Root Cap Cells Research Articles

Nostoc sp. extract induces oxidative stress-mediated root cell destruction in Mimosa pigra L.

BackgroundMimosa pigra is an invasive weed in some regions of South East Asia and Australia. Our previous study has revealed that a cyanobacterium, Nostoc sp., extract can inhibit root growth in M. pigra seedlings. In this study, some physiological processes involve oxidative stress-mediated cell death and root ultrastructure were investigated to clarify the mechanisms of root growth suppression and bioherbicidal potential of the extract.ResultsNostoc sp. extract enhanced overproduction of reactive oxygen species (ROS) at 24 h, the intensity of red fluorescence increased at 72 h, and caused a slightly increased H2O2 consistent with the activation of scavenging enzymes (catalase, ascorbic acid peroxidase, glutathione reductase, and peroxidases). This suggests that oxidative stress occurred in the presence of the extract which was supported by increased cell death and lipid peroxidation at 24 h. Reduction of malondialdehyde content and an increase in cell death at 72 h indicated oxidative damage and cellular leakage. Ultrastructural changes were determined at 72 h by scanning electron micrographs which confirmed the damage of epidermal and root cap cells and the disaggregation and destruction of root tip cells. Transmission electron micrographs showed the dissolution of the middle lamella, deposition of some substances in vacuoles, and abnormal mitochondria (swollen mitochondria and indistinct cristae).ConclusionsNostoc sp. extract enhance oxidative stress by ROS production resulting in lipid peroxidation and massive cell death despite the activation of antioxidative enzymes. Understanding mechanism of action of Nostoc sp. extract will provide information for application of the extract to use as natural herbicide for control of M. pigra.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-014-0081-3) contains supplementary material, which is available to authorized users.

Cytoplasmic segregation in onion root tip cells and formation of vacuoles

Onion root tips were studied both with transmission and scanning electron microscope. The cells in the meristematic region of initials were found to be little vacuolated. At early stages of cell differentiation areas free of ribosomes are segregated in the cytoplasm. No (or only incomplete) membranes delimiting such areas could be distinguished in most cases. Seemingly, the membraneous structures may form later or simultaneously with the progress of breakdown of biostructure of the cytoplasm in the segregated area. The microscopic image of cytoplasm in the segregated areas (and even of the vacuolar sap at early stages of vacuole formation) resembles the matrix of cytoplasm populated with ribosomes. The cytoplasm in the whole central area is segregated at early stages of differentiation of root cap cells. The process of autophagic vacuoles formation in which the preexisting endomembranes seemingly are involved is described. It is proposed that such vacuoles may form after separation of two unit membranes of a cisternae surrounding a portion of the cytoplasm or an organelle, followed by independent growth of an outer unit membrane.

Over-expression of AtEXLA2 alters etiolated arabidopsis hypocotyl growth.

Plant stature and shape are largely determined by cell elongation, a process that is strongly controlled at the level of the cell wall. This is associated with the presence of many cell wall proteins implicated in the elongation process. Several proteins and enzyme families have been suggested to be involved in the controlled weakening of the cell wall, and these include xyloglucan endotransglucosylases/hydrolases (XTHs), yieldins, lipid transfer proteins and expansins. Although expansins have been the subject of much research, the role and involvement of expansin-like genes/proteins remain mostly unclear. This study investigates the expression and function of AtEXLA2 (At4g38400), a member of the expansin-like A (EXLA) family in arabidposis, and considers its possible role in cell wall metabolism and growth. Transgenic plants of Arabidopsis thaliana were grown, and lines over-expressing AtEXLA2 were identified. Plants were grown in the dark, on media containing growth hormones or precursors, or were gravistimulated. Hypocotyls were studied using transmission electron microscopy and extensiometry. Histochemical GUS (β-glucuronidase) stainings were performed. AtEXLA2 is one of the three EXLA members in arabidopsis. The protein lacks the typical domain responsible for expansin activity, but contains a presumed cellulose-interacting domain. Using promoter::GUS lines, the expression of AtEXLA2 was seen in germinating seedlings, hypocotyls, lateral root cap cells, columella cells and the central cylinder basally to the elongation zone of the root, and during different stages of lateral root development. Furthermore, promoter activity was detected in petioles, veins of leaves and filaments, and also in the peduncle of the flowers and in a zone just beneath the papillae. Over-expression of AtEXLA2 resulted in an increase of >10 % in the length of dark-grown hypocotyls and in slightly thicker walls in non-rapidly elongating etiolated hypocotyl cells. Biomechanical analysis by creep tests showed that AtEXLA2 over-expression may decrease the wall strength in arabidopsis hypocotyls. It is concluded that AtEXLA2 may function as a positive regulator of cell elongation in the dark-grown hypocotyl of arabidopsis by possible interference with cellulose metabolism, deposition or its organization.

The production, localization and spreading of reactive oxygen species contributes to the low vitality of long-term stored common beech (Fagus sylvatica L.) seeds

The common beech (Fagus sylvatica L.) is propagated by seeds, but the seed set is irregular with five to ten years in between crops. It is therefore necessary to store the seeds. However, beech seeds lose germinability during long-term storage. In this study, beech seeds were stored at −10°C under controlled conditions for 2, 5, 8, 11 and 13 years. Our results show that beech seeds lose germinability during storage in proportion to the duration of storage. The decrease in germinability correlated with increased electrolyte leakage and accumulation of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. Furthermore, a strong positive correlation was observed among the releases of superoxide anion radicals, hydrogen peroxide and hydroxyl radicals. In situ localization showed that superoxide anion radicals and hydrogen peroxide were first detectable in root cap cells. When the seed storage time was extended, the reactive oxygen species fluorescence expanded to more areas of the radicle, reaching the root apical meristem. A storage time-dependent decrease in catalase activity, observed in both embryonic axes and cotyledons, was also positively correlated with germinability. DNA fragmentation was observed in beech seeds during storage and occurred predominantly in embryonic axes stored for 5 years and more. Altogether, these results suggest that the loss of germinability in beech seeds during long-term storage depends on several factors, including strong of reactive oxygen species accumulation accompanied by reduced catalase activity as well as membrane injury and DNA alternations, which may be aging-related and ROS-derived. We suggest that the accumulating reactive oxygen species that spread to the root apical meristem are key factors that affect seed germinability after long-term storage.

The soybean mycorrhiza-inducible phosphate transporter gene, GmPT7, also shows localized expression at the tips of vein endings of senescent leaves.

GmPT7 was originally identified as an arbuscular mycorrhiza-inducible gene of soybean that encodes a member of subfamily I in the PHOSPHATE TRANSPORTER 1 family. In the present study, we established conditions under which a number of dwarf soybean plants complete their life cycles in a growth chamber. Using this system, we grew transgenic soybean with a GmPT7 promoter-β-glucuronidase fusion gene and evaluated GmPT7 expression in detail. GmPT7 was highly expressed in mature, but not in collapsed, arbuscule-containing cortical cells, suggesting its importance in the absorption of fungus-derived phosphate and/or arbuscule development. GmPT7 was also expressed in the columella cells of root caps and in the lateral root primordia of non-mycorrhizal roots. The expression of GmPT7 occurred only in the late stage of phosphorus translocation from leaves to seeds, after water evaporation from the leaves ceased, and later than the expression of GmUPS1-2, GmNRT1.7a and GmNRT1.7b, which are possibly involved in nitrogen export. GmPT7 expression was localized in a pair of tracheid elements at the tips of vein endings of senescent leaves. Transmission electron microscopy revealed that the tip tracheid elements in yellow leaves were still viable and had intact plasma membranes. Thus, we think that GmPT7 on the plasma membranes transports phosphate from the apoplast into the tip elements. GmPT7 knockdown resulted in no significant effects, the function of GmPT7 remaining to be clarified. We propose a working model in which phosphate incorporated in vein endings moves to seeds via xylem to phloem transfer.

The dual effects of root-cap exudates on nematodes: from quiescence in plant-parasitic nematodes to frenzy in entomopathogenic nematodes.

To defend themselves against herbivores and pathogens, plants produce numerous secondary metabolites, either constitutively or de novo in response to attacks. An intriguing constitutive example is the exudate produced by certain root-cap cells that can induce a state of reversible quiescence in plant-parasitic nematodes, thereby providing protection against these antagonists. The effect of such root exudates on beneficial entomopathogenic nematodes (EPNs) remains unclear, but could potentially impair their use in pest management programmes. We therefore tested how the exudates secreted by green pea (Pisum sativum) root caps affect four commercial EPN species. The exudates induced reversible quiescence in all EPN species tested. Quiescence levels varied with the green pea cultivars tested. Notably, after storage in root exudate, EPN performance traits were maintained over time, whereas performances of EPNs stored in water rapidly declined. In sharp contrast to high concentrations, lower concentrations of the exudate resulted in a significant increase in EPN activity and infectiousness, but still reduced the activity of two plant-parasitic nematode species. Our study suggests a finely tuned dual bioactivity of the exudate from green pea root caps. Appropriately formulated, it can favour long-term storage of EPNs and boost their infectiousness, while it may also be used to protect plants from plant-parasitic nematodes.

Functional and Evolutionary Analysis of the CASPARIAN STRIP MEMBRANE DOMAIN PROTEIN Family.

CASPARIAN STRIP MEMBRANE DOMAIN PROTEINS (CASPs) are four-membrane-span proteins that mediate the deposition of Casparian strips in the endodermis by recruiting the lignin polymerization machinery. CASPs show high stability in their membrane domain, which presents all the hallmarks of a membrane scaffold. Here, we characterized the large family of CASP-like (CASPL) proteins. CASPLs were found in all major divisions of land plants as well as in green algae; homologs outside of the plant kingdom were identified as members of the MARVEL protein family. When ectopically expressed in the endodermis, most CASPLs were able to integrate the CASP membrane domain, which suggests that CASPLs share with CASPs the propensity to form transmembrane scaffolds. Extracellular loops are not necessary for generating the scaffold, since CASP1 was still able to localize correctly when either one of the extracellular loops was deleted. The CASP first extracellular loop was found conserved in euphyllophytes but absent in plants lacking Casparian strips, an observation that may contribute to the study of Casparian strip and root evolution. In Arabidopsis (Arabidopsis thaliana), CASPL showed specific expression in a variety of cell types, such as trichomes, abscission zone cells, peripheral root cap cells, and xylem pole pericycle cells.

Abundance and composition of ammonia oxidizers in response to degradation of root cap cells of rice in soil microcosms

Nitrification is a key process in the global nitrogen cycle, of which the first and rate-limiting step is catalyzed by ammonia monooxygenase. Root cap cells are one of substrates for microorganisms that thrive in the rhizosphere. The degradation of root cap cells brings about nitrification following ammonification of organic nitrogen derived from the root cap cells. This study was designed to gain insights into the response of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to mineralized N from root cap cells and the composition of active bacterial and archaeal ammonia oxidizers in rice soil. Rice callus cells were used as a model for root cap cells, and unlabelled (12C) and 13C-labelled callus cells were allowed to decompose in aerobic soil microcosms. Real-time quantitative polymerase chain reaction (PCR), DNA-based stable isotope probing (SIP), and denaturing gradient gel electrophoresis (DGGE) were applied to determine the copy number of bacterial and archaeal amoA genes and the composition of active AOB and AOA. The growth of AOB was significantly stimulated by the addition of callus cells compared with the growth of AOA with a much lesser extent. AOB communities assimilated 13C derived from the callus cells, whereas no AOA communities grew on 13C-callus. Sequencing of the DGGE bands in the SIP experiments revealed that the AOB communities belonging to Nitrosospira spp. dominated microbial ammonia oxidation with rice callus amendment in soil. The present study suggests that root cap cells of rice significantly stimulated the growth of AOB, and the active members dominating microbial ammonia oxidation belonged to Nitrosospira spp. in rice rhizosphere.

Programmed Cell Death Controlled by ANAC033/SOMBRERO Determines Root Cap Organ Size in Arabidopsis

The root cap is a plant organ that ensheathes the meristematic stem cells at the root tip. Unlike other plant organs, the root cap shows a rapid cellular turnover, balancing constant cell generation by specific stem cells with the disposal of differentiated cells at the root cap edge. This cellular turnover is critical for the maintenance of root cap size and its position around the growing root tip, but how this is achieved and controlled in the model plant Arabidopsis thaliana remains subject to contradictory hypotheses. Here, we show that a highly organized cell death program is the final step of lateral root cap differentiation and that preparation for cell death is transcriptionally controlled by ANAC033/SOMBRERO. Precise timing of cell death is critical for the elimination of root cap cells before they fully enter the root elongation zone, which in turn is important in order to allow optimal root growth. Root cap cell death is followed by a rapid cell-autonomous corpse clearance and DNA fragmentation dependent on the S1-P1 type nuclease BFN1. Based on these results, we propose a novel concept in plant development that recognizes programmed cell death as a mechanism for maintaining organ size and tissue homeostasis in the Arabidopsis root cap.

Specific Expression of DR5 Promoter in Rice Roots Using a tCUP Derived Promoter-Reporter System

Variation of transgene expression caused by either position effect at the insertion site or the promoter/enhancer elements employed for the expression of selectable marker genes has complicated phenotype characterization and caused misinterpretation. We have developed a reporter system in rice to analyze the influence of vector configuration, spacer and selectable marker gene promoter on the expression of the promoterless GUS reporter and DR5 promoter. Our results indicate that a spacer inserted between the reversed 35S promoter and the GUS reporter could reduce leaky expression of the reporter but was unable to block the nonspecific expression of DR5::GUS. Stacking the selectable marker unit in head to tail with the GUS reporter aided the gene specific expression of the GUS reporter under the DR5 promoter even when the 35S promoter is used for expression of the selectable marker. Compared to 35S under this configuration, a quick and distinctive expression of DR5::GUS was observed in the root cap, quiescent center and xylem cells in the root apical meristem by using the tCUP derived promoter (tCUP1) for selection, that is similar to the pattern obtained by a sensitive DR5 variant (DR5rev) in Arabidopsis. These data suggest a conserved property of the tCUP promoter in preventing enhancer-promoter interactions in rice as it does in Arabidopsis, and also demonstrate that an analogous distal auxin maximum exists in roots of rice. Therefore, the tCUP promoter based selection system provides a new strategy for specific expression of transgenes in rice.

Influence of lead on the development of lupin seedlings and ultrastructural localization of this metal in the roots

The effect of lead on the early phases of development of yellow lupin seedlings was investigated. In the presence of this metal the number of germinating seeds was found to diminish distinctly, the hypocotyls and roots were shorter and the fresh weight and anthocyanin content in the cotyledones were markedly decreased. In the root cap cells lead was present in the vacuoles, ER, dictyosomes, the nuclear envelope and cell walls.

Growth of hydrogenotrophic and acetoclastic methanogens on substrate from rice plant callus cells in anaerobic soil: an estimation to the role of slough-off root cap cells to their growth

Flooded paddy fields are the major anthropogenic sources of methane (CH4) emission, and organic materials of rice plant origin were estimated to be important as its source. This study used rice (Oryza sativa L. cv, Yukihikari) callus cells as a model material for slough-off root cap cells, and carbon-13 (13C)-labelled callus cells were subjected to decomposition in aerobic and anaerobic soil microcosms for 56 days. DNA was extracted from a soil incubated with carbon-12 (12C)- and 13C-callus cells and subjected to buoyant density gradient centrifugation to identify methanogenic archaeal species that assimilated carbon from the callus cells. 13C-labelled 16S rRNA gene (16S rDNA) fragments from methanogenic archaea were not polymerase chain reaction (PCR)-amplified in heavy fractions under aerobic soil conditions, while they were successfully done from day 3 onwards under anaerobic soil conditions. Eighty-four denaturing gradient gel electrophoresis (DGGE) bands in heavy fractions were sequenced, revealing that they were members of Methanosarcina spp. (20 clones), Methanosaeta spp. (18 clones), Methanocella spp. (25 clones), Methanomicrobiales (10 clones), Methanobacterium spp. (7 clones) and Cluster ZC-I (2 clones). They included hydrogenotrophic and acetoclastic methanogens and were phylogenetically different from those residing in rice roots and, presumably, from those assimilating root exudate and mucilage-derived carbon. This study indicates that carbon of slough-off root cap cells propagates specific methanogenic species in rice rhizosphere under anaerobic soil conditions and thus augments the diversity of the total rhizospheric methanogenic community.

Tissue-Specific Epigenetic Modifications in Root Apical Meristem Cells of Hordeum vulgare

Epigenetic modifications of chromatin structure are essential for many biological processes, including growth and reproduction. Patterns of DNA and histone modifications have recently been widely studied in many plant species, although there is virtually no data on the spatial and temporal distribution of epigenetic markers during plant development. Accordingly, we have used immunostaining techniques to investigate epigenetic modifications in the root apical meristem of Hordeum vulgare. Histone H4 acetylation (H4K5ac), histone H3 dimethylation (H3K4me2, H3K9me2) and DNA methylation (5mC) patterns were established for various root meristem tissues. Distinct levels of those modifications were visualised in the root cap, epidermis, cortex and vascular tissues. The lateral root cap cells seem to display the highest level of H3K9me2 and 5mC. In the epidermis, the highest level of 5mC and H3K9me2 was detected in the nuclei from the boundary of the proximal meristem and the elongation zone, while the vascular tissues were characterized by the highest level of H4K5ac. Some of the modified histones were also detectable in the cytoplasm in a highly tissue-specific manner. Immunolocalisation of epigenetic modifications of chromatin carried out in this way, on longitudinal or transverse sections, provides a unique topographic context within the organ, and will provide some answers to the significant biological question of tissue differentiation processes during root development in a monocotyledon plant species.

Expression of the QrCPE gene is associated with the induction and development of oak somatic embryos

Somatic embryogenesis is a powerful tool for plant regeneration and also provides a suitable material for investigating the molecular events that control the induction and development of somatic embryos. This study focuses on expression analysis of the QrCPE gene (which encodes a glycine-rich protein) during the initiation of oak somatic embryos from leaf explants and also during the histodifferentiation of somatic embryos. Northern blot and in situ hybridization were used to determine the specific localisation of QrCPE mRNA. The results showed that the QrCPE gene is developmentally regulated during the histodifferentiation of somatic embryos and that its expression is tissue- and genotype-dependent. QrCPE was strongly expressed in embryogenic cell aggregates and in embryogenic nodular structures originated in leaf explants as well as in the protodermis of somatic embryos from which new embryos are generated by secondary embryogenesis. This suggests a role for the gene during the induction of somatic embryos and in the maintenance of embryogenic competence. The QrCPE gene was highly expressed in actively dividing cells during embryo development, suggesting that it participates in embryo histodifferentiation. The localised expression in the root cap initial cells of cotyledonary somatic embryos and in the root cap of somatic seedlings also suggests that the gene may be involved in the fate of root cap cells.

Immobilization of aluminum with mucilage secreted by root cap and root border cells is related to aluminum resistance in Glycine max L

The root cap and root border cells (RBCs) of most plant species produced pectinaceous mucilage, which can bind metal cations. In order to evaluate the potential role of root mucilage on aluminum (Al) resistance, two soybean cultivars differing in Al resistance were aeroponic cultured, the effects of Al on root mucilage secretion, root growth, contents of mucilage-bound Al and root tip Al, and the capability of mucilage to bind Al were investigated. Increasing Al concentration and exposure time significantly enhanced mucilage excretion from both root caps and RBCs, decreased RBCs viability and relative root elongation except roots exposed to 400 μM Al for 48 h in Al-resistant cultivar. Removal of root mucilage from root tips resulted in a more severe inhibition of root elongation. Of the total Al accumulated in root, mucilage accounted 48-72 and 12-27 %, while root tip accounted 22-52 and 73-88 % in Al-resistant and Al-sensitive cultivars, respectively. A (27)Al nuclear magnetic resonance spectrum of the Al-adsorbed mucilage showed Al tightly bound to mucilage. Higher capacity to exclude Al in Al-resistant soybean cultivar is related to the immobilization and detoxification of Al by the mucilage secreted from root cap and RBCs.

Coordinated action of β‐galactosidases in the cell wall of embryonic axes during chickpea germination and seedling growth

The plant cell wall is a dynamic structure whose constant modification is necessary for plant cells to grow and divide. In the cell walls of chickpea (Cicer arietinum) there are at least four β-galactosidases, whose presence and location in embryonic axes during the first 48 h of seed imbibition are discussed in this paper. We examined their roles as cell wall-modifying enzymes in germinative and/or post-germinative events. At the start of germination, only βV-Gal, and to a lesser extent βIV-Gal, appear in the axes before rupture of the testa, suggesting they are related to germination sensu stricto. Once the testa has broken, the four β-galactosidases are involved in growth and differentiation of the axes. Immunolocation of the different proteins in axes, which in part confirms previous results in seedlings and plants, allows assignment of post-germinative roles to βI-Gal and βIII-Gal as cell wall modifiers in vascular tissue elements. βIV-Gal and βV-Gal participate in the initial events of germination in which cell walls are involved: βV-Gal in cell proliferation, detachment of root cap cells and initial vascular tissue differentiation; both of them in xylem maturation; and βIV-Gal in thickening of the primary cell wall. Together with other cell wall-modifying enzymes, such as expansins and XTH, chickpea galactosidases might function in a sequential order in turnover of the primary cell wall, allowing the elongation of embryonic axes during seed germination.

Identification of the major capsid gene (g23) of T4-type bacteriophages that assimilate substrates from root cap cells under aerobic and anaerobic soil conditions using a DNA–SIP approach

As the most abundant biological entities, viruses are increasingly recognised as a major driving force of global biogeochemical nutrient cycles. This study demonstrated that T4-type bacteriophages drive the microbial loop of carbon from root cap cells in rice rhizospheres based on an analysis of the major capsid gene (g23). Rice callus cells were used as a model for root cap cells, and 13C-labelled callus cells were allowed to decompose. DNA extracted from the soils after incubation under aerobic and anaerobic soil conditions was subjected to PCR–DGGE after density gradient centrifugation. Although 13C-labelled g23 fragments were not detected in soil incubated under anaerobic conditions, many 13C-labelled g23 fragments belonging to Paddy Groups V, VIII and IX were obtained from the soil incubated under aerobic conditions. Some g23 fragments were detected throughout the incubation period, and others were obtained only during the early or late incubation period. This study demonstrated that the level of infection of soil bacteria by T4-type phages was very different between aerobic and anaerobic soil conditions. Based on the results of this study, the roles of phages in the decomposition of the root cap cells of rice plants in rice fields are discussed.

Ammonium Inhibits Primary Root Growth by Reducing the Length of Meristem and Elongation Zone and Decreasing Elemental Expansion Rate in the Root Apex in Arabidopsis thaliana

The inhibitory effect of ammonium on primary root growth has been well documented; however the underlying physiological and molecular mechanisms are still controversial. To avoid ammonium toxicity to shoot growth, we used a vertical two-layer split plate system, in which the upper layer contained nitrate and the lower layer contained ammonium. In this way, nitrogen status was maintained and only the apical part of the root system was exposed to ammonium. Using a kinematic approach, we show here that 1 mM ammonium reduces primary root growth, decreasing both elemental expansion and cell production. Ammonium inhibits the length of elongation zone and the maximum elemental expansion rate. Ammonium also decreases the apparent length of the meristem as well as the number of dividing cells without affecting cell division rate. Moreover, ammonium reduces the number of root cap cells but appears to affect neither the status of root stem cell niche nor the distal auxin maximum at the quiescent center. Ammonium also inhibits root gravitropism and concomitantly down-regulates the expression of two pivotal auxin transporters, AUX1 and PIN2. Insofar as ammonium inhibits root growth rate in AUX1 and PIN2 loss-of-function mutants almost as strongly as in wild type, we conclude that ammonium inhibits root growth and gravitropism by largely distinct pathways.

Overexpression of AtHsfB4 induces specific effects on root development of Arabidopsis

The functions of plant class B-heat shock factors (Hsfs) are not well understood. Hsfs belonging to this group differ from class A-Hsfs in structural features of the oligomerization domain and by the absence of a typical AHA motif for transcriptional activation. AtHsfB4 is expressed in different parts of the plants with highest levels in root tissue. Transgenic Arabidopsis plants overexpressing (OE) HsfB4 by CaMV-35S-promoter showed massively enhanced levels of Hsf mRNAs. The root surface of OE-plants was rough and cells became detached. Crossings with cell type specific root marker lines and confocal laser scanning microscopy provided clear evidence for a duplication of cells in the ground tissue and ectopic layers of lateral root cap (LRC) cells in HsfB4-OE plants. A duplication of endodermis cells occurs already during embryonic development, while the ectopic LRC cells are only detected during postembryonic growth. The mutant phenotypes of Hsf-OE plants are without precedence and indicate that class B-Hsfs may play an important role in root development.

Bacterial communities that decompose root cap cells in an anaerobic soil: estimation by DNA-SIP method using rice plant callus cells

Root cap cells are an important substrate for rhizospheric microorganisms. In this study carbon (13C)-labelled callus cells of rice (Oryza sativa L. cv, Yukihikari) (84 atom % 13C) were used as a model material for root cap cells and subjected to decomposition in an anaerobic soil microcosm for 56 days. DNA was extracted from soils incubated with 13C-labelled and unlabelled callus cells and subjected to buoyant density (BD) gradient centrifugation to identify bacterial species that assimilated callus cells. Many denaturing gradient gel electrophoresis (DGGE) bands were detected in the heavy BD fractions in the soil with 13C-callus cells from day 3 onwards. Sequencing 13C-labelled DGGE bands revealed that they were mainly derived from Gram-negative bacteria and that Acidobacteria, δ-Proteobacteria and Firmicutes were predominant bacteria assimilating rice callus cells. Strictly anaerobic bacteria such as Clostridium spp., Geothrix spp. and Holophaga spp. were predominant decomposers of callus cells. These species were phylogenetically distinct from the bacteria of rice callus assimilation in the aerobic soil and from the bacteria in rice roots. This study indicates that root cap cells are decomposed by different bacterial species during the upland nursery stage and after transplanting to flooded rice fields.