Andrea Polle

Universitätsmedizin Göttingen, Göttingen, Lower Saxony, Germany

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Publications (283)1012.41 Total impact

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    ABSTRACT: To elucidate the physiological and transcriptional regulatory mechanisms that underlie the responses of poplars to high temperature (HT) and/or drought in woody plants, we exposed Populus alba × P. tremula var. glandulosa saplings to ambient temperature (AT) or HT under 80% or 40% field capacities, or no watering. HT increased the foliar total carbon (C) concentrations, and foliar δ(13) C and δ(18) O. HT triggered heat stress signaling via increasing levels of ABA and IAA in poplar roots and leaves. After perception of HT, poplars initiated osmotic adjustment by increasing foliar sucrose and root galactose levels. In agreement with the HT-induced heat stress and the changes in the levels of ABA and carbohydrates, we detected increased transcript levels of HSP18 and HSP21, as well as NCED3 in the roots and leaves, and the sugar transporter gene STP14 in the roots. Compared with AT, drought induced greater enhancement of foliar δ(13) C and δ(18) O in poplars at HT. Similarly, drought caused greater stimulation of the ABA and foliar glucose levels in poplars at HT than at AT. Correspondingly, desiccation led to greater increases in the mRNA levels of HSP18, HSP21, NCED3, STP14 and INT1 in poplar roots at HT than at AT. These results suggest that HT has detrimental effects on physiological processes and it induces the transcriptional regulation of key genes involved in heat stress responses, ABA biosynthesis and sugar transport, and HT can cause greater changes in drought-induced physiological and transcriptional responses in poplar roots and leaves.
    No preview · Article · Oct 2015 · Physiologia Plantarum
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    ABSTRACT: Nitrogen (N) starvation and excess have distinct effects on N uptake and metabolism in poplars, but the global transcriptomic changes underlying morphological and physiological acclimation to altered N availability are unknown. We found that N starvation stimulated the fine root length and surface area by 54 and 49%, respectively, decreased the net photosynthetic rate by 15% and reduced the concentrations of NH 4 + , NH4+, NO 3 − NO3− and total free amino acids in the roots and leaves of Populus simonii Carr. in comparison with normal N supply, whereas N excess had the opposite effect in most cases. Global transcriptome analysis of roots and leaves elucidated the specific molecular responses to N starvation and excess. Under N starvation and excess, gene ontology (GO) terms related to ion transport and response to auxin stimulus were enriched in roots, whereas the GO term for response to abscisic acid stimulus was overrepresented in leaves. Common GO terms for all N treatments in roots and leaves were related to development, N metabolism, response to stress and hormone stimulus. Approximately 30–40% of the differentially expressed genes formed a transcriptomic regulatory network under each condition. These results suggest that global transcriptomic reprogramming plays a key role in the morphological and physiological acclimation of poplar roots and leaves to N starvation and excess.
    Full-text · Article · Sep 2015 · Tree Physiology
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    ABSTRACT: Phosphorus (P) and nitrogen (N) are the two essential macronutrients for tree growth and development. To elucidate the P and N physiology of woody plants during acclimation to P and/or N starvation, we exposed saplings of the slow-growing Populus simonii Carr (Ps) and the fast-growing Populus × euramericana Dode (Pe) to complete nutrients or starvation of P, N or both elements (NP). P. × euramericana had lower P and N concentrations and greater P and N amounts due to higher biomass production, thereby resulting in greater phosphorus use efficiency/N use efficiency (PUE/NUE) compared with Ps. Compared with the roots of Ps, the roots of Pe exhibited higher enzymatic activities in terms of acid phosphatases (APs) and malate dehydrogenase (MDH), which are involved in P mobilization, and nitrate reductase (NR), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH), which participate in N assimilation. The responsiveness of the transcriptional regulation of key genes encoding transporters for phosphate, ammonium and nitrate was stronger in Pe than in Ps. These results suggest that Pe possesses a higher capacity for P/N uptake and assimilation, which promote faster growth compared with Ps. In both poplars, P or NP starvation caused significant decreases in the P concentrations and increases in PUE. Phosphorus deprivation induced the activity levels of APs, phosphoenolpyruvate carboxylase and MDH in both genotypes. Nitrogen or NP deficiency resulted in lower N concentrations, amino acid levels, NR and GOGAT activities, and higher NUE in both poplars. Thus, in Ps and Pe, the mRNA levels of PHT1;5, PHT1;9, PHT2;1, AMT2;1 and NR increased in the roots, while PHT1;9, PHO1;H1, PHO2, AMT1;1 and NRT2;1 increased in the leaves during acclimation to P, N or NP deprivation. These results suggest that both poplars suppress P/N uptake, mobilization and assimilation during acclimation to P, N or NP starvation.
    No preview · Article · Sep 2015 · Tree Physiology
  • Dejuan Euring · Andrea Polle
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    ABSTRACT: Poplars (Populus spp.) and their hybrids are widely considered to be the premier woody crops for bioenergy feedstock production. While nitrogen (N) fertilisation is a common practice in agriculture, the responses of poplar plantations to this treatment are heterogeneous. In this chapter, N utilisation relative to soil conditions is discussed for poplar varieties Max 1 and H275, which is often used in short rotation coppice plantations in Germany. The allocation by Max 1 trees of N to the leaves contrasted with that by trees of the variety H275. Leaf size, found to be correlated with wood production, is proposed as a useful indicator of productivity. Water availability impacts on nitrogen use in poplar and adequate irrigation can reinforce the effects of N fertilisation. The photosynthetic N use of poplar relative to other energy crops, such as willow (Salix spp.), oilseed rape and maize, is discussed.
    No preview · Chapter · Sep 2015
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    ABSTRACT: Conversion of tropical forests into intensely managed plantations is a threat to ecosystem functions. On Sumatra, Indonesia, oil palm (Elaeis guineensis) plantations are rapidly expanding, displacing rain forests and extensively used rubber (Hevea brasiliensis) agro-forests. Here, we tested the influence of land use systems on root traits including chemical traits (carbon, nitrogen, mineral nutrients, potentially toxic elements [aluminium, iron] and performance traits (root mass, vitality, mycorrhizal colonization). Traits were measured as root community-weighed traits (RCWTs) in lowland rain forests, in rubber agro-forests mixed with rain forest trees, in rubber and oil palm plantations in two landscapes (Bukit Duabelas and Harapan, Sumatra). We hypothesized that RCWTs vary with land use system indicating increasing transformation intensity and loss of ecosystem functions. The main factors found to be related to increasing transformation intensity were declining root vitality and root sulfur, nitrogen, carbon, manganese concentrations and increasing root aluminium and iron concentrations as well as increasing spore densities of arbuscular mycorrhizas. Mycorrhizal abundance was high for arbuscular and low for ectomycorrhizas and unrelated to changes in RCWTs. The decline in RCWTs showed significant correlations with soil nitrogen, soil pH and litter carbon. Thus, our study uncovered a relationship between deteriorating root community traits and loss of ecosystem functionality and showed that increasing transformation intensity resulted in decreasing root nutrition and health. Based on these results we suggest that land management that improves root vitality may enhance the ecological functions of intense tropical production systems.
    Full-text · Article · Sep 2015 · PLoS ONE
  • Ivo Feussner · Andrea Polle
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    ABSTRACT: The proteome and metabolome of the plant provide a wealth of additional information on plant-microbe interactions since they not only represent additional levels of regulation, but often they harbor the end products of regulatory processes. Proteomics has contributed to our understanding of plant-microbe research by increasing the spatial resolution of the analysis within the infected tissue, because components of the basal immunity were uncovered in the apoplast. Metabolomics has developed into a powerful approach to discover the role of small molecules during plant-microbe interactions in non-model plants since it does not depend on the availability of genome or transcriptome data. Moreover, novel molecules involved in systemic acquired resistance and the precursors for the formation of molecules that provide physical barriers to prevent spreading of pathogens were identified. Copyright © 2015 Elsevier Ltd. All rights reserved.
    No preview · Article · Aug 2015 · Current opinion in plant biology
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    Xu Jin · Jorma Zimmermann · Andrea Polle · Urs Fischer
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    ABSTRACT: Timing of leaf abscission is an important trait for biomass production and seasonal acclimation in deciduous trees. The signaling leading to organ separation, from the external cue (decreasing photoperiod) to ethylene-regulated hydrolysis of the middle lamellae in the abscission zone, is only poorly understood. Data from annual species indicate that the formation of an auxin gradient spanning the abscission zone regulates the timing of abscission. We established an experimental system in Populus to induce leaf shedding synchronously under controlled greenhouse conditions in order to test the function of auxin in leaf abscission. Here, we show that exogenous auxin delayed abscission of dark-induced leaves over short and long distances and that a new auxin response maximum preceded the formation of an abscission zone. Several auxin transporters were down-regulated during abscission and inhibition of polar auxin transport delayed leaf shedding. Ethylene signaling was not involved in the regulation of these auxin transporters and in the formation of an abscission zone, but was required for the expression of hydrolytic enzymes associated with cell separation. Since exogenous auxin delayed abscission in absence of ethylene signaling auxin likely acts independently of ethylene signaling on cell separation.
    Full-text · Article · Aug 2015 · Frontiers in Plant Science
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    ABSTRACT: Virus-induced gene silencing (VIGS) has been shown to be an effective tool for investigating gene functions in herbaceous plant species, but has rarely been tested in trees. The establishment of a fast and reliable transformation system is especially important for woody plants, many of which are recalcitrant to transformation. In this study, we established a tobacco rattle virus (TRV)-based VIGS system for two Populus species, Populus euphratica and P. × canescens. Here, TRV constructs carrying a 266 bp or a 558 bp fragment of the phytoene desaturase (PDS) gene were Agrobacterium-infiltrated into leaves of the two poplar species. Agrobacterium-mediated delivery of the shorter insert, TRV2-PePDS266, into the host poplars resulted in expected photobleaching in both tree species, but not the longer insert, PePDS558. The efficiency of VIGS was temperature-dependent, increasing by raising the temperature from 18 to 28 °C. The optimized TRV-VIGS system at 28 °C resulted in a high silencing frequency and efficiency up to 65-73 and 83-94%, respectively, in the two tested poplars. Moreover, syringe inoculation of Agrobacterium in 100 mM acetosyringone induced a more efficient silencing in the two poplar species, compared with other agroinfiltration methods, e.g., direct injection, misting and agrodrench. There were plant species-related differences in the response to VIGS because the photobleaching symptoms were more severe in P. × canescens than in P. euphratica. Furthermore, VIGS-treated P. euphratica exhibited a higher recovery rate (50%) after several weeks of the virus infection, compared with TRV-infected P. × canescens plants (20%). Expression stability of reference genes was screened to assess the relative abundance of PePDS mRNA in VIGS-treated P. euphratica and P. × canescens. PeACT7 was stably expressed in P. euphratica and UBQ-L was selected as the most suitable reference gene for P. × canescens using three different statistical approaches, geNorm, NormFinder and BestKeeper. Quantitative real-time PCR showed significant reductions in PDS transcripts (55-64%) in the photobleached leaves of both VIGS-treated poplar species. Our results demonstrate that the TRV-based VIGS provides a practical tool for gene functional analysis in Populus sp., especially in those poplar species which are otherwise recalcitrant to transformation. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
    Full-text · Article · Jul 2015 · Tree Physiology
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    ABSTRACT: Chrysomela populi (poplar leaf beetle) is a common herbivore in poplar plantations whose infestation causes major economic losses. Because plant volatiles act as infochemicals, we tested whether isoprene, the main volatile organic compound (VOC) produced by poplars (Populus x canescens), affects the performance of C. populi employing isoprene emitting (IE) and transgenic isoprene non-emitting (NE) plants. Our hypothesis was that isoprene is sensed and affects beetle orientation or that the lack of isoprene affects plant VOC profiles and metabolome with consequences for C. populi feeding. Electroantennographic analysis revealed that C. populi can detect higher terpenes, but not isoprene. In accordance to the inability to detect isoprene, C. populi showed no clear preference for IE or NE poplar genotypes in the choice experiments, however, the beetles consumed a little bit less leaf mass and laid fewer eggs on NE poplar trees in field experiments. Slight differences in the profiles of volatile terpenoids between IE and NE genotypes were detected by gas chromatography - mass spectrometry. Non-targeted metabolomics analysis by Fourier Transform Ion Cyclotron Resonance Mass Spectrometer revealed genotype-, time- and herbivore feeding-dependent metabolic changes both in the infested and adjacent undamaged leaves under field conditions. We show for the first time that C. populi is unable to sense isoprene. The detected minor differences in insect feeding in choice experiments and field bioassays may be related to the revealed changes in leaf volatile emission and metabolite composition between the IE and NE poplars. Overall our results indicate that lacking isoprene emission is of minor importance for C. populi herbivory under natural conditions, and that the lack of isoprene is not expected to change the economic losses in poplar plantations caused by C. populi infestation.
    Full-text · Article · Jul 2015 · BMC Plant Biology
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    ABSTRACT: Earthworms (EWs) and mycorrhizal fungi are key components of soil biota participating in N recycling from leaf litter. The extent to which their interactions impact leaf litter-derived N uptake by tree species colonized by different mycorrhizal types and the variation of these interactions with leaf litter quality is unknown. We used a greenhouse experiment to investigate the effects of EWs on plant acquisition of N from 15N enriched ash (Fraxinus excelsior) and beech (Fagus sylvatica) leaf litter. We employed arbuscular mycorrhizal (AM) ash and ectomycorrhizal (EM) beech trees. EW presence did not affect the overall root mycorrhizal colonization, but in the beech leaf litter treatment it caused a shift in the EM fungal community, favoring species with a ruderal life strategy at the expense of more specialized species able to degrade organic compounds. No differences in 15N capture were found between EM and AM plants. Generally, 2-7% of the N released from leaf litter was taken up by the plants. EWs uniformly increased plant acquisition of N from leaf litter. This effect was more pronounced in treatments with ash than in those with beech leaf litter, presumably because of higher degradability of ash than of beech litter. The results suggest that leaf litter quality dominates the impact of EWs on plant N acquisition from leaf litter while the mycorrhizal type is of minor importance.
    Full-text · Article · Jun 2015 · Environmental and Experimental Botany
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    ABSTRACT: Beech (Fagus sylvatica), a dominant forest species in Central Europe, competes for nitrogen with soil microbes and suffers from N limitation under dry conditions. We hypothesized that ectomycorrhizal communities and the free living rhizosphere microbes from beech trees of two contrasting climatic conditions exhibit differences in N acquisition that contribute to differences in host N uptake and are related to differences in host below-ground carbon allocation. To test these hypotheses young trees from the natural regeneration of two genetically similar populations, one from dryer conditions (SW) and the other from cooler, moist climate (NE) were transplanted into a homogeneous substrate in the same environment and labelled with (13)CO2 and (15)NH4 (+). Free living rhizosphere microbes were characterized by marker genes for the N cycle, but no differences between the rhizosphere of SW or NE trees were found. Lower (15)N enrichment was found in the ectomycorrhizal communities of NE compared with the SW communities, whereas no significant differences were observed for non-mycorrhizal root tips of SW and NE trees. Neither ectomycorrhizal communities nor non-mycorhizal root tips showed differences in (13)C signatures between the NE and SW origins. Because (15)N accumulation in fine roots and transfer to leaves were lower in NE compared to SW trees, our data support that ectomycorrhizal community influence N transfer to their host and demonstrate that the fungal community from the dry condition was more efficient in N acquisition when environmental constraints were relieved. These findings highlight the importance of adapted ectomycorrhizal communities for forest nutrition in a changing climate. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    No preview · Article · Jun 2015 · Applied and Environmental Microbiology
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    ABSTRACT: Woody crops such as poplars (Populus) can contribute to meet the increasing energy demand of a growing human population and can therefore enhance the security of energy supply. Using energy from biomass increases ecological sustainability as biomass is considered to play a pivotal role in abating climate change. Because areas for establishing poplar plantations are often confined to marginal sites drought tolerance is one important trait for poplar genotypes cultivated in short rotation coppice. We tested 9-month-old plants of four tetraploid Populus tremula (L.) × P. tremuloides (Michx.) lines that were generated by protoplast fusion and their diploid counterpart for water consumption and drought stress responses in a greenhouse experiment. The fusion lines showed equivalent or decreased height growth, stem biomass and total leaf area compared to the diploid line. The relative height increment of the fusion lines was not reduced compared to the diploid line when the plants were exposed to drought. The fusion lines were distinguished from the diploid counterpart by stomatal characteristics such as increased size and lower density. The changes in the stomatal apparatus did not affect the stomatal conductance. When exposed to drought the carbohydrate concentrations increased more strongly in the fusion lines than in the diploid line. Two fusion lines consumed significantly less water with regard to height growth, producing equivalent or increased relative stem biomass under drought compared to their diploid relative. Therefore, these tetraploid fusion lines are interesting candidates for short rotation biomass plantation on dry sites.
    Full-text · Article · May 2015 · Frontiers in Plant Science
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    ABSTRACT: The mutualistic association of roots with ectomycorrhizal fungi promotes plant health and is a hallmark of boreal and temperate forests worldwide. In the pre-colonization phase, before direct contact, lateral root (LR) production is massively stimulated, yet little is known about the signals exchanged during this step. Here, we identify sesquiterpenes (SQTs) as biologically active agents emitted by Laccaria bicolor while interacting with Populus or Arabidopsis. We show that inhibition of fungal SQT production by lovastatin strongly reduces LR proliferation and that (-)-thujopsene, a low-abundance SQT, is sufficient to stimulate LR formation in the absence of the fungus. Further, we show that the ectomycorrhizal ascomycote, Cenococcum geophilum, which cannot synthesize SQTs, does not promote LRs. We propose that the LR-promoting SQT signal creates a win-win situation by enhancing the root surface area for plant nutrient uptake and by improving fungal access to plant-derived carbon via root exudates.
    Full-text · Article · Feb 2015 · Nature Communications
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    Dejuan Euring · Hua Bai · Dennis Janz · Andrea Polle
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    ABSTRACT: Background Nitrogen is an important nutrient, often limiting plant productivity and yield. In poplars, woody crops used as feedstock for renewable resources and bioenergy, nitrogen fertilization accelerates growth of the young, expanding stem internodes. The underlying molecular mechanisms of nitrogen use for extension growth in poplars are not well understood. The aim of this study was to dissect the nitrogen-responsive transcriptional network in the elongation zone of Populus trichocarpa in relation to extension growth and cell wall properties.ResultsTranscriptome analyses in the first two internodes of P. trichocarpa stems grown without or with nitrogen fertilization (5 mM NH4NO3) revealed 1037 more than 2-fold differentially expressed genes (DEGs). Co-expression analysis extracted a network containing about one-third of the DEGs with three main complexes of strongly clustered genes. These complexes represented three main processes that were responsive to N-driven growth: Complex 1 integrated growth processes and stress suggesting that genes with established functions in abiotic and biotic stress are also recruited to coordinate growth. Complex 2 was enriched in genes with decreased transcript abundance and functionally annotated as photosynthetic hub. Complex 3 was a hub for secondary cell wall formation connecting well-known transcription factors that control secondary cell walls with genes for the formation of cellulose, hemicelluloses, and lignin. Anatomical and biochemical analysis supported that N-driven growth resulted in early secondary cell wall formation in the elongation zone with thicker cell walls and increased lignin. These alterations contrasted the N influence on the secondary xylem, where thinner cell walls with lower lignin contents than in unfertilized trees were formed.Conclusion This study uncovered that nitrogen-responsive elongation growth of poplar internodes is linked with abiotic stress, suppression of photosynthetic genes and stimulation of genes for cell wall formation. Anatomical and biochemical analysis supported increased accumulation of cell walls and secondary metabolites in the elongation zone. The finding of a nitrogen-responsive cell wall hub may have wider implications for the improvement of tree nitrogen use efficiency and opens new perspectives on the enhancement of wood composition as a feedstock for biofuels.
    Full-text · Article · Dec 2014 · BMC Plant Biology
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    Jasmin Seven · Andrea Polle
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    ABSTRACT: Mycorrhizas are the chief organ for plant mineral nutrient acquisition. In temperate, mixed forests, ash roots (Fraxinus excelsior) are colonized by arbuscular mycorrhizal fungi (AM) and beech roots (Fagus sylvatica) by ectomycorrhizal fungi (EcM). Knowledge on the functions of different mycorrhizal species that coexist in the same environment is scarce. The concentrations of nutrient elements in plant and fungal cells can inform on nutrient accessibility and interspecific differences of mycorrhizal life forms. Here, we hypothesized that mycorrhizal fungal species exhibit interspecific differences in mineral nutrient concentrations and that the differences correlate with the mineral nutrient concentrations of their associated root cells. Abundant mycorrhizal fungal species of mature beech and ash trees in a long-term undisturbed forest ecosystem were the EcM Lactarius subdulcis, Clavulina cristata and Cenococcum geophilum and the AM Glomus sp. Mineral nutrient subcellular localization and quantities of the mycorrhizas were analysed after non-aqueous sample preparation by electron dispersive X-ray transmission electron microscopy. Cenococcum geophilum contained the highest sulphur, Clavulina cristata the highest calcium levels, and Glomus, in which cations and P were generally high, exhibited the highest potassium levels. Lactarius subdulcis-associated root cells contained the highest phosphorus levels. The root cell concentrations of K, Mg and P were unrelated to those of the associated fungal structures, whereas S and Ca showed significant correlations between fungal and plant concentrations of those elements. Our results support profound interspecific differences for mineral nutrient acquisition among mycorrhizas formed by different fungal taxa. The lack of correlation between some plant and fungal nutrient element concentrations may reflect different retention of mineral nutrients in the fungal part of the symbiosis. High mineral concentrations, especially of potassium, in Glomus sp. suggest that the well-known influence of tree species on chemical soil properties may be related to their mycorrhizal associates.
    Full-text · Article · Dec 2014 · PLoS ONE
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    Andrea Polle · Zhi-Bin Luo

    Full-text · Article · Dec 2014 · Environmental and Experimental Botany
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    ABSTRACT: Rapidly decreasing water availability as a consequence of climate change is likely to endanger the range of long-lived tree species. A pressing question is, therefore, whether adaptation to drought exists in important temperate tree species like European beech (Fagus sylvatica L.), a wide-spread, dominant forest tree in Central Europe. Here, five beech stands were selected along a precipitation gradient from moist to dry conditions. Neutral genetic markers revealed strong variation within and little differentiation between the populations. Natural regeneration from these stands was transferred to a common garden and used to investigate the expression of genes for abscisic acid (ABA)-related drought signaling [9-cis-epoxy-dioxygenase (NCED), protein phosphatase 2C (PP2C), early responsive to dehydration (ERD)] and stress protection [ascorbate peroxidase (APX), superoxide dismutase (SOD), aldehyde dehydrogenase (ALDH), glutamine amidotransferase (GAT)] that are involved in drought acclimation. We hypothesized that progenies from dry sites exhibit constitutively higher expression levels of ABA-and stress-related genes and are less drought responsive than progenies from moist sites. Transcript levels and stress responses (leaf area loss, membrane integrity) of well-irrigated and drought-stressed plants were measured during the early, mid-and late growing season. Principal component (PC) analysis ordered the beech progenies according to the mean annual precipitation at tree origin by the transcript levels of SOD, ALDH, GAT and ERD as major loadings along PC1. PC2 separated moist and drought treatments with PP2C levels as important loading. These results suggest that phosphatase-mediated signaling is flexibly acclimated to the current requirements, whereas stress compensatory measures exhibited genotypic variation, apparently underlying climate selection. In contrast to expectation, the drought responses were less pronounced than the progeny-related differences and the transcript levels were constitutively lower in beeches from dry than from moist sites. These results imply that beeches from dry origins may have evolved mechanisms to avoid oxidative stress.
    Full-text · Article · Dec 2014 · Tree Physiology
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    Zhi-Bin Luo · Chenhan Wu · Chao Zhang · Hong Li · Ulrike Lipka · Andrea Polle
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    ABSTRACT: Ectomycorrhizas (EMs) are mutualistic associations between certain soil fungi and higher plants. EMs can modulate the cellular, physiological and molecular processes of host plants, resulting in altered responses of the colonized plants to heavy metals. Progress in elucidating the role of EMs in modulating heavy metal tolerance of host trees is reviewed. In the last decade, a number of ectomycorrhizal fungal isolates and host plants have been characterized for their tolerance to heavy metals. Additionally, the cellular processes have been investigated with regard to heavy metal uptake, transport, distribution, toxicity and detoxification by ectomycorrhizal fungi and/or host plants. At the cellular level, mechanisms of heavy metal detoxification include (i) binding of heavy metals to cell wall and extracellular exudates, (ii) decreased uptake and/or pumping metal ions out of cytosol, (iii) chelation of metal ions in cytosol, (iv) compartmentation of metals in vacuoles or other subcellular structures, and (v) repair of damaged biomolecules. The efficiency of these protective measures is often increased by EMs, resulting in improved physiological status and rescued growth. While physiological and cellular responses to heavy metals have been well studied, experimental data on the underlying molecular mechanisms, especially those induced by the interaction of ectomycorrhizal fungi and hosts, are scattered. Progress in genome sequencing of EM partners has revealed the importance of metal transporters in mediating tolerance. A better understanding of the molecular mechanisms is essential for effective application of selected fungal isolates and hosts to improve the efficiency of bioremediation on heavy metal polluted sites.
    Full-text · Article · Dec 2014 · Environmental and Experimental Botany
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    ABSTRACT: The Paxillus involutus strains MAJ and NAU improve ion homeostasis under salt stress although only strain MAJ forms a functional ectomycorrhiza with poplar roots, whereas strain NAU induces defense reactions. The goal of the present study was to determine whether beneficial effects of MAJ and NAU on root nutrient element fluxes are induced during early stages of fungal-root interaction or require long-term co-culture. Salt-induced flux profiles of H+, Na+, K+, and Ca2+ were examined in the salt-sensitive poplar Populus × canescens after inoculation for 10 d and 20 d with the P. involutus strains, MAJ and NAU and after short-term (24 h) and long-term (7 d) salt stress. Inoculation with P. involutus for 10 d and 20 d increased the capacity of P. × canescens roots to retain K+ after short and long-term exposure to NaCl stress (100 mM). P. involutus-inoculated plants reduced the influx of Na+, especially in the NAU-inoculated roots. The salt-elicited Na+ efflux corresponded with an apparent decline of H+ extrusion in NAU-inoculated roots, which was presumably the result of increased Na+/H+ exchange activity across the plasma membrane. After 10 days of fungal inoculation, P. × canescens roots exhibited an enhanced Ca2+ uptake ability upon salt treatments, whereas a prolonged inoculation time of 20 d caused a marked Ca2+ efflux from P. × canescens roots. The P. involutus-elicited Ca2+ enrichment was probably replaced by Na+ at the later stage of fungal colonization. Ca2+ enrichment is known to mediate K+/Na+ homeostasis in poplar roots under salt stress and therefore both NAU- and MAJ-impeded Na+ accumulation compared with non-inoculated roots. NAU provided greater benefit to the inoculated roots to the maintenance of the K+/Na+ homeostasis because of the pronounced Na+ extrusion during the early stage of fungal colonization when the Ca2+ enrichment was greater than in MAJ-inoculated roots. In accordance with flux data, the whole-plant assessment revealed that inoculation with P. involutus attenuated NaCl-induced leaf damage in P. × canescens. Overall, our results support that the formation of a mature ectomycorrhiza is not required for the amelioration of the protection from salinity stress.
    Full-text · Article · Dec 2014 · Environmental and Experimental Botany
  • Lara Danielsen · Andrea Polle
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    ABSTRACT: The nutrient status and physiological responses to drought were investigated in young poplar (Populus x canescens) trees, which were either non-mycorrhizal (NM) or colonized with the ectomycorrhizal fungus Paxillus involutus (EM). Stomatal conductance declined rapidly with limited water availability indicating that Populus x canescens is a strongly water-saving tree species. EM trees showed higher stomatal conductance than NM trees but the magnitude of the effect was very small. Nitrogen uptake was traced by 15N. 15N enrichment was higher in EM root tips than in NM root tips. The 15N enrichment in root tips and in roots was significantly linked with stomatal conductance, whereas the enrichment in leaves was correlated with the enrichment in roots, indicating that N uptake is influenced by photosynthetic processes and that the internal translocation to leaves depends on the concentration in the below-ground tissues. Phosphorus and cations, in particular the main osmolyte potassium K, were enriched leaves of EM plants, but not in roots. Under drought, K and Mg increased in roots regardless the EM status, whereas the foliar concentrations increased only in EM plants. A decline in the leaf water content was prevented by increases in both, cations and soluble sugars. EM also delayed root tip mortality compared with NM plants, thus, suggesting transiently positive effects of EM on poplar performance under drought. Under stronger stress at water potentials of about -1.1 MPa, the transcript levels of stress marker genes (aquaporin PIP2.5, ABA-responsive RD26, ammonium transporter AMT3.1) were increased regardless the mycorrhizal status of the trees.
    No preview · Article · Dec 2014 · Environmental and Experimental Botany

Publication Stats

10k Citations
1,012.41 Total Impact Points

Institutions

  • 1999-2015
    • Universitätsmedizin Göttingen
      Göttingen, Lower Saxony, Germany
  • 1970-2015
    • Georg-August-Universität Göttingen
      • Department of Forest Botany and Tree Physiology
      Göttingen, Lower Saxony, Germany
  • 1994-2010
    • University of Freiburg
      • Institute of Forest Botany and Tree Physiology
      Freiburg, Baden-Württemberg, Germany
    • Klinikum Garmisch-Partenkirchen
      Markt Garmisch-Partenkirchen, Bavaria, Germany
  • 2007
    • Xinjiang University
      Hsin-chien, Jiangxi Sheng, China
  • 1988-1989
    • University of Cologne
      • Botanical Institute
      Köln, North Rhine-Westphalia, Germany