Showing papers on "Root hair published in 2006"
TL;DR: A transcriptome analysis identified NIP5;1 as a major plasma membrane boric acid channel crucial for the B uptake required for plant growth and development under B limitation.
Abstract: Boron (B) is essential in plants but often present at low concentrations in the environment. To investigate how plants survive under conditions of B limitation, we conducted a transcriptome analysis and identified NIP5;1, a member of the major intrinsic protein family, as a gene upregulated in B-deficient roots of Arabidopsis thaliana. Promoter-beta-glucuronidase fusions indicated that NIP5;1 is strongly upregulated in the root elongation zone and the root hair zone under B limitation, and green fluorescent protein-tagged NIP5;1 proteins localized to the plasma membrane. Expression in Xenopus laevis oocytes demonstrated that NIP5;1 facilitated the transport of boric acid in addition to water. Importantly, two T-DNA insertion lines of NIP5;1 displayed lower boric acid uptake into roots, lower biomass production, and increased sensitivity of root and shoot development to B deficiency. These results identify NIP5;1 as a major plasma membrane boric acid channel crucial for the B uptake required for plant growth and development under B limitation.
642 citations
TL;DR: The results identify a component of an intriguing signal process requiring interaction at the cell plasma membrane and at intracellular nuclear and plastid organelle-membranes to induce a second messenger.
Abstract: Nuclear-cytoplasmic partitioning and traffic between cytoplasmic and nuclear compartments are fundamental processes in eukaryotic cells. Nuclear pore complexes mediate transport of proteins, RNAs and ribonucleoprotein particles in and out of the nucleus. Here we present positional cloning of a plant nucleoporin gene, Nup133, essential for a symbiotic signal transduction pathway shared by Rhizobium bacteria and mycorrhizal fungi. Mutation of Nup133 results in a temperature sensitive nodulation deficient phenotype and absence of mycorrhizal colonization. Root nodules developing with reduced frequency at permissive temperatures are ineffective and electron microscopy show that Rhizobium bacteria are not released from infection threads. Measurement of ion fluxes using a calcium-sensitive dye show that Nup133 is required for the Ca2+ spiking normally detectable within minutes after application of purified rhizobial Nod-factor signal molecules to root hairs. Localization of NUP133 in the nuclear envelope of root cells and root hair cells shown with enhanced yellow fluorescent protein fusion proteins suggests a novel role for NUP133 nucleoporins in a rapid nuclear–cytoplasmic communication after host–plant recognition of symbiotic microbes. Our results identify a component of an intriguing signal process requiring interaction at the cell plasma membrane and at intracellular nuclear and plastid organelle-membranes to induce a second messenger.
388 citations
TL;DR: The authors' data indicate that, in wild-type A. thaliana, the AtMTP3 protein contributes to basic cellular Zn tolerance and controls Zn partitioning, particularly under conditions of high rates of Zn influx into the root symplasm.
Abstract: Summary Zinc ions are required to maintain the biological activity of numerous proteins. However, when mislocalized or accumulated in excess, Zn2þ ions are toxic because of adventitious binding to proteins and displacement of other metal ions, among them Fe2þ , from their binding sites. Heterologous expression of a previously uncharacterized Arabidopsis thaliana metal tolerance protein, MTP3, in the zrc1 cot1 mutant of budding yeast restores tolerance to, and cellular accumulation of, zinc and cobalt. An MTP3‐GFP fusion protein localizes to the vacuolar membrane when expressed in Arabidopsis. Ectopic over-expression of MTP3 increases Zn accumulation in both roots and rosette leaves of A. thaliana, and enhances Zn tolerance. Exposure of wild-type plants to high but non-toxic concentrations of Zn or Co, or Fe deficiency, strongly induce MTP3 expression specifically in epidermal and cortex cells of the root hair zone. Silencing ofMTP3 by RNA interference causes Zn hypersensitivity and enhances Zn accumulation in above-ground organs of soil-grown plants and of seedlings exposed to excess Zn or to Fe deficiency. Our data indicate that, in wild-type A. thaliana, the AtMTP3 protein contributes to basic cellular Zn tolerance and controls Zn partitioning, particularly under conditions of high rates of Zn influx into the root symplasm.
372 citations
TL;DR: Genetic evidence is presented that root flavonoids are necessary for nodule initiation in M. truncatula and suggestions that they act as auxin transport regulators are suggested.
Abstract: Legumes form symbioses with rhizobia, which initiate the development of a new plant organ, the nodule. Flavonoids have long been hypothesized to regulate nodule development through their action as auxin transport inhibitors, but genetic proof has been missing. To test this hypothesis, we used RNA interference to silence chalcone synthase (CHS), the enzyme that catalyzes the first committed step of the flavonoid pathway, in Medicago truncatula. Agrobacterium rhizogenes transformation was used to create hairy roots that showed strongly reduced CHS transcript levels and reduced levels of flavonoids in silenced roots. Flavonoid-deficient roots were unable to initiate nodules, even though normal root hair curling was observed. Nodule formation and flavonoid accumulation could be rescued by supplementation of plants with the precursor flavonoids naringenin and liquiritigenin. The flavonoid-deficient roots showed increased auxin transport compared with control roots. Inoculation with rhizobia reduced auxin transport in control roots after 24 h, similar to the action of the auxin transport inhibitor N-(1-naphthyl)phthalamic acid (NPA). Rhizobia were unable to reduce auxin transport in flavonoid-deficient roots, even though NPA inhibited auxin transport. Our results present genetic evidence that root flavonoids are necessary for nodule initiation in M. truncatula and suggest that they act as auxin transport regulators.
352 citations
TL;DR: These loci of NO generation and accumulation suggest novel functions for NO in these cell types, and the arginine-dependent NOS activity was constitutive and sensitive to aminoguanidine, a well-known irreversible inhibitor of animal NOS, and this NOSActivity was differentially modulated depending on the plant organ and seedling developmental stage.
Abstract: Nitric oxide (NO) is an important signalling molecule in different animal and plant physiological processes. Little is known about its biological function in plants and on the enzymatic source or site of NO production during plant development. The endogenous NO production from L-arginine (NO synthase activity) was analyzed in leaves, stems and roots during plant development, using pea seedlings as a model. NOS activity was analyzed using a novel chemiluminescence-based assay which is more sensitive and specific than previous methods used in plant tissues. In parallel, NO accumulation was analyzed by confocal laser scanning microscopy using as fluorescent probes either DAF-2 DA or DAF-FM DA. A strong increase in NOS activity was detected in stems after 11 days growth, coinciding with the maximum stem elongation. The arginine-dependent NOS activity was constitutive and sensitive to aminoguanidine, a well-known irreversible inhibitor of animal NOS, and this NOS activity was differentially modulated depending on the plant organ and seedling developmental stage. In all tissues studied, NO was localized mainly in the vascular tissue (xylem) and epidermal cells and in root hairs. These loci of NO generation and accumulation suggest novel functions for NO in these cell types.
304 citations
Book•
01 Jan 2006
TL;DR: This chapter discusses Roots and the Biological Environment, which focuses on the development and growth of root systems in the context of the soil chemical environment.
Abstract: Preface. 1. Plants, Roots and the Soil. 1.1 The evolution of roots. 1.2 Functional interdependence of roots and shoots. 1.2.1 Balanced growth of roots and shoots. 1.2.2 Communication between roots and shoots. 1.3 Roots and the soil. 1.3.1 The root-soil interface. 1.3.2 Root-induced soil processes. 2. Roots and the Architecture of Root Systems. 2.1 Nomenclature and types of root. 2.2 Root structure. 2.2.1 Primary structure. 2.2.2 Secondary structure. 2.3 Extension and branching. 2.3.1 Extension. 2.3.2 Branching. 2.3.3 Root hairs. 2.4 The root tip. 2.4.1 The root cap and border cells. 2.4.2 Mucilage. 2.5 Architecture of root systems. 3. Development and Growth of Root Systems. 3.1 Measurement of root systems. 3.1.1 Washed soil cores. 3.1.2 Rhizotrons and minirhizotrons. 3.1.3 Other techniques. 3.2 Root system development. 3.3 Size and distribution of root systems. 3.3.1 Mass and length. 3.3.2 Depth of rooting. 3.3.3 Distribution of roots. 3.4 Root:shoot allocation of dry matter. 3.5 Root longevity and turnover. 3.6 Modelling of root systems. 4. The Functioning Root System. 4.1 Root anchorage. 4.1.1 Uprooting. 4.1.2 Overturning. 4.2 Water uptake. 4.2.1 The concept of water potential. 4.2.2 The soil-plant-atmosphere continuum. 4.2.3 Water uptake by plant root systems. 4.3 Nutrient uptake. 4.3.1 Nutrient requirements of plants and the availability of nutrients. 4.3.2 Nutrient movement in soil solution. 4.3.3 Nutrient uptake and movement across the root. 4.3.4 Nutrient uptake by root systems. 5. Roots and the Physico-Chemical Environment. 5.1 Temperature. 5.1.1 Root development and growth. 5.1.2 Root orientation. 5.1.3 Other root functions. 5.2 Gravity and other tropistic responses. 5.2.1 Gravisensing and the response of roots. 5.2.2 Phototropism, hydrotropism and thigmotropism. 5.3 Soil mechanical properties. 5.3.1 Root elongation and mechanical impedance. 5.3.2 Root responses to mechanical impedance. 5.3.3 Roots and soil structure. 5.4 Soil pores and their contents. 5.4.1 Soil water. 5.4.2 Soil aeration. 5.4.3 Waterlogging and aerenchyma. 5.5 The soil chemical environment. 5.5.1 Plant nutrients. 5.5.2 Low pH and aluminium. 5.5.3 Salinity. 5.6 Atmospheric CO2 concentration. 6. Roots and the Biological Environment. 6.1 Interactions of roots with soil organisms. 6.1.1 Root-rhizosphere communication. 6.1.2 Interactions with bacteria. 6.1.3 Interactions with fungi. 6.1.4 Interactions with protozoa. 6.1.5 Interactions with nematodes and mesofauna. 6.2 Symbiotic associations. 6.2.1 Rhizobia and N fixation. 6.2.2 Mycorrhizas. 6.3 Root pathogens and parasitic associations. 6.3.1 Fungal diseases. 6.3.2 Nematodes. 6.3.3 Parasitic weeds. 6.4 Root herbivory by insects. 7. The Rhizosphere and Root Modification of Soils. 7.1 Rhizodeposition. 7.1.1 Quantities of rhizodeposits. 7.1.2 Composition of rhizodeposits. 7.1.3 Nitrogen rhizodeposits. 7.2 Chemical changes affecting nutrient acquisition. 7.2.1 Rhizosolution composition and replenishment. 7.2.2 Changes in pH. 7.2.3 Changes in redox conditions. 7.2.4 Root exudates and phytosiderophores. 7.2.5 Enzyme activity. 7.3 Physical changes in the rhizosphere. 7.3.1 Bulk density and porosity. 7.3.2 Water. 8. Genetic Control of Root System Properties. 8.1 Genotypic differences in root systems. 8.1.1 Size and architecture. 8.1.2 Functional properties. 8.2 Genetics of root systems. 8.2.1 Genetic control of root development and growth. 8.2.2 Genetic control of root properties. 8.3 Breeding better root systems. 8.3.1 Use of markers and QTL.. 9. Root Systems as Management Tools. 9.1 Optimal root systems and competition for resources. 9.2 Intercropping and agroforestry. 9.3 Crop rotations. 9.3.1 Biological drilling. 9.3.2 Utilization of subsoil water. 9.3.3 Allelopathy. 9.3.4 Biofumigation by brassicas. 9.4 Phytoremediation. Index.
292 citations
TL;DR: A new nodulation-defective mutant of Lotus japonicus does not initiate nodule cortical cell division in response to Mesorhizobium loti, but induces root hair deformation, Nod factor-induced calcium spiking, and mycorrhization, which suggests that NSP1 is also involved in infection, bacterial release, and normal bacteroid formation in nodule cells.
Abstract: A new nodulation-defective mutant of Lotus japonicus does not initiate nodule cortical cell division in response to Mesorhizobium loti, but induces root hair deformation, Nod factor-induced calcium spiking, and mycorrhization. This phenotype, together with mapping data, suggested that the mutation could be in the ortholog of the Medicago truncatula NSP1 gene (MtNSP1). The sequence of the orthologous gene (LjNSP1) in the L. japonicus mutant (Ljnsp1-1) revealed a mutation causing a premature stop resulting in loss of the C-terminal 23 amino acids. We also sequenced the NSP2 gene from L. japonicus (LjNSP2). A mutant (Ljnsp2-3) with a premature stop codon was identified by TILLING showing a similar phenotype to Ljnsp1-1. Both LjNSP1 and LjNSP2 are predicted GRAS (GAI, RGA, SCR) domain transcriptional regulators. Transcript steady-state levels of LjNSP1 and LjNSP2 initially decreased and then increased following infection by M. loti. In hairy root transformations, LjNSP1 and MtNSP1 complemented both Mtnsp1-1 and Ljnsp1-1 mutants, demonstrating that these orthologous proteins have a conserved biochemical function. A Nicotiana benthamiana NSP1-like gene (NbNSP1) was shown to restore nodule formation in both Ljnsp1-1 and Mtnsp1-1 mutants, indicating that NSP1 regulators from legumes and non-legumes can propagate the Nod factor-induced signal, activating appropriate downstream targets. The L. japonicus nodules complemented with NbNSP1 contained some cells with abnormal bacteroids and could fix nitrogen. However, the NbNSP1-complemented M. truncatula nodules did not fix nitrogen and contained very few bacteria released from infection threads. These observations suggest that NSP1 is also involved in infection, bacterial release, and normal bacteroid formation in nodule cells.
276 citations
TL;DR: It is proposed that RabA4b recruitment of PI-4Kβ1 results in Ca2+-dependent generation of PI,5P2–dependent signals during the polarized secretion of cell wall components in tip-growing root hair cells.
Abstract: The RabA4b GTPase labels a novel, trans-Golgi network compartment displaying a developmentally regulated polar distribution in growing Arabidopsis thaliana root hair cells. GTP bound RabA4b selectively recruits the plant phosphatidylinositol 4-OH kinase, PI-4Kβ1, but not members of other PI-4K families. PI-4Kβ1 colocalizes with RabA4b on tip-localized membranes in growing root hairs, and mutant plants in which both the PI-4Kβ1 and -4Kβ2 genes are disrupted display aberrant root hair morphologies. PI-4Kβ1 interacts with RabA4b through a novel homology domain, specific to eukaryotic type IIIβ PI-4Ks, and PI-4Kβ1 also interacts with a Ca2+ sensor, AtCBL1, through its NH2 terminus. We propose that RabA4b recruitment of PI-4Kβ1 results in Ca2+-dependent generation of PI-4P on this compartment, providing a link between Ca2+ and PI-4,5P2–dependent signals during the polarized secretion of cell wall components in tip-growing root hair cells.
272 citations
TL;DR: In the growing apex of Arabidopsis thaliana primary roots, cells proceed through four distinct phases of cellular activities, whose zones and their boundaries can be well defined based on their characteristic cellular activities.
Abstract: In the growing apex of Arabidopsis thaliana primary roots, cells proceed through four distinct phases of cellular activities. These zones and their boundaries can be well defined based on their characteristic cellular activities. The meristematic zone comprises, and is limited to, all cells that undergo mitotic divisions. Detailed in vivo analysis of transgenic lines reveals that, in the Columbia-0 ecotype, the meristem stretches up to 200 microm away from the junction between root and root cap (RCJ). In the transition zone, 200 to about 520 microm away from the RCJ, cells undergo physiological changes as they prepare for their fast elongation. Upon entering the transition zone, they progressively develop a central vacuole, polarize the cytoskeleton and remodel their cell walls. Cells grow slowly during this transition: it takes ten hours to triplicate cell length from 8.5 to about 35 microm in the trichoblast cell files. In the fast elongation zone, which covers the zone from 520 to about 850 microm from the RCJ, cell length quadruplicates to about 140 microm in only two hours. This is accompanied by drastic and specific cell wall alterations. Finally, root hairs fully develop in the growth terminating zone, where root cells undergo a minor elongation to reach their mature lengths.
270 citations
TL;DR: In this paper, conditions for analyzing the ability of two fast growing rhizobia, Sinorhizobium meliloti and Rhizobiam leguminosarum bv. viciae, to produce biofilms on abiotic surfaces such as glass, plastic microtiter plates, sand and soil were developed.
241 citations
TL;DR: Results indicate that NO is a critical molecule in the process leading to RHF, and NO is involved in the auxin-signaling cascade leading toRHF.
Abstract: THE ROOT EPIDERMIS IS COMPOSED OF TWO CELL TYPES: trichoblasts (or hair cells) and atrichoblasts (or non-hair cells). In lettuce (Lactuca sativa cv. Grand Rapids var. Rapidmor oscura) plants grown hydroponically in water, the root epidermis did not form root hairs. The addition of 10 microM sodium nitroprusside (SNP), a nitric oxide (NO) donor, resulted in almost all rhizodermal cells differentiated into root hairs. Treatment with the synthetic auxin 1-naphthyl acetic acid (NAA) displayed a significant increase of root hair formation (RHF) that was prevented by the specific NO scavenger carboxy-PTIO (cPTIO). In Arabidopsis, two mutants have been shown to be defective in NO production and to display altered phenotypes in which NO is implicated. Arabidopsis nos1 has a mutation in an NO synthase structural gene (NOS1), and the nia1 nia2 double mutant is null for nitrate reductase (NR) activity. We observed that both mutants were affected in their capacity of developing root hairs. Root hair elongation was significantly reduced in nos1 and nia1 nia2 mutants as well as in cPTIO-treated wild type plants. A correlation was found between endogenous NO level in roots detected by the fluorescent probe DAF-FM DA and RHF. In Arabidopsis, as well as in lettuce, cPTIO blocked the NAA-induced root hair elongation. Taken together, these results indicate that: (1) NO is a critical molecule in the process leading to RHF and (2) NO is involved in the auxin-signaling cascade leading to RHF.
TL;DR: Pharmacological compounds known to alter cytoplasmic calcium levels revealed that ATP release is a calcium-dependent process and may occur through vesicular fusion, an important step in the polar growth of actively growing root hairs.
Abstract: Extracellular ATP (eATP) in animals is well documented and known to play an important role in cellular signaling (e.g. at the nerve synapse). The existence of eATP has been postulated in plants; however, there is no definitive experimental evidence for its presence or an explanation as to how such a polar molecule could exit the plant cell and what physiological role it may play in plant growth and development. The presence of eATP in plants (Medicago truncatula) was detected by constructing a novel reporter; i.e. fusing a cellulose-binding domain peptide to the ATP-requiring enzyme luciferase. Application of this reporter to plant roots allowed visualization of eATP in the presence of the substrate luciferin. Luciferase activity could be detected in the interstitial spaces between plant epidermal cells and predominantly at the regions of actively growing cells. The levels of eATP were closely correlated with regions of active growth and cell expansion. Pharmacological compounds known to alter cytoplasmic calcium levels revealed that ATP release is a calcium-dependent process and may occur through vesicular fusion, an important step in the polar growth of actively growing root hairs. Reactive oxygen species (ROS) activity at the root hair tip is not only essential for root hair growth, but also dependent on the cytoplasmic calcium levels. Whereas application of exogenous ATP and a chitin mixture increased ROS activity in root hairs, no changes were observed in response to adenosine, AMP, ADP, and nonhydrolyzable ATP (βγmeATP). However, application of exogenous potato (Solanum tuberosum) apyrase (ATPase) decreased ROS activity, suggesting that cytoplasmic calcium gradients and ROS activity are closely associated with eATP release.
TL;DR: Using the Bay-0 x Shahdara recombinant inbred line (RIL) population, three quantitative trait loci (QTL) involved in the root growth response to low P are mapped and one of these, LPR1, explains 52% of the variance of the PRL.
Abstract: One of the responses of plants to low sources of external phosphorus (P) is to modify root architecture. In Arabidopsis thaliana plantlets grown on low P, the primary root length (PRL) is reduced whereas lateral root growth is promoted. By using the Bay-0 x Shahdara recombinant inbred line (RIL) population, we have mapped three quantitative trait loci (QTL) involved in the root growth response to low P. The Shahdara alleles at these three QTL promote the response of the primary root to low P (i.e., root length reduction). One of these QTL, LPR1, located in a 2.8 Mb region at the top of chromosome 1, explains 52% of the variance of the PRL. We also detected a single QTL associated with primary root cell elongation in response to low P which colocalizes with LPR1. LPR1 does not seem to be involved in other typical P-starvation responses such as growth and density of root hairs, excretion of acid phosphatases, anthocyanin accumulation or the transcriptional induction of the P transporter Phtl;4. LPR1 might highlight new aspects of root growth that are revealed specifically under low P conditions.
TL;DR: The role of ROS in the control of root hair growth is reviewed and results are highlighted that may provide insight into the mechanism of plant cell growth in general.
Abstract: Reactive oxygen species (ROS) play a diversity of roles in plants. In recent years, a role for NADPH oxidase-derived ROS during cell growth and development has been discovered in a number of plant model systems. These studies indicate that ROS are required for cell expansion during the morphogenesis of organs such as roots and leaves. Furthermore, there is evidence that ROS are required for root hair growth where they control the activity of calcium channels required for polar growth. The role of ROS in the control of root hair growth is reviewed here and results are highlighted that may provide insight into the mechanism of plant cell growth in general.
TL;DR: Ryser et al. as mentioned in this paper investigated the variation in specific root length and root surface area in response to variation in N and P supply among 10 temperate pasture species with contrasting root morphologies and contrasting N andP requirements.
Abstract: reflecting the difficulty in extracting fine roots from the soil, and the enormous length these roots can attain. For example, Dittmer (1937) excavated the entire root system of a single rye plant, which consisted of 13,815,672 branches and had a total length of 622 km with a surface area of 237 m, and a total root hair length of 11,000 km. Since then, progress has been made in the methodology of assessing root length and in understanding the variation in it, but there still remains an air of mystery around root length as even the newest findings are often contradictory. Investigations have often focused on Specific Root Length (SRL), a trait which characterizes the economical aspects of a root system, stating the costs––mass––per potential return––root length. SRL has been shown to increase, decrease, or stay constant in response to nutrient limitation (Ryser 1998). Furthermore, root length does not always respond to specific ions, such as nitrate or phosphate, in manner like theories based on the mobility of these ions would predict (Robinson 1996; Leyser and Fitter 1998). In this issue, Hill et al. (2006) describe an elegant experiment to tackle this mystery. They investigate the variation in specific root length and root surface area in response to variation in N and P supply among 10 temperate pasture species with contrasting root morphologies and contrasting N and P requirements. They investigate the traits contributing to variation in root surface area: biomass allocation to roots, SRL, root fineness and tissue mass density. The results show that the root morphology of a species indeed corresponds well with its phosphorus requirements. The data also clearly illustrate the general importance of phenotypic plasticity for the maintenance of resource acquisition capacity at low levels of the resource, as all species were able to maintain a fairly constant root length across a wide range of P treatments, despite a large variation in total plant mass and root mass. However, the degree of the plastic response was not related to the P uptake capacity of the species, and the patterns cannot readily be generalized. In response to P limitation, some species changed their biomass allocation pattern, some changed root fineness, and others root tissue mass density. There was no consistent relationship in the nutrient level at which the species began to modify their root characteristics and their nutrient requirement. P. Ryser (&) Department of Biology, Laurentian University, Ramsey Lake Road, Sudbury, Ontario, Canada, P3E 2C6 e-mail: pryser@laurentian.ca Plant Soil (2006) 286:1–6 DOI 10.1007/s11104-006-9096-1
TL;DR: It is suggested that differences among the studied species in use of different P pools and in the width of the rhizosphere are relatively small, irrespective of plant species.
Abstract: This study investigates the distribution of carboxylates and acid phosphatases as well as the depletion of different phosphorus (P) fractions in the rhizosphere of three legume crop species and a cereal, grown in a soil with two different levels of residual P. White lupin (Lupinus albus L.), field pea (Pisum sativum L.), faba bean (Vicia faba L.) and spring wheat (Triticum aestivum L.) were grown in small sand-filled PVC tubes to create a dense root mat against a 38-μm mesh nylon cloth at the bottom, where it was in contact with the soil of interest contained in another tube. The soil had either not been fertilised (P0) or fertilised with 15 (P15) kg P ha−1 in previous years. The mesh size did not allow roots to grow into the soil, but penetration of root hairs and diffusion of nutrients and root exudates was possible, and a rhizosphere was established. At harvest, thin (1 mm) slices of this rhizosphere soil were cut, down to a 10-mm distance from the mesh surface. The rhizosphere of white lupin, particularly in the P0 treatment, contained citrate, mostly in the first 3 mm, with concentrations decreasing with distance from the root. Acid phosphatase activity was enhanced in the rhizosphere of all species, as compared with bulk soil, up to a distance of 4 mm. Phosphatase activity was highest in the rhizosphere of white lupin, followed by faba bean, field pea and wheat. Both citrate concentrations and phosphatase activities were higher in P0 compared with P15. The depletion of both inorganic (Pi) and organic (Po) phosphorus fractions was greatest at the root surface, and decreased gradually with distance from the root. The soil P fractions that were most depleted as a result of root activity were the bicarbonate-extractable (0.5 M) and sodium hydroxide-extractable (0.1 M) pools, irrespective of plant species. This study suggests that differences among the studied species in use of different P pools and in the width of the rhizosphere are relatively small.
TL;DR: Genetic support is provided for the role of P as an important signal for postembryonic root development and root meristem maintenance and show a crosstalk in developmental and biochemical responses to P deprivation.
Abstract: Low phosphorus (P) availability is one of the most limiting factors for plant productivity in many natural and agricultural ecosystems. Plants display a wide range of adaptive responses to cope with low P stress, which generally serve to enhance P availability in the soil and to increase its uptake by roots. In Arabidopsis (Arabidopsis thaliana), primary root growth inhibition and increased lateral root formation have been reported to occur in response to P limitation. To gain knowledge of the genetic mechanisms that regulate root architectural responses to P availability, we designed a screen for identifying Arabidopsis mutants that fail to arrest primary root growth when grown under low P conditions. Eleven low phosphorus insensitive (lpi) mutants that define at least four different complementation groups involved in primary root growth responses to P availability were identified. The lpi mutants do not show the typical determinate developmental program induced by P stress in the primary root. Other root developmental aspects of the low P rescue system, including increased root hair elongation and anthocyanin accumulation, remained unaltered in lpi mutants. In addition to the insensitivity of primary root growth inhibition, when subjected to P deprivation, lpi mutants show a reduced induction in the expression of several genes involved in the P starvation rescue system (PHOSPHATE TRANSPORTER 1 and 2, PURPLE ACID PHOSPHATASE 1, ACID PHOSPHATASE 5, and INDUCED BY PHOSPHATE STARVATION 1). Our results provide genetic support for the role of P as an important signal for postembryonic root development and root meristem maintenance and show a crosstalk in developmental and biochemical responses to P deprivation.
TL;DR: Results indicate that PLDζ1 and PLD⩽2 play a role in regulating root development in response to nutrient limitation, and this results indicate that root elongation and root hair formation are important in nutrient absorption.
Abstract: Root elongation and root hair formation are important in nutrient absorption. We found that two Arabidopsis (Arabidopsis thaliana) phospholipase Ds (PLDs), PLDζ1 and PLDζ2, were involved in root elongation during phosphate limitation. PLDζ1 and PLDζ2 are structurally different from the majority of plant PLDs by having phox and pleckstrin homology domains. Both PLDζs were expressed more in roots than in other tissues. It was reported previously that inducible suppression or inducible overexpression of PLDζ1 affected root hair patterning. However, gene knockouts of PLDζ1, PLDζ2, or the double knockout of PLDζ1 and PLDζ2 showed no effect on root hair formation. The expression of PLDζs increased in response to phosphate limitation. The elongation of primary roots in PLDζ1 and PLDζ2 double knockout mutants was slower than that of wild type and single knockout mutants. The loss of PLDζ2, but not PLDζ1, led to a decreased accumulation of phosphatidic acid in roots under phosphate-limited conditions. These results indicate that PLDζ1 and PLDζ2 play a role in regulating root development in response to nutrient limitation.
TL;DR: It is proposed that this cell-to-cell communication is governed more by the in situ spatial proximity of cells within AHL-gradients than the requirement for a quorum group of high population density.
TL;DR: Efforts to manage rhizosphere bacteria for sustainable agricultural systems should continue to focus on root cap and mucilage chemistry, and remnant roots as sources of beneficial bacteria.
Abstract: Native bacteria, Pseudomonas and filamentous bacteria were quantified and localized on wheat roots grown in the field using fluorescence in situ hybridization (FISH). Seminal roots were sampled through the season from unploughed soil in a conservation farming system. Such soils are spatially heterogeneous, and many roots grow slowly through hard soil with cracks and pores containing dead roots remnant from previous crops. Root and rhizosphere morphology, and contact with soil particles were preserved, and autofluorescence was avoided by observing sections in the far-red with Cy5 and Cy5.5 fluorochromes. Spatial analyses showed that bacteria were embedded in a stable matrix (biofilm) within 11 microm of the root surface (range 2-30 microm) and were clustered on 40% of roots. Half the clusters co-located with axial grooves between epidermal cells, soil particles, cap cells or root hairs; the other half were not associated with visible features. Across all wheat roots, although variable, bacteria averaged 15.4 x 10(5) cells per mm(3) rhizosphere, and of these, Pseudomonas and filaments comprised 10% and 4%, respectively, with minor effects of sample time, and no effect of plant age. Root caps were most heavily colonized by bacteria along roots, and elongation zones least heavily colonized. Pseudomonas varied little with root development and were 17% of bacteria on the elongation zone. Filamentous bacteria were not found on the elongation zone. The most significant factor to rhizosphere populations along a wheat root, however, was contact with dead root remnants, where Pseudomonas were reduced but filaments increased to 57% of bacteria (P < 0.001). This corresponded with analyses of root remnants showing they were heavily colonized by bacteria, with 48% filaments (P < 0.001) and 1.4%Pseudomonas (P = 0.014). Efforts to manage rhizosphere bacteria for sustainable agricultural systems should continue to focus on root cap and mucilage chemistry, and remnant roots as sources of beneficial bacteria.
TL;DR: The results suggest that this regulatory module of root hair–specific genes has been conserved across angiosperms despite the divergence of upstream fate-determining machinery.
Abstract: Vascular plants develop distinctive root hair distribution patterns in the root epidermis, depending on the taxon. The three patterns, random (Type 1), asymmetrical cell division (Type 2), and positionally cued (Type 3), are controlled by different upstream fate-determining factors that mediate expression of root hair cell-specific genes for hair morphogenesis. Here, we address whether these root hair genes possess a common transcriptional regulatory module (cis-element) determining cell-type specificity despite differences in the final root hair pattern. We identified Arabidopsis thaliana expansinA7 (At EXPA7) orthologous (and paralogous) genes from diverse angiosperm species with different hair distribution patterns. The promoters of these genes contain conserved root hair-specific cis-elements (RHEs) that were functionally verified in the Type-3 Arabidopsis root. The promoter of At EXPA7 (Type-3 pattern) also showed hair cell-specific expression in the Type 2 rice (Oryza sativa) root. Root hair-specific genes other than EXPAs also carry functionally homologous RHEs in their promoters. The RHE core consensus was established by a multiple alignment of functionally characterized RHEs from different species and by high-resolution analysis of At EXPA7 RHE1. Our results suggest that this regulatory module of root hair-specific genes has been conserved across angiosperms despite the divergence of upstream fate-determining machinery.
TL;DR: It is demonstrated that the protein kinase PINOID (PID) positively regulates cellular auxin efflux, most likely by modulating the trafficking of PIN and/or some other molecular partners involved in aux in efflux.
Abstract: Intercellular transport of auxin is mediated by influx and efflux carriers in the plasma membrane and subjected to developmental and environmental regulation. Here, using the auxin-sensitive Arabidopsis thaliana root hair cell system and the tobacco (Nicotiana tabacum) suspension cell system, we demonstrate that the protein kinase PINOID (PID) positively regulates auxin efflux. Overexpression of PID (PIDox) or the auxin efflux carrier component PINFORMED3 (PIN3, PIN3ox), specifically in the root hair cell, greatly suppressed root hair growth. In both PIDox and PIN3ox transformants, root hair growth was nearly restored to wild-type levels by the addition of auxin, protein kinase inhibitors, or auxin efflux inhibitors. Localization of PID or PIN3 at the cell boundary was disrupted by brefeldin A and staurosporine. A mutation in the kinase domain abrogated the ability of PID to localize at the cell boundary and to inhibit root hair growth. These results suggest that PIDox- or PIN3ox-enhanced auxin efflux results in a shortage of intracellular auxin and a subsequent inhibition of root hair growth. In an auxin efflux assay using transgenic tobacco suspension cells, PIDox or PIN3ox also enhanced auxin efflux. Collectively, these results suggest that PID positively regulates cellular auxin efflux, most likely by modulating the trafficking of PIN and/or some other molecular partners involved in auxin efflux.
TL;DR: The effects of ABA on root morphogenesis change were Ca(2+) dependent and required the participation of calmodulin and de novo protein synthesis; a model is presented that illustrates how ABA acts through a potential cellular and signal transduction mechanism to induce morphological and physiological changes in rice roots.
Abstract: Plant roots retain developmental plasticity and respond to environmental stresses or exogenous plant growth regulators by undergoing profound morphological and physiological alteration. In this study, we investigated the effects of exogenous ABA on root growth and development in Taichung native 1 (TN1) rice. Exogenous application of 10 microM ABA leads to swelling, root hair formation and initiation of lateral root primodia in the tips of young, seminal rice roots. Cortex cells increased in size and were irregularly shaped. ABA treatment significantly increased 2, 3, 5-triphenyl tetrazolium chloride (TTC) reductase ability in the root tips and the exudation rate of xylem sap. In addition, the K(+) ion content in xylem sap increased nearly 2-fold, but not that of Ca(2+) or Mg(2+). Analysis of proteins expressed in the root tips identified several ABA-induced or -repressed proteins, including actin depolymerization factor (ADF), late embryo abundant protein (LEA), putative steroid membrane-binding protein, ferredoxin thionine reductase and calcium-binding protein. The effects of ABA on root morphogenesis change were Ca(2+) dependent and required the participation of calmodulin and de novo protein synthesis. A model is presented that illustrates how ABA acts through a potential cellular and signal transduction mechanism to induce morphological and physiological changes in rice roots.
TL;DR: A systemic spreading of S. enterica to the plant shoot (stems and leaves) was demonstrated using a specific PCR analysis and plate count technique and the FISH/CSLM approach demonstrated not only high-density colonization of the root hairs and the root surface by S.Enterica but also a spreading to subjacent rhizodermis layers and the inner root cortex.
TL;DR: The result indicates that in addition to its known function in trichome and root hair development, GLABRA2 is involved in the control of seed oil accumulation.
Abstract: Despite a good understanding of genes involved in oil biosynthesis in seed, the mechanism(s) that controls oil accumulation is still not known. To identify genes that control oil accumulation in seed, we have developed a simple screening method to isolate Arabidopsis seed oil mutants. The method includes an initial screen for seed density followed by a seed oil screen using an automated Nuclear Magnetic Resonance (NMR). Using this method, we isolated ten low oil mutants and one high oil mutant. The high oil mutant, p777, accumulated 8% more oil in seed than did wild type, but it showed no differences in seed size, plant growth or development. The high-oil phenotype is caused by the disruption of the GLABRA2 gene, a previously identified gene that encodes a homeobox protein required for normal trichome and root hair development. Knockout of GLABRA2 did not affect LEAFY COTYLEDON 1 and PICKLE expression in developing embryo. The result indicates that in addition to its known function in trichome and root hair development, GLABRA2 is involved in the control of seed oil accumulation.
TL;DR: In this article, the critical Cu2+ activity associated with a reduction in the growth of solution-grown cowpea (Vigna unguiculata (L.) Walp. cv Caloona) was determined in a system in which Cu was maintained constant through the use of a cation exchange resin.
Abstract: Accurate determination of the rhizotoxicity of Cu in dilute nutrient solutions is hindered by the difficulty of maintaining constant, pre-determined concentrations of Cu (micromolar) in solution. The critical Cu2+ activity associated with a reduction in the growth of solution-grown cowpea (Vigna unguiculata (L.) Walp. cv Caloona) was determined in a system in which Cu was maintained constant through the use of a cation exchange resin. The growth of roots and shoots was found to be reduced at solution Cu2+ activities ≥ 1.7 µM (corresponding to 90 % maximum growth). Although root growth was most likely reduced due to a direct Cu2+ toxicity, it is considered that the shoot growth reduction is attributable to a decrease in tissue concentrations of K, Ca, Mg, and Fe and the formation of interveinal chlorosis. At high Cu2+ activities, roots were brown in color, short and thick, had bent root tips with cracking of the epidermis and outer cortex, and had local swellings behind the roots tips due to a reduction in cell elongation. Root hair growth was reduced at concentrations lower than that which caused a significant reduction in overall root fresh weight.
TL;DR: The lrx1 mutant phenotype is likely to be suppressed by changes in pectic polysaccharides or other cell wall components, and the rol1 mutations cause a change in the expression of a number of cell wall–related genes.
Abstract: Cell and cell wall growth are mutually dependent processes that must be tightly coordinated and controlled. LRR-extensin1 (LRX1) of Arabidopsis thaliana is a potential regulator of cell wall development, consisting of an N-terminal leucine-rich repeat domain and a C-terminal extensin-like domain typical for structural cell wall proteins. LRX1 is expressed in root hairs, and lrx1 mutant plants develop distorted root hairs that often swell, branch, or collapse. The aberrant cell wall structures found in lrx1 mutants point toward a function of LRX1 during the establishment of the extracellular matrix. To identify genes that are involved in an LRX1-dependent developmental pathway, a suppressor screen was performed on the lrx1 mutant, and two independent rol1 (for repressor of lrx1) alleles were isolated. ROL1 is allelic to Rhamnose Biosynthesis1, which codes for a protein involved in the biosynthesis of rhamnose, a major monosaccharide component of pectin. The rol1 mutations modify the pectic polysaccharide rhamnogalacturonan I and, for one allele, rhamnogalacturonan II. Furthermore, the rol1 mutations cause a change in the expression of a number of cell wall–related genes. Thus, the lrx1 mutant phenotype is likely to be suppressed by changes in pectic polysaccharides or other cell wall components.
TL;DR: It is proposed that the process of growth promotion triggered by A. brasilense inoculation involves a signaling pathway that has ethylene as a central, positive regulator.
Abstract: Tomato seeds were inoculated with the plant growth–promoting rhizobacteria Azospirillum brasilense FT326, and changes in parameters associated with plant growth were evaluated 15 days after inoculation. Azospirilla were localized on roots and within xylematic tissue. An increase in shoot and root fresh weight, main root hair length, and root surface indicated that inoculation with A. brasilense FT 326 resulted in plant growth improvement. The levels of indole-3-acetic acid (IAA) and ethylene, two of the phytohormones related to plant growth, were higher in inoculated plants. Exogenously supplied ethylene mimicked the effect of inoculation, and the addition of an inhibitor of its synthesis or of its physiological activity completely blocked A. brasilense growth promotion. Based on our results, we propose that the process of growth promotion triggered by A. brasilense inoculation involves a signaling pathway that has ethylene as a central, positive regulator.
TL;DR: In isolation and partial characterization of a novel high molecular weight surface polysaccharide from a strain of Rhizobium leguminosarum that nodulates Pisum sativum and Vicia sativa roots, data are consistent with the hypothesis that rhizobia can use (at least) two mechanisms for docking at the root surface, with use of a lectin–glycan mechanism under slightly acidic conditions.
Abstract: Rhizobium bacteria produce different surface polysaccharides which are either secreted in the growth medium or contribute to a capsule surrounding the cell. Here, we describe isolation and partial characterization of a novel high molecular weight surface polysaccharide from a strain of Rhizobium leguminosarum that nodulates Pisum sativum (pea) and Vicia sativa (vetch) roots. Carbohydrate analysis showed that the polysaccharide consists for 95% of mannose and glucose, with minor amounts of galactose and rhamnose. Lectin precipitation analysis revealed high binding affinity of pea and vetch lectin for this polysaccharide, in contrast to the other known capsular and extracellular polysaccharides of this strain. Expression of the polysaccharide was independent of the presence of a Sym plasmid or the nod gene inducer naringenin. Incubation of R. leguminosarum with labelled pea lectin showed that this polysaccharide is exclusively localized on one of the poles of the bacterial cell. Vetch roots incubated with rhizobia and labelled pea lectin revealed that this bacterial pole is involved in attachment to the root surface. A mutant strain deficient in the production of this polysaccharide was impaired in attachment and root hair infection under slightly acidic conditions, in contrast to the situation at slightly alkaline conditions. Our data are consistent with the hypothesis that rhizobia can use (at least) two mechanisms for docking at the root surface, with use of a lectin-glycan mechanism under slightly acidic conditions.
TL;DR: The stimulation observed with velvetleaf root crude extract suggests that sorghum seedlings may respond to the presence of other plants by releasing more of this allelochemical.
Abstract: Sorgoleone is the major component of the hydrophobic root exudate of sorghum [Sorghum bicolor (L.) Moench]. The presence of this allelochemical is intrinsically linked to root growth and the development of mature root hairs. However, factors modulating root formation and the biosynthesis of sorgoleone are not well known. Sorgoleone production was independent of early stages of plant development. The optimum temperature for root growth and sorgoleone production was 30°C. Seedling development and sorgoleone levels were greatly reduced at temperatures below 25°C and above 35°C. The level of sorgoleone was also sensitive to light, being reduced by nearly 50% upon exposure to blue light (470 nm) and by 23% with red light (670 nm). Applying mechanical pressure over developing seedlings stimulated root formation but did not affect the biosynthesis of this lipid benzoquinone. Sorgoleone production did not change in seedlings exposed to plant defense elicitors. On the other hand, sorgoleone levels increased in plants treated with a crude extract of velvetleaf (Abutilon theophrasti Medik.) root. This stimulation was not associated with increased osmotic stress, since decreases in water potential (Ψw) by increasing solute concentrations with sorbitol reduces sorgoleone production. Sorgoleone production appears to be constitutively expressed in young developing sorghum plants. Other than with temperature, changes in the environmental factors had either no effect or caused a reduction in sorgoleone levels. However, the stimulation observed with velvetleaf root crude extract suggests that sorghum seedlings may respond to the presence of other plants by releasing more of this allelochemical.