Salt tolerance conferred by overexpression of Arabidopsis vacuolar Na+/H+ antiporter gene AtNHX1 in common buckwheat (Fagopyrum esculentum)

Agriculture productivity is severely affected by soil salinity. One possible mechanism by which plants could survive salt stress is to compartmentalize sodium ions away from the cytosol. In the present work, transgenic buckwheat plants overexpressing AtNHX1, a vacuolar Na⁺/H⁺ antiporter gene from Arabidopsis thaliana, were regenerated after transformation with Agrobacterium tumefaciens. These plants were able to grow, flower and accumulate more rutin in the presence of 200 mmol/l sodium chloride. Moreover, the content of important nutrients in buckwheat was not affected by the high salinity of the soil. These results demonstrated the potential value of these transgenic plants for agriculture use in saline soil.     

Earthworm survival in oil contaminated soil

Earthworms are an important component of the soil biota and their response to oil pollution needs to be better understood. Laboratory investigations were undertaken to determine the concentrations of crude oil in soil that leads to death of Lumbricus terrestris and Eisenia fetida and to determine the propensity of L. terrestris to move away from contaminated soil. Clemville sandy clay loam was amended to contain maximum oil contents of 1.5 – 2.5% depending on the particular experiment. Additionally, the ability of L. terrestristo survive in bioremediated oil-contaminated soil was evaluated. An oil content of 0.5% was not harmful to survival of earthworms for 7 d but an oil concentration of 1.5% reduced survival to less than 40%. Bioremediated soil containing 1.2% oil did not reduce survival of L. terrestrisduring 10 d. Survival of L. terrestrisin unweathered oil was improved when free movement between contaminated and uncontaminated soil was possible. Casts of earthworms exposed to oil-containing soil contained 0.2% total petroleum hydrocarbons. An allowable regulatory level of 1% oil contamination in soil may not allow for survival of earthworms.     

Field persistence of the entomopathogenic nematode <Emphasis Type="Italic">Heterorhabditis bacteriophora</Emphasis> in different crops

To investigate nematode establishment and persistence, dauer juveniles (DJs) of Heterorhabditis bacteriophora were applied at 50 cm^-2 in different crops in June and July with conventional spraying equipment and 420 l water ha^-1. Application hardly had any effects on survival and infectivity. The number of DJs reaching the soil was assessed and the establishment and persistence recorded by baiting soil samples with larvae of the wax moth Galleria mellonella. The better the plant canopy was developed the fewer DJs reached the soil during application. Whereas in pasture 77% and in potatoes 78% of the applied nematodes reached the soil, in wheat and peas little less than 50%, in oil-seed rape only 5% and in lupine 6% were recorded. Between 50 and 60% of the soil samples contained H. bacteriophora a month after application with the exception of wheat (>90%) and potatoes (<5%) indicating that the number of nematodes reaching the soil during application had no influence on their establishment in the soil. Probably DJs can survive in the plant canopy and reach the soil later after application. The percentage of nematode-positive soil samples dropped considerably after tillage. In potatoes no nematodes were recovered after two months, which probably was also due to the intensive movement of the soil. Although nematodes are susceptible to freezing, temperatures below 0°C during the winter did not extinguish the H. bacteriophora population. In field crops EPN usually persisted not much longer than one year. The longest persistence of H. bacteriophora was detected 23 months after release in beans followed in rotation by wheat with red clover as cover crop. In this field larvae of the pea weevil Sitona lineatus (Coleoptera: Curculionidae) were detected in soil samples and found infected with the released nematode population. In the laboratory the field soils were tested for persistence of H. bacteriophora at 8°C and a half-life of 24.8 days was recorded in the absence of host insects and plants. Thus long-term persistence in the field was a result of recycling in host insects, which could not be detected in other crops than beans and clover. As H. bacteriophora seems to be restricted in its host potential, this species disappears after release once the host population is not available anymore.     

Toxicity degradation of waste soil from a chlor-alkali factory byAzolla pinnata Lam

Cultures ofAzolla pinnata Lam., grown in various mixtures of soil plus industrial waste from a chlor-alkali factory for 30 to 60 days, resulted in the addition of significant amounts of nitrogen and organic carbon to the growing medium. A considerable decrease in the alkaline pH of the waste/soil was also recorded. On transplantation of rice seedlings into the waste/soil mixtures, after 60 days of Azolla culture it was observed that the rice survived and continued to grow in mixtures containing 30% waste whereas, in control conditions, seedlings failed to survive in above 15% waste/soil combinations.     

Ecophysiological observations on Drosophyllum lusitanicum

The carnivorous plant Drosophyllum lusitanicum inhabits heathland and ruderal sites in Portugal, Spain and Morocco. In the literature, various theories have been discussed concerning the ability of Drosophyllum to survive the annual dry period in summer. In August 2004, we examined: (1) the microclimate, (2) soil parameters and (3) the physiological conditions of the plants on two sites in Portugal and Spain. First, during the day, plants are exposed to very high air and soil temperatures and very low air humidity. The climatic extremes are not significantly softened by the population, only the wind speed is drastically decreased. During the night, on the other hand, very high air humidity and dew formation could be observed. The harsh climate is accompanied by stressful soil conditions. Second, the soil is completely dry, poor in fine earth, calcium and nutrients and more or less acid. Third, in spite of these climatic and edaphic extremes, all plants were green, produced trapping mucilage and caught numerous animals. Far from being affected by these conditions, Drosophyllum showed even better growth and reproduction on more extreme sites. We analysed the root system and found living fine roots missing. The osmotic value of the plants is rather low and water storage organs are absent. Therefore we conclude that in summer Drosophyllum is nourished by the dew at night.     

Growth of Rhizobium sp. in the presence of catechol

The ability of Rhizobium sp., isolated from Lablab purpureus to survive in soil containing a phenolic derivative catechol was investigated. It survived for 9 months in soil containing catechol. In synthetic medium, Rhizobium sp. utilized catechol up to 10 mM as sole carbon source and catechol 1, 2-dioxygenase was present in the catechol grown cells. In the presence of organic acids and sugars, catechol was co-metabolized; but catechol 1, 2-dioxygenase induction was inhibited. The ability of Rhizobium sp. to utilize various phenolic substances provides potential advantage to overcome the phenolic toxicants present in soils.     

Arbuscular mycorrhizal fungi and plant symbiosis in a saline-sodic soil

The seasonality of arbuscular mycorrhizal (AM) fungi–plant symbiosis in Lotus glaber Mill. and Stenotaphrum secundatum (Walt.) O.K. and the association with phosphorus (P) plant nutrition were studied in a saline-sodic soil at the four seasons during a year. Plant roots of both species were densely colonized by AM fungi (90 and 73%, respectively in L. glaber and S. secundatum) at high values of soil pH (9.2) and exchangeable sodium percentage (65%). The percentage of colonized root length differed between species and showed seasonality. The morphology of root colonization had a similar pattern in both species. The arbuscular colonization fraction increased at the beginning of the growing season and was positively associated with increased P concentration in both shoot and root tissue. The vesicular colonization fraction was high in summer when plants suffer from stress imposed by high temperatures and drought periods, and negatively associated with P in plant tissue. Spore and hyphal densities in soil were not associated with AM root colonization and did not show seasonality. Our results suggest that AM fungi can survive and colonize L. glaber and S. secundatum roots adapted to extreme saline-sodic soil condition. The symbiosis responds to seasonality and P uptake by the host altering the morphology of root colonization.     

<Emphasis Type="Italic">Agrobacterium</Emphasis>-<Emphasis Type="Italic">tumefaciens</Emphasis>-mediated transformation of<Emphasis Type="Italic"> Helminthosporium turcicum</Emphasis>, the maize leaf-blight fungus

Agrobacterium tumefaciens has the ability to transfer its T-DNA to plants, yeast, filamentous fungi, and human cells and integrate it into their genome. Conidia of the maize pathogen Helminthosporium turcicum were transformed to hygromycin B resistance by a Agrobacterium-tumefaciens-mediated transformation system using a binary plasmid vector containing the hygromycin B phosphotransferase (hph) and the enhanced green fluorescent protein (EGFP) genes controlled by the gpd promoter from Agaricus bisporus and the CaMV 35S terminator. Agrobacterium-tumefaciens-mediated transformation yielded stable transformants capable of growing on increased concentrations of hygromycin B. The presence of hph in the transformants was confirmed by PCR, and integration of the T-DNA at random sites in the genome was demonstrated by Southern blot analysis. Agrobacterium-tumefaciens-mediated transformation of Helminthosporium turcicum provides an opportunity for advancing studies of the molecular genetics of the fungus and of the molecular basis of its pathogenicity on maize.     

The population of the hypogeous fungus<Emphasis Type="Italic"> Tuber aestivum</Emphasis> syn.<Emphasis Type="Italic"> T. uncinatum</Emphasis> on the island of Gotland

The aim of our study was to examine the genetic variation within Tuber aestivum on the Baltic island of Gotland, Sweden. Variation in such a limited geographical area should help illuminate the dispersal abilities of T. aestivum. Knowledge of the genetic variation in this northern outpost could also be useful in the selection of inoculum for the establishment of truffle orchards. Genetic structure and homogeneity of the population were studied using principal component and parsimony analyses of randomly amplified polymorphic DNA data. Our inventories showed that T. aestivum is abundantly distributed in suitable habitats on Gotland. The genetic variation observed suggests sexual reproduction and slow dispersal on the island. It is possible that the present population was established from one introduction, which may be due to ability to survive in this habitat rather than to rare colonising events. The T. aestivum population on Gotland may be an ecotype adapted to the climate and soil conditions on the island.     

荒漠土壤因子和DSE定殖对克隆植物入侵的响应

克隆植物,尤其是游击型克隆植物,具有很强的扩展能力,通过克隆扩展可侵入到不同生境斑块。克隆植物入侵可能会影响入侵地土壤营养状况和微生物群落。为了探明克隆植物入侵对DSE(dark septate endophytes)活动和土壤理化性质的影响,于2013年6月在克隆植物羊柴(Hedysarum laeve)和沙鞭(Psammochloa villosa)群落空地沿根状茎延伸方向设置样方,分别于6月、8月和10月在样方内分0—10、10—20、20—30、30—40、40—50 cm土层采集土样和根样,研究了不同采样时间羊柴和沙鞭群落空地DSE和土壤理化性质时空变化。结果表明,从6月到10月,随时间后延,克隆植物逐渐侵入群落空地,沙鞭入侵群落空地数和分株数高于羊柴。羊柴群落空地根系DSE定殖率随采样时间后延,逐渐降低,最大值在6月;沙鞭群落空地根系DSE定殖率随采样时间后延,逐渐升高,最大值在10月。随着克隆植物入侵,入侵地土壤中可利用的营养物质含量显著提高,羊柴入侵提高了入侵群落空地土壤碱解N、有效P和速效K含量,沙鞭入侵提高了入侵群落空地土壤碱解N和有效P含量。相关性分析表明,羊柴群落空地DSE定殖率与土壤p H值和电导率显著正相关,沙鞭群落空地DSE定殖率与土壤p H值极显著负相关,与电导率、碱解N和有效P极显著正相关。克隆植物入侵使得土壤环境更有利于克隆植物自身生长,为荒漠植被恢复提供了前提。     

The survival of the pentachlorophenol-degrading Rhodococcus chlorophenolicus PCP-1 and Flavobacterium sp. in natural soil

The survival of two different pentachlorophenol (PCP)-degrading bacteria were studied in natural soil. The PCP-degraders Rhodococcus chlorophenolicus and Flavobacterium sp., both able to mineralize PCP into CO₂ and chloride in axenic culture, were tested for the capacity to survive and degrade PCP in natural soil. These bacteria were immobilized on polyurethane (PUR) foam and introduced into natural peaty soil to give about 10⁹ cells g^-1 of soil (dry weight). R. chlorophenolicus induced PCP-degrading activity in soil remained detectable for 200 days whether or not a carbon source was added (distillery waste or wood chips). Electron microscopic investigation performed almost a year after inoculation, revealed the presence of R. chlorophenolicus-like cells in the PUR foam particles. PCP-degrading activity of Flavobacterium sp. declined within 60 days of burial in the soil without enhancing the PCP removal. R. chlorophenolicus degraded PCP in soil at a mean rate of 3.7 mg of PCP day^-1 kg^-1 of soil, which corresponds to ca. 5×10^-3 pg of PCP degraded per inoculated R. chlorophenolicus cell day^-1. The solvent extractable organic chlorine contents of the soil decreased stoichiometrically (>95%) with that of PCP indicating that PCP was essentially mineralized.Abbreviations ATCC American type culture collection - DSM Deutsche Sammlung für Mikroorganismen - DW distillery waste - EM electron microscopy - EOX extractable organic halogen - GC/ECD gas chromatograph/electron capture detector - GC/MS gas chromatograph/mass spectrometer - PCP pentachlorophenol - WC wood chips - d.wt. dry weight - w.wt. wet weight - d.s. dry soil - d.H₂O distilled water - PCA polychlorinated aromatics     

A novel ABA-hypersensitive mutant in Arabidopsis defines a genetic locus that confers tolerance to xerothermic stress

Hot and dry air (harmattan or xerothermic climate) greatly inhibits plant growth, particularly flowering and seed setting of crops. Little is known about the mechanism of plant response to this extreme environmental stress due to the lack of valuable genetic resource. Here, we report the isolation and characteristics of a unique Arabidopsis mutant, hat1 (h armattan t olerant 1), which shows high tolerance to hot and dry air. Under normal growth conditions, the mutant does not differ in morphology and soil drought tolerance compared to the wild type. When subjected to high temperature (42°C) and low humidity (10–15%), however, it could survive up to 6 days, while the wild type (Col-0) died after 24 h. The hat1 mutant also exhibits enhanced tolerance to soil drought, but only under xerothermic conditions. Mutant plants tightly close their stomata to retain water under xerothermic stress, and are more tolerant to high salinity at all developmental stages, accumulating less Na⁺ and more K⁺ than wild-type plants during NaCl treatment. Interestingly, hat1 plants are also ABA-hypersensitive. Genetic analysis revealed that the hat1 phenotype is caused by a dominant mutation at a single nuclear locus. Mapping studies indicate that Hat1 is located at an interval of 168 kb on chromosome 5 in which 21 genes are known to be regulated by diverse abiotic stresses. A mutant of this kind, to our knowledge, has not been previously reported. Thus, this report serves as a starting point in the genetic dissection of the plant response to xerothermic stress, and provides physiological and genetic evidence of the existence of a novel abiotic stress response pathway that is also ABA-dependent.     

Introduction and recovery of Clavibacter michiganensis subsp. michiganensis from agricultural soil

Twelve phytopathogenic Clavibacter michiganensis subsp. michiganensis strains were introduced into non-sterile agricultural loam soil at an inoculum density of about log. 6.0 cfu g^–1 dry weight soil. The soil samples were incubated at 22°C under a 12h light, 12h dark cycle and the population densities followed over a 30-day period by plating subsamples of serial dilutions of soil on Brain Heart Infusion agar amended with 0.5% (w/v) yeast extract and 30 g mL^–1 nalidixic acid. In 5 soil samples C. michiganensis cfu were not detected after 30 days incubation. Initially, C. michiganensis cfu accounted for about 90% of the cfu recovered but decreased to less than 10% after 30 days. These results suggested that some C. michiganensis strains survive in this particular soil, while other strains exhibit poor survival and/or may be difficult to detect when present in low numbers.     

丝核菌的分类系统：现状及存在问题

以重要植物病原菌为特征的丝核菌是一类在土壤中广泛分布的丝状真菌,通常不产孢,以菌丝或菌核的形式存在,多样性非常丰富。本文基于国内外最新研究进展,对依据菌丝体的细胞核数目、菌丝融合、有性生殖和系统进化等方面的基本特征展开的丝核菌分类体系及分类现状进行了综述。基于菌丝的细胞核数目,丝核菌被分为单核、双核和多核丝核菌三大类群。自然界中单核丝核菌数量极少,多核和双核丝核菌在全球分布广泛,占丝核菌的绝大多数。基于菌丝融合试验的结果,目前多核丝核菌被分为13个菌丝融合群,双核丝核菌被分为18个菌丝融合群。部分融合群内又根据一些稳定的特征分了亚群,但亚群的建立标准并不统一。目前的分子系统学研究结果基本支持丝核菌的菌丝融合群及亚群的分类。基于部分有性世代被发现的菌株的形态特征,多核和双核丝核菌分别被鉴定为亡革菌属和角担菌属。此外,目前已有分属重要植物病原菌和兰科菌根菌类群的至少9个融合群或亚群的17个菌株完成了基因组测序,比较基因组学和线粒体组学开始在丝核菌分类和进化研究中发挥作用。丝核菌分类系统特殊且复杂,作者在文末提出了目前丝核菌分类学研究面临的问题和今后研究的趋势,期待更多的学者参与到这个重要菌...     

Field ecology of the ochratoxin A-producing Penicillium verrucosum: Survival and resource colonisation in soil

A field experiment was conducted to elucidate the survival of P. verrucosum in infested bulk soil(T1) and infested soil with waste grain (T2). The infested soil and reference soil (T3) was filled into steel cylinders, which were buried and sampled 13 times during a period from October 1994 to March 1996.The abundance of P. verrucosum and indigenous soil fungi were assessed by dilution plating on a selective and diagnostic medium (DYSG). Kernel infection was examined in T2. According to our results, P. verrucosum seems well adapted to survival in arable soil and little affected by indigenous fungi. During the first autumn and winter the grain caused a proliferation of P. verrucosum while its abundance in bulk soil was more constant except for a decrease in February 95, which is ascribed to frost/thaw alternations. In T2, P. verrucosum initially infected more than 50% of the kernels but during the first few months it was ousted by other fungi. A hypothesis regarding waste grain as the natural niche for the fungus in the field was therefore partly rejected. A gradual decrease in the abundance of P. verrucosum in soil during spring, a die-off in the dry summer and aproliferation during the second winter were found in both T1 and T2. Our results cannot provide the reason for the increase during the second winter. On an overall basis, however, they show that P. verrucosum can survive in the field, proliferate on soil organic matter and probably become an integral part of the soil ecosystem. This may constitute a risk of grain contamination when given appropriate environmental conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Can R*s Predict Invasion in Semi-arid Grasslands?

We estimated R*s and tested the applicability of R* theory on nonindigenous plant invasions in semi-arid rangeland. R* is the concentration of a resource that a species requires to survive in a habitat. R* theory predicts that a species with a lower R* for the most limiting resource will competitively displace a species with a higher R* under equilibrium conditions. In a greenhouse, annual sunflower (Helianthus annuus L.), bluebunch wheatgrass (Agropyron spicatum Pursh), and spotted knapweed (Centaurea maculosa Lam.) were grown in monoculture and 2- and 3-species mixtures for three growth periods in an attempt to reduce soil NO₃-N concentrations below each species’ R*. At the end of each growth period, aboveground biomass by species and soil plant available nitrogen were sampled. Decreasing biomass coupled with decreasing soil plant available nitrogen was used to quantify R*s for the three species. R*s for annual sunflower, bluebunch wheatgrass, and spotted knapweed were estimated to be 0.6±0.16 ppm NO₃⁻, less than 0.05 ppm NO₃⁻, and 0.6±0.13 ppm NO₃⁻, respectively. Estimated R*s did not predict the outcome of competition among species. To successfully predict plant community dynamics on semi-arid rangeland with and without the presence of a nonindigenous invasive species, a more comprehensive model that includes mechanisms in addition to competition may have to be considered. We speculate that R* theory may prove most useful for predicting the outcome of competition within functional groups.     

Effectiveness of rodents as local seed dispersers of Holm oaks

In this study we assessed the effectiveness of rodents as dispersers of Quercus ilex in a patchy landscape in southeastern Spain. We experimentally followed the fates of 3,200 marked and weighed acorns from dispersal through the time of seedling emergence over three years. Rodents handled about 99% of acorns, and dispersed 67% and cached 7.4% of the dispersed acorns. Most caches were recovered and consumed, and only 1.3% of the original experimental acorns were found alive in caches the following spring. Dispersal distances were short (mean = 356.2 cm, median = 157 cm) and strongly right-skewed. Heavier acorns were dispersed further and were more likely to be cached and survive than lighter acorns. All caches were in litter or soil, and each contained a single acorn. Rodents moved acorns nonrandomly, mostly to oaks and pines. Most surviving acorns were either in oaks, a poor microhabitat for oak recruitment, or shrubs, a suitable microhabitat for oak recruitment. Our results suggest that rodents, by burying a relatively high proportion of acorns singly in shrubs and pines, act as moderately effective dispersers of Q. ilex. Nonetheless, this dispersal comes at a very heavy cost.     

Edaphic limitations to growth and photosynthesis in Sierran and Great Basin vegetation

Summary Soils derived from hydrothermally altered andesite support unique communities of Sierran conifers (Pinus ponderosa Laws. and P. jeffreyi Grev. and Balf.) amongst sagebrush (Artemisia tridentata Nutt.) vegetation in the western Great Basin. Plants grown in soil derived from hydrothermally altered bedrock had lower growth rates, total biomass, and net photosynthetic rates than plants grown in soil derived from unaltered andesite of the same formation. Total dry mass was 10 to 28% lower for conifers grown in altered soil whereas dry mass of Artemisia tridentata and Bromus tectorum L. was reduced by over 90%. Results from a nutrient amendment experiment indicated that low phosphorus was the dominant limitation in altered soil, and phosphorus-deficiency affected growth primarily by limiting leaf area development rather than direct inhibition of photosynthesis. The proportionately greater reduction of biomass for Artemisia and Bromus grown in altered soil supports our hypothesis that Great Basin vegetation is excluded from altered soil by intolerance to nutrient deficiency. The Sierran conifers growing on this rock type are therefore free of competition for water with Great Basin vegetation and are able to persist in an exceptionally dry climate.     

Hatchling painted turtles (Chrysemys picta) survive exposure to subzero temperatures during hibernation by avoiding freezing

Hatchling painted turtles (Chrysemys picta) were placed individually into artificial nests constructed in jars of damp soil and then were cooled slowly to temperatures between-7.7 and-12.7 °C. Distinct exotherms were recorded in all jars when water in the soil began to freeze at temperatures between-0.9 and-2.4 °C. A second (animal) exotherm was subsequently detected in some of the jars when water in hatchlings also began to freeze. An animal exotherm occurred in the temperature records for all 23 hatchlings that died in tests terminating at temperatures between-7.7 and-10.8 °C, but no such exotherm was apparent in the temperature records for the 23 turtles that survived these treatments. Moreover, the 4 hatchlings that produced exotherms in tests terminating between-11.5 and-12.7 °C failed to survive, but 5 of 7 hatchlings that produced no exotherm in these tests also died. Thus, turtles that die at subzero temperatures above-11 °C apparently succumb to freezing when ice propagates across their integument from the frozen soil, but animals that die at temperatures below-11 °C generally perish from some other cause. These findings indicate that hatchling painted turtles overwintering inside their shallow, subterranean nests survive exposure to subzero temperatures by avoiding freezing instead of by tolerating freezing.     

Metal uptake byCaryophyllaceae species from metalliferous soils in northern Greece

Plant samples collected from 17 populations of 9 taxa of the generaDianthus, Minuartia, Scleranthus, andSilene (Caryophyllaceae), growing in 14 metalliferous sites of N Greece, and surface soil samples from their growth area were analysed for Cu, Pb, Zn, Cd, Ni, Cr, Fe, Mn, Ca, Mg. Metal uptake varies considerably between the populations. A resistance mechanism excluding Cu and Pb from the aerial parts of the plants over a wide range of the soil concentrations up to a critical soil level appeared to exist, whereas Zn concentrations in plants were analogously related to those of the soil.Scleranthus perennis subsp.perennis showed the highest Cu concentration (205 µg/g), whereasMinuartia cf.bulgarica hyperaccumulated Pb (1175 µg/g). Ca concentrations in plants were in most cases much higher than those in soil, whereas the contrary was true for Mg. As a result the Ca/Mg ratio, which was in almost all cases lower than 1 in the soil, was much increased in the plants.