Dual inoculation of pretransplant stage Oryza sativa L. plants with indigenous vesicular-arbuscular mycorrhizal fungi and fluorescent Pseudomonas spp.

Summary This study examined the response of rice (Oryza sativa L.) plants at the pretransplant/nursery stage to inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi and fluorescent Pseudomonas spp., singly or in combination. The VAM fungi and fluorescent Pseudomonas spp. were isolated from the rhizosphere of rice plants. In the plants grown in soil inoculated with fluorescent Pseudomonas spp. alone, I found increases in shoot growth, and in root length and fine roots, and decreases in root growth, and P and N concentrations. In contrast, in the plants colonized by VAM fungi alone, the results were the reverse of those of the pseudomonad treatment. Dual inoculation of soil with VAM fungi and fluorescent Pseudomonas spp. yielded plants with the highest biomass and nutrient acquisition. In contrast, the plants of the control treatment had the lowest biomass and nutrient levels. The dual-inoculated plants had intermediate root and specific root lengths. The precentages of mycorrhizal colonization and colonized root lengths were significantly lower in the dual-inoculated treatment than the VAM fungal treatment. Inoculation of plants with fluorescent Pseudomonas spp. suppressed VAM fungal colonization and apparently reduced photosynthate loss to the mycorrhizal associates, which led to greater biomass and nutrient levels in dual-inoculated plants compared with plants inoculated with VAM fungi alone. Dual inoculation of seedlings with fluorescent Pseudomonas spp. and VAM fungi may be preferable to inoculation with VAM alone and may contribute to the successful establishment of these plants in the field.     

The flavonoid naringenin enhances intercellular colonization of rice roots by<Emphasis Type="Italic"> Azorhizobium caulinodans</Emphasis>

The intercellular colonization of rice roots by Azorhizobium caulinodans and other diazotrophic bacteria has been studied using strains marked with the lacZ reporter gene. A. caulinodans were able to enter the roots of rice at emerging lateral roots (lateral root cracks) by crack entry and this was observed by light microscopy. After colonization of lateral roots, bacteria moved into intercellular space within the cortical cell layer of roots. Naringenin at 1×10^-5 and 5×10^-5 M concentration significantly enhanced root colonization. The role of nodABC and regulatory nodD genes was also studied; lateral root crack (LRC) colonization of rice was shown to be Nod factor and NodD independent. Lateral root crack colonization of rice was also observed with similar frequency following inoculation with Azospirillum brasilense and the colonization by A. brasilense was stimulated by naringenin and other flavonoid molecules.     

Susceptibility and effectiveness of vesicular-arbuscular mycorrhizae in wheat cultivars under different growing conditions

Summary Wheat cultivars assumed to be non-susceptible to vesicular-arbuscular (VA) mycorrhizae became colonized, and this effect persisted under different growth conditions. Colonization of all cultivars was similar regardless of the amount of inoculum and the time interval of inoculation. Different plant growth temperatures and the support given by the culture media, inoculation with different endophytes, and inoculation with sterilized and unsterilized spores affected VA colonization levels, although the level of colonization reached in cv. Champlein was similar to that reached in cv. 7-Cerros under each condition. VA mycorrhizal colonization was also affected by different plant growth conditions. After VA reinoculation, the plant dry weight of Castan and 7-Cerros increased, but not Negrillo and Champlein cultivars. VA mycorrhizae increased the shoot dry weight of 7-Cerros only, but not of Champlein, when grown at 35/24°C, and had no effect on the dry weight of either cultivar grown at 18/12°C and 42/24°C. Inoculation with Glomus mosseae increased the dry weight of the cultivars more than inoculation with G. fasciculatum or G. agregatum. The effect on the plant dry weight was greater in plants grown in soil than in sand/vermiculite pots. Inoculation with sterilized and unsterilized spores of G. mosseae, either in soil pots or in sand/vermiculite tubes, did not increase the plant dry weight. Our results indicate that there was no close relationship between the level of root colonization and the effect on plant growth. The effects of accompanying microorganisms in the VA inoculum on VA mycorrhizal symbiosis are discussed.     

粪产碱菌与水稻根的联合过程

应用~(15)N同位素标记菌体和Tn5转座子诱变的突变株研究固氮粪产碱菌对宿主水稻的联合进程,结果表明,粘附作用是结合过程的第一步,接种3h后粘附在根表的菌体数量达最大值,约占接种量的3.7％。粘附的菌体易脱离根表,表明粘附作用是细菌与宿主植物间的弱的相互作用。在根表定位是结合过程的第二步。接种15h后,定位菌体数量达最大值,约占接种量的21％。经振荡处理不能使定位菌体脱离根表。定殖是结合过程的第三步,接种20h后定殖菌体紧密结合于根表,剧烈振荡亦不易使其脱离根表。定殖后菌体开始出现果胶酶活性。采用趋化(Che)和胞外多糖(Exo)突变株研究表明,趋化性和胞外多糖的合成是影响细菌在根表结合的重要因素。粪产碱菌在水稻根表没有专一的粘附部位,但粪产碱菌的定位和定殖主要发生在主根根表,尤其是主、侧根交接处。     

Association of Azospirillum brasilense with pearl millet (Pennisetum americanum (L.) Leeke)

Summary Microscopic observations of the root system of pearl millet (Pennisetum americanum (L.) Leeke) var. BJ 104 after surface sterilization and incubation in phosphate malate triphenyl tetrazolium chloride (TTC) revealed extensive colonization by Azospirillum spp. when plants were grown in sterile, partially sterile and field conditions as evidenced by the TTC-reducing property of active cells of the bacterium. Quantitative studies showed the need to standardize the techniques further to ensure more precise monitoring of the bacteria in the rhizosphere, as large numbers of soil bacteria were found capable of growth on specific media, thus interfering with the plate counts. Seed inoculation with A. brasilense increased the mean grain yield of pearl millet under different agroclimatic conditions in India. The mean increase in grain yield due to inoculation over uninoculated controls was also noticed with graded levels of fertilizer nitrogen (urea). Inoculation alone contributed to increased nitrogen uptake of plants with varying levels of fertilizer nitrogen application under sandy loam soil conditions (pH 7.3). The effects of inoculation were more prominent under lower levels of nitrogen than at the higher levels. The root biomass under field conditions was increased with Azospirillum spp. inoculation at 10 and 20 kg N/ha than their corresponding uninoculated controls.     

Mycorrhizal colonization with Glomus intraradices and development stage of transformed tomato roots significantly modify the chemotactic response of zoospores of the pathogen Phytophthora nicotianae

The chemotaxic response of zoospores of the plant pathogen, Phytophthora nicotianae, towards exudates from mycorrhizal and non-mycorrhizal transformed tomato roots was studied. A bi-compartmental in vitro system was used to grow Ri T-DNA-transformed tomato roots colonized or non-colonized with the arbuscular mycorrhizal fungus, Glomus intraradices, and to collect root and mycorrhizal exudates. The root and mycorrhizal growth dynamics were first characterized in order to determine two times of exudate sampling. Exudates collected from 16-wk-old mycorrhizal roots were significantly more attractive for P. nicotianae zoospores than exudates from non-inoculated roots. On the contrary, concentrated exudates harvested from 24-wk-old mycorrhizal roots were repulsive to zoospores compared to exudates from non-colonized roots and the water control. In exudates of G. intraradices-inoculated roots, HPLC–MS analyses revealed significantly higher concentrations of proline and isocitrate after 24 wk of growth, while after 16 wk of growth, proline concentration did not differ between exudate types, and the isocitrate concentration was lower in mycorrhizal root exudates. Mycorrhizal inoculation had no effect on the amounts of other amino acids and organic acids and on the sugars quantified within exudates. Our results suggest that modification in exudate composition of mature roots by mycorrhizal colonization may provoke the repulsion of P. nicotianae, and that their capacity to infect host roots may in this manner be reduced.     

Mycorrhizae,biocides, and biocontrol. 4. Response of a mixed culture of arbuscular mycorrhizal fungi and host plant to three fungicides

The effects of three commonly used fungicides on the colonization and sporulation by a mixture of three arbuscular mycorrhizal (AM) fungi consisting of Glomus etunicatum (Becker & Gerd.), Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, and Gigaspora rosea (Nicol. & Schenck) in symbiosis with pea plants and the resulting response of the host-plant were examined. Benomyl, PCNB, and captan were applied as soil drenches at a rate of 20 mg active ingredient kg^-1 soil 2 weeks after transplanting pea seedlings in a silty clay-loam soil containing the mixed inocula of AM fungi (AM plants). Effects of fungicides were compared to untreated plants that were inoculated with fungi (AM control). The effect of mycorrhizal inoculation on plant growth was also examined by including nonmycorrhizal, non-fungicide-treated plants (non-AM control). Fungicides or inoculation with AM fungi had only a small effect on the final shoot weights of pea plants, but had greater effects on root length and seed yield. AM control plants had higher seed yields and lower root lengths than the corresponding non-AM plants, and the fungicide-treated AM plants had intermediate yields and root lengths. Seed N and P contents were likewise highest in AM control plants, lowest in non-AM plants, and intermediate in fungicide-treated AM plants. All three fungicides depressed the proportion (%) of root length colonized by AM fungi, but these differences did not translate to reductions in the total root length that was colonized, since roots were longer in the fungicide-treated AM plants. Pea plants apparently compensated for the reduction in AM-fungal metabolism due to fungicides by increasing root growth. Fungicides affected the population of the three fungi as determined by sporulation at the final harvest. Captan significantly reduced the number, relative abundance, and relative volume of G. rosea spores in the final population relative to the controls. The relative volume of G. etunicatum spores was greater in all the fungicide-treated soils, while G. mosseae relative volumes were only greater in the captan-treated soil. These findings show that fungicides can alter the species composition of an AM-fungal community. The results also show that AM fungi can increase seed yield without enhancing the vegetative shoot growth of host plants.     

The role of the earthworm Lumbricus terrestris in the transport of bacterial inocula through soil

Two laboratory experiments were used to investigate the effect of the earthworm Lumbricus terrestris on transport of genetically marked Pseudomonas fluorescens inocula through soil microcosms. The microcosms comprised cylindrical cores of repacked soil with or without earthworms. Late log-phase cells of P. fluorescens, chromosomally marked with lux genes encoding bioluminescence, were applied to the surface of soil cores as inoculated filter paper discs. In one experiment, 5 and 10 days after inoculation, cores were destructively harvested to determine concentrations of marked pseudomonads with depth relative to the initial inoculum applied. Transport of the bacteria occurred only in the presence of earthworms. In a second experiment cores were subjected to simulated rainfall events 18 h after inoculation with lux-marked bacteria at 3-day intervals over a 24-day period. Resulting leachates were analysed for the appearance of the marked bacteria, and after 28 days cores were destructively harvested. Although some marked cells (less than 0.1% of the inoculum applied) were leached through soil in percolating water, particularly in the presence of earthworms, the most important effect of earthworms on cell transport was through burial of inoculated litter rather than an increase in bypass flow due to earthworm channels.     

The effects on N2 fixation (C2H2 reduction), bacterial population and rice plant growth of two modes of straw application to a wetland rice field

Summary The effects of incorporation and surface application of straw to a wetland rice field on nitrogen fixation (C₂H₂ reduction), bacterial population and rice plant growth were studied. Rice straw (5 t ha^–1) was chopped (10- to 15-cm pieces) and applied to the field 2 weeks before transplanting IR42, a long-duration variety, and IR50, a short-duration variety. The acetylene-reducing activity (ARA) of IR42 and IR50 measured at heading stage for 3 consecutive days showed significantly higher ARA in IR42 as a result of the 2 straw application methods. Mostly up to 20 days after straw surface application and incorporation, the dark ARA in the soil, total and N₂-fixing heterotrophs, and photoorganotrophic purple nonsulphur bacteria (POPNS) in the soil and in association with degrading straw were stimulated. Higher bacterial populations were associated with straw on the surface than with straw incorporated. The POPNS counts, in particular, were increased hundreds fold in the surface-applied straw treatment. Straw applications also increased the root, shoot and total plant biomass at heading stage and the total dry matter yield at harvest in both varieties. The data show the potentials of straw as a source of substrate for the production of microbial biomass and for the non-symbiotic N₂ fixation to improve soil fertility and plant nutrition.     

Rhizodeposition and net release of soluble organic compounds by pine and beech seedlings inoculated with rhizobacteria and ectomycorrhizal fungi

Summary A lysimetric experiment was performed in a greenhouse to evalute root deposition and net release of soluble organic compounds after 1 and 2 years from pine and beech seedlings inoculated with an ectomycorrhizal fungus (Laccaria laccata) and/or rhizobacteria (Agrobacterium radiobacter for beech and Agrobacterium sp. for pine). Total C compounds released in the rhizosphere of both plants increased after inoculation with the bacteria or ectomycorrhizal fungus. The rhizobacteria increased root and plant growth and rhizodeposition, but the mycorrhizal fungi appeared to increase only root deposition. Soluble C compounds, collected after 2 years, represented only 0.1–0.3% of the total C compounds released into the rhizosphere, and were modified by inoculation with the microorganisms. After inoculation with the bacteria, levels of sugars and amino acids decreased in pine and beech rhizospheres, whereas organic acids increased, especially in the pine rhizosphere. In the rhizosphere of mycorrhizal beeches, sugar and amino acids increased, and organic acids differed from those released from non-mycorrhizal beeches. In the mycorrhizal pine rhizosphere, however, all compounds decreased. Following dual inoculations, mycorrhizal colonization increased, no effect on plant growth was observed, and virtually no organic acids were detected.     

Infection and colonization of aseptically micropropagated sugarcane seedlings by nitrogen-fixing endophytic bacterium, Herbaspirillum sp. B501gfp1

In this study, we used Herbaspirillum sp. B501gfp1 (B501gfp1), an isolate from wild rice, to investigate the interaction between a non-host nitrogen-fixing endophytic bacterium and micropropagated sugarcane plants under aseptic condition. Two Japanese sugarcane plants (Saccharum sp.) cultivars (cvs) NiF8 and Ni15 were inoculated using B501gfp1 in two inoculum doses of 10⁸ and 10² bacterial-cells-per-milliliter suspension. The results showed that bacterial cells colonized both the root and stem tissues, and colonization was apparent in the intercellular spaces. Higher bacterial numbers were detected in plant tissues inoculated with the higher inoculum concentration treatment. Bacterial numbers also varied between the two cultivars, with the higher values determined in cv Ni15. This study provides evidence that Herbaspirillum sp. B501gfp1, a rice isolate, could colonize sugarcane tissues, suggesting non-specificity of host plant among endophytes.     

Responses by iron-efficient and inefficient oat cultivars to inoculation with siderophore-producing bacteria in a calcareous soil

Rhizosphere bacteria may enhance plant uptake of Fe by producing siderophores that chelate sparingly soluble Fe³⁺ in calcareous soils. To evaluate the extent to which plants benefit from colonization of the roots by prolific siderophore-producing bacteria, we inoculated two oat cultivars with six strains of bacteria that produced high concentrations of siderophores under Felimiting conditions in vitro. Oat cv Coker 227, an Fe-efficient cultivar, which produces the phytosiderophore avenic acid, and cv TAM 0-312, and Fe-inefficient cultivar, which does not produce the phytosiderophore, were grown in a calcareous soil (Weswood silt loam) on a light bench in the laboratory. Half of the plants were fertilized with a nutrient solution containing 5 mM Fe and half with a nutrient solution containing no Fe. After 6 weeks of growth, we compared colonization of the roots by the inoculant bacteria and the dry weight and Fe content of roots and shoots. Three species of Pseudomonas colonized the roots of both oat cultivars in high numbers (10⁶ cells g^-1 root dry weight), whereas the remaining bacteria colonized the roots in substantially lower numbers (10⁴ cells g^-1 root dry weight). Plants fertilized with 5 mM Fe were larger and supported greater numbers or rhizosphere bacteria per gram of root than plants not supplied with Fe. Comparisons of the Fe content and dry weight of roots and shoots revealed few significant differences between inoculated and uninoculated plants, or among the plants inoculated with the different strains of siderophore-producing bacteria. The differences that were observed revealed no consistent response to inoculation. We conclude that inoculation of the roots of the two oat cultivars with bacteria that produce high concentrations of siderophores in response to an Fe deficiency had little or no effect on Fe acquisition by the plants.     

Effects of inoculation with N2-fixing cyanobacteria on the nitrogenase activity in soil and rhizosphere of wetland rice (Oryza sativa L.)

Summary A greenhouse experiment was conducted with wetland rice (Oryza sativa cv. IR-50) in a clay-loam soil (Fluventic Eutrochrept) to study the effect of cyanobacterial inoculation a mixed culture of Aulosira fertilissima, Nostoc muscorum, Nostoc spp., and Anabaena spp., applied at the rate of 0.15 g (dry weight pot^-1 or 43 kg ha^-1) on acetylene reduction activity in soil and the root system (excised root), and the grain and straw yield. The effects of applying P (40 kg ha^-1), N (60 kg ha^-1), and P+N to the soil were also evaluated. Cyanbacterial inoculation significantly increased (more than 200% on average) photo-dependent acetylene reduction activity in soils, particularly where the indigenous activity was considerably low, i.e. under unfertilized and N-fertilized conditions. The effect of inoculation was prominent at the maximum tillering and grain formation stages of the crop. This inoculation benefit was, however, marginal in P-applied soils (P and P+N), where the indigenous activity was stimulated more than threefold. The inoculation led to a remarkable increase in root-associative acetylene reduction activity after the maximum tillering stage of the crop, particularly with applied N but for other treatments this inoculation effect was not significant. Cyanobacterial inoculation also increased the grain and straw yield of the crop when N was not applied. The grain and straw yield was significantly correlated with the acetylene reduction activity in flooded soils and in the root system during the tillering and maximum tillering stages of rice growth, respectively.     

Effects of endophytic Bacillus spp. on accumulation and distribution of iron in the shoots of lowland rice grown under iron toxic conditions

Background

The tolerance of plants against abiotic stresses can be greatly influenced by their interaction with microbes. In lowland rice (Oryza sativa) production, the iron toxicity of the soils constitutes a major constraint. Although there are tolerant cultivars, the mechanisms underlying the tolerance against excess iron are not fully understood. Even less is known about the role of microbes in the response to iron toxicity.

Aim

In the study presented here, the effects of different Bacillus isolates on the accumulation and distribution of iron within the shoots of different rice cultivars grown under iron toxicity were analyzed.

Methods

Three lowland rice cultivars with contrasting tolerance to iron toxicity (IR31785-58-1-2-3-3, Sahel 108, Suakoko 8) were inoculated with three Bacillus isolates (two B. pumilus and one B. megaterium) and, after 1 week, exposed to excess iron (1,000 ppm) for 8 days. Tolerance was evaluated by leaf symptom scoring.

Results

Bacterial inoculation mitigated leaf symptoms in the sensitive cultivar IR31785-58-1-2-3-3 despite no significant differences in shoot iron concentration between inoculated and noninoculated plants. In the tolerant excluder cultivar, Suakoko 8, leaf symptoms were exacerbated when inoculated with B. pumilus Ni9MO12. While the total shoot Fe concentration was not affected in this bacteria × cultivar combination, the distribution of iron within the shoot was clearly disturbed. Tolerance to iron toxicity of the tolerant includer cultivar, Sahel 108, was not affected by Bacillus inoculation.

Conclusion

In conclusion, our results show that Bacillus inoculation can affect the tolerance of lowland rice to iron toxicity and that the effects strongly depend on the bacteria × cultivar combination.     

The influence of inorganic nutrient fertilization on the growth,nutrient composition and vesicular-arbuscular mycorrhizal colonization of pretransplant rice (Oryza sativa L.) plants

Summary The effects of P, N and Ca+Mg fertilization on biomass production, leaf area, root length, vesiculararbuscular mycorrhizal (VAM) colonization, and shoot and root nutrient concentrations of pretransplant rice (Oryza sativa L.) plants were investigated. Mycorrhizal plants generally had a higher biomass and P, N, K, Ca, Mn, Fe, Cu, Na, B, Zn, Al, Mg, and S shoot-tissue nutrient concentrations than non-mycorrhizal plants. Although mycorrhizal plants always had higher root-tissue nutrient concentrations than non-mycorrhizal plants, they were not significantly different, except for Mn. N fertilization stimulated colonization of the root system (colonized root length), and increased biomass production and nutrient concentrations of mycorrhizal plants. Biomass increases due to N were larger when the plants were not fertilized with additional P. P fertilization reduced the colonized root length and biomass production of mycorrhizal plants. The base treatment (Ca+Mg) did not significantly affect biomass production but increased the colonized root length. These results stress the importance of evaluating the VAM rice symbiosis under various fertilization regimes. The results of this study suggest that pretransplant mycorrhizal rice plants may have a potential for better field establishment than non-mycorrhizal plants.     

Interactions of Glomus clarum with Acetobacter diazotrophicus in infection of sweet potato (Ipomoea batatas), sugarcane (Saccharum spp.), and sweet sorghum (Sorghum vulgare)

Summary Spores of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus clarum obtained from sweet potatoes grown in soil inoculated with this fungus and with an enrichment culture of Acetobacter diazotrophicus contained A. diazotrophicus and several other bacteria, including a diazotrophic Klebsiella sp. Inoculation of micropropagated sweet potatoes with G. clarum and A. diazotrophicus enhanced spore formation in soil compared to VAM inoculation alone. Plants inoculated with VAM spores containing the bacteria showed additional increases in the number of spores formed within roots. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM or when present within VAM spores. Micropropagated sugarcane seedlings inoculated with the same VAM spores containing the diazotrophs also contained much higher numbers of A. diazotrophicus in aerial parts than seedlings inoculated in vitro with the bacteria alone. When grown in non-sterile soil, the sugarcane seedlings again showed the greatest infection of aerial parts after inoculation with VAM spores containing the diazotrophs. This treatment also increased VAM colonization and the numbers of spores formed within roots. Similar effects were observed in sweet sorghum except that the aerial plant parts were not infected by A. diazotrophicus.     

Sesbania rostrata as a green manure for lowland rice: Growth,N2 fixation,Azorhizobium sp. inoculation,and effects on succeeding crop yields and nitrogen balance

Summary Root and stem nodulation, nitrogen fixation (acetylene-reducing activity), growth and N accumulation bySesbania rostrata as affected by season and inoculation were studied in a pot experiment. The effects ofS. rostrata as a green manure on succeeding wet-season and dry-season rice yields and total N balance were also studied.S. rostrata grown during the wet season showed better growth, nodulation, and greater acetylene-reducing activity than that grown during the dry season. Inoculation withAzorhizobium caulinodans ORS 571 StrSpc® (resistant to streptomycin and spectinomycin) on the stem alone or on both root and stem significantly increased N₂ fixation by the plants. Soil and seed inoculation yielded active root nodules under flooded conditions. Plants that were not inoculated on the stem did not develop stem nodules. The nitrogenase activity of the root nodules was greater than that of the stem nodules in about 50-day-oldS. rostrata. S. rostrata incorporation, irrespective of inoculation, significantly increased the grain yield and N uptake of the succeeding wet season and dry season rice crops. The inoculated treatments produced a significantly greater N gain (873 mg N pot^–1) than the noinoculation (712 mg N pot^–1) treatment. About 80% of the N gained was transferred to the succeeding rice crops and about 20% remained in the soil. The soil N in the flooded fallow-rice treatment significantly declined (–140 mg N pot^–1) but significantly increased in bothS. rostrata-rice treatments (159 and 151 mg N pot^–1 in uninoculated and inoculated treatments respectively). The N-balance data gave extrapolated values of N₂ fixed per hectare at about 303 kg N ha^–1 per two crops forS. rostrata (uninoculated)-rice and 383 forS. rostrata (inoculated)-rice.     

水稻品种间铝耐性差异的探究

铝毒是酸性土壤中限制植物生长的主要因子之一,探讨植物耐铝特性与机理对提高酸性土壤植物生产力具有重要意义。通过一系列生理和分子生物学试验,主要探究了Nipponbare和Kasalath两个水稻品种的铝耐性差异。结果发现,与Kasalath相比,Nipponbare在铝胁迫下不仅拥有较长的根伸长,且根尖铝含量较少,表明Nipponbare是水稻铝耐性品种,而Kasalath为铝敏感品种。进一步研究发现,水稻根尖控制铝吸收的NRAT1基因在Kasalath中表达量更高,表明,NRAT1基因的高表达量可能是导致铝敏感品种Kasalath根尖铝含量较高的主要原因。此外,铝胁迫下,Nipponbare根系柠檬酸的分泌量显著高于Kasalath。而且,水稻中控制柠檬酸分泌的OsFRDL4基因在铝耐性品种Nipponbare中的表达量显著高于Kasalath,由此证明,柠檬酸在这两个品种水稻耐铝途径中可能起着重要的作用,并且,该品种水稻可以通过调控OsFRDL4基因的表达量来控制柠檬酸的分泌量。本研究中还分析了其他4个与铝胁迫相关的基因,但并未发现明显的相关性,值得进一步的探究。     

Selection of efficient vesicular-arbuscular mycorrhizal fungi for wetland rice (Oryza sativa L.)

Summary We tested the response of the wetland rice cultivar Prakash to inoculation with ten vescular-arbucular mycorrhizal (VAM) fungi (three selected from the first screening and seven isolated from local paddy fields) in a pot experiment under flooded conditions in order to select the most efficient mycorrhizal fungi to inoculate the rice nursery. A sandy clay loam soil was used as the substrate, fertilized with the recommended N and K levels (100 kg N ha^–1 as ammonium sulphate and 50 kg K ha^–1 as muriate of potash) and half the recommended level of P (25 kg ha^–1 as super phosphate). The inoculation was made into dry nursery beds and the beds were flooded when the seedlings were about 25 cm high, in 15 days. Twenty-eight-day old seedlings were transferred to pots filled with well puddled soil flooded with 5 cm of standing water. Based on the increase in grain yield and total biomass, Glomus intraradices and Acaulospora sp. were considered efficient and suitable for inoculation into rice nurseries.     

田菁茎瘤固氮根瘤菌在小麦体内的定殖及营养元素相关miRNA的表达

【目的】随着化肥过度使用引起的环境问题的出现,无公害农业的推广,以及新型肥料研究领域不断拓宽,微生物肥料,尤其是植物根际促生菌的研究成为近年来的热点。然而微生物肥料的增产机理还基本停留在作物农学性状的表观调查上,没有从分子水平进行研究。因此,本文用田菁茎瘤固氮根瘤菌（Azorhizobium caulinodans ORS571）侵染小麦,探索GFP-A.caulinodans在小麦幼苗组织中的分布与定殖规律以及营养元素相关miRNAs在小麦与A.caulinodans互作中的作用机制。【方法】使用A.caulinodans侵染小麦种子（品种为小偃22）,将接菌6 d后的小麦幼苗的根和接菌12 d后的叶制作玻片,利用激光共聚焦显微镜对样品进行逐层扫描,检测GFP-A.caulinodans在幼苗不同组织中的分布与定殖情况。同时,采集接菌后0 h、 6 h、 12 h、 24 h、 48 h、 72 h、 96 h的小麦幼根取样,用Trizol法提取总RNA。利用试剂盒进行加尾和反转录反应,将样品总RNA中的miRNA合成为cDNA,使用-tubulin作为内参基因,进行实时定量PCR反应,使用2-CT方法计算相对表达量。利用psRNATarget 在线软件,采用默认参数,对miRNA的靶基因进行预测。【结果】 1）激光共聚焦结果显示,GFP-A.caulinodans可定殖于根的表皮细胞、 细胞间隙、 根尖破损处和根毛,在根维管组织和叶片气孔部位,也发现有GFP-A.caulinodans存在。2）实时定量PCR分析结果表明,6条与营养元素代谢有关的miRNA表达发生变化,其中miR164、 miR167和miR827相对表达量呈现出先上调后下调的趋势,miR169 和miR398相对表达量也基本呈现出这一趋势。miR164、 miR167、 miR169和miR398的相对表达量在接菌12 h时上调至最高点,分别为对照的4.13、 2.84、 2.46和3.99倍; miR827相对表达量在接菌24 h时达到最高点,为对照的2.17倍。miR399相对表达量呈现出先下调后上调的趋势,在接菌24 h时降至最低点,为对照的0~21倍。3）通过靶基因预测,6条miRNA的靶基因分别编码了NAC1转录因子、 生长素响应因子、 HAP转录因子、 Cu/Zn 超氧化物歧化酶、 蛋白缀合酶PHO2和SPX-MFS亚家族蛋白。【结论】GFP-A.caulinodans能够从根毛和根尖破损处等部位进入小麦幼苗根部定殖,并可通过向上迁移到达叶片,在气孔处定殖。接种A.caulinodans可不同程度增加小麦根中响应氮素、 磷素、 微量元素的miRNAs相对表达量,增强小麦幼苗对营养元素的吸收和利用,促进小麦根的形态建成。