Root Axis Research Articles

Analysis of root growth from a phenotyping data set using a density-based model.

Major research efforts are targeting the improved performance of root systems for more efficient use of water and nutrients by crops. However, characterizing root system architecture (RSA) is challenging, because roots are difficult objects to observe and analyse. A model-based analysis of RSA traits from phenotyping image data is presented. The model can successfully back-calculate growth parameters without the need to measure individual roots. The mathematical model uses partial differential equations to describe root system development. Methods based on kernel estimators were used to quantify root density distributions from experimental image data, and different optimization approaches to parameterize the model were tested. The model was tested on root images of a set of 89 Brassica rapa L. individuals of the same genotype grown for 14 d after sowing on blue filter paper. Optimized root growth parameters enabled the final (modelled) length of the main root axes to be matched within 1% of their mean values observed in experiments. Parameterized values for elongation rates were within ±4% of the values measured directly on images. Future work should investigate the time dependency of growth parameters using time-lapse image data. The approach is a potentially powerful quantitative technique for identifying crop genotypes with more efficient root systems, using (even incomplete) data from high-throughput phenotyping systems.

Root development and structure in seedlings of Ginkgo biloba.

The popular, highly recognizable, well-known gymnosperm, Ginkgo biloba, was studied to document selected developmental features, which are little known in its primary root system from root tips to cotyledonary node following seed germination. Using seedlings grown in soil, vermiculite, or a mixture, we examined sections at various distances from the root cap to capture a developmental sequence of anatomical structures by using standard brightfield, epifluorescence, and confocal microscopic techniques. The vascular cylinder is usually a diarch stele, although modified diarchy and triarchy are found. Between exarch protoxylem poles, metaxylem usually develops into a complete disc, except near the transition region, which has irregularly arranged tracheary cells. The disc of primary xylem undergoes secondary growth on its metaxylem flanks with many tracheids added radially within a few weeks. Production of fibers in secondary phloem also accompanies secondary growth. In the cortex, endodermis produces Casparian bands early in development and continues into the upper transition region. Phi cells with phi-thickenings (bands of lignified walls) of a layer of inner cortex are often evident before endodermis, and then adjoining, additional layers of cortex develop phi cells; phi cells do not occur in the upper transition region or stem. An exodermis is produced early in root development and is continuous into the transition region and cotyledonary node. Seedling root axes of Ginkgo biloba are more complex than the literature suggests, and our findings contribute to our knowledge of root structure of this ancient gymnosperm.

The resistance of teeth to vertical root fractures after mechanical preparation and irrigation of root canal (pilot study)

The aim of the study was to assess the influence of external root anatomy, time of irrigation and the rate of mechanical enlargement of root canals on root fracture resistance. Thirty six bovine teeth were decoronated and divided into 2 groups: with round and oval forms of axial root slices. The root canals were mechanically enlarged according to standard protocol and prepared for post placement. Individual cast posts were made for each tooth, the diameter of posts comprised 1/2 or 1/3 of the root diameter in different subgroups. After mechanical enlargement, the canals were irrigated with 3% sodium hypochlorite for 10 or 60 minutes in different subgroups. The teeth with posts were subjected to static vertical load by universal testing machine with the speed of 1 mm per minute. The load that had led to fracture initiation was noted. Analysis of variances was used to assess the statistical significance of the No statistically significant differences were found between the groups with different protocols of mechanical preparation and irrigation. Teeth with round axial root slice were significantly less susceptible to fractures than ones with oval shape of axial root slice taking into consideration the protocols of mechanical preparation and irrigation.

CARACTERIZAÇÃO MORFOLÓGICA DE PLÂNTULAS DURANTE A GERMINAÇÃO DE SEMENTES DE <i>Psidium cattleianum</i> E <i>Acca sellowiana</i> (MYRTACEAE)

http://dx.doi.org/10.5902/19805098Objetivou-se neste trabalho descrever as características morfológicas de plântulas durante a germinação de Psidium cattleianum Sabine e Acca sellowiana (O. Berg) Burret. Para a descrição da germinação e das características morfológicas das plântulas, 100 sementes foram colocadas para germinar em substrato papel tipo germitest à temperatura de 25ºC. Foram analisados: tipo, forma e coloração da raiz; pilosidade, forma e coloração do hipocótilo e do epicótilo; consistência, textura, forma, nervação, coloração, tipo de bordo, ápice e base dos cotilédones e protófilos. A germinação de ambas é epígea fanerocotiledonar, formando plântula com sistema radicial axial, raiz principal pivotante longa, com paracotilédones e eofilos simples e opostos. Foram registradas glândulas e células secretoras em todos os órgãos, exceto na raiz, para as duas espécies. A semente de Psidium cattleianum inicia germinação aproximadamente 10 dias após a semeadura quando ocorre a abertura do opérculo e a protrusão radicular. Acca sellowiana, após 28 dias, apresenta hipocótilo longo, cilíndrico, ereto, de coloração marrom-avermelhada, glabro. Na ocorrência de total exposição dos paracotilédones, estes já apresentam coloração verde intensa, demonstrando o potencial fotossintetizante pela plântula em crescimento. A descrição do processo germinativo juntamente com a morfologia de plântulas constitui importante elemento de reconhecimento de espécies.

C3-P-033-D cell geometrical analysis of epidermal and cortical cells in hypocotyl-root axes in arabidopsis seeds using X-ray micro-CT

Plants are composed of various types of cells. How these cells contribute to the overall body shape of plants is an important question in studies of plant development. Because plant cells are surrounded by rigid cell walls, newly formed cells are unable to migrate, and the geometrical relationships among neighboring cells are maintained for a long time during plant development. In arabidopsis (Arabidopsis thaliana (L.) Heynh. ecotype Columbia) seeds, one cortical cell layer exists between the epidermis and endodermis in the radicle, and two cortical cell layers are present in the hypocotyl. However, how the shape and geometry of these cells in the epidermis and cortex contribute to the embryo form remains unknown. We previously determined the three-dimensional (3-D) cell and tissue shapes and geometries in the embryo of an arabidopsis dry seed with X-ray micro computed tomography (micro-CT) using beamline BL20XU of SPring-8 synchrotron radiation facility [1]. In the present study, we constructed 3-D models of cell arrangement based on X-ray micro-CT images (8 keV, 0.2 μm/pixel) of whole seeds of arabidopsis, and analyzed the geometrical characteristics of epidermal and cortical cells. The size of the cross-sectional area of hypocotyl–root axis is largest in the proximal region of the hypocotyl, ~80 μm from the hypocotyl–root transition zone. Comparison between the cell division pattern and the change in cell size along the hypocotyl–root axis revealed that the increment in the lateral expansion of cortical cells contributed to the lateral expansion of the hypocotyl axis. In contrast, only the number of cell files, and not the size of cross-sectional area, increased when the area of epidermis increased. This work was partly supported by a grant from Hyogo Science and Technology Association. Experiments were performed with the approval of JASRI (Proposal nos 2012A1364 and 2014A1265). [1] D Yamauchi et al., AIP Conf. Proc. 1466 (2012) 237-242. C3-P-02 doi:10.1093/jmicro/dfv305

Polyethylene Glycol (PEG)-Treated Hydroponic Culture Reduces Length and Diameter of Root Hairs of Wheat Varieties

Wheat is an important cereal crop worldwide that often suffers from moisture deficits at the reproductive stage. Polyethylene glycol (PEG)-treated hydroponic conditions create negative osmotic potential which is compared with moisture deficit stress. An experiment was conducted in a growth chamber to study the effects of PEG on root hair morphology and associated traits of wheat varieties. Plants of 13 wheat varieties were grown hydroponically and three different doses of PEG 6000 (w/v): 0% (control), 0.3% and 0.6% (less than −1 bar) were imposed on 60 days after sowing for 20 days’ duration. A low PEG concentration was imposed to observe how initial low moisture stress might affect root hair development. PEG-treated hydroponic culture significantly decreased root hair diameter and length. Estimated surface area reduction of root hairs at the main axes of wheat plants was around nine times at the 0.6% PEG level compared to the control plants. Decrease in root hair diameter and length under PEG-induced culture decreased “potential” root surface area per unit length of main root axis. A negative association between panicle traits, length and dry weight and the main axis length of young roots indicated competition for carbon during their development. Data provides insight into how a low PEG level might alter root hair development.

Root-type-specific plasticity in response to localized high nitrate supply in maize (Zea mays).

Shoot-borne roots contribute to most of the nutrient uptake throughout the life cycle of maize (Zea mays). Compared with numerous studies with embryonic roots, detailed information on the phenotypic plasticity of shoot-borne roots in response to a heterogeneous nitrogen supply is scarce. The present study therefore provides a comprehensive profile of fine-scale plastic responses of distinct root types to localized high nitrate supply. Seedlings of the maize inbred line B73 were grown in split-root systems. The anatomy and morphological plasticity of the primary root and the roots initiated from the 2nd, 5th and 7th shoot nodes, and their lateral roots, were studied in response to local high nitrate supply to one side of the root system. In contrast to the insensitivity of axial roots, local high nitrate supply increased the length of 1st-order lateral roots on the primary root and the three whorls of shoot-borne roots at different growth stages, and increased the density of 1st-order lateral roots on the 7th shoot-borne root after silking. The length and density of 2nd-order lateral roots on the three whorls of shoot-borne roots displayed a more flexible response to local high nitrate than 1st-order lateral roots. Root diameter and number, and total area and diameter of metaxylem vessels increased from the primary root to early and then later developed shoot-borne roots, which showed a positive relationship with shoot growth and N accumulation. Maize axial roots and lateral roots responded differently to local high nitrate, and this was related to their function. The extent of morphological plasticity of lateral roots in response to local high nitrate depended on the initiation time of the shoot-borne roots on which the lateral roots developed. Morphological plasticity was higher on 2nd-order than on 1st-order lateral roots. The results suggest that higher order lateral root branching might be a potential target for genetic improvement in future maize breeding.

Reduced Lateral Root Branching Density Improves Drought Tolerance in Maize.

An emerging paradigm is that root traits that reduce the metabolic costs of soil exploration improve the acquisition of limiting soil resources. Here, we test the hypothesis that reduced lateral root branching density will improve drought tolerance in maize (Zea mays) by reducing the metabolic costs of soil exploration, permitting greater axial root elongation, greater rooting depth, and thereby greater water acquisition from drying soil. Maize recombinant inbred lines with contrasting lateral root number and length (few but long [FL] and many but short [MS]) were grown under water stress in greenhouse mesocosms, in field rainout shelters, and in a second field environment with natural drought. Under water stress in mesocosms, lines with the FL phenotype had substantially less lateral root respiration per unit of axial root length, deeper rooting, greater leaf relative water content, greater stomatal conductance, and 50% greater shoot biomass than lines with the MS phenotype. Under water stress in the two field sites, lines with the FL phenotype had deeper rooting, much lighter stem water isotopic signature, signifying deeper water capture, 51% to 67% greater shoot biomass at flowering, and 144% greater yield than lines with the MS phenotype. These results entirely support the hypothesis that reduced lateral root branching density improves drought tolerance. The FL lateral root phenotype merits consideration as a selection target to improve the drought tolerance of maize and possibly other cereal crops.

Cytokinin as a positional cue regulating lateral root spacing in Arabidopsis.

The root systems of plants have developed adaptive architectures to exploit soil resources. The formation of lateral roots (LRs) contributes to root system architecture. Roots of plants with a lower cytokinin status form LR primordia (LRP) in unusually close proximity, indicating a role for the hormone in regulating the positioning of LRs along the main root axis. Data obtained from cytokinin-synthesis mutants of Arabidopsis thaliana combined with gene expression analysis indicate that cytokinin synthesis by IPT5 and LOG4 occurring early during LRP initiation generates a local cytokinin signal abbreviating LRP formation in neighbouring pericycle cells. In addition, IPT3, IPT5, and IPT7 contribute to cytokinin synthesis in the vicinity of existing LRP, thus suppressing initiation of new LRs. Interestingly, mutation of CYP735A genes required for trans-zeatin biosynthesis caused strong defects in LR positioning, indicating an important role for this cytokinin metabolite in regulating LR spacing. Further it is shown that cytokinin and a known regulator of LR spacing, the receptor-like kinase ARABIDOPSIS CRINKLY4 (ACR4), operate in a non-hierarchical manner but might exert reciprocal control at the transcript level. Taken together, the results suggest that cytokinin acts as a paracrine hormonal signal in regulating root system architecture.

A high-resolution tissue-specific proteome and phosphoproteome atlas of maize primary roots reveals functional gradients along the root axes.

A high-resolution proteome and phosphoproteome atlas of four maize (Zea mays) primary root tissues, the cortex, stele, meristematic zone, and elongation zone, was generated. High-performance liquid chromatography coupled with tandem mass spectrometry identified 11,552 distinct nonmodified and 2,852 phosphorylated proteins across the four root tissues. Two gradients reflecting the abundance of functional protein classes along the longitudinal root axis were observed. While the classes RNA, DNA, and protein peaked in the meristematic zone, cell wall, lipid metabolism, stress, transport, and secondary metabolism culminated in the differentiation zone. Functional specialization of tissues is underscored by six of 10 cortex-specific proteins involved in flavonoid biosynthesis. Comparison of this data set with high-resolution seed and leaf proteome studies revealed 13% (1,504/11,552) root-specific proteins. While only 23% of the 1,504 root-specific proteins accumulated in all four root tissues, 61% of all 11,552 identified proteins accumulated in all four root tissues. This suggests a much higher degree of tissue-specific functionalization of root-specific proteins. In summary, these data illustrate the remarkable plasticity of the proteomic landscape of maize primary roots and thus provide a starting point for gaining a better understanding of their tissue-specific functions.

Visualization of water transport into soybean nodules by Tof-SIMS cryo system

This paper examined the route of water supply into soybean nodules through the new visualization technique of time of flight secondary ion mass spectrometry (Tof-SIMS) cryo system, and obtained circumstantial evidence for the water inflow route. The maximum resolution of the Tof-SIMS imaging used by this study was 1.8μm (defined as the three pixel step length), which allowed us to detect water movement at the cellular level. Deuterium-labeled water was supplied to soybean plants for 4h and the presence of deuterium in soybean nodules was analyzed by the Tof-SIMS cryo system. Deuterium ions were found only in the endodermis tissue surrounding the central cylinder in soybean nodules. Neither xylem vessels nor phloem complex itself did not indicate any deuterium accumulation. Deuterium-ion counts in the endodermis tissue were not changed by girdling treatment, which restricted water movement through the phloem complex. The results strongly indicated that nodule tissues did not receive water directly from the phloem complex, but received water through root cortex apoplastic pathway from the root axis.

Reduced frequency of lateral root branching improves N capture from low-N soils in maize.

Suboptimal nitrogen (N) availability is a primary constraint for crop production in developing countries, while in developed countries, intensive N fertilization is a primary economic, energy, and environmental cost for crop production. We tested the hypothesis that under low-N conditions, maize (Zea mays) lines with few but long (FL) lateral roots would have greater axial root elongation, deeper rooting, and greater N acquisition than lines with many but short (MS) lateral roots. Maize recombinant inbred lines contrasting in lateral root number and length were grown with adequate and suboptimal N in greenhouse mesocosms and in the field in the USA and South Africa (SA). In low-N mesocosms, the FL phenotype had substantially reduced root respiration and greater rooting depth than the MS phenotype. In low-N fields in the USA and SA, the FL phenotype had greater rooting depth, shoot N content, leaf photosynthesis, and shoot biomass than the MS phenotype. The FL phenotype yielded 31.5% more than the MS phenotype under low N in the USA. Our results are consistent with the hypothesis that sparse but long lateral roots improve N capture from low-N soils. These results with maize probably pertain to other species. The FL lateral root phenotype merits consideration as a selection target for greater crop N efficiency.

Evaluation of Sealing Ability of Three Root-end Filling Materials

Introduction: Reinfection of root canal treated tooth leads to endodontic failure. In such case surgical endodontic therapy is the treatment of choice which provides obturation of radicular space with 3-dimensional sealing.Objective: To evaluate and compare the sealing ability of Mineral trioxide aggregate (MTA) with Glass ionomer cement (GIC) and Super EBA (Epoxybenzoic acid) root-end filling materials.Materials & Method: 94 extracted single rooted upper anterior teeth were selected for root canal preparation and obturation. Root were apically resected 3 mm; and 3 mm deep Class-I root-end cavities were prepared. Teeth were randomly distributed into 3 groups comprising 30 teeth in each group. Group-1 was retrofilled with MTA, Group-2 with GIC and Group-3 with Super EBA. 2 positive and 2 negative control teeth were instrumented and obturated but not filled on root-end cavity. In experimental groups and positive control group the whole surface of teeth except 3 mm adjacent to resected area were covered with twocoats of nail polish but in negative control group whole surface of teeth were covered, dried, immersed in 1% methylene blue for 72 hours. Each root was sectioned labio-lingually to the long axis of root. Depth of dye penetration was evaluated by 10x stereo-microscope.Result: MTA retrograde filling showed the best hermetic seal property whereas, few GIC and Super EBA samples showed microleakage in retrograde filling. GIC showed better sealing ability than Super EBA. Conclusion: MTA has potential to provide better hermetic-seal than GIC and Super EBA as root-end filling material.

Establishment of embryonic shoot-root axis is involved in auxin and cytokinin response during Arabidopsis somatic embryogenesis.

Auxin and cytokinin signaling participates in regulating a large spectrum of developmental and physiological processes in plants. The shoots and roots of plants have specific and sometimes even contrary responses to these hormones. Recent studies have clearly shown that establishing the spatiotemporal distribution of auxin and cytokinin response signals is central for the control of shoot apical meristem (SAM) induction in cultured tissues. However, little is known about the role of these hormones in root apical meristem (RAM) initiation. Here, we found that the expression patterns of several regulatory genes critical for RAM formation were correlated with the establishment of the embryonic root meristem during somatic embryogenesis in Arabidopsis. Interestingly, the early expression of the WUS-RELATED HOMEOBOX 5 (WOX5) and WUSCHEL genes was induced and was nearly overlapped within the embryonic callus when somatic embryos (SEs) could not be identified morphologically. Their correct expression was essential for RAM and SAM initiation and embryonic shoot–root axis establishment. Furthermore, we analyzed the auxin and cytokinin response during SE initiation. Notably, cytokinin response signals were detected in specific regions that were correlated with induced WOX5 expression and subsequent SE formation. Overexpression of the ARABIDOPSIS RESPONSE REGULATOR genes ARR7 and ARR15 (feedback repressors of cytokinin signaling), disturbed RAM initiation and SE induction. These results provide new information on auxin and cytokinin-regulated apical–basal polarity formation of shoot–root axis during somatic embryogenesis.

Effects of Reciproc, Mtwo and ProTaper Instruments on Formation of Root Fracture.

Introduction:The aim of this study was to compare the formation of dentinal crack and craze lines in the root dentin during root canal preparation with three different NiTi endodontic systems, naming Reciproc (RCP), ProTaper Universal (PTU) and Mtwo. Methods and Materials:One hundred extracted mandibular premolars with single canals were selected and decoronated. The teeth were randomly divided into four groups of 25 each (n=25). In groups 1, 2 and 3 the teeth were prepared using Mtwo, PTU and RCP, respectively. While in group 4 (control group) the samples were left unprepared. After preparation, all specimens were sectioned perpendicular to the long axis of root at 3, 5 and 9-mm distances from the apex. The sections were then individually observed under 12× magnification using stereomicroscope. The data was analyzed using the chi-square and Fisher’s exact tests. The level of significance was set at 0.05. Results:No cracks were observed in the control group. All engine-driven systems caused dentinal cracks. Mtwo and PTU caused cracks significantly more than RCP (P<0.05). There was no significant difference between RCP and control group (P>0.05). Conclusion:All three engine-driven systems created dentinal defects. Reciproc caused less cracks than Mtwo and ProTaper Universal.

Comparative evaluation of microleakage of four different retrograde filling materials with or without root end bevel: An in vitro study

Aim: To compare the microleakage of four different root end filling materials with or without root end bevels using dye penetration technique under stereomicroscope. Materials and methods: Subsequent to decontamination and decoronation, 90 human maxillary central incisor were instrumented and obturated with gutta percha using lateral compaction technique. Ten samples were used as control group where no retrograde cavity preparation was done except removal of 3mm of apex at 0 degree bevel and 45 degree bevel in 5 samples each. 40 teeth were apically resected at an angle of 45 degrees and the remaining 40 teeth were subjected to 0 degree resection to the long axis of root. Root end cavities were then prepared to 3 mm depth. The samples were thus divided into nine groups with ten samples each in the eight experimental groups and ten samples in the control group. In each experimental group, root end cavities were filled with one of the following materials: Silver Amalgam, Intermediate Restorative Material (IRM), Mineral Trioxide Aggregate(MTA) and Giomer. Following this, the teeth were stored in incubator for 2 weeks. The samples were coated with nail varnish and after drying were immersed in Indian ink dye for 72 hours. The teeth were then rinsed, sectioned longitudinally and observed under stereomicroscope. The depth of dye penetration was measured in millimetres. Results: The results showed that microleakage was found to be least in case of MTA followed by IRM, Silver Amalgam and Giomer. Regarding the choice of apical preparation of bevel as demonstrated in this study, retrograde preparations without bevel demonstrated less leakage as compared to retrograde preparations with the use of bevel for all the test materials. Conclusion: MTA as root end filling material without bevelling the root end may be considered as a clinical procedure of choice with predictable clinical results.

Early indirect selection for nitrogen use efficiency in maize

Several studies to evaluate nitrogen use efficiency (NUE) have been carried out using early growth stages. However, there are no scientific reports on the ideal stage for evaluation and on which characteristics have the highest correlation with the NUE at that stage. The aim therefore was to identify the phenological stages and secondary characteristics which maximize accuracy in early indirect selection for NUE in maize. To do this, three endogamic maize strains were evaluated in a completely randomised design with five replications, in a triple factorial scheme (strains x N levels x phenological stage), at two contrasting nitrogen levels: low and high nitrogen. The plants were evaluated at five growth stages: stage nine (V9), with 14 fully-developed leaves (V14), tasseling (VT), flowering (R1) and physiological maturity (R6). The following characteristics were evaluated: efficiency in the usage, absorption, use and translocation of nitrogen; activity of nitrate reductase and glutamine synthetase; length of the lateral and axial roots; specific root area; chlorophyll content; number of leaves; plant height; stem diameter; and the levels of phosphorus and potassium. Considering the estimated direct and indirect gains, it can be concluded that the activities of glutamine synthetase at the V9 and V14 stages permit early indirect selection for nitrogen use efficiency in maize under conditions of low and high N availability respectively.

Activation of embryo during rape (Brassica napus L.) seed germination. I. Structure of embryo and organization of root apical meristem

The Structure of the mature rape embryo was examined on longitudirna microtome sections, and1, its developmental interpretation is given, based on the author's own studies and literature data. The boundaries between the epicotyl, hypocotyl and radicle are recognized and identified with the limits between the proembryo segments. The radicle Structure and root apical meristem organization are described. In the dermatogen and periblem cell patterns four segments are distinguished, separated successively from the initial cells. Their position is recognized as almost the same on both sides of the root axis and in different embryos. The easily discernible limits between the dermatogen sectors are to be utilized as reference points in studies on the root apical meristem activation and growth during rape seed germination.

Immunohistochemical expression of fibrillin-1 and fibrillin-2 during tooth development.

Oxytalan fibers are categorized as a microfibril assembly without elastin deposition, and are unique components in the periodontal ligament (PDL). However, little is known about their formation during PDL development. To clarify the mechanisms of oxytalan fiber formation in developing PDL, we performed immunohistochemical analysis to detect the direct expression of fibrillin-1 and fibrillin-2, which are major components of microfibrils. Frozen sections of lower molars from mice at several stages of growth were prepared without chemical fixation and decalcification using the film transfer method. Immunostaining was performed with anti-fibrillin-1 and -2, and anticytokeratin antibodies. Fibrillin-1 was not expressed in the dental follicle during the crown forming stage. At postneonatal day 9, fibrillin-1 expression started with meshwork appearance between the epithelial cells from Hertwig's epithelial root sheath at the root dentin surface. Fibirillin-2 was detected much earlier than fibrillin-1 expression. Fibrillin-2 was expressed with a liner appearance, running parallel to the root axis in PDL, and was partially co-expressed with cytokeratin 14 expression in Hertwig's epithelial root sheath. Furthermore, we detected both fibrillin-1 and fibrillin-2 expression in human PDL. Fibrillin-1 was detected in fibers with a vertically oriented root axis in PDL. Fibrillin-2 was widely expressed in PDL, including around the epithelial cell rests of Malassez. Fibrillin-1 and fibrillin-2 were clearly co-expressed in thick fiber structures in human PDL. Our results suggest that both fibrillin-1 and fibrillin-2 expression is required to form thick oxytalan fibers in PDL. Based on the expression patterns for fibrillin-1 and fibrillin-2, they have different functions during tooth root and PDL development. Early expression of fibrillin-2 may regulate dental epithelial cell behavior during root and PDL development.

Estresse hídrico e massa de sementes na germinação e crescimento de plântulas de Amburana cearensis (Allemão) A.C. Smith

Amburana cearensis, conhecida como cumaru, é uma espécie presente em todo bioma caatinga, sendo recomendada para recuperação de áreas degradadas e usos fitoterápicos. O objetivo do presente trabalho foi determinar os níveis de tolerância ao estresse hídrico na germinação e no crescimento de plântulas de cumaru em função da massa das sementes. Inicialmente as sementes foram pesadas e separadas em três classes (leves, médias e pesadas), sendo estas submetidas ao estresse hídrico, utilizando soluções de Polietilenoglicol 6000, em diferentes potenciais (0,0; -0,2; -0,4; - 0,6; -0,8 e -1,0 MPa) e colocadas para germinar na temperatura de 30 °C em câmaras de germinação. O delineamento experimental foi inteiramente casualizado em esquema fatorial 3 x 6 (classes de massa x potencial hídrico). Para a avaliação da germinação, foram determinados a primeira contagem, porcentagem final e índice de velocidade de germinação, enquanto para a avaliação do crescimento das plântulas determinou-se o comprimento e massa seca do epicótilo e do eixo raiz + hipocótilo e a razão parte aérea/raiz. Os dados foram submetidos ao teste de normalidade e quando se apresentaram normais, realizou-se análise de variância, comparação de médias e regressão. O decréscimo do potencial hídrico prejudica a germinação e o crescimento de plântulas oriundas de sementes médias e pesadas em relação às leves, sendo a partir do potencial -0,6 MPa uma condição estritamente limitante na formação de plântulas normais de A. cearensis.