & Taylor 1976); whereas, the light dependent ARA by cyanobacteria and members of the Rhodospirillaceae in mangal sediments also occurs (Gotto & Taylor 1976; Zuberer & Silver 1978; Potts 1979, 1980). In general, mangal community muds are anaerobic with high rates of denitrification (Nedwell 1975). The only reported epicaulous ARA resulted from bacteria (812 nmol C2H4 gfw of bark-l'hr-') on the warty bark of Bruguiera gymnorrhiza (Uchino et al. 1984). This paper reports a study of cyanobacterial, epicaulous crusts that reduce acetylene at rates representing a potentially substantial contribution of nitrogen to the Canal Perrin mangal community on the island of Guadeloupe, Lesser Antilles, French West Indies (16?40'N, 61?10'W). It is the first report on epicaulous nitrogenase activity due to cyanobacteria on mangrove species. This mangal community, which borders the shore of the Cul-de-Sac Marin, consists of Rhizophora mangle, Avicennia germinans and Laguncularia racemosa (Imbert & Portecop 1986, Imbert 1985). The trunks and even i Received 30 June 1990, revision accepted 15 March 1991. 2 Formerly R. Fritz-Sheridan.

Development of acetylene reduction (nitrogen-fixation) activity on and around imbibed plant seeds

The development of acetylene reduction activity (ARA) formed prior to germination on the surfaces of seeds was investigated with various kinds of seeds. Cocklebur ( Xanthium pennsylvanicum Wallr.) seeds exhibited ARA regardless of dormancy status when exposed on a river sand stratum in a Petri dish, although the seeds themselves did not have ARA. The ARA on cocklebur seeds increased with time, reaching a maximum after ca 6 days, and the increase in ARA corresponded with that in the number of N 2-fixing bacteria living on the seed surface. The population of bacteria on the seed surface differed from that in the sand stratum: N 2-fixing bacteria were more dominant on the seed surface than in the sand incubated with or without seeds. Similarly. ARAs were associated with the seeds of barley, rice. grape, melon, eggplant and cherry, exposed to river sand. Cocklebur and eggplant seeds showed high ARAs in anoxia, whereas the others showed high ARAs in hypoxia. The ARA of the cocklebur seedlings grown from the seeds which had been in contact with the river sand was much higher than that of the non-contacted seedlings. It was concluded that a bacterial habitat, the “spermosphere”, is established around soaked seeds prior to germination and promotes the subsequent development of the rhizosphere.

Growth and nitrogen fixation ofAzolla pinnata andAzolla caroliniana as affected by urea fertilizer and their influence on rice yield

Azolla pinnata (India) andAzolla caroliniana (USA), were grown with rice variety IR-36 using no urea as well as with urea at 10 and 20 kg N ha−1. Azolla received only the urea applied at transplanting which amounted to 50% of that provided to the rice crop. The results indicated that increasing levels of urea nitrogen decreased the fresh biomass, acetylene reduction activity (ARA) and N yield of bothAzolla species.A. caroliniana out performedA. pinnata, attaining greater biomass, higher ARA and more total N under all nitrogen regimes. Grain yield and crop N uptake also were greater withA. caroliniana than withA. pinnata.

Acetylene reduction activity of pearl millet inbred lines grown in soil

Pearl millet inbred lines previously selected for differences in acetylene reduction activity (ARA) in seedling agar tubes were found to support low soil ARA. Lines selected for high ARA gave better performance than lines selected for low ARA. None of the high ARA lines was found to approach the ARA of alfalfa with their average rates over 40 fold lower.

Effect of different nitrogen sources on growth, acetylene reduction activity ofAzolla pinnata and yield of rice

The effect of nitrogenous sources like ammonium sulphate (AS), prilled urea (U), urea super granule (USG) and farm yard manure (FYM) was studied on the fresh biomass (FB) and acetylene reduction activity (ARA) ofAzolla pinnata, R. Brown (Bangkok isolate), grown as a dual crop with rice, and rice yield in three successive seasons. Irrespective of the N-sources and seasons, the FB and ARA of Azolla were observed to be maximum on 14th day after Azolla inoculation (DAI). The different N-sources had significant effect on the ARA and to a lesser extent on the FB of Azolla. The treatment without fertilizer-N (control) exhibited highest ARA, FB and total N-content of Azolla. These were inhibited to a lesser extent by USG and FYM, though used at higher rates of 75 kg N ha−1 and 90 kgN ha−1 respectively, compared to that by AS and U, used at lower rates of 45kg N ha−1 each.

An SEM/TEM study of structures associated with bacteroids in peanut (Arachis hyppogaea L.) root nodules

Nitrogen-fixing peanut root nodules have highly specialized, large spherical bacteroids and show higher acetylene-reduction activity than the nodules of other legumes induced by the same strain of rhizobia. Differences are also found in their anatomical organization and with regard to bacteroid-associated organelles and other structures (dense bodies) found on the host-symbiont interface. In this investigation, further description of these organelles and structures was made at different stages of development in a correlated SEM/TEM study.Arachis hypogaea L. cv. Jumbo Virginia plants were grown in environmental growth chambers and inoculated with Rhizobium sp. 32Hl. For TEM, slices of nodules were fixed in Karnovsky's fixative in Sorensen's phosphate buffer, pH 7.2 for 1 h at 4°C. Tissues were rinsed in buffer, post-fixed with 1% phosphate-buffered osmium tetroxide for 1 h at 4°C and dehydrated in ethanol. 1% p-phenylenediamine was added at the 70% ethanol step (30 min) to preserve lipids.

Germintion, nodulation and early growth response of a hard-seeded legume,Lathyrus sylvestris L. (flatpea)

Flatpea (Lathyrus sylvestris L.) requires seed scarification for rapid germination and specificRhizobium leguminosarum strain for nodulation. Methods of inoculation were investigated to determine which would be effective for at least two weeks after seeding. Application of powdered peat to wet seeds was inadequate. Lime pelleting and granular soil implants were effective inoculants, but there appears to be a different advantage to seedling for earch metod. Granular soil implant caused nodulation to a greater depth on the tap root, and lime pelleting caused plants to exhibit higher acetylene reduction activity.