Rhizodermal Cells Research Articles

Two novel Archaeorhizomyces species isolated from ericoid mycorrhizal roots and their association with ericaceous plants in vitro

Archaeorhizomyces is a diverse and ubiquitous genus of the subphylum Taphrinomycotina, which contains soil-inhabiting/root-associated fungi. Although ecological importance and root-associating lifestyles of Archaeorhizomyces can be postulated, morphological aspects of fungal body and root colonization are largely unknown due to the scarcity of cultures. We obtained three unidentified Archaeorhizomyces isolates from ericoid mycorrhizal (ErM) roots of Rhododendron scabrum and Rhododendron × obtusum collected in Japan. To advance our understanding of lifestyle of the genus, we investigated their general morphology, phylogeny, and in vitro root-colonizing ability in ericoid mycorrhizal hosts, Vaccinium virgatum and Rhododendron kaempferi. Some morphological characteristics, such as slow glowing white-to-creamy-colored colonies and formation of yeast-like or chlamydospore-like cells, were shared between our strains and two described species, Archaeorhizomycesfinlayi and Archaeorhizomyces borealis, but they were phylogenetically distant. Our strains were clearly distinguished as two undescribed species based on morphology and phylogenetic relationship. As seen in typical ErM fungi, both species frequently formed hyphal coils within vital rhizodermal cells of ErM plants in vitro. The morphology of hyphal coils was also different between species. Consequently, two novel species, Archaeorhizomyces notokirishimae sp. nov. and Archaeorhizomyces ryukyuensis sp. nov., were described.

A cryptic root isolate belonging to Geoglossales from potted Rhododendron: its molecular phylogeny and ability to colonize an ericoid mycorrhizal host in vitro.

Although the lifestyle of Geoglossales remains largely unknown, recent advancements have established a hypothesis regarding the ericoid mycorrhizal lifestyle of geoglossoid fungi. In this study, we focused on one isolate of Geoglossales sp. obtained from surface-sterilized roots of potted Rhododendron transiens. We aimed to reveal the phylogenetic position and in vitro colonizing ability of this species in the hair roots of ericoid mycorrhizal plants. Based on our multigene phylogenetic tree, this species is a sister of the genus Sarcoleotia which has not been reported from either other studies or field environment. Its ascocarps could not be obtained, and conspecific sequences were not found in the databases and repositories examined. The Geoglossales sp. colonized the vital rhizodermal cells of blueberries in vitro with hyphal coils. There were relatively large morphological variations of coils consistent with extraradical hyphae; however, overall, the colonization morphologically resembled those by Sarcoleotia globosa and representative ericoid mycorrhizal fungi. The taxonomy and ecological significance of the species remain to be resolved; nevertheless, our results suggest that the ericoid mycorrhizal lifestyle may be widespread within Geoglossales.

Exploring structural and molecular diversity of Ericaceae hair root mycobionts: a comparison between Northern Bohemia and Argentine Patagonia.

Core Ericaceae produce delicate hair roots with inflated rhizodermal cells that host plethora of fungal symbionts. These poorly known mycobionts include various endophytes, parasites, saprobes, and the ericoid mycorrhizal (ErM) fungi (ErMF) that form the ErM symbiosis crucial for the fitness of their hosts. Using microscopy and high-throughput sequencing, we investigated their structural and molecular diversity in 14 different host × site combinations in Northern Bohemia (Central Europe) and Argentine Patagonia (South America). While we found typical ericoid mycorrhiza in all combinations, we did not detect ectomycorrhiza and arbuscular mycorrhiza. Superficial mantles of various thickness formed by non-clamped hyphae were observed in all combinations except Calluna vulgaris from N. Bohemia. Some samples contained frequent intercellular hyphae while others possessed previously unreported intracellular haustoria-like structures linked with intracellular hyphal coils. The 711 detected fungal OTU were dominated by Ascomycota (563) and Basidiomycota (119), followed by four other phyla. Ascomycetes comprised Helotiales (255), Pleosporales (53), Chaetothyriales (42), and other 19 orders, while basidiomycetes Sebacinales (42), Agaricales (28), Auriculariales (7), and other 14 orders. While many dominant OTU from both hemispheres lacked close relatives in reference databases, many were very similar to identical to unnamed sequences from around the world. On the other hand, several significant ericaceous mycobionts were absent in our dataset, incl. Cairneyella, Gamarada, Kurtia, Lachnum, and Leohumicola. Most of the detected OTU could not be reliably linked to a particular trophic mode, and only two could be reliably assigned to the archetypal ErMF Hyaloscypha hepaticicola. Probable ErMF comprised Hyaloscypha variabilis and Oidiodendron maius, both detected only in N. Bohemia. Possible ErMF comprised sebacinoid fungi and several unnamed members of Hyaloscypha s. str. While H. hepaticicola was dominant only in C. vulgaris, this model ErM host lacked O. maius and sebacinoid mycobionts. Hyaloscypha hepaticicola was absent in two and very rare in six combinations from Patagonia. Nine OTU represented dark septate endophytes from the Phialocephala fortinii s. lat.-Acephala applanata species complex, including the most abundant OTU (the only detected in all combinations). Statistical analyses revealed marked differences between N. Bohemia and Patagonia, but also within Patagonia, due to the unique community detected in a Valdivian temperate rainforest. Our results show that theericaceous hair roots may host diverse mycobionts with mostly unknown functions and indicate that many novel ErMF lineages await discovery. Transhemispheric differences (thousands of km) in their communities may be evenly matched by local differences (scales of km, m, and less).

Fungi in hair roots of Vaccinium spp. (Ericaceae) growing on decomposing wood: colonization patterns, identity, and in vitro symbiotic potential

Most of our knowledge on the ericoid mycorrhizal (ErM) symbiosis comes from temperate heathlands characterized by acidic peaty soils and many experiments with a few ascomycetous fungi. However, ericaceous plants thrive in many other ecosystems and in temperate coniferous forests, their seedlings often prosper on decomposing wood. While wood is typically exploited by basidiomycetous ectomycorrhizal (EcM) and saprobic fungi, the role of ErM fungi (ErMF) is much less clear. We explored the cultivable mycobiota of surface sterilized hair roots of Vaccinium spp. growing on decomposing wood in two coniferous forests in Mid-Norway (Scandinavia) and Northern Bohemia (Central Europe). Obtained isolates were identified using molecular tools and their symbiotic potential was tested in vitro. While the detected community lacked the archetypal ErMF Hyaloscypha hepaticicola and the incidence of dark septate endophytes and EcM fungi was negligible, it comprised other frequent asexual ascomycetous ErMF, namely H. variabilis and Oidiodendron maius, together with several isolates displaying affinities to sexual saprobic H. daedaleae and H. fuckelii. Ascomycete-suppressing media revealed representatives of the saprobic basidiomycetous genera Coprinellus, Gymnopilus, Mycena (Agaricales), and Hypochnicium (Polyporales). In the resyntheses, the tested basidiomycetes occasionally penetrated the rhizodermal cells of their hosts but never formed ericoid mycorrhizae and in many cases overgrew and killed the inoculated seedlings. In contrast, a representative of the H. daedaleae/H. fuckelii-related isolates repeatedly formed what morphologically appears as the ErM symbiosis and supported host's growth. In conclusion, while basidiomycetous saprobic fungi have a potential to colonize healthy-looking ericaceous hair roots, the mode(-s) of their functioning remain obscure. For the first time, a lineage in Hyaloscypha s. str. (corresponding to the former Hymenoscyphus ericae aggregate) where sexual saprobes are intermingled with root symbionts has been revealed, shedding new light on the ecology and evolution of these prominent ascomycetous ErMF.

Two novel Oidiodendron species isolated from roots of Vaccinium boninense in the Bonin Islands, Japan

Four strains of the fungal genus Oidiodendron were isolated from the fine roots of Vaccinium boniense which is distributed only on the Bonin Islands, Japan. Two new species, Oidiodendron tokumasui (NBRC 115411T) and Oidiodendron boninense (NBRC 115392T), are described in this paper. Molecular phylogenetic analyses based on multigene sequence-data showed that each novel species formed a unique clade. Oidiodendron tokumasui is phylogenetically related to O. maius but can be distinguished from O. maius by good growth at 25‒30 ˚C and pH 7‒9, colony diameter after 28 days, and length of the conidiophores. Oidiodendron boninense is phylogenetically related to O. setiferum, O. rammosum, O. muniellense, and O. fuscum but differs from those four species in the following aspects: good growth at 25 ˚C and pH 7, absence of melanized appendages, spinulate and thick-walled conidia, and length of the conidiophores. Both new species formed ericoid mycorrhizal-like hyphal coils in the rhizodermal cells of sterile blueberry seedlings in vitro.

Morphological, Histological and Ultrastructural Changes in Hordeum vulgare (L.) Roots That Have Been Exposed to Negatively Charged Gold Nanoparticles

In recent years, there has been an impressive development of nanotechnology. This has resulted in the increasing release of nanomaterials (NM) into the environment, thereby causing the risk of an uncontrolled impact on living organisms, including plants. More studies indicated the biotoxic effect of NM on plants, including crops. The interaction of nanoparticles (NP) with food crops is extremely important as they are a link to the food chain. The objective of this study was to investigate the effect of negatively charged gold nanoparticles (-) AuNP (at two concentrations; 25 µg/mL or 50 µg/mL) on barley (Hordeum vulgare L.) root development. Morphological, histological and ultrastructural analyses (with the use of stereomicroscope, bright filed microscope and transmission electron microscope) revealed that regardless of the concentration, (-) AuNP did not enter into the plant body. However, the dose of (-) AuNP proved to be important for the plant’s response because different morphological, histological and ultrastructural changes were observed in the treated roots. The NP treatment caused: red root colouration, a local increase in the root diameter and a decreased formation of the root hair cells (on morphological level), damage to the rhizodermal cells, vacuolisation of the cortical cells, a detachment of the cell files between the cortical cells, atypical divisions of the cells, disorder of the meristem organisation (on the histological level), the appearance of periplasmic space, numerous vesicles and multivesicular bodies, electron-dense spots in cytoplasm, alterations in the structure of the mitochondria, breakdown of the tonoplast and the plasmalemma (on the ultrastructural level).

Genetic variations and in vitro root-colonizing ability for an ericaceous host in Sarcoleotia globosa (Geoglossomycetes)

We discovered that Sarcoleotia globosa (Geoglossomycetes) fruited on the soil of ornamental Erica pot cultures, and its ascospores can germinate on plain agar. These findings prompted us to collect isolates from horticultural and natural environments in Japan and analyze their phylogeny and root colonizing ability. Pure cultures were successfully obtained from ascospores and surface-sterilized ericaceous roots. Phylogenetic analysis based on rRNA internal transcribed spacer sequences revealed that Japanese samples were separated into three strongly supported clades. Individual clade consisted of samples derived from (1) Erica pot cultures, (2) Rhododendron planted in a garden or Vaccinium pot culture, and (3) natural habitats in Hokkaido. Colony characteristics and in vitro root-colonizing morphology observed may correspond to these phylogenetic variations. Irrespective of the clades, all tested strains formed hyphal coils in vital rhizodermal cells of V. virgatum seedlings, which resembled those of ericoid mycorrhizae. Our results represent novel findings that can be the first step in unraveling the currently unknown ecology of geoglossoid fungi.

Slow-growing fungi belonging to the unnamed lineage in Chaetothyriomycetidae form hyphal coils in vital ericaceous rhizodermal cells in vitro

The diversity and functionality of ericoid mycorrhizal (ErM) fungi are still being understudied. Members of Chaetothyriomycetidae evolved a specific lifestyle of inhabiting extreme, poor, or toxic environments. Some taxa in this subclass, especially in Chaetothyriales, are also putative ErM taxa, but their mycorrhizal ability is mostly unknown because the members are generally hard to isolate from roots. This study herein focused on eight root isolates and provided their phylogeny and morphology of root colonization. Phylogenetic analysis based on rRNA sequences clarified that the isolated strains were not classified into Chaetothyriales, but in an unnamed lineage in Chaetothyriomycetidae. This lineage also contains rock isolates, bryosymbionts, and a resinicolous species as well as various environmental sequences obtained from soil/root samples. All strains grew extremely slow by mycelia on cornmeal or malt extract agar (2.9–8.5 mm/month) and formed hyphal coils in vital rhizodermal cells of sterile blueberry seedlings in vitro. This study illustrated the presence of a novel putative ErM lineage in Chaetothyriomycetidae.

Aluminum Alters the Histology and Pectin Cell Wall Composition of Barley Roots

Aluminum (Al) is one of the most important crust elements causing reduced plant production in acidic soils. Barley (Hordeum vulgare L.) is considered to be one of the crops that is most sensitive to Al, and the root cell wall is the primary target of Al toxicity. In this study, we evaluate the possible involvement of specific pectic epitopes in the cells of barley roots in response to aluminum exposure. We targeted four different pectic epitopes recognized by LM5, LM6, LM19, and LM20 antibodies using an immunocytochemical approach. Since Al becomes available and toxic to plants in acidic soils, we performed our analyses on barley roots that had been grown in acidic conditions (pH 4.0) with and without Al and in control conditions (pH 6.0). Differences connected with the presence and distribution of the pectic epitopes between the control and Al-treated roots were observed. In the Al-treated roots, pectins with galactan sidechains were detected with a visually lower fluorescence intensity than in the control roots while pectins with arabinan sidechains were abundantly present. Furthermore, esterified homogalacturonans (HGs) were present with a visually higher fluorescence intensity compared to the control, while methyl-esterified HGs were present in a similar amount. Based on the presented results, it was concluded that methyl-esterified HG can be a marker for newly arising cell walls. Additionally, histological changes were detected in the roots grown under Al exposure. Among them, an increase in root diameter, shortening of root cap, and increase in the size of rhizodermal cells and divisions of exodermal and cortex cells were observed. The presented data extend upon the knowledge on the chemical composition of the cell wall of barley root cells under stress conditions. The response of cells to Al can be expressed by the specific distribution of pectins in the cell wall and, thus, enables the knowledge on Al toxicity to be extended by explaining the mechanism by which Al inhibits root elongation.

Drought stress stimulates endocytosis and modifies membrane lipid order of rhizodermal cells of Medicago truncatula in a genotype-dependent manner

BackgroundDrought stress negatively affects plant growth and productivity. Plants sense soil drought at the root level but the underlying mechanisms remain unclear. At the cell level, we aim to reveal the short-term root perception of drought stress through membrane dynamics.ResultsIn our study, 15 Medicago truncatula accessions were exposed to a polyethylene glycol (PEG)-induced drought stress, leading to contrasted ecophysiological responses, in particular related to root architecture plasticity. In the reference accession Jemalong A17, identified as drought susceptible, we analyzed lateral roots by imaging of membrane-localized fluorescent probes using confocal microscopy. We found that PEG stimulated endocytosis especially in cells belonging to the growth differentiation zone (GDZ). The mapping of membrane lipid order in cells along the root apex showed that membranes of root cap cells were more ordered than those of more differentiated cells. Moreover, PEG triggered a significant increase in membrane lipid order of rhizodermal cells from the GDZ. We initiated the membrane analysis in the drought resistant accession HM298, which did not reveal such membrane modifications in response to PEG.ConclusionsOur data demonstrated that the plasma membranes of root cells from a susceptible genotype perceived drought stress by modulating their physical state both via a stimulation of endocytosis and a modification of the degree of lipid order, which could be proposed as mechanisms required for signal transduction.

Increased root hair density by loss of WRKY6 in Arabidopsis thaliana.

Root hairs are unicellular elongations of certain rhizodermal cells that improve the uptake of sparingly soluble and immobile soil nutrients. Among different Arabidopsis thaliana genotypes, root hair density, length and the local acclimation to low inorganic phosphate (Pi) differs considerably, when analyzed on split agar plates. Here, genome-wide association fine mapping identified significant single nucleotide polymorphisms associated with the increased root hair density in the absence of local phosphate on chromosome 1. A loss-of-functionmutant of the candidate transcription factor gene WRKY6, which is involved in the acclimation of plants to low phosphorus, had increased root hair density. This is partially explained by a reduced cortical cell diameter in wrky6-3, reducing the rhizodermal cell numbers adjacent to the cortical cells. As a consequence, rhizodermal cells in positions that are in contact with two cortical cells are found more often, leading to higher hair density. Distinct cortical cell diameters and epidermal cell lengths distinguish other Arabidopsis accessions with distinct root hair density and −Pi response from diploid Col-0, while tetraploid Col-0 had generally larger root cell sizes, which explain longer hairs. A distinct radial root morphology within Arabidopsis accessions and wrky6-3explains some, but not all, differences in the root hair acclimation to –Pi.

Is the root-colonizing endophyte Acremonium strictum an ericoid mycorrhizal fungus?

In previous investigations, we found that Acremonium strictum (strain DSM 100709) developed intracellular structures with similarity to mycelia of ericoid mycorrhizal fungi in the rhizodermal cells of flax plants and in hair roots of Rhododendron plantlets. A. strictum had also been isolated from roots of ericaceous salal plants and was described as an unusual ericoid mycorrhizal fungus (ERMF). As its mycorrhizal traits were doubted, we revised the hypothesis of a mycorrhizal nature of A. strictum. A successful synthesis of mycorrhiza in hair roots of inoculated ericaceous plants was a first step of evidence, followed by fluorescence microscopy with FUN(®)1 cell stain to observe the vitality of the host cells at the early infection stage. In inoculation trials with in vitro-raised mycorrhiza-free Rhododendron plants in axenic liquid culture and in greenhouse substrate culture, A. strictum was never observed in living hair root cells. As compared to the ERMF Oidiodendron maius and Rhizoscyphus ericae that invaded metabolically active host cells and established a symbiotic unit, A. strictum was only found in cells that were dead or in the process of dying and in the apoplast. In conclusion, A. strictum does not behave like a common ERMF-if it is one at all. A comparison of A. strictum isolates from ericaceous and non-ericaceous hosts could reveal further identity details to generalize or specify our findings on the symbiotic nature of A. strictum. At least, the staining method enables to discern between true mycorrhizal and other root endophytes-a tool for further studies.

Arabidopsis FH1 Formin Affects Cotyledon Pavement Cell Shape by Modulating Cytoskeleton Dynamics.

Plant cell morphogenesis involves concerted rearrangements of microtubules and actin microfilaments. We previously reported that FH1, the main Arabidopsis thaliana housekeeping Class I membrane-anchored formin, contributes to actin dynamics and microtubule stability in rhizodermis cells. Here we examine the effects of mutations affecting FH1 (At3g25500) on cell morphogenesis and above-ground organ development in seedlings, as well as on cytoskeletal organization and dynamics, using a combination of confocal and variable angle epifluorescence microscopy with a pharmacological approach. Homozygous fh1 mutants exhibited cotyledon epinasty and had larger cotyledon pavement cells with more pronounced lobes than the wild type. The pavement cell shape alterations were enhanced by expression of the fluorescent microtubule marker GFP-microtubule-associated protein 4 (MAP4). Mutant cotyledon pavement cells exhibited reduced density and increased stability of microfilament bundles, as well as enhanced dynamics of microtubules. Analogous results were also obtained upon treatments with the formin inhibitor SMIFH2 (small molecule inhibitor of formin homology 2 domains). Pavement cell shape in wild-type (wt) and fh1 plants in some situations exhibited a differential response towards anti-cytoskeletal drugs, especially the microtubule disruptor oryzalin. Our observations indicate that FH1 participates in the control of microtubule dynamics, possibly via its effects on actin, subsequently influencing cell morphogenesis and macroscopic organ development.

Protein Dynamics in Young Maize Root Hairs in Response to Macro- and Micronutrient Deprivation.

Plants increase their root surface with root hairs to improve the acquisition of nutrients from the soil. The unicellular character of root hairs and their position at the root surface make them an attractive system to investigate adaptive processes of rhizodermal cells that are in direct contact with the soil solution. In young maize seedlings, roots are densely covered with root hairs, although nutrient reserves in the seed are sufficient to support seedling growth rates for a few days. We used a label-free quantitative proteomics approach to study protein abundance adjustments in 4 day old root hairs grown in aeroponic culture in the presence and absence of several macro- and micronutrients. Compared to the proteome of root hairs developed under full nutrition, protein abundance changes were observed in pathways related to macronutrient (N, P, K, and Mg) deficiencies. For example, lack of N in the medium repressed the primary N metabolism pathway, increased amino acid synthesis, but repressed their degradation, and affected the primary carbon metabolism, such as glycolysis. Glycolysis was similarly affected by K and P deprivation, but the glycolytic pathway was negatively regulated by the absence of the micronutrients Fe and Zn. In contrast, the deprivation of Mn had almost no affect on the root hair proteome. Our results indicate either that the metabolism of very young root hairs adjusts to cellular nutrient deficiencies that have been already experienced or that root hairs sense the external lack of specific nutrients in the nutrient solution and adjust their metabolism accordingly.

Anatomically and morphologically unique dark septate endophytic association in the roots of the Mediterranean endemic seagrass Posidonia oceanica.

Roots of terrestrial plants host a wide spectrum of soil fungi that form various parasitic, neutral and mutualistic associations. A similar trend is evident in freshwater aquatic plants and plants inhabiting salt marshes or mangroves. Marine vascular plants (seagrasses), by contrast, seem to lack specific root-fungus symbioses. We examined roots of two Mediterranean seagrasses, Posidonia oceanica and Cymodocea nodosa, in the northwestern Mediterranean Sea for fungal colonization using light and scanning and transmission electron microscopy. We found that P. oceanica, but not C. nodosa, is regularly associated with melanized septate hyphae in a manner resembling colonization by the ubiquitous dark septate endophytes (DSE) in roots of most terrestrial plants. P. oceanica roots were found to be colonized by sparse dematiaceous running hyphae as well as dense parenchymatous nets/hyphal sheaths on the root surface, intracellular melanized microsclerotia and occasionally also intra- and intercellular hyphae. The colonization was most prominent in the thick-walled hypodermis of the thinnest healthy looking roots, and the mycobiont seemed to colonize both living and dead host cells. Dark septate hyphae infrequently occurred also inside rhizodermal cells, but never colonized vascular tissues. The biological significance of this overlooked marine symbiosis remains unknown, but its morphology, extent, distribution across the NW Mediterranean Sea and absence in C. nodosa indicate an intriguing relationship between the dominant Mediterranean seagrass and its dark septate root mycobionts.

A nitrogen-dependent switch in the high affinity ammonium transport in Medicago truncatula

Ammonium transporters (AMTs) are crucial for the high affinity primary uptake and translocation of ammonium in plants. In the model legume Medicago truncatula, the genomic set of AMT-type ammonium transporters comprises eight members. Only four genes were abundantly expressed in young seedlings, both in roots and shoots. While the expression of all AMTs in the shoot was not affected by the nitrogen availability, the dominating MtAMT1;1 gene was repressed by nitrogen in roots, despite that cellular nitrogen concentrations were far above deficiency levels. A contrasting de-repression by nitrogen was observed for MtAMT1;4 and MtAMT2;1, which were both expressed at intermediate level. Weak expression was found for MtAMT1;2 and MtAMT2;3, while the other AMTs were not detected in young seedlings. When expressed from their endogenous promoters, translational fusion proteins of MtAMT1;1 and MtAMT2;1 with green fluorescent protein were co-localized in the plasma membrane of rhizodermal cells, but also detected in cortical root layers. Both transporter proteins similarly functionally complemented a yeast strain that is deficient in high affinity ammonium transport, both at acidic and neutral pH. The uptake into yeast mediated by these transporters saturated with Km AMT1;1 = 89 µM and Km AMT2;1 = 123 µM, respectively. When expressed in oocytes, MtAMT1;1 mediated much larger (15)N-ammonium uptake than MtAMT2;1, but NH4 (+) currents were only recorded for MtAMT1;1. These currents saturated with a voltage-dependent Km = 90 µM at -80 mV. The cellular localization and regulation of the AMTs suggests that MtAMT1;1 encodes the major high affinity ammonium transporter gene in low nitrogen grown young M. truncatula roots and despite the similar localization and substrate affinity, MtAMT2;1 appears functionally distinct and more important at higher nitrogen supply.

Microtubule dynamics is required for root elongation growth under osmotic stress in Arabidopsis

Osmotic stress caused by drought and soil salinity is one of the factors that affect plant root system growth and development. Previous studies have shown that microtubule plays a critical role in plant roots response to osmotic stress, however, the underlying mechanism remains unclear. In the present study, the microtubule orientations in Arabidopsis roots growing under osmotic stress were determined using confocal fluorescence microscopy. The results showed that osmotic stress could significantly inhibit primary root elongation in Arabidopsis, and pharmacological tests confirmed that microtubules were involved in Arabidopsis roots response to osmotic stress. In vivo visualization of microtubule structures with the microtubule-binding domain–green fluorescent protein (GFP) reporter revealed altered microtubule orientation in rhizodermal cells under osmotic stress. These results above indicated that osmotic stress could inhibit the elongation growth of Arabidopsis primary root, and the inhibition effects might result from the changes in microtubule orientation.

Restoration of cell growth and proliferation in the wheat roots after their inhibition by nickel sulfate

The dynamics of cell growth and proliferation restoration in different tissues and quiescent center (QC) in the wheat (Triticum aestivum L.) seedling roots and also the differentiation of rhizodermal cells and lateral root initiation after 48-h treatment with 100 μM NiSO4 were studied. Within 24 h after nickel removal from medium, root growth was resumed due to the increase in the rate of cell growth in the meristem and the region where cell elongation started in control roots. Stimulation of cell proliferation was restored in the main part of the meristem and later in the initial cells of the files and QC. Cell proliferation was not observed in the QC. The time of cell proliferation resumption in the roots and in tested tissues depended on the degree of their injury by nickel treatment. In most tested roots, DNA synthesis and cell division were restored in 32 h. In the cells leaving the meristem due to the resumption of their growth and proliferation, growth of root hairs started. In 48 h, the number of roots with perished cells in the rhizodermis in the meristem was sharply increased and the regeneration of the damaged region by the cells of outer cortex was observed. Only after the appearance of root hairs, the cells coming from the meristem started to elongate. In most roots, the formation of the new elongation zone occurred in 56 h. During its formation, the initiation of lateral root primordia was shifted in the basipetal direction. It was concluded that the cessation of cell growth and proliferation under the influence of high concentration of heavy metal (HM) ions is not lethal for the root. At the action of toxic HM concentrations, the plant strategy is the maintenance of meristematic cell capacity for cell growth and proliferation resumption. The cellular mechanism of this capacity maintenance is the transition of meristematic cells from G1 phase to dormancy due to growth inhibition and the inhibition of the transition to DNA synthesis.

Root response in Pisum sativum and Zea mays under fluoranthene stress: Morphological and anatomical traits

Introduced organic pollutants in all ecosystem compartments can cause stress resulting in a wide range of responses including different root development. In this study, the effects of a polycyclic aromatic hydrocarbon–fluoranthene (FLT; 0.1, 1 and 7mgL−1) on the growth, morphology and anatomical structure of roots of pea and maize was evaluated. In comparison with pea, significant stimulation of root system growth of maize caused by 0.1mgL−1 (total length longer by 25%, number of lateral roots by 35%) and its reduction (total length by 34%) already by 1mgL−1 FLT is the proof of different interspecies sensitivity to low and higher environmental loading. Nevertheless in both plant species a high loading 7mgL−1 FLT significantly reduced both growth (total length by 95% in pea, 94% in maize) and the number of lateral roots (by 78% in pea, 94% in maize).Significantly increased thickness of root of both maize and pea was caused by 7mgL−1 FLT and in maize already by 0.1mgL−1 FLT. It may be mainly connected with an enlargement of stele area (up to 50% in pea and 25% in maize). Increased xylem area in root tip (by up to 385% in pea, 167% in maize) and zone of maturation (up to 584% in pea, 70% in maize) and its higher portion in stele area of root tip (by 9% in pea, 21% in maize), mainly in roots exposed 7mgL−1 FLT, are a proof of an early differentiation of vascular tissue and a shortening of root elongation zone. Moreover in both plant species exposed to this treatment, the decline of rhizodermis cells and external layers of primary cortex was found and also significant deformation of primordia of lateral roots was recorded.

Copper accumulation, translocation, and toxic effects in grapevine cuttings

Although the ecotoxicological effects of copper (Cu) on grapevine are of global concern due to the intensive and long-term application of Cu-based fungicides in vineyards, comparatively little is known about the phytotoxicity, accumulation, and translocation of Cu in grapevines. Therefore, this study was to conduct a hydroponic experiment to determine the influence of solution Cu concentration not only on bioaccumulation and the translocation of Cu in grapevine roots, stems, and leaves, but also on the subsequent growth inhibition of the roots. Grapevine cuttings were grown for 30 days and then exposed to various Cu concentrations (0.1-50 μM) for 15 days. The dose-response profile was described by a sigmoid Hill equation. Optical microscopy was used to examine the cytotoxicity of Cu on the roots. In addition, bioaccumulation factors (BAFs) and translocation factors (TFs) were calculated from the results of the hydroponic experiment. Copper was tolerated by grapevines at a concentration ≤1 μM. The median inhibition concentration (IC(50)) obtained from the Hill model was 3.94 μM (95% confidence interval, 3.65-4.24). From the light micrographs of root tip cells, signs of toxicity including increased vacuolization and plasmolysis were observed at solution Cu concentrations ≥10 μM. In addition, a higher Cu concentration was found in the roots (25-12,000 mg kg(-1)) than in the stems (5-540 mg kg(-1)) and leaves (7-46 mg kg(-1)), indicating a very limited translocation of Cu from the roots to the aboveground parts. This study investigated not only the macroscopic root growth and Cu accumulation by grapevine, but also the microscopic changes in root tissue at the cell level after the exposure experiment. Based on the BAFs and TFs, the grapevine could be considered a Cu-exclusive plant. For toxic effects on the exposure of roots to Cu, this study also revealed that root growth, as well as the histological changes in rhizodermal cells, can be used as phytotoxic indicators of grapevine under Cu stress.