Number Of Root Hairs Research Articles

IMPROVEMENT OF TOMATO WATER PRODUCTIVITY BY THE USE OF A PARTIAL ROOTZONE DRYING IRRIGATION STRATEGY

Water scarcity is becoming a major problem for agricultural development in the Mediterranean area. The Moroccan Massa region is a major supplier of tomato (Lycopersicum esculentum L.) both for export and for the domestic market. Current average water use for the tomato is 8,000 m3/ha for an 8-9 month production cycle. This research aims to develop irrigation strategies with this goal water saving with no effect on yield or fruit characteristics. The objective of the work was to assess the effects of the partial root zone drying irrigation (PRD) on leaf stomatal conductance, relative leaf water content (RWC), stem maximum daily shrinkage (MDS), root development and water use efficiency (WUE) of tomato grown in a greenhouse on a sandy substrate. Three treatments were applied: a control that received 100% of the water requirement, PRD-70 and PRD-50 in which 70% and 50% of water requirements were applied. The root system was divided in two sides with alternation of irrigation every three days. When vapor pressure deficit rises, PRD treatments showed a decrease in leaf stomatal conductance with, respectively, 17% and 26% compared to control. PRD-50 had the highest leaf water content during the experimental period. During periods of low and moderate climatic demand, MDS of all treatments showed the same trend. Whereas when vapor pressure deficit rose, PRD-50 had lower signal intensity. Compared to the control, number of root hairs increased by 120% and 190% in PRD-70 and PRD-50, respectively. Water use efficiency (WUE) was the highest (P < 0.001) for PRD-50 with 43 kg of fresh fruit per m3 of applied water.

Morphological, anatomical, and ultrastructural changes (visualized through scanning electron microscopy) induced in Triticum aestivum by Pb²⁺ treatment.

Lead (Pb) causes severe damage to crops, ecosystems, and humans, and alters the physiology and biochemistry of various plant species. It is hypothesized that Pb-induced metabolic alterations could manifest as structural variations in the roots of plants. In light of this, the morphological, anatomical, and ultrastructural variations (through scanning electron microscopy, SEM) were studied in 4-day-old seedlings of Triticum aestivum grown under Pb stress (0, 8, 16, 40, and 80 mg Pb(2+) l(-1); mild to highly toxic). The toxic effect was more pronounced in radicle growth than on the plumule growth. The SEM of the root of T. aestivum depicted morphological alterations and surface ultrastructural changes. Compared to intact and uniform surface cells in the control roots, cells were irregular and desiccated in Pb(2+)-treated roots. In Pb(2+)-treated roots, the number of root hairs increased manifold, showing dense growth, and these were apparently longer. Apart from the deformity in surface morphology and anatomy of the roots in response to Pb(2+) toxicity, considerable anatomical alterations were also observed. Pb(2+)-treated root exhibited signs of injury in the form of cell distortion, particularly in the cortical cells. The endodermis and pericycle region showed loss of uniformity post Pb(2+) exposure (at 80 mg l(-1) Pb(2+)). The cells appeared to be squeezed with greater depositions observed all over the tissue. The study concludes that Pb(2+) treatment caused structural anomalies and induced anatomical and surface ultrastructural changes in T. aestivum.

A banana aquaporin gene, MaPIP1;1, is involved in tolerance to drought and salt stresses

BackgroundAquaporin (AQP) proteins function in transporting water and other small molecules through the biological membranes, which is crucial for plants to survive in drought or salt stress conditions. However, the precise role of AQPs in drought and salt stresses is not completely understood in plants.ResultsIn this study, we have identified a PIP1 subfamily AQP (MaPIP1;1) gene from banana and characterized it by overexpression in transgenic Arabidopsis plants. Transient expression of MaPIP1;1-GFP fusion protein indicated its localization at plasma membrane. The expression of MaPIP1;1 was induced by NaCl and water deficient treatment. Overexpression of MaPIP1;1 in Arabidopsis resulted in an increased primary root elongation, root hair numbers and survival rates compared to WT under salt or drought conditions. Physiological indices demonstrated that the increased salt tolerance conferred by MaPIP1;1 is related to reduced membrane injury and high cytosolic K+/Na+ ratio. Additionally, the improved drought tolerance conferred by MaPIP1;1 is associated with decreased membrane injury and improved osmotic adjustment. Finally, reduced expression of ABA-responsive genes in MaPIP1;1-overexpressing plants reflects their improved physiological status.ConclusionsOur results demonstrated that heterologous expression of banana MaPIP1;1 in Arabidopsis confers salt and drought stress tolerances by reducing membrane injury, improving ion distribution and maintaining osmotic balance.

Impact of IAA, GA 3 , and ABA on Negative Root Phototropism and Root Growth of Rice

The objective of this research was to investigate the relationship between rice roots negative phototropism and endogenous plant hormone levels, as well as the impact of exogenous hormones on rice root growth. The adventitious roots and primary roots of conventional cultivars Yangdao 6(indica), Nipponbare(japonica), Zhonghua 11(japonica) and its OsPIN1 a over expressed transgenic seedlings were used to observe the process of root negative phototropism, measure contents of endogenous auxin(IAA), gibberellin(GA3) and abscisic acid(ABA) in the bending part of root tips, and investigate the impact of exogenous hormones to rice root morphology and anatomy. Results indicated that seedling roots of both Yangdao 6 and Nipponbare had negative phototropism, and the lateral roots and adventitious roots of Yangdao 6 showed stronger negative phototropism. Plant hormones and negative phototropism of rice root and root development are closely linked. Under unilateral illumination, endogenous IAA, GA3 and ABA levels declined. The content of these phytohormones in the irradiated side was lower than that in the shaded side. The treatment of unilateral light and exogenous IAA induced a large number of root hairs in Yangdao 6. Compared with conventional rice, the angle of negative phototropism was lager in OsPIN1 a transgenic plant. There was no direct relationship between exogenous GA3 and ABA treatments and root negative phototropism of rice. Exogenous ABA inhibited root growth obviously. The total absorption surface area, root number and root length per plant were significantly reduced by ABA treatment. The treatment of 10 μmol L–1ABA not only caused a dysplasia of both meristematic and elongation zone but also promoted the development of the central vascular tissue in root tips.

Phenotypical and molecular responses of Arabidopsis thaliana roots as a result of inoculation with the auxin‐producing bacterium Azospirillum brasilense

The auxin-producing bacterium Azospirillum brasilense Sp245 can promote the growth of several plant species. The model plant Arabidopsis thaliana was chosen as host plant to gain an insight into the molecular mechanisms that govern this interaction. The determination of differential gene expression in Arabidopsis roots after inoculation with either A.brasilense wild-type or an auxin biosynthesis mutant was achieved by microarray analysis. Arabidopsis thaliana inoculation with A.brasilense wild-type increases the number of lateral roots and root hairs, and elevates the internal auxin concentration in the plant. The A.thaliana root transcriptome undergoes extensive changes on A.brasilense inoculation, and the effects are more pronounced at later time points. The wild-type bacterial strain induces changes in hormone- and defense-related genes, as well as in plant cell wall-related genes. The A.brasilense mutant, however, does not elicit these transcriptional changes to the same extent. There are qualitative and quantitative differences between A.thaliana responses to the wild-type A.brasilense strain and the auxin biosynthesis mutant strain, based on both phenotypic and transcriptomic data. This illustrates the major role played by auxin in the Azospirillum-Arabidopsis interaction, and possibly also in other bacterium-plant interactions.

Elevating vitamin C content via overexpression of myo-inositol oxygenase and l-gulono-1,4-lactone oxidase in Arabidopsis leads to enhanced biomass and tolerance to abiotic stresses.

l-Ascorbic acid (vitamin C) is an abundant metabolite in plant cells and tissues. Ascorbate functions as an antioxidant, as an enzyme cofactor, and plays essential roles in multiple physiological processes including photosynthesis, photoprotection, control of cell cycle and cell elongation, and modulation of flowering time, gene regulation, and senescence. The importance of this key molecule in regulating whole plant morphology, cell structure, and plant development has been clearly established via characterization of low vitamin C mutants of Arabidopsis, potato, tobacco, tomato, and rice. However, the consequences of elevating ascorbate content in plant growth and development are poorly understood. Here we demonstrate that Arabidopsis lines over-expressing a myo-inositol oxygenase or an l-gulono-1,4-lactone oxidase, containing elevated ascorbate, display enhanced growth and biomass accumulation of both aerial and root tissues. To our knowledge this is the first study demonstrating such a marked positive effect in plant growth in lines engineered to contain elevated vitamin C content. In addition, we present evidence showing that these lines are tolerant to a wide range of abiotic stresses including salt, cold, and heat. Total ascorbate content of the transgenic lines remained higher than those of controls under the abiotic stresses tested. Interestingly, exposure to pyrene, a polycyclic aromatic hydrocarbon and known inducer of oxidative stress in plants, leads to stunted growth of the aerial tissue, reduction in the number of root hairs, and inhibition of leaf expansion in wild type plants, while these symptoms are less severe in the over-expressers. Our results indicate the potential of this metabolic engineering strategy to develop crops with enhanced biomass, abiotic stress tolerance, and phytoremediation capabilities.

Drought and salt tolerance enhancement of transgenic Arabidopsis by overexpression of the vacuolar pyrophosphatase 1 (EVP1) gene from Eucalyptus globulus

Vacuolar solute accumulation has been shown to be a mechanism by which plants are capable of increasing drought and salt tolerance. The exposure of plants to NaCl induces H+ transport into the vacuole by specialized pumps. One of them corresponds to the vacuolar H+-pyrophosphatase, which generates a H+ gradient across the vacuolar membrane. In our laboratory we isolated the first cDNA sequence of a vacuolar pyrophosphatase type I (EVP1) from Eucalyptus globulus. Using real-time PCR we confirmed that EVP1 participates in Eucalyptus plants' response to drought and salt stress through an ABA independent pathway. Additionally, the overexpression of EVP1 in transgenic Arabidopsis resulted in an enhancement of drought and salt tolerance. Interestingly we established that the transgenic plants had a higher number of root hairs, which may have a positive effect on the plant's response to drought and salt stress. These results suggest that EVP1 plays an active role in abiotic stress tolerance in E. globulus, and that it may be potentially used to enhance drought and stress tolerance of plants.

An improved culture solution technique for Plasmodiophora brassicae infection and the dynamic infection in the root hair

We developed an improved solution culture technique that enabled clear and comprehensive observation of dynamic root hair infection by Plasmodiophora brassicae. Brassica oleracea seedlings were sown directly into 10 mL centrifuge tubes containing half-strength Hoagland nutrient solution. Seedlings were fastened in 1 cm thick foam in the tube top and tubes were wrapped with black tape to block light and prevent algal growth. Maximal root hair infection was observed under conditions of pH 5.5, temperature of 20 to 25 °C, and an inoculation concentration of 1 × 107 spores/mL. Infection efficiency was obviously higher in fresh nutrient. Under optimum infection conditions, plasmodia were found in the root hair 4 days after inoculation (DAI), with some undergoing cleavage and developing into round zoosporangia 3 days later. At ten DAI, the number of root hairs containing zoosporangia per root reached 208, and the cytoplasm within the zoosporangia began to cleave and form incipient zoospores. Most zoosporangia released the zoospores and became diaphanous at ten DAI. Root hairs became swollen during the experimental trial and small galls appeared clearly on the root at 20 DAI. In addition, sectioned specimens showed that some cortical cells contained resting spores. We sequentially tested the germination of the resting spores in tubes from 1 to 11 DAI and the temporal dynamics of germination corresponding to the infection. Zoosporangia were found in epidermal cells at the same time as in the root hair.

Genotypic Characterization of Azotobacteria Isolated from Argentinean Soils and Plant‐Growth‐Promoting Traits of Selected Strains with Prospects for Biofertilizer Production

The genetic diversity among 31 putative Azotobacter isolates obtained from agricultural and non-agricultural soils was assessed using rep-PCR genomic fingerprinting and identified to species level by ARDRA and partial 16S rRNA gene sequence analysis. High diversity was found among the isolates, identified as A. chroococcum, A. salinestris, and A. armeniacus. Selected isolates were characterized on the basis of phytohormone biosynthesis, nitrogenase activity, siderophore production, and phosphate solubilization. Indole-3 acetic-acid (IAA), gibberellin (GA3) and zeatin (Z) biosynthesis, nitrogenase activity, and siderophore production were found in all evaluated strains, with variation among them, but no phosphate solubilization was detected. Phytohormones excreted to the culture medium ranged in the following concentrations: 2.2–18.2 μg IAA mL−1, 0.3–0.7 μg GA3 mL−1, and 0.5–1.2 μg Z mL−1. Seed inoculations with further selected Azotobacter strains and treatments with their cell-free cultures increased the number of seminal roots and root hairs in wheat seedlings. This latter effect was mimicked by treatments with IAA-pure solutions, but it was not related to bacterial root colonization. Our survey constitutes a first approach to the knowledge of Azotobacter species inhabiting Argentinean soils in three contrasting geographical regions. Moreover, this phenotypic characterization constitutes an important contribution to the selection of Azotobacter strains for biofertilizer formulations.

Arsenic-induced morphogenic response in roots of arsenic hyperaccumulator fern Pteris vittata

On the assumption that arsenic induces stress morphogenetic responses involved in As tolerance and hyperaccumulation in the Pteris vittata fern, we analyzed the root system of young sporophytes grown in 250, 334, and 500μM As for five days and for 14 days. Anatomical and histological analyses were performed in plants grown for five days to evaluate the number, position, length and differentiation pattern of root hairs. AgNOR staining, employed to study nucleolus behavior in root apices, showed that arsenic influences nucleolar activity (evaluated by nucleolus size, number and absorbance) in the root meristem. In plants treated with 250 and 334μM As an acropetal shift of root hair development and an increase in hair length and density were observed, linked to an ectopic pattern of differentiation. The opposite trend was recorded in plants treated with 500μM As. It is worth noting the presence of living border-like cells, not yet observed in ferns, and their increase following As treatments. Analysis and vitality of border-like cells were surveyed after 14 days of treatments. In conclusion As treatments elicited a stress-induced morphogenic response which, by modifying the differentiation pattern, number and length of root hairs, modulating nucleolar activity and interacting with the rhizosphere by inducing border-like cell production, may adjust the rate of root uptake and its metabolic activity.

A comparative proteomics analysis in roots of soybean to compatible symbiotic bacteria under flooding stress

A proteomics approach was used to evaluate the effects of flooding stress on early symbiotic interaction between soybean roots and soil bacteria, Bradyrhizobium japonicum. Three-day-old soybean was inoculated with B. japonicum followed by flooding. The number of root hairs in seedlings, without or with flooding stress, was increased after 3 days of inoculation. Proteins were extracted from roots and separated by two-dimensional polyacrylamide gel electrophoresis. Out of 219 protein spots, 14 and 8 proteins were increased and decreased, respectively, by inoculation under flooding compared with without flooding. These proteins were compared in untreated and flooded seedlings. Increased level of 6 proteins in flooded seedlings compared with untreated seedlings was suppressed by inoculation in seedlings under flooding. They were related to disease/defense, protein synthesis, energy, and metabolism. Differential abundance of glucan endo-1,3-beta-glucosidase, phosphoglycerate kinase, and triosephosphate isomerase, based on their localization in middle and tip of root, indicated that they might be related to increase in number of root hairs. These results suggest that disease/defense, energy, and metabolism-related proteins may be particularly subjected to regulation in flooded soybean seedlings, when inoculated with B. japonicum and that this regulation may lead to increase in number of root hair during early symbiotic differentiation.

Amino acid substitution converts WEREWOLF function from an activator to a repressor of Arabidopsis non-hair cell development

Root hair cell or non-hair cell fate determination in Arabidopsis thaliana root epidermis is model system for plant cell development. Two types of MYB transcription factors, the R2R3-type MYB, WEREWOLF (WER), and an R3-type MYB, CAPRICE (CPC), are involved in this cell fate determination process. To study the molecular basis of this process, we analyzed the functional relationship of WER and CPC. WER–CPC chimeric constructs were made from WER where all or parts of the MYB R3 region were replaced with the corresponding regions from CPC R3, and the constructs were introduced into the cpc-2 mutant. Although, the WER gene did not rescue the cpc-2 mutant ‘small number of root hairs’ phenotype, the WER–CPC chimera with two amino acids substitution ( WC6) completely rescued the cpc-2 mutant phenotype. Furthermore, the WER–CPC chimera with 37 amino acids substitution ( WC5) excessively rescued the cpc-2 mutant and induced 2.5 times more root hairs than wild-type. Consistent with this phenotype, GL2 gene expression was strongly reduced in WC5 in a cpc-2 background. Our results suggest that swapping at least two amino acids is sufficient to convert WER to CPC function. Therefore, these key residues may have strongly contributed to the selection of these important functions over evolution.

A novel function for a redox‐related LEA protein (SAG21/AtLEA5) in root development and biotic stress responses

SAG21/AtLEA5 belongs to the late embryogenesis-associated (LEA) protein family. Although it has been implicated in growth and redox responses, its precise roles remain obscure. To address this problem, we characterized root and shoot development and response to biotic stress in SAG21/AtLEA5 over-expressor (OEX) and antisense (AS) lines. AS lines exhibited earlier flowering and senescence and reduced shoot biomass. Primary root length was reduced in AS lines, as was the number of laterals relative to the primary root. Root hair number was unchanged but root hair length was proportional to SAG21/AtLEA5 expression level, with longer root hairs in OEX lines and shorter root hairs in AS, relative to wild type. Growth of the fungal nectroph, Botrytis cinerea and of a virulent bacterial pathogen (Pseudomonas syringae pv. tomato) was affected by SAG21/AtLEA5 expression; however, growth of an avirulent P.syringae strain was unaffected. A SAG21/AtLEA5-YFP fusion was localized to mitochondria, raising the intriguing possibility that SAG21 interacts with proteins involved in mitochondrial ROS signalling, which in turn, impacts on root development and pathogen responses.

The Plant Growth-Promoting Fungus Aspergillus ustus Promotes Growth and Induces Resistance Against Different Lifestyle Pathogens in Arabidopsis thaliana

To deal with pathogens, plants have evolved sophisticated mechanisms including constitutive and induced defense mechanisms. Phytohormones play important roles in plant growth and development, as well as in the systemic response induced by beneficial and pathogen microorganisms. In this work, we identified an Aspergillus ustus isolate that promotes growth and induces developmental changes in Solanum tuberosum and Arabidopsis thaliana. A. ustus inoculation on A. thaliana and S. tuberosum roots induced an increase in shoot and root growth, and lateral root and root hair numbers. Assays performed on Arabidopsis lines to measure reporter gene expression of auxin-induced/ repressed or cell cycle controlled genes (DR5 and CycB1, respectively) showed enhanced GUS activity, when compared with mock-inoculated seedlings. To determine the contribution of phytohormone signaling pathways in the effect elicited by A. ustus, we evaluated the response of a collection of hormone mutants of Arabidopsis defective in auxin, ethylene, cytokinin, or abscisic acid signaling to the inoculation with this fungus. All mutant lines inoculated with A. ustus showed increased biomass production, suggesting that these genes are not required to respond to this fungus. Moreover, we demonstrated that A. ustus synthesizes auxins and gibberellins in liquid cultures. In addition, A. ustus induced systemic resistance against the necrotrophic fungus Botrytis cinerea and the hemibiotrophic bacterium Pseudomonas syringae DC3000, probably through the induction of the expression of salicylic acid, jasmonic acid/ethylene, and camalexin defense-related genes in Arabidopsis.

Surface colonization by Azospirillum brasilense SM in the indole‐3‐acetic acid dependent growth improvement of sorghum

The key to improving plant productivity is successful bacterial-plant interaction in the rhizosphere that can be maintained in the environment. The results presented here confirm Azospirillum brasilense strain SM as a competent plant growth promoting bacterium over mid- and long-term associations with sorghum. This study establishes that plant growth can be directly correlated with the associated bacterium's indole-3-acetic acid (IAA) production capability as IAA over-expressing variants, SMp30 and SMΔi3-6 fared better than the wild type strain. The auxin antagonist, p-chlorophenoxy isobutyric acid confirmed the role of bacterial IAA in plant growth promotion and verified the presence of larger amount of IAA available to the seeds on inoculation with IAA over-expressing mutants. Microscopic analysis identified the bacterial association at root tips, root-shoot junction and elongation zone and their surface colonizing nature. Scanning electron microscopy identified larger number of root hairs and extensive exopolysaccharide covering in comparison to untreated ones. In addition, vibroid-shaped Azospirilla attached by means of fibrillar material were dispersed along the elongation zone. The notable difference with IAA over-expressing variants was enhanced number of root hairs. Thus, the variant strains may be more efficient surface colonizers of the sorghum root and used as superior bio-inoculants for improving plant productivity.

Root Hairs Play a Key Role in the Endophytic Colonization of Olive Roots by Pseudomonas spp. with Biocontrol Activity

The use of indigenous bacterial root endophytes with biocontrol activity against soil-borne phytopathogens is an environmentally-friendly and ecologically-efficient action within an integrated disease management framework. The earliest steps of olive root colonization by Pseudomonas fluorescens PICF7 and Pseudomonas putida PICP2, effective biocontrol agents (BCAs) against Verticillium wilt of olive (Olea europaea L.) caused by the fungus Verticillium dahliae Kleb., are here described. A gnotobiotic study system using in vitro propagated olive plants, differential fluorescent-protein tagging of bacteria, and confocal laser scanning microscopy analysis have been successfully used to examine olive roots–Pseudomonas spp. interactions at the single-cell level. In vivo simultaneous visualization of PICF7 and PICP2 cells on/in root tissues enabled to discard competition between the two bacterial strains during root colonization. Results demonstrated that both BCAs are able to endophytically colonized olive root tissues. Moreover, results suggest a pivotal role of root hairs in root colonization by both biocontrol Pseudomonas spp. However, colonization of root hairs appeared to be a highly specific event, and only a very low number of root hairs were effectively colonized by introduced bacteria. Strains PICF7 and PICP2 can simultaneously colonize the same root hair, demonstrating that early colonization of a given root hair by one strain did not hinder subsequent attachment and penetration by the other. Since many environmental factors can affect the number, anatomy, development, and physiology of root hairs, colonization competence and biocontrol effectiveness of BCAs may be greatly influenced by root hair’s fitness. Finally, the in vitro study system here reported has shown to be a suitable tool to investigate colonization processes of woody plant roots by microorganisms with biocontrol potential.

Phytotoxicity of Carbon Nanotubes Assessed by &lt;I&gt;Brassica Juncea&lt;/I&gt; and &lt;I&gt;Phaseolus Mungo&lt;/I&gt;

Two agronomic plant species were evaluated for the phytotoxicity of multi-walled carbon nanotubes (CNTs) using germination and seedling growth of Brassica juncea and Phaseolus mungo. Both B. juncea and P. mungo seeds showed 100% germination with the application of CNTs, which indicated their non-hazardous nature for the germination of the seeds. As the B. juncea seed was grown with CNTs at 10 � g/ml, 20 � g/ml, and 40 � g/ml, the enhancement of root growth was evidenced up to 138%, 202%, and 135%, respectively, compared to the control. In the case of B. juncea, the heights of the shoot and root were not affected at all by the studied CNTs’ concentrations; however, phytotoxicity was evidenced at 40 � g/ml CNTs by optical microscopy of the hairy root system, since a severe reduction in both the number of root hairs and their length was observed.

Histone H2A.Z Regulates the Expression of Several Classes of Phosphate Starvation Response Genes But Not as a Transcriptional Activator

Phosphate (Pi) availability is a major constraint to plant growth. Consequently, plants have evolved complex adaptations to tolerate low Pi conditions. Numerous genes implicated in these adaptations have been identified, but their chromatin-level regulation has not been investigated. The nuclear actin-related protein ARP6 is conserved among all eukaryotes and is an essential component of the SWR1 chromatin remodeling complex, which regulates transcription via deposition of the H2A.Z histone variant into chromatin. Here, we demonstrate that ARP6 is required for proper H2A.Z deposition at a number of Pi starvation response (PSR) genes in Arabidopsis (Arabidopsis thaliana). The loss of H2A.Z at these target loci results in their derepression in arp6 mutants and correlates with the presence of multiple Pi-starvation-related phenotypes, including shortened primary roots and increases in the number and length of root hairs, as well as increased starch accumulation and phosphatase activity in shoots. Our data suggest a model for chromatin-level control of Pi starvation responses in which ARP6-dependent H2A.Z deposition modulates the transcription of a suite of PSR genes.

Both the arbuscular mycorrhizal fungus Gigaspora rosea and Frankia increase root system branching and reduce root hair frequency in Alnus glutinosa

Alnus glutinosa is an important pioneer species that forms effective symbioses with Frankia and ecto and arbuscular mycorrhizal fungi (AMF). There is evidence that Frankia and AMF interact and the focus of this study was to investigate how interactions affected root system and root hair development. A. glutinosa seedlings were grown in pots in soil pre-inoculated with the AMF Gigaspora rosea. Seedlings were inoculated with Frankia either immediately on transfer to AMF-inoculated pots (day 0) on day 15 or on day 30 following AMF inoculation so the effect of timing of inoculation on interactions could be determined. Seedlings were harvested in batches at intervals of 10, 15, 20, 25 and 30 days after the commencement of each treatment. Both G. rosea and Frankia increased root branching and effects were greater when both were present. By contrast, both G. rosea and Frankia decreased root hair numbers markedly. Effects on root hair development were not a consequence of phosphorous, as P levels were not changed significantly in seedlings colonised by G. rosea or nodulated by Frankia. Effects are not due to differences in root system size but conceivably could offset some of the carbon costs incurred by the symbioses.

Reactive oxygen species localization in roots of Arabidopsis thaliana seedlings grown under phosphate deficiency

Arabidopsis plants responding to phosphorus (P) deficiency increase lateral root formation and reduce primary root elongation. In addition the number and length of root hairs increases in response to P deficiency. Here we studied the patterns of radical oxygen species (ROS) in the roots of Arabidopsis seedlings cultured on media supplemented with high or low P concentration. We found that P availability affected ROS distribution in the apical part of roots. If plants were grown on high P medium, ROS were located in the root elongation zone and quiescent centre. At low P ROS were absent in the elongation zone, however, their synthesis was detected in the primary root meristem. The proximal part of roots was characterized by ROS production in the lateral root primordia and in elongation zones of young lateral roots irrespective of P concentration in the medium. On the other hand, plants grown at high or low P differed in the pattern of ROS distribution in older lateral roots. At high P, the elongation zone was the primary site of ROS production. At low P, ROS were not detected in the elongation zone. However, they were present in the proximal part of the lateral root meristem. These results suggest that P deficiency affects ROS distribution in distal parts of Arabidopsis roots. Under P-sufficiency ROS maximum was observed in the elongation zone, under low P, ROS were not synthesized in this segment of the root, however, they were detected in the apical root meristem.