AM真菌对留兰香和常夏石竹耐盐性的影响

为探究接种丛枝菌根(arbuscular mycorrhiza,AM)真菌对不同盐胁迫水平下留兰香和常夏石竹侵染特性与生理指标的影响,该研究采用盆栽试验的方法,将留兰香和常夏石竹分为接种处理与对照处理,并施加不同浓度(0、50、100、150、200 mmol/L)的NaCl胁迫,胁迫结束后测定两种植物的侵染特性与生理...     

Arbuscular mycorrhizal inoculation improves growth and antioxidative response of Jatropha curcas (L.) under Na2SO4 salt stress

This study investigated the effect of arbuscular mycorrhizal (AM) fungal consortia on growth, photosynthetic pigments, solutes concentration (e.g., sugars and proline), and antioxidant responses at different levels of Na₂SO₄ stress (0–0.5%, w:w) in potted culture of Jatropha. Results showed that increasing salt levels caused a significant reduction in survival (%), growth parameters, leaf relative water content (LRWC) (%), and chlorophyll content with an increase in electrolyte leakage (%) and lipid peroxidation of membranes of Jatropha. AM inoculation improved biomass yields as well as other physiological parameters (LRWC (%), chlorophyll, proline, and soluble sugar) of salt-stressed Jatropha over noninoculated plants. Tolerance index of Jatropha was higher with AM fungi than without at all salt levels; however, a decline in its value was recorded with increased salinity levels. AM inoculation also enhanced the activities of antioxidant enzymes (e.g., superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione reductase) and decreased oxidative damage to lipids. In conclusion, results indicate that AM inoculation was capable of alleviating the damage caused by salinity stress on Jatropha plants by reducing lipid peroxidation of membrane and membrane permeability and increasing the accumulation of solutes and antioxidant enzyme activity.     

Synergistic interactions of arbuscular mycorrhizal fungi and rhizobia promoted the growth of <Emphasis Type="Italic">Lathyrus sativus</Emphasis> under sulphate salt stress

In order to examine the influence of microsymbionts on plants, arbuscular mycorrhizal (AM) fungi and rhizobia were used to examine the growth of Lathyrus sativus under sulphate salt stress. Seedlings of L. sativus were inoculated with a combination of selected microsymbionts. Plants were grown under greenhouse conditions with five Na₂SO₄ concentrations (0, 1%, 2%, 3% and 4% (weight : weight)). The inoculations combinations used were the AM fungus, Glomus mosseae and/or the rhizobium, Mesorhizobium mediterraneum. The results showed that sulphate salinity inhibited plant growth and biomass production. However, compared with the control treatments, dual-inoculation of G. mosseae and M. mediterraneum reduced the harmful influence of sulphate salinity. Parmeters including plant height, the extent of AM colonization, total biomass, nodules biomass, P concentration, N concentration and proline concentration confirmed that dual inoculation plays a vital role in promoting the growth of L. sativus under sulphate salt stress. The results suggested that the use of this dual inoculation could be exploited in grassland plantation establishment and in pastoral ecosystem reclamation programmes in arid and semi-arid areas subject to moderate salt contamination.     

Mycorrhizal associations of an invasive tree are enhanced by both genetic and environmental mechanisms

Biotic interactions involving exotic plants in their introduced ranges may differ from those of co‐occurring plant species and from interactions in their native ranges. When interactions are less negative, or more positive compared to native plant species, this may increase invasion success, and differences among ranges may cause changes in exotic plant traits. Here, we investigated arbuscular mycorrhizae (AM) associated with Triadica sebifera seedlings from populations in native (China) and introduced ranges (US) and with seedlings from US and China species within three co‐occurring genera (Liquidambar, Ulmus, Celtis) grown in multiple common gardens in both ranges. No general pattern of higher or lower AM colonization was found in the introduced range for China and US Celtis, Liquidambar, or Ulmus species. However, AM colonization was significantly higher for Triadica than for other genera, particularly in the introduced range, suggesting AM may improve Triadica's invasion success. Triadica AM colonization was higher in US than China gardens, decreased with increasing soil nitrogen in China, but was independent of soil nitrogen in the US. This might reflect a different effect of soil fertility on this mutualism among ranges. Introduced Triadica populations had higher AM colonization than native populations, particularly in US gardens, implying a possible advantage from greater AM association in the introduced range. This is the first field study demonstrating post‐introduction changes in mycorrhizal colonization of an invasive species. It indicates that there are ecological and evolutionary components to the effect of positive interactions on plant invasions.     

The differential behavior of arbuscular mycorrhizal fungi in interaction with Astragalus sinicus L. under salt stress

Three arbuscular mycorrhizal (AM) fungi (Glomus mosseae, Glomus claroideum, and Glomus intraradices) were compared for their root colonizing ability and activity in the root of Astragalus sinicus L. under salt-stressed soil conditions. Mycorrhizal formation, activity of fungal succinate dehydrogenase, and alkaline phosphatase, as well as plant biomass, were evaluated after 7 weeks of plant growth. Increasing the concentration of NaCl in soil generally decreased the dry weight of shoots and roots. Inoculation with AM fungi significantly alleviated inhibitory effect of salt stress. G. intraradices was the most efficient AM fungus compared with the other two fungi in terms of root colonization and enzyme activity. Nested PCR revealed that in root system of plants inoculated with a mix of the three AM fungi and grown under salt stress, the majority of mycorrhizal root fragments were colonized by one or two AM fungi, and some roots were colonized by all the three. Compared to inoculation alone, the frequency of G. mosseae in roots increased in the presence of the other two fungal species and highest level of NaCl, suggesting a synergistic interaction between these fungi under salt stress.     

Functional study of a salt‐inducible TaSR gene in Triticum aestivum

The gene expression chip of a salt‐tolerant wheat mutant under salt stress was used to clone a salt‐induced gene with unknown functions. This gene was designated as TaSR (Triticum aestivum salt‐response gene) and submitted to GenBank under accession number EF580107. Quantitative polymerase chain reaction (PCR) analysis showed that gene expression was induced by salt stress. Arabidopsis and rice (Oryza sativa) plants expressing TaSR presented higher salt tolerance than the controls, whereas AtSR mutant and RNA interference rice plants were more sensitive to salt. Under salt stress, TaSR reduced Na⁺ concentration and improved cellular K⁺ and Ca²⁺ concentrations; this gene was also localized on the cell membrane. β‐Glucuronidase (GUS) staining and GUS fluorescence quantitative determination were conducted through fragmentation cloning of the TaSR promoter. Salt stress‐responsive elements were detected at 588–1074 bp upstream of the start codon. GUS quantitative tests of the full‐length promoter in different tissues indicated that promoter activity was highest in the leaf under salt stress. Bimolecular fluorescence complementation and yeast two‐hybrid screening further showed the correlation of TaSR with TaPRK and TaKPP. In vitro phosphorylation of TaSR and TaPRK2697 showed that TaPRK2697 did not phosphorylate TaSR. This study revealed that the novel TaSR may be used to improve plant tolerance to salt stress.     

Arbuscular mycorrhizal fungi native from a Mediterranean saline area enhance maize tolerance to salinity through improved ion homeostasis

Soil salinity restricts plant growth and productivity. Na⁺ represents the major ion causing toxicity because it competes with K⁺ for binding sites at the plasma membrane. Inoculation with arbuscular mycorrhizal fungi (AMF) can alleviate salt stress in the host plant through several mechanisms. These may include ion selection during the fungal uptake of nutrients from the soil or during transfer to the host plant. AM benefits could be enhanced when native AMF isolates are used. Thus, we investigated whether native AMF isolated from an area with problems of salinity and desertification can help maize plants to overcome the negative effects of salinity stress better than non‐AM plants or plants inoculated with non‐native AMF. Results showed that plants inoculated with two out the three native AMF had the highest shoot dry biomass at all salinity levels. Plants inoculated with the three native AMF showed significant increase of K⁺ and reduced Na⁺ accumulation as compared to non‐mycorrhizal plants, concomitantly with higher K⁺/Na⁺ ratios in their tissues. For the first time, these effects have been correlated with regulation of ZmAKT2, ZmSOS1 and ZmSKOR genes expression in the roots of maize, contributing to K⁺ and Na⁺ homeostasis in plants colonized by native AMF.     

Salt glands of recretohalophyte Tamarix under salinity: Their evolution and adaptation

Here, we studied the evolution of salt glands in 11 species of Tamarix and determined their role in adaptation to saline environments by measuring the effect of NaCl on plant growth and salt gland characteristics. Cluster analysis divided Tamarix species into three types (types I–III) according to salt‐gland characteristics. A phylogenetic tree based on ITS sequences indicated an evolutionary relationship consistent with the geographical distribution of Tamarix. We measured growth under different NaCl conditions (0, 100, 200, and 300 mM) for 40 days in three species (T. gallica, T. ramosissima, and T. laxa) representing the three Tamarix types. With increasing NaCl concentration, the biomass of all species was significantly reduced, especially that of T. gallica. Salt secretion ability and salt‐gland density showed similar trends in three types. The order of salt tolerance was type I > type II > type III. We conclude that during Tamarix adaptation to salinity, salt‐gland evolution followed two directions: one increasing salt‐gland density, and the other increasing salt secretion rate per salt‐gland. This study provides a basis for potential mechanisms of recretohalophyte adaptation to salinity.     

In vitro rapid regeneration of plantlets from nodal explants of Mucuna pruriens– a valuable medicinal plant

A rapid and efficient protocol for the large‐scale propagation of a potential medicinal plant, Mucuna pruriens, through in vitro culture of nodal segment explants obtained from 15‐day‐old aseptic seedlings is described. Of the three different cytokinins, 6‐benzyladenine (BA), kinetin (Kin) and 2‐isopentenyl adenine (2‐iP) evaluated as supplements to Murashige and Skoog (MS) medium, BA at an optimal concentration of 5.0 μM was effective in inducing multiple shoots. Strength of the basal media also influenced the efficiency of shoot regeneration. The frequency of shoot regeneration tended to increase when the salt concentration in the basal media was reduced. Highest number of multiple shoots (23.3) and maximum average length (5.6 cm) were standardised on half‐strength MS medium supplemented with 5.0 μM BA along with 0.5 μM α‐naphthalene acetic acid (NAA) at pH 5.8. Rooting was best induced in shoots excised from proliferated shoot cultures on MS medium augmented with an optimal concentration of 1.0 μM indole‐3‐butyric acid (IBA). The in vitro‐raised plantlets with well‐developed shoots and roots were successfully established in earthen pots containing garden soil and were grown in greenhouse with 90% survival rate. The results of this study provide the first report on in vitro plant regeneration of M. pruriens.     

Arbuscular mycorrhizal fungi enhance root cadmium and copper accumulation in the roots of the salt marsh plant Aster tripolium L.

It is known that vegetation plays an important role in the retention of heavy metals in salt marshes by taking up and accumulating the metals. In this study, we investigated whether arbuscular mycorrhizal fungi (AMF) increase Cd and Cu uptake and accumulation in the root system of the salt marsh species Aster tripolium L., and whether indigenous AMF isolated from polluted salt marshes have higher capacity to resist and alleviate metal stress in A. tripolium than isolates of the same species originated from non-polluted sites. Plants inoculated with Glomus geosporum, either isolated from a polluted salt marsh site (PL isolate) or from a non-polluted site (NP isolate), and non-mycorrhizal (NM) plants were compared in a pot experiment at four different Cd and Cu concentrations. Cd had no effect in root colonization, whereas high concentrations of Cu decreased colonization level in plants inoculated with the NP isolate. AM colonization did not increase plant dry weight or P concentration but influenced root Cd and Cu concentrations. Inoculation with PL and NP isolates enhanced root Cd and Cu concentrations, especially at highest metal addition levels, as compared to NM plants, without increasing shoot Cd and Cu concentrations. There was no evidence of intraspecific variation in the effects between AMF isolated from polluted and non-polluted sites, since there were no differences between plants inoculated with PL or NP isolate in any of the tested plant variables. The results of this study showed that AMF enhance metal accumulation in the root system of A. tripolium, suggesting a contribution of AMF to the sink of metals within vegetation in the salt marshes.     

Profilin 1 is required for abscission during late cytokinesis of chondrocytes

Profilins are key factors for dynamic rearrangements of the actin cytoskeleton. However, the functions of profilins in differentiated mammalian cells are uncertain because profilin deficiency is early embryonic lethal for higher eukaryotes. To examine profilin function in chondrocytes, we disrupted the profilin 1 gene in cartilage (Col2pfn1). Homozygous Col2pfn1 mice develop progressive chondrodysplasia caused by disorganization of the growth plate and defective chondrocyte cytokinesis, indicated by the appearance of binucleated cells. Surprisingly, Col2pfn1 chondrocytes assemble and contract actomyosin rings normally during cell division; however, they display defects during late cytokinesis as they frequently fail to complete abscission due to their inability to develop strong traction forces. This reduced force generation results from an impaired formation of lamellipodia, focal adhesions and stress fibres, which in part could be linked to an impaired mDia1‐mediated actin filament elongation. Neither an actin nor a poly‐proline binding‐deficient profilin 1 is able to rescue the defects. Taken together, our results demonstrate that profilin 1 is not required for actomyosin ring formation in dividing chondrocytes but necessary to generate sufficient force for abscission during late cytokinesis.     

Two Lotus japonicus symbiosis mutants impaired at distinct steps of arbuscule development

Arbuscular mycorrhiza (AM) fungi form nutrient‐acquiring symbioses with the majority of higher plants. Nutrient exchange occurs via arbuscules, highly branched hyphal structures that are formed within root cortical cells. With a view to identifying host genes involved in AM development, we isolated Lotus japonicus AM‐defective mutants via a microscopic screen of an ethyl methanesulfonate‐mutagenized population. A standardized mapping procedure was developed that facilitated positioning of the defective loci on the genetic map of L. japonicus, and, in five cases, allowed identification of mutants of known symbiotic genes. Two additional mutants representing independent loci did not form mature arbuscules during symbiosis with two divergent AM fungal species, but exhibited signs of premature arbuscule arrest or senescence. Marker gene expression patterns indicated that the two mutants are affected in distinct steps of arbuscule development. Both mutants formed wild‐type‐like root nodules upon inoculation with Mesorhizobium loti, indicating that the mutated loci are essential during AM but not during root nodule symbiosis.     

On the mechanisms of cadmium stress alleviation in Medicago truncatula by arbuscular mycorrhizal symbiosis: A root proteomic study

The arbuscular mycorrhizal (AM) symbiosis belongs to the strategies plants have developed to cope with adverse environmental conditions including contamination by heavy metals such as cadmium (Cd). In the present work, we report on the protective effect conferred by AM symbiosis to the model legume Medicago truncatula grown in presence of Cd, and on the 2‐D‐based proteomic approach further used to compare the proteomes of M. truncatula roots either colonised or not with the AM fungus Glomus intraradices in Cd‐free and Cd‐contaminated substrates. The results indicated that at the proteome level, 9 out of the 15 cadmium‐induced changes in nonmycorrhizal roots were absent or inverse in those Cd‐treated and colonized by G. intraradices, including the G. intraradices‐dependent down‐accumulation of Cd stress‐responsive proteins. Out of the twenty‐six mycorrhiza‐related proteins that were identified, only six displayed changes in abundance upon Cd exposure, suggesting that part of the symbiotic program, which displays low sensitivity to Cd, may be recruited to counteract Cd toxicity through the mycorrhiza‐dependent synthesis of proteins having functions putatively involved in alleviating oxidative damages, including a cyclophilin, a guanine nucleotide‐binding protein, an ubiquitin carboxyl‐terminal hydrolase, a thiazole biosynthetic enzyme, an annexin, a glutathione S‐transferase (GST)‐like protein, and a S‐adenosylmethionine (SAM) synthase.     

Enhanced tolerance of photosynthesis against high temperature damage in salt-adapted halophyte Atriplex centralasiatica plants

Thermotolerance of photosynthesis in salt‐adapted Atriplex centralasiatica plants (100–400 mm NaCl) was evaluated in this study after detached leaves and whole plants were exposed to high temperature stress (30–48 °C) either in the dark or under high light (1200 mol m^?2 s^?1). In parallel with the decrease in stomatal conductance, intercellular CO₂ concentration and CO₂ assimilation rate decreased significantly with increasing salt concentration. There was no change in the maximal efficiency of PSII photochemistry (F_v/F_m) with increasing salt concentration, suggesting that there was no damage to PSII in salt‐adapted plants. On the other hand, there was a striking difference in the response of PSII and CO₂ assimilation capacity to heat stress in non‐salt‐adapted and salt‐adapted leaves. Leaves from salt‐adapted plants maintained significantly higher F_v/F_m values than those from non‐salt‐adapted leaves at temperatures higher than 42 °C. The F_v/F_m differences between non‐salt‐adapted and salt‐adapted plants persisted for at least 24 h following heat stress. Leaves from salt‐adapted plants also maintained a higher net CO₂ assimilation rate than those in non‐salt‐adapted plants at temperatures higher than 42 °C. This increased thermotolerance was independent of the degree of salinity since no significant changes in F_v/F_m and net CO₂ assimilation rate were observed among the plants treated with different concentrations of NaCl. The increased thermotolerance of PSII induced by salinity was still evident when heat treatments were carried out under high light. Given that photosynthesis is considered to be the physiological process most sensitive to high temperature damage, increased thermotolerance of photosynthesis may be of significance since A. centralasiatica, a typical halophyte, grows in the high salinity regions in the north of China, where the temperature in the summer is often as high as 45 °C.     

Mycorrhizal colonization alleviates drought-induced oxidative damage and lignification in the leaves of drought-stressed perennial ryegrass (Lolium perenne)

To investigate the effects of arbuscular mycorrhizal (AM) fungus Glomus intraradices on antioxidative activity and lignification under drought‐stressed (DS) conditions, the enzyme activities, growth, lignin contents and some stress symptomatic parameters as affected by drought treatment were compared in AM colonized or non‐colonized (non‐AM) perennial ryegrass plants for 28 days. Drought significantly decreased leaf water potential (Ψ_w), photosynthesis rate and biomass. The negative impact of drought on these parameters was much highly relived in AM plants compared to non‐AM ones. Drought increased H₂O₂, lipid peroxidation, phenol and lignin levels, with significantly higher in non‐AM relative to AM plants at day 28 after drought treatment. The enhanced activation of guaiacol peroxidase (GPOX), coniferyl alcohol peroxidase (CPOX), syringaldazine peroxidase (SPOX) and polyphenol oxidase (PPO) was closely related with the decrease in Ψ_w in both AM and non‐AM plants. GPOX, CPOX, SPOX and PPO highly activated with a concomitant increase in lipid peroxidation and lignin as the Ψ_w decreased below ?2.11 MPa in non‐AM plants, while much less activated by maintaining Ψ_w≥?1.15 MPa in AM ones. These results indicate that AM symbiosis plays an integrative role in drought stress tolerance by alleviating oxidative damage and lignification, which in turn mitigate the reduction of forage growth and digestibility under DS conditions.     

Refining trophic dynamics through multi‐factor Bayesian mixing models: A case study of subterranean beetles

Food web dynamics are vital in shaping the functional ecology of ecosystems. However, trophic ecology is still in its infancy in groundwater ecosystems due to the cryptic nature of these environments. To unravel trophic interactions between subterranean biota, we applied an interdisciplinary Bayesian mixing model design (multi‐factor BMM) based on the integration of faunal C and N bulk tissue stable isotope data (δ¹³C and δ¹⁵N) with radiocarbon data (Δ¹⁴C), and prior information from metagenomic analyses. We further compared outcomes from multi‐factor BMM with a conventional isotope double proxy mixing model (SIA BMM), triple proxy (δ¹³C, δ¹⁵N, and Δ¹⁴C, multi‐proxy BMM), and double proxy combined with DNA prior information (SIA + DNA BMM) designs. Three species of subterranean beetles (Paroster macrosturtensis, Paroster mesosturtensis, and Paroster microsturtensis) and their main prey items Chiltoniidae amphipods (AM1: Scutachiltonia axfordi and AM2: Yilgarniella sturtensis), cyclopoids and harpacticoids from a calcrete in Western Australia were targeted. Diet estimations from stable isotope only models (SIA BMM) indicated homogeneous patterns with modest preferences for amphipods as prey items. Multi‐proxy BMM suggested increased—and species‐specific—predatory pressures on amphipods coupled with high rates of scavenging/predation on sister species. SIA + DNA BMM showed marked preferences for amphipods AM1 and AM2, and reduced interspecific scavenging/predation on Paroster species. Multi‐factorial BMM revealed the most precise estimations (lower overall SD and very marginal beetles' interspecific interactions), indicating consistent preferences for amphipods AM1 in all the beetles' diets. Incorporation of genetic priors allowed crucial refining of the feeding preferences, while integration of more expensive radiocarbon data as a third proxy (when combined with genetic data) produced more precise outcomes but close dietary reconstruction to that from SIA + DNA BMM. Further multidisciplinary modeling from other groundwater environments will help elucidate the potential behind these designs and bring light to the feeding ecology of one the most vital ecosystems worldwide.