No significant contribution of arbuscular mycorrhizal fungi to transfer of radiocesium from soil to plants

The diffuse pollution by fission and activation products following nuclear accidents and weapons testing is of major public concern. Among the nuclides that pose a serious risk if they enter the human food chain are the cesium isotopes 137Cs and 134Cs (with half-lives of 30 and 2 years, respectively). The biogeochemical cycling of these isotopes in forest ecosystems is strongly affected by their preferential absorption in a range of ectomycorrhiza-forming basidiomycetes. An even more widely distributed group of symbiotic fungi are the arbuscular mycorrhizal fungi, which colonize most herbaceous plants, including many agricultural crops. These fungi are known to be more efficient than ectomycorrhizas in transporting mineral elements from soil to plants. Their role in the biogeochemical cycling of Cs is poorly known, in spite of the consequences that fungal Cs transport may have for transfer of Cs into the human food chain. This report presents the first data on transport of Cs by these fungi by use of radiotracers and compartmented growth systems where uptake by roots and mycorrhizal hyphae is distinguished. Independent experiments in three laboratories that used different combinations of fungi and host plants all demonstrated that these fungi do not contribute significantly to plant uptake of Cs. The implications of these findings for the bioavailability of radiocesium in different terrestrial ecosystems are discussed.     

Nutrient transfer from soil nematodes to plants: a direct pathway provided by the mycorrhizal mycelial network

A pathway for the transfer of nutrients from dead nematodes to mycorrhizal plants is described for the first time. Plants of Betula pendula were grown in transparent microcosms in the mycorrhizal (M) or non‐mycorrhizal (NM) condition, either with or without nematode necromass of known nitrogen (N) and phosphorus (P) contents as the major potential source of these elements. Plants colonized by the mycorrhizal fungus Paxillus involutus produced greater yields and had larger N and P contents in the presence of nematodes than did their NM counterparts. The symbiotic systems were shown to exploit the N and P originally contained in necromass more effectively, and to transfer the nutrients to the plants in quantities approximately double those seen in NM systems. Even so, NM plants obtained sufficient N and P from dead nematodes to enable some enhancement of growth. Our observations confirm that mycorrhizal fungi provide the potential for the recycling of nutrients contained in this quantitatively important component of the soil mesofauna and demonstrate that the symbiotic pathway is considerably more effective than that provided by saprotrophs alone. The consequences of this nutrient transfer pathway for nutrient recycling in temperate forest ecosystems are considered.     

The impact of increased soil risk elements on carotenoid contents

A pot experiment was conducted to compare the responses of a non-transgenic tobacco plant (WT) and plants with genetically prolonged life-span (SAG) to risk elements of As, Cd and Zn. Plants were grown in control soil and in soil with higher levels of risk elements. The pigment contents were established by HPLC and chlorophyll fluorescence parameters were measured from slow kinetics after a 15 min dark period with the PAM fluorometer. Top (i.e. young) leaves of both WT and SAG plants were more sensitive to photoinhibition caused by these risk elements but plants showed acclimation to such elements in the bottom leaves. Plants differed in the participation of individual pigments of xanthophyll cycle: increased levels of risk elements seem to stimulate especially first (violaxanthin to antheraxanthin) and second (anhtheraxanthin to zeaxanthin) steps of the cycle in WT plants. In SAG plants, toxic elements caused an increase in the content, particularly of the initial compound of the cycle — violaxanthin.     

The effect of transposable elements on phenotypic variation: insights from plants to humans

Transposable elements (TEs), originally discovered in maize as controlling elements, are the main components of most eukaryotic genomes. TEs have been regarded as deleterious genomic parasites due to their ability to undergo massive amplification. However, TEs can regulate gene expression and alter phenotypes. Also, emerging findings demonstrate that TEs can establish and rewire gene regulatory networks by genetic and epigenetic mechanisms. In this review, we summarize the key roles of TEs in fine-tuning the regulation of gene expression leading to phenotypic plasticity in plants and humans, and the implications for adaption and natural selection.     

土壤pH调控固氮植物和非固氮植物间的氮转移

氮作为构成蛋白质的主要成分, 是植物生长的必要营养物质。陆地生态系统普遍存在土壤氮缺乏的现象, 混交种植模式中固氮植物可以将生物固定的氮转移给非固氮植物, 是满足非固氮植物氮需求的途径之一。明确固氮和非固氮植物间氮转移的影响因素有助于恢复退化生态系统, 构建稳定群落, 增加生态系统生产力。为了量化环境及生物等因素对氮转移的影响, 该研究采用文献调研法, 对118组氮转移比例(氮转移量占非固氮植物氮含量的比值, P_transfer)文献和实验数据(包括21种固氮植物和23种非固氮植物)进行了线性混合模型分析。结果表明土壤pH是影响P_transfer变化的最主要因素(解释量为44.04%), 其次为年平均温度(解释量为9.14%)以及固氮与非固氮植物生物量比值(解释量为2.95%), 而作为随机因素的固氮和非固氮植物物种差异的解释量为16.52%。此外, 碱性土壤中P_transferr显著高于酸性土壤。在酸性土壤中, 年平均温度(解释量为12.49%)和土壤总氮含量(解释量为11.72%)是影响P_transfer差异的主要因素, P_transfer随着年平均温度和土壤总氮含量的增加而显著增加。而在碱性土壤中, P_transfer差异主要受到固氮与非固氮植物生物量比值(解释量为13.29%)、年降水量(解释量为10.73%)和土壤总氮含量(解释量为9.33%)的调控。相对于酸性土壤, 碱性土壤能够显著增加固氮与非固氮植物生物量比值进而增加P_transfer。同时, 在碱性土壤中P_transfer与年降水量和土壤总氮含量呈显著正相关关系。这些结果对提高固氮和非固氮植物间的氮转移, 有效缓解土壤氮对非固氮植物生长的限制以及构建稳定群落具有重要意义。     

Rare earth elements in soil and in soil-grown plants

Concentrations of the rare earth elements (REEs) La, Ce, Nd, Sm, Eu, Gd, Tb, Yb and Lu were determined in leaves of 6 plant species (Norway spruce, silver fir, maple, ivy, blackberry, and wood fern), and in pertinent soils and soil extracts, also taken from the same site. The distribution of the individual REEs in plants showed little or no agreement with that in the soil or the soil extracts. Ce had a negative anomaly with respect to the soil in all plants. The REE distribution patterns of fir and spruce were almost identical, but differed profoundly from that of the other species. In most cases, concentration ratios between species were a smooth function of the atomic number of the REE. Very similar results were obtained at 2 additional sites.     

Evaluation of possible horizontal gene transfer from transgenic plants to the soil bacterium Acinetobacter calcoaceticus BD413

 The use of genetically engineered crop plants has raised concerns about the transfer of their engineered DNA to indigenous microbes in soil. We have evaluated possible horizontal gene transfer from transgenic plants by natural transformation to the soil bacterium Acinetobacter calcoaceticus BD413. The transformation frequencies with DNA from two sources of transgenic plant DNA and different forms of plasmid DNA with an inserted kanamycin resistance gene, nptII, were measured. Clear effects of homology were seen on transformation frequencies, and no transformants were ever detected after using transgenic plant DNA. This implied a transformation frequency of less than 10^-13 (transformants per recipient) under optimised conditions, which is expected to drop even further to a minimum of 10^-16 due to soil conditions and a lowered concentration of DNA available to cells. Previous studies have shown that chromosomal DNA released to soil is only available to A. calcoaceticus for limited period of time and that A. calcoaceticus does not maintain detectable competence in soil. Taken together, these results suggest that A. calcoaceticus does not take up non-homologous plant DNA at appreciable frequencies under natural conditions. Received: 1 November 1996 / Accepted: 18 April 1997     

Multivariate statistical analysis of nutrients and trace elements in plants and soil from northwestern Russia

Results are summarized of several field and greenhouse experiments designed to estimate differences in the ability of some plant species to take up from soil essential nutrients and various trace elements and transfer them from roots to upper plant parts. Instrumental neutron activation analysis was used to determine concentrations of 22 elements in plant and soil samples. Correlation and principal component analysis were applied for interpreting a large volume of experimental results. In many cases there was no statistically significant positive correlation between element concentrations in soil and concentrations of these elements in plants. Moreover, relationships between elements were often different in soil and in different plant parts, thereby suggesting quite different element behaviours in soil and in plants. Our experimental results and data published in the literature revealed that macro- and trace element concentrations might serve as a specific indicator of plant taxonomy, thus allowing for differentiation of the plants in accordance with concentrations of certain elements in roots or in leaves. Short-term variations in concentrations of elements typical for different plant species and factors affecting these variations indicated that diurnal dynamics of plant element concentrations were regular and species-specific.     

Grazing impact on desert plants and soil seed banks: Implications for seed-eating animals

We assess whether the knowledge of livestock diet helps to link grazing effects with changes in plant cover and soil seed bank size, aiming at inferring the consequences of grazing on seed-eating animals. Specifically, we test whether continuous and heavy grazing reduce the cover, number of reproductive structures and seed reserves of the same grass species whose seeds are selected and preferred by granivorous animals in the central Monte desert, Argentina. Grass cover and the number of grass spikes usually diminished under grazing conditions in the two localities studied (Telteca and Ñacuñán), and soil seed bank was consistently reduced in all three years evaluated owing to a decline of perennial grass and forb seeds. In particular, the abundance of those seeds selected and preferred by birds and ants (in all cases grass species) declined 70–92% in Ñacuñán, and 52–72% in Telteca. Reduction of perennial grass cover and spike number in grazed sites reinforced the causal link between livestock grazing and the decline of grass soil seed reserves throughout failed plant reproduction. Grass seed bank depletion suggests that grazing may trigger a “cascade” of mechanisms that affect the abundance and persistence of valuable fodder species as well as the availability of seed resources for granivorous animals.     

Cesium and cobalt transfer from soil to vegetation on permanent pastures

Summary The Cs transfer from soil into pasture vegetation was investigated by using a variation of experimental conditions: (I) 67 pots with 7 kg soil from 3 marshy and 1 sandy site in the lower Weser region in Northwest Germany are used in a greenhouse with¹³⁴CS under 8 different experimental procedures for 2 harvests; (II) 3 undisturbed 50 kg lysimeters were observed for¹³⁷Cs and⁶⁰Co transfer under outdoor conditions for 4 harvests, depth profiles of the activity were determined afterwards; (III) the transfer of the atmospheric fallout¹³⁷Cs directly to the vegetation and from soil to vegetation after preventing its direct uptake by plastic covers was determined at 4 locations in the open pasture.The experiments resulted in higher Cs transfer in the case of podzolic soil and/or direct injection of Cs solution into the rooting zone of old permanent pasture vegetation while the Cs transfer was about 2–4 fold lower when the radioactive solution was applied to newly sown grass. Transfer often decreases with increasing age of Cs in the soil. In addition, statistical analysis of the widely scattered data did not show significant results for the influence of type of marsh, experimental procedure, soil factors with pH of (4.5–6.1), organic carbon, amount of added Cs (microquantity), exchangeable, K, and total Ca.Some figures are given for⁶⁰Co. The observed transfer factors, combined from all experiments appear lognormally distributed with median values 0.22 on podzolic and 0.09 on marshy soils (Bq/kg fresh plant per Bq/kg air dried soil).Research performed under contract with the Bundesminister des Innern (Federal Minister of Interior), Bonn, Federal Republic of Germany     

T-DNA transfer to maize plants

Agrobacterium-mediated transformation is the method of choice to engineer desirable genes into plants. Here we describe a protocol for demonstrating T-DNA transfer from Agrobacterium into the economically important graminaceous plant maize. Expression of the T-DNA-located GUS gene was observed with high efficiency on shoots of young maize seedlings after cocultivation with Agrobacterium.     

Direct gene transfer to plants

Evidence for direct, gene-mediated stable genetic transformation of plant cells of Nicotiana tabacum is presented. A selectable hybrid gene comprising the protein coding region of the Tn5 aminoglycoside phosphotransferase type II gene under control of cauliflower mosaic virus gene VI expression signals was introduced into plant protoplasts as part of an Escherichia coli plasmid. The gene was stably integrated into plant genomic DNA and constitutively expressed in selected, drug resistant, protoplast-derived cell clones. The mode of integration of the foreign gene into the plant genome resembled that observed for DNA transfection of mammalian cells. Plants regenerated from transformed cell lines were phenotypically normal and fertile, and they maintained and expressed the foreign gene throughout the development of vegetative and generative organs. Microspores, grown in anther culture, developed into resistant and sensitive haploid plantlets. Genetic crossing analysis of one of the transformed plants revealed the presence of one dominant trait for kanamycin resistance segregating in a Mendelian fashion in the F₁ generation.     

Mercuric reductase gene transfer from soil to rumen bacteria

Conjugal transfer between soil bacterial population and microorganisms isolated from the rumen of herbivores from mercury-polluted area was investigated. The transfer of merA encoding mercury-resistance plasmids from soil bacteria Enterobacter cloacae and Enterococcus durans into two ruminal isolates Citrobacter freundii and Bacillus subtilis was observed. Approximately the same frequency of mobilization in mating experiments was observed for both Gram-negative (approximately 2.5 x 10(-8), transconjugants-to-recipient ratio) and Gram-positive (approximately 1.3 x 10(-8)) bacteria.     

Quantifying root water extraction by rangeland plants through soil water modeling

We used soil water modeling as a tool to quantify water use of non-cultivated plant communities based on easily measured field data of soil water contents, soil hydraulic properties, and leaf area index. The model was applied in the mixed-grass prairie, considering a dynamic and non-uniform root distribution, the effect of soil water stress on plant water uptake, as well as the compensation effect of root water uptake. The simulation was conducted for the 111 days from mid May to early September of 2009. A good agreement between the model simulated and field measured soil water contents was obtained, with a maximum rooting depth estimated within the depth range of 1.3–1.6 m. The results suggest that a reasonable estimate of soil water retention parameters, and especially the use of the root uptake compensation significantly improved both numerical accuracy in predicted soil water dynamics, and the biological importance in the predicted seasonal root water extraction. In particular, the model gave a reasonable simulation of the seasonal progression of the drying zone in the soil profile in the summer of 2009. The method and analyses used in this paper may be useful in a wider context of soil-plant relationships.     

Programming desiccation-tolerance: from plants to seeds to resurrection plants

Desiccation-tolerance (DT) evolved as the key solution to survival on land by the early algal ancestors of terrestrial plants. This 'first' DT involved utilizing rapidly mobilisable repair mechanisms and is still found today in mosses, such as Tortula ruralis, and ferns, such as Mohria caffrorum. The first seed plants lost vegetative DT while investing their seeds with tolerance mechanisms improving their survival in unfavourable environments. The mechanisms of DT in seeds are strongly connected to their developmentally regulated maturation programs. We propose that angiosperm resurrection plants acquired tolerance by re-activating their innate DT mechanisms in their vegetative tissues. Here we review the current hypotheses regarding the genetic evidence for the evolution of DT in resurrection plants. We also present strong evidence showing the activation of seed specific genetic elements in the vegetative tissues of resurrection plants.