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1.
Soybean plants autoregulate to suppress excessive nodulation. It has been revealed recently that the autoregulation of various legumes controls both nodulation and arbuscular mycorrhizal (AM) fungal colonization. We investigated the involvement of autoregulation in the interaction between rhizobial nodulation and AM fungal colonization. We used a wild-type soybean cv. Enrei and its hypernodulating mutant Kanto100, defective in the autoregulation. We included four different treatments: an uninoculated control, inoculation with rhizobium Bradyrhizobium japonicum alone, inoculation with AM fungus Gigaspora rosea alone, and dual inoculation with rhizobium and AM fungus. In both Enrei and Kanto100, AM fungal colonization enhanced the weight and N2 fixation of nodules, suggesting that autoregulation of host plant is not involved in the stimulatory effect of AM fungal colonization on rhizobial nodulation. In plants with the AM fungus alone, the AM fungal colonization of Enrei was comparable to that of Kanto100. In plants with dual inoculation, however, this was significantly (P?<?0.05) lower than in Kanto100. To confirm the control of AM fungal colonization by the autoregulation of host plant, a reciprocal grafting experiment was performed between Enrei and Kanto100. In plants with the AM fungus alone, AM fungal colonization was comparable among Enrei (shoot)/Enrei (root), Enrei/Kanto100, Kanto100/Enrei, and Kanto100/Kanto100 grafts. In plants with dual inoculation, however, AM fungal colonization of Enrei/Enrei and Enrei/Kanto100 grafts was significantly (P?<?0.05) lower than that of Kanto100/Enrei and Kanto100/Kanto100. These results indicate that rhizobial nodulation suppresses AM fungal colonization, and the autoregulation of host plant, initiated by nodulation, is involved in this phenomenon.  相似文献   

2.
The purpose of this study was to evaluate the responses of lentil (Lens culinariscv. ‘Ziba’) to co-inoculation with arbuscular mycorrhizal (AM) fungi and some indigenous rhizobial strains varying in phosphorus (P)-solubilizing ability in a calcareous soil with high pH and low amounts of available P and nitrogen (N). A factorial experiment with completely randomized block design was conducted under controlled greenhouse conditions. The treatments consisted of (1) three inoculants of Rhizobium leguminosarum bv. viciae strains and a mixed rhizobial inoculant with an effective P-solubilizer strain of Mesorhizobium ciceri, (2) two AM fungal species, Glomus mosseae and Glomus intraradices, (3) two P sources, superphosphate and phosphate rock. Four replications were prepared for each treatment and a related control. After the growth period of three months, the dry matter of shoots plus seeds, their P and N contents, and percent of root colonized by AM fungus were measured. The results showed that the effects of AM fungi, rhizobial strains, and P fertilizers were highly significant (p < 0.01) for all the characteristics studied. The rhizobial strain with P-solubilizing ability showed a more beneficial effect on plant growth and nutrient uptake than the strain without this ability, although both strains had similar effectiveness for N2-fixation in symbiosis with lentil. Synergistic relationships were observed between AM fungi and some rhizobial strains that related to the compatible pairing of these two microsymbionts. The P-uptake efficiency was increased when P fertilizers were applied along with AM fungi and/or P-solubilizer rhizobial strains.  相似文献   

3.
Over half of the 21 Mha of soybean planted in Brazil is now transgenic glyphosate-resistant (GMRR). A field experiment was carried out to investigate whether the application of glyphosate or imazethapyr to the GMRR variety reduced the input of N2 fixation (BNF). No effects on yield, total N accumulation, nodulation and BNF (δ15N) could be assigned to the genetic modification of the plant. Imazethapyr reduced soybean yield but had no significant effect on BNF. Even though yields were not affected by glyphosate, the significant reduction of nodule mass and BNF to the GMRR suggests that the use of this herbicide could lead to an increased dependence on soil N and consequently an eventual decrease of SOM reserves.  相似文献   

4.
This study is the first report assessing the effect of soil inoculation on the signalling interaction of Bradyrhizobium japonicum, arbuscular mycorrhizal fungi (AMF) and soybean plants throughout the early stages of colonisation that lead to the tripartite symbiosis. In a study using soil disturbance to produce contrasting indigenous AMF treatments, the flavonoids daidzein, genistein and coumestrol were identified as possible signals for regulating the establishment of the tripartite symbiosis. However, it was unclear whether soil disturbance induced changes in flavonoid root accumulation other than through changing the potential for AMF colonization. In this study, soil treatments comprising all possible combinations of AMF and B. japonicum were established to test whether (1) modifications in root flavonoid accumulation depend on the potential for AMF colonization, and (2) synthesis and accumulation of flavonoids in the roots change over time as a function of the early plant-microbial interactions that lead to the tripartite symbiosis. The study was comprised of two phases. First, maize was grown over 3-week periods to promote the development of the AM fungus Glomus clarum. Second, the interaction between soybean, G. clarum and B. japonicum was evaluated at 6, 10, 14 and 40 days after plant emergence. Root colonization by G. clarum had a positive effect on nodulation 14 days after emergence, producing, 30% more nodules which were 40% heavier than those on roots solely inoculated with B. japonicum. The tripartite symbiosis resulted in 23% more N2 being fixed than did the simpler symbiosis between soybean and B. japonicum. The presence of both symbionts changed accumulation of flavonoids in roots. Daidzein and coumestrol increased with plant growth. However, development of the tripartite symbiosis caused a decrease in coumestrol; accumulation of daidzein, the most abundant flavonoid, was reduced in the presence of AMF.  相似文献   

5.
Rhizobial and arbuscular mycorrhizal (AM) symbioses each may consume 4-16% of recently photosynthetically-fixed carbon to maintain their growth, activity and reserves. Rhizobia and AM fungi improve plant photosynthesis through N and P acquisition, but increased nutrient uptake by these symbionts does not fully explain observed increases in the rate of photosynthesis of symbiotic plants. In this paper, we test the hypothesis that carbon sink strength of rhizobial and AM symbioses stimulates the rates of photosynthesis. Nutrient-independent effects of rhizobial and AM symbioses result in direct compensation of C costs at the source. We calculated the response ratios of photosynthesis and nutrient mass fraction in the leaves of legumes inoculated with rhizobial and/or AM fungi relative to non-inoculated plants in a number of published studies. On average, photosynthetic rates were significantly increased by 28 and 14% due to rhizobial and AM symbioses, respectively, and 51% due to dual symbiosis. The leaf P mass fraction was increased significantly by 13% due to rhizobial symbioses. Although the increases were not significant, AM symbioses increased leaf P mass fraction by 6% and dual symbioses by 41%. The leaf N mass fraction was not significantly affected by any of the rhizobial, AM and dual symbioses. The rate of photosynthesis increased substantially more than the C costs of the rhizobial and AM symbioses. The inoculation of legumes with rhizobia and/or AM fungi, which resulted in sink stimulation of photosynthesis, improved the photosynthetic nutrient use efficiency and the proportion of seed yield in relation to the total plant biomass (harvest index). Sink stimulation represent an adaptation mechanism that allows legumes to take advantage of nutrient supply from their microsymbionts without compromising the total amount of photosynthates available for plant growth.  相似文献   

6.
Burr medic (Medicago polymorpha L.) is an annual pasture legume that is widely distributed in southern Australian farming systems. Burr medic is nodulated by rhizobia (Sinorhizobium meliloti and Sinorhizobium medicae) that reside in many Australian soils, but the symbioses that develop are often sub-optimal in their rate of N2 fixation. We attempted to identify burr medic lines, which are able to form effective symbioses with the naturalised Sinorhizobium in Australian field soils, as potential parents for a breeding program. There were three glasshouse experiments. Initially, 222 lines (including the M. polymorpha cvv. Santiago, Serena and Circle Valley) were inoculated with extracts of two soils that had been collected near Waikerie (soil S109) and Lochiel (soil S142) in South Australia. These soils were used because they contained numerically large communities of naturalised Sinorhizobium spp. that produced sub-optimal rates of N2 fixation with cv. Santiago. None of the 222 lines of burr medic were able to form an effective symbiosis with the rhizobia from soil S109. However, when nodulated by the rhizobia from soil S142, some lines (e.g. SA8194) formed a very effective symbiosis, producing up to double the shoot dry matter (DM) of Santiago and eight times the DM of uninoculated plants. Seven promising lines were selected for further testing (with extracts of nine soils). Subsequently, two lines (SA20056 and SA8194) were selected and their symbiotic performance compared with that of Santiago, using extracts from 28 soils. While soil treatment had a major effect on mean shoot DM (soil N103=120 mg, soil N105=17 mg), the three medic lines performed similarly. Santiago, SA20056 and SA8914 all formed ineffective symbioses with the rhizobia in at least half of the 28 soils, even though >95% of the plants were nodulated. These experiments confirm that ineffective symbioses are common between burr medics and the rhizobia that have become naturalised in many Australian soils. Although some lines of burr medic were identified that were able to form more effective symbioses with the rhizobia in individual soils, none were able to form effective symbioses with a wide range of soil rhizobia. If a plant breeding approach is to be used to improve symbiotic performance of burr medic we propose that its hybridisation with other medic species, that have less specific rhizobial needs, will be required.  相似文献   

7.
Glyphosate is a widely used nonselective herbicide for the control of agricultural weeds. It is being increasingly used in glyphosate resistant genetically modified plants. However, there are few studies on its effects on the nutritional status of soybean, particularly on the uptake of zinc (Zn). Two experiments were conducted under field conditions in a Typic Quartzipsamment and an Orthic Ferralsol to investigate the effect of glyphosate application × Zn interaction on soil fertility, yield components, seed yield (SY), shoot dry weight (SDW) yield, and nutritional status of soybean. The five Zn rates 0, 3, 6, 9, and 12 kg ha?1 were used in two soybean varieties [BRS 133 (conventional—NGM) and its essentially derived transgenic line BRS 245RR (GM), which was divided into: with (+Gly) and without (–Gly) glyphosate application. Only the P (phosphorus) and Zn available concentrations in the soil were impacted by Zn rates. However, the available P concentration only decreased in the soil planted with GM soybean. Mehlich 1 and diethylenetriaminepenta acetic acid–triethanolamine (DTPA–TEA), 7.3 extractants were effective to determine the available Zn. In the two crop sites, the number of pods per plant (NPP) and the SDW yield were affected by the interaction varieties × Zn. SY was influenced by the application of the herbicide, reducing a potential phytotoxic effect with the use of high rates. Regarding the nutrients, only the foliar calcium (Ca), boron (B), iron (Fe), and manganese (Mn) concentrations were negatively affected by glyphosate, and in the case of Zn, the difference occurred only between the varieties BRS 133 and BRS 245RR.  相似文献   

8.
The effect of glyphosate on N2 fixation, denitrification, and nitrification in an agricultural soil was investigated. Effects of the pure herbicide and commercial formulation, Roundup+ (Monsanto Company), were compared in soil under aerobic and anaerobic conditions. Anaerobic C2H2 reduction was inhibited by high herbicide levels. Denitrification in non-amended soil was either unaffected (N2O reduction) or stimulated (NO inf3 sup? reduction); in glucose-amended soil, N2O reduction was inhibited and NO3-reduction unaffected by both glyphosate and Roundup. Roundup caused greater stimulation of N2O reduction than pure glyphosate; no other significant formulation effects were observed. Nitrification was inhibited by the two formulations. Ammonium oxidation were both influenced. Pure glyphosate was more inhibitory than Roundup. No toxicity to any of these activities should be seen at recommended field application rates of the herbicide.  相似文献   

9.
Abstract

The widespread use of glyphosate‐resistant (GR) cropping systems may impact rhizosphere microbial associations and crop productivity. It was previously reported that glyphosate accumulation in the rhizosphere may stimulate colonization of soybean [Glycine max (L.) Merr.] roots by soilborne Fusarium. Field studies often reveal inconsistent root colonization by Fusarium, especially during growing seasons characterized by contrasting rainfall patterns. Therefore, this study was conducted to determine the impact of different soil moisture contents on root colonization of glyphosate‐treated soybean by Fusarium species. Glyphosate (0.84 kg ae ha?1) was applied to greenhouse‐grown glyphosate‐resistant (GR) soybean at the two to three trifoliate-leaf (V2–V3) growth stage growing in a Mexico silt loam at 27%, 13%, and 10% soil moisture contents. Soil and plant samples were sampled periodically after herbicide application and selectively cultured for Fusarium. Highest Fusarium colonization was associated with the glyphosate treatment, with maximum levels occurring at the highest soil moisture level. Thus, glyphosate interactions with root colonization by Fusarium in glyphosate‐resistant soybean are greatly influenced by soil moisture content.  相似文献   

10.
Application of glyphosate herbicide in genetically modified (GM) soybean [Glycine max (L.) Merrill] in soils with low zinc (Zn) concentration may interfere in the uptake of this and other nutrients, with negative impact on productivity. Thus, an experiment was conducted in greenhouse conditions on Ustoxix Quatzipsamment soil to investigate the effects of the interaction of glyphosate with Zn for the yield, photosynthesis, soil fertility and nutritional status of soybean. The treatments consisted of two soybean varieties [BRS 133 (conventional—NGM) and its essentially derived transgenic line BRS 245RR (GM) with and without glyphosate application] and five Zn rates (0, 5, 10, 20 and 40 mg kg?1, source zinc sulfate (ZnSO4)), with four replicates. Except for the copper (Cu) and iron (Fe) concentrations, the introduction of the herbicide-resistant gene is the predominant factor reducing nutrient uptake, photosynthetic (A) rate, stomatal conductance (Gs), leaf chlorophyll and ureide concentrations. The administration of Zn rates lowered the leaf phosphorus (P) concentration, and there was significant increase in Zn concentration in the soil and in the plant. Except for the 20 mg kg?1 of Zn rate, the use of the herbicide did not affect the shoot dry weight (SDW) and seed yield, and on average, the maximum seed yield was obtained with Zn concentrations of 26.4 and 18.7 mg kg?1 extracted by Mehlich 1 and diethylenetriaminepentaacetic acid-triethanolamine (DTPA-TEA), respectively.  相似文献   

11.
Glyphosate is the most widely used herbicide in the world, but its effects on non-target organisms, such as arbuscular mycorrhizal fungi (AMF), are unclear. No studies have been found that made reference to effects of glyphosate on AMF spore viability despite its importance as a source of propagules for the perpetuation and spread of AMF in the system. The objective of this study was to evaluate the effect of glyphosate application on AMF spore viability, and their ability to colonize roots. Soil samples were collected from a grassland area located in the Flooding Pampa region (Argentina). We evaluated three herbicide rates: 0, 0.26 and 1× recommended field rate, 10 and 30 days after application. Part of the soil from each tray was used to estimate the spore viability, and the remainder was used as substrate for growing Lolium multiflorum Lam. One month after sowing, total root colonization and percentage of arbuscules and vesicles were determined. The spore viability in herbicide untreated soils was between 5.8- and 7.7-fold higher than in treated soils. This reduction was detected even when the lower rate was applied. Root colonization was significantly lower in plants grown in glyphosate treated soil than in untreated ones. A decrease in arbuscular colonization (but not in vesicles) was found in plants grown in soils treated with the highest herbicide rate. That would indicate that symbiosis functionality was affected, given that arbuscules are the main site for host–fungus nutrient exchange. The results indicate that soil residence time of glyphosate and/or its degradation products was enough to reduce AMF spore viability and their ability to colonize roots. This decrease in propagules viability may affect plant diversity, taking into account the different degrees of mycorrhizal dependency between plant species that may coexist in grassland communities.  相似文献   

12.
Many legume plants benefit from the tripartite symbiosis of arbuscular mycorrhizal fungi (AMF) and rhizobia. Beneficial effects for the plant have been assumed to rely on increased P supply through the mycorrhizas. Recently, we demonstrated that P does not regulate the establishment of the tripartite symbiosis. Flavonoids appear to play a role as early signals for both rhizobia and AMF. Four soybean lines known to express different concentrations of the isoflavones genistein, daidzein and glycitein in the seed were used to test three hypotheses: (i) The establishment of the tripartite symbiosis is not dependent of a nutrient mediated effect; (ii) There is a positive correlation between seed isoflavone concentrations of different soybean lines and the progress of the tripartite symbiosis; (iii) Specific flavonoids control the establishment of the tripartite symbiosis in that a change in flavonoid root accumulation resulting from the development of one microbial partner can stimulate colonization of soybean roots by the other. Disturbed versus undisturbed soil treatments were produced to vary the potential for indigenous AMF colonization of soybean. In contrast, the potential for Bradyrhizobium was kept identical in both soil disturbance treatments. The uptake of P and Zn and the concentration of flavonoids in mycorrhizal soybean roots at 10 d after emergence were analysed either separately of Bradyrhizobium or in context of the tripartite symbiosis. Zinc nutrition did not differ between AMF treatments which supports the first hypothesis. The concentration of daidzein was at least four times greater in the root than in the seed reaching 3958±249 μg g−1 dry across soybean lines. Coumestrol, which was absent in the seed, was synthesized to reach 2154±64 μg g−1 dry. Conversely, the concentration of genistein was approximately three times smaller in the root that in the seed (301±15 μg g−1 dry), while glycitein and formononetin were never detected. The establishment of the tripartite symbiosis was identical across soybean lines which does not support the second hypothesis. Concentrations of flavonoids were significantly greater in roots under disturbed soil, for which both symbioses were not as developed as in plants from undisturbed soil. This clearly supports the third hypothesis. This research provides the first data linking the function of different flavonoids to the establishment of the tripartite symbiosis, and suggests that these compounds are produced and released into the rhizosphere as a function of the colonization process.  相似文献   

13.
The interactions between Phaseolus vulgaris, Rhizobium spp. strains nodulating P. vulgaris, and arbuscular mycorrhizal (AM) fungi were assessed under greenhouse conditions in a nonsterilized Typic Haplustalf soil from Cauca, Colombia. Our results indicate a specific involvement of AM fungal species in nitrogen acquisition by the legume plants from symbiotic nitrogen fixation and from soil. A significant specific influence of inoculation with Glomus spp. on the 15N/14N ratio in plant shoots was dependent on the inoculated rhizobial strain, but AM fungal inoculation had no significant effect on shoot dry weight or nodule occupancy in the two different rhizobial strain treatments. The results imply that in low P soils the effects of an improved mycorrhizal symbiosis may include improved symbiotic N2 fixation efficiency and/or improved soil N uptake. Received: 11 May 1996  相似文献   

14.
Legumes are prized for their seed protein and lipid mass fractions. Since legumes spend up to 4-16% of photosynthesis on each of the rhizobial and arbuscular mycorrhizal (AM) fungal symbioses, it might be expected that positive responses in yield due to rhizobial and AM symbioses are accompanied by decreases in seed protein and lipid mass fractions due to a photosynthate (C) limitation. We performed a meta-analysis of 348 data points from published studies with 12 legume species to test whether yield, harvest index, and seed protein and lipid mass fractions are affected by symbioses. There was a significant increase in yield due to rhizobial inoculation (16% in the field; 59% in pot experiments). There were no responses of yield to AM fungi and rhizobial + AM fungi inoculations in the field (presumably because an AM fungi-free control cannot be ensured), but significant responses in pots (45% with AM fungi; 44% with rhizobial + AM fungi). Rhizobial inoculation improved seed protein mass fraction by 7% in the field; AM fungi increased this parameter by 14% in pots. There were no discernable effects of symbioses on seed lipid mass fraction. Rhizobial symbioses in the field increased harvest index (+5%), but AM fungi did not affect harvest index. In conclusion, increases in yield due to symbioses also resulted in increases in seed protein and constant lipid mass fractions, indicating that legumes are not C-limited under symbiotic conditions.  相似文献   

15.
A salinity-tolerant strains of Rhizohium able to grow and fix nitrogen in symbiosis with lentil (Lens esculenta) in saline soil was derived frorn effective Rhizobium strain RL 5. A forced mutation with the mutagen nitrosoguanidine resulted in the isolation of five different mutant strains. The salinity tolerance, streptomycin resistance, growth, nodulation behaviour and relative efficiency of symbiotic N2-fixation of these strains were studied. Among the five mutants and parent, LM 4 and LM 1 successfully tolerated 200 μ g ml?1 streptomycin and 1.5%NaCl. These two mutants also significantly increased number and dry weight of nodules per plant, dry matter yield of the crop and N2-fixation. Between the two, LM 4 seemed generally the better.  相似文献   

16.
N2-fixation by free-living (diazotrophic) microorganism is a key process affecting ecosystem functioning in soils. Understanding drivers affecting diazotrophic community assemblages and activities may lead to management practices to increase primary production and/or environmental sustainability. We used PCR-DGGE to determine the fundamental relationships between diazotrophic community structure and in a wide range of soils across southern Australia. In addition qPCR, RT-qPCR and N2-fixation (acetylene reduction) were used to investigate factors influencing gene abundance, expression and processes in similar soils with different agricultural inputs. Across 22 soils, the structural composition of the nifH community was significantly influenced by site (ANOSIM R = 0.876; P = 0.001). The effects of management practices were evident, and often larger than between-soil differences, but were only present at some sites. Differences in nifH communities between sites correlated to particulate organic carbon (POC; measured by mid-infrared spectroscopy) content of the soils (BIO-ENV test; ρ = 0.502; P = 0.001), but not other factors including total soil C. In 3 soils from the Murrumbidgee irrigation region of NSW, intensification of the farming systems was associated with increasing N2-fixation (P < 0.05), except where rice was cultivated. N2-fixation correlated either with nifH abundance or gene expression in soils, but not both. Our data shows that soil C is closely linked to diazotrophic ecology. Principally, the amount of C entering the soil system is directly related to the abundance and N2-fixation activity of free-living bacteria. However, we also show that C in the POC pool has associative links to the genetic diversity of the soil diazotroph community. Given the importance of diversity and abundance of functional organisms in supporting ecosystem processes, we suggest that soil C inputs should be considered for both qualitative and quantitative properties when considering impacts on diazotrophic bacterial ecology.  相似文献   

17.
Soil stresses such as salinity and acidity may adversely affect nitrogen (N)2-fixation. The hypothesis of this study is that soil salinity and acidity inhibit soybean [Glycine max (L.) Merr.] nodulation and N2-fixation due to, at least in part, disruption of the signal exchange process. The objectives were: 1) to determine the effects of stressful soil salinity and acidity on the signal exchange processes between soybean and Bradyrhizobium japonicum, and 2) to determine whether or not the addition of signal molecule genistein to B. japonicum can overcome at least part of the inhibition of nodulation, caused by stressful soil salinity and acidity. Salt (sodium chloride) and sulfur (S) were applied. Genistein (0, 5, and 20μ M) was tested. Genistein addition could partially overcome the salt and acidity stresses by increasing soybean yields up to 21% and 23%, respectively. These novel findings may be very useful for planting soybean under salinity and acidity stresses.  相似文献   

18.
Atmospheric nitrogen that is fixed by associative cyanobacteria can be released into the surrounding soil environment providing a key source of N for arctic ecosystems. Yet, little is known about nitrogen fixation by Biological Soil Crusts (BSCs) within hummock-hollow complexes that are typical of many arctic environments. In this study, we examined spatial and temporal patterns in N2-fixation, dinitrogenase reductase (nifH) gene abundance and release of N in a low arctic hummock-hollow ecosystem. The impacts of cyanobacteria on N status in soil were evaluated by assessing soil nitrogen in relation to the cyanobacterial associations found on Hummock and Hollow BSCs. In addition, potential P limitation of N2-fixation by cyanobacteria was assessed for Hummock and Hollow BSCs. The tops of hummocks and the bottoms of hollows were areas of high N2-fixation, whereas minimal N2-fixation occurred on the sides of hummock-hollow complexes. Compared with Hummock BSCs, Hollow BSCs had a higher mean growing season N2-fixation rate, a higher mean growing season nifH abundance, a higher mean total %N and δ15N values closer to that of atmospheric N2. Soil N status was linked to rates of N2-fixation by BSCs indicating that these N2-fixing associations act as important point sources of soil N in this low arctic ecosystem. Over the course of a growing season temporal variation in N2-fixation and nifH abundance were weakly linked suggesting that N2-fixation was carried out by complex communities of diazotrophic microorganisms and that factors such as nutrient availability may limit N2-fixation to a greater extent than nifH abundance.  相似文献   

19.
Easy observation methods to assess the colonization levels of arbuscular mycorrhizal (AM) fungi in plant roots are crucial for studying the biology of AM symbiosis and for considering agricultural use. Many AM studies employ Trypan Blue (TB) coupled with lactic acid to stain AM fungal structures as bright-field images; however, TB staining can be difficult to use owing to its noxiousness and high viscosity. Here, we report the development of an easy method for visualizing AM fungal structures as bright-field images using 3,3′-diaminobenzidine (DAB). Wheat germ agglutinin (WGA)-conjugated horseradish peroxidase (HRP), which specifically targets N-acetylglucosamine polymers and detects AM fungal cell walls, penetrated the cortical layers of 10% potassium hydroxide (KOH)-treated soybean roots and stained AM fungal mycelia in the presence of DAB and hydrogen peroxide (H2O2). Comparison between DAB and TB staining of soybean (Glycine max L.) roots suggested that the intactness of root systems and image contrast using DAB staining were superior. Background signals in stele observed by DAB staining were negligible as compared with those observed by WGA-fluorescein isothiocyanate staining. DAB staining, which combines the advantages of TB (easy bright-field imaging) and WGA-fluorophore (specific and high-quality) staining, provides a robust imaging method for macro- and micro-level analyses of AM roots and is applicable to at least six crops: soybean, onion (Alium cepa L.), potato (Solanum tuberosum L.), maize (Zea mays L.), rice (Oryza sativa L.), and sunflower (Helianthus annuus L.).  相似文献   

20.
Abstract

The roots of soybean (Glycine max [L.] Merr.) establish symbiosis with nodule-inducing rhizobia and arbuscular mycorrhizal (AM) fungi. The existing nodules systemically suppress subsequent nodule formation, a phenomenon known as autoregulation. Grafting experiments revealed that some forms of autoregulation are controlled by the shoot. In the present study, we examined shoot-controlled regulation of AM fungal colonization using a reciprocal grafting technique. Ten-day-old seedlings of wild-type soybean cv. Enrei and its hypernodulating mutant En6500 were cut below the cotyledons and the shoots were grafted to self or reciprocal roots. Grafted seedlings were inoculated with Bradyrhizobium japonicum and Gigaspora rosea and grown in a glasshouse for 60 days. The arbuscule abundance of the En6500 (shoot)/En6500(root) graft was 1.5-fold higher than that of the Enrei/Enrei graft. In grafts between Enrei and En6500, an increased arbuscule abundance was detected only when En6500 was used as the shoot. The arbuscule abundance of Enrei/En6500 when Enrei was used as the shoot was comparable to that of Enrei/Enrei. The intensity of AM fungal colonization was lower in Enrei/En6500 than in the other grafting treatments. From the results obtained, we suggest that soybean shoots systemically control arbuscule formation in both AM symbiosis and nodule formation.  相似文献   

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