Mycorrhizas and root architecture

Aim. To study ivermectin’s influence on morphology of roots and root hairs of Arabidopsis thaliana L. seedlings. Methods. In vitro seedlings’ cultivation, microscopy, statistical data analysis. Results. Morphological changes of roots were determined after 12 days of seedlings growth on the nutrient medium (Murashige and Skoog) with ivermectin in concentration of 250 µg/ml. It was determined that ivermectin at the concentration of 250 µg/ml causes main roots curling, elongation zone shortening, lateral roots growth retardation, decrease in length and deformation of root hairs. Statistically significant differences in length of root hairs were observed on the 12th day of cultivation. Particularly, the mean length of root hairs was 163.63±57.97 µm in seedlings, which grew on medium without ivermectin, and 28.14±9.36 µm in seedlings, which grew on medium with 250 µg/ml of ivermectin. Conclusions. Morphological alterations of roots and root hairs сaused by 250 µg/ml of ivermectin were analyzed. According to the proposed explanation of the obtained results, ivermectin disrupts arrangements of microtubules in cells of A. thaliana main root leading to pathological changes in roots’ morphology.

The effect of a low-molecular weight, water-extractable fraction of humic substances (WEHS) derived from sphagnum peat on post-embryonic plant development has been studied using Arabidopsis roots. Application of humic substances caused an array of changes in root morphology, such as an increase in root hair length and density, formation of ectopic root hairs, and an increase in cell proliferation in the root ground tissue. Application of WEHS affected genes involved in epidermal cell fate specification, suggesting that humic substances can alter developmental programs at an early stage of root cell differentiation. The WEREWOLF and GLABRA2 genes, encoding negative regulators of the root hair cell fate, were significantly down-regulated in the presence of WEHS. Thus, the presence of humic substances caused an ordered remodeling of the root morphology, leading to an increased absorptive surface of the root. Growth in the presence of WEHS did not rescue the phenotype of the root hair defective rhd6 mutant. Analyzing BA3:uidA and DR5:uidA transgenic plants, carrying auxin response elements, and monitoring the expression of the auxin-responsive GH3 gene by real-time RT-PCR did not provide evidence for a WEHS-induced expression of auxin-related genes. It is concluded that WEHS do not exert their effects in an auxin-like manner.

Relationship between mycorrhizal responsiveness and root traits in European sand dune species

Understanding the development of roots exposed to contaminants and the potential of plant-associated bacteria for optimization of growth.

SPACSYS: Integration of a 3D root architecture component to carbon, nitrogen and water cycling—Model description

IntroductionRoot hairs increase the surface area of a plant’s root system that is in contact with the soil, thus facilitating plant water and nutrient uptake. However, little is known about the characteristics of the root hairs of herbaceous and woody plants and their specific response patterns to biotic and abiotic variables from the perspective of resource acquisition strategies in the context of global change.MethodsHere, we analyzed 74 published case studies with 1074 observations of root hair traits to identify patterns of root hair length, density and diameter in relation to soil (e.g., soil pH, nutrient levels), growing environments (e.g., greenhouse, field) and climatic factors (e.g., air temperature), as well as genome size and plant age.ResultsRoot hairs were longer, denser and thicker in woody plants compared with herbaceous plants, and the length and diameter of root hairs in herbaceous plants increased with genome size. With increasing plant age, woody plants had significantly longer and thicker root hairs, while root hair density and diameter declined significantly for herbaceous plants. Soil-cultured plants had longer root hairs than solution-cultured plants. The length and density of root hairs were greater in greenhouse-cultured plants than in field-grown plants, and the latter had thicker root hairs than the former. As soil pH increased, root hair length increased but diameter decreased in woody plants, while root hair density increased in herbaceous plants. Increased soil total nitrogen (N) and potassium (K) significantly increased root hair length, density and diameter in herbaceous plants, while soil total N significantly decreased root hair density in woody plants. Root hair length increased significantly, while root hair density decreased significantly, with higher mean annual temperature and greater precipitation seasonality, while the opposite pattern was true for a wider annual temperature range.DiscussionOur findings emphasize the life-form-specific responses of root hairs to soil and climatic variables. These findings will help deepen our understanding of resource acquisition strategies and their mechanisms in different plant forms under global climate change.

The activity of soil pathogens, competition for assimilates, and the changing availability of below-ground resources make root systems subject to a continuous and dynamic process of formation and loss of both fine and coarse roots. As hypocotyl borne roots appear later than other root classes, they may serve to functionally replace basal and primary roots lost to biotic and abiotic stress. Using common bean (Phaseolus vulgaris L.), we conducted experiments in solution and solid media culture with treatments involving the removal of part of the root system (basal, hypocotyl borne or primary roots), phosphorus availability, and depth of seeding to test the hypothesis that there are compensation mechanisms among basal, hypocotyl borne and primary roots to cope with the loss of part of the root system. The root system was highly plastic in response to root excision, which resulted in the maintenance of below-ground biomass accumulation. In most cases, this compensation among root classes was enough to maintain plant performance in both phosphorus sufficient and phosphorus stressed plants. Removal of a specific root class induced an increase in the growth of the remaining root classes. All root classes, but especially the primary root, contributed to the compensation mechanism in some way. Primary roots represented around 10% of the root system in control plants and this proportion increased dramatically (up to 50%) when other root classes were removed. In contrast, negligible compensatory re-growth was observed following removal of the primary root. Greater planting depth increased the production of hypocotyl borne roots at the expense of basal roots. The proportion of hypocotyl borne roots increased from 25% of the whole root system when seeds were placed at a depth of 2 cm to 30% when they were placed at 5 cm and to 38% when placed at 8 cm, with corresponding decreases in the proportion represented by basal roots. The common feature of our observations is the innate ability of the root system for its own regeneration. Total root biomass maintained strict allometric relationships with total shoot biomass in all treatments. Re-stabilization of root to shoot balance after partial root loss is governed by overall plant size following allometric relationships similar to undisturbed plants. However, the pattern of this root regeneration was not uniform since the way the three root classes compensated each other after the removal of any one of them varied among the different growth media and phosphorus supply conditions. The resulting changes in root architecture could have functional significance for soil resource acquisition.

Root hair formation is controlled by environmental signals. We found significantly increased Arabidopsis root hair density and length in response to low-dose vanadate (V). Reactive oxygen species (ROS) production was induced with V treatment. We investigated the possible role of NADPH oxidase in altering root system architecture induced by V by using diphenylene iodonium (DPI), an inhibitor of NADPH oxidase, and an NADPH oxidase mutant (rhd2/AtrbohC). NADPH oxidase was involved in root hair elongation induced by V. As well, ethylene receptor (ETR1) and ROOT HAIR DEFECTIVE (RHD6) participated in inducing root hair formation induced by V. Furthermore, the kinase inhibitors, genistein (tyrosine kinase inhibitor) and K252a (ser/thr kinase inhibitor), and a phosphatase inhibitor, cantharidin (ser/thr phosphatase inhibitor), suppressed root hair formation induced by V. To elucidate the regulation of gene expression in response to V, we investigated transcriptional changes in roots by microarray assay. Exposure to V triggered changes in transcript levels of genes related to cell wall formation, ROS activity and signaling. Several genes involved in root hair formation were also regulated.

We compared root system morphogenesis of micropropogated transplants of Prunus cerasifera L. inoculated with either of the arbuscular mycorrhizal (AM) fungi Glomus mosseae or Glomus intraradices or with the ericoid mycorrhizal species Hymenoscyphus ericae. All plants were grown in sand culture, irrigated with a nutrient solution that included a soluble source of phosphorus, for 75 days after transplanting. Arbuscular mycorrhizal colonization increased both the survival and growth (by over 100%) of transplants compared with either uninoculated controls or transplants inoculated with H. ericae. Arbuscular mycorrhizal colonization increased root, stem and leaf weights, leaf area, root length and specific leaf area, and it decreased root length/leaf area ratio, root/shoot weight ratio and specific root length. Both uptake of phosphorus and its concentration in leaves were increased by AM infection, although the time course of the relationships between intensity of AM infection and P nutrition were complex and suggested a role for factors other than nutrition. The time course for the development of infection varied. It was most rapid with G. mosseae, but it was ultimately higher with G. intraradices. None of the treatments significantly affected the lengths of adventitious roots or the first-, second- or third-order laterals that developed from them. Arbuscular mycorrhizal colonization increased the intensity of branching in all root orders with the effect being most obvious on first-order lateral roots where the number of branches increased from under 100 to over 300 brances m(-1). As a result, although first-order laterals made up 55% of the root systems of control plants, the comparable value was 36% in AM-infected plants. In contrast, second-order laterals represented 25% of control root systems, but 50% of AM-colonized root systems. Glomus intraradices but not G. mosseae increased root diameter. Anatomical studies revealed no changes in the overall form of the root tip, although there were changes in the diameter of the root cap, cell numbers and cell size. Hymenoscyphus ericae increased the duration of the metaphase index. Both AM fungal treatments increased the concentrations of soluble proteins in root extracts and modified the protein profiles by the elimination and addition of protein bands detected by PAGE analysis. We conclude that AM fungal inoculation influenced processes in the root system at different levels, but not all effects were due to improved P nutrition or increased physiological age.

Juvenile nitrogen uptake capacities and root architecture of two open-pollinated families of Picea abies. Effects of nitrogen source and ectomycorrhizal symbiosis

Frontiers in molecular mycorrhizal research – genes, loci, dots and spins

BackgroundRoot system architecture is important for water acquisition and nutrient acquisition for all crops. In soybean breeding programs, wild soybean alleles have been used successfully to enhance yield and seed composition traits, but have never been investigated to improve root system architecture. Therefore, in this study, high-density single-feature polymorphic markers and simple sequence repeats were used to map quantitative trait loci (QTLs) governing root system architecture in an inter-specific soybean mapping population developed from a cross between Glycine max and Glycine soja.ResultsWild and cultivated soybean both contributed alleles towards significant additive large effect QTLs on chromosome 6 and 7 for a longer total root length and root distribution, respectively. Epistatic effect QTLs were also identified for taproot length, average diameter, and root distribution. These root traits will influence the water and nutrient uptake in soybean. Two cell division-related genes (D type cyclin and auxin efflux carrier protein) with insertion/deletion variations might contribute to the shorter root phenotypes observed in G. soja compared with cultivated soybean. Based on the location of the QTLs and sequence information from a second G. soja accession, three genes (slow anion channel associated 1 like, Auxin responsive NEDD8-activating complex and peroxidase), each with a non-synonymous single nucleotide polymorphism mutation were identified, which may also contribute to changes in root architecture in the cultivated soybean. In addition, Apoptosis inhibitor 5-like on chromosome 7 and slow anion channel associated 1-like on chromosome 15 had epistatic interactions for taproot length QTLs in soybean.ConclusionRare alleles from a G. soja accession are expected to enhance our understanding of the genetic components involved in root architecture traits, and could be combined to improve root system and drought adaptation in soybean.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1334-6) contains supplementary material, which is available to authorized users.

Changes in root architecture are one of the adaptive strategies used by plants to compensate for local phosphate (Pi) deficiency in soils. Root architecture variables triggered by Pi availability are well documented in Arabidopsis (Arabidopsis thaliana), but the molecular mechanisms behind these adaptive responses remain to be elucidated. By the use of transcriptomic and quantitative RT-PCR analysis, we observed that an AINTEGUMENTA-like gene, named PRD for Phosphate Root Development, was rapidly repressed in roots under low Pi conditions. The physiological function of the PRD gene was analyzed through the null allele mutant prd, which displayed less development of primary and lateral roots under Pi-starvation conditions than wild-type plants. Complementation of the prd mutant with the wild-type gene led to a similar response to Pi starvation as wild-type plants, indicating the complete rescue of the mutant phenotype. These results suggest that PRD gene is involved in the regulation of root architectural responses to Pi starvation by controlling primary and lateral root elongation. This model is in agreement with the tissue-specific pattern of PRD gene expression, which was observed to occur specifically in the apex in both the primary and lateral roots. However, Pi influx, anionic profiles and root expression of genes typically induced by Pi starvation, such as high affinity Pi transporters (PHT1;1 and PHT1;4) and an acid phosphatase (AtACP5), were similar in wild type and prd plants in response to Pi starvation. These results support the hypothesis that the PRD gene is not a checkpoint for Pi-starvation responses, but acts specifically as a regulator of root architectural responses to Pi starvation.

ABSTRACTIn this work, the effect of inoculation with the arbuscular mycorrhizal fungus Glomus iranicum var. tenuihypharum on the root development and yield of melon plants (Cucumis melo L. cv. Hispano de Nunhems), grown in soil under intensive agriculture for four months, was evaluated. The parameters root length, root volume, area, number of root tips, rhizosphere activity, yield, and crop quality were measured. The inoculated melon plants had an increased percentage of colonisation, which reached 75% at the end of experiment. As a consequence, the inoculated plants exhibited greater rhizospheric activity with higher bacterial and fungal population than the control plants. Inoculation produced a greater volume of roots. It was also observed a higher area of roots with a diameter less than 0.2 mm, and a greater number of tips in roots with a diameter less than 0.5 mm. This suggested a proliferation of lateral roots and significant changes on the root architecture. In addition, these plants had greater fruit number and length, yield, and fruit sugar content than untreated plants. Therefore, the mycorrhizal association had a strong positive effect on the architecture and root activity, which stimulated the capacity for nutrient absorption, resulting in a higher yield and fruit quality.

Early literature on peanut [Arachis hypogcrea (L.)] indicates the existence of two forms of root hairs: (i) a rosette form of root hair (4 mm long) occurring; radially where a lateral root initiates from a primary root, and (ii) shorter (0.30 mm), more profuse root hairs occurring along root lengths usually behind the root tip. Since little is known about the factors that influence peanut root hair formation, the purpose of this study was to quantify root hair formation under various soils and water stress conditions. Separate rhizotron, field, and greenhouse studies were conducted. The rhizotron study showed no differences in the percentage of roots having root hairs regardless of water stress treatments imposed 20 to 50 and 50 to 80 days after planting (DAP). Thirty‐seven to 43% of the roots had root hairs. In the field, peanut root systems growing within dialysis root bags in a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudults) showed a significant increase in root hair formation from 7% at 70 DAP to 31% at harvest. In the greenhouse using three soil types, Greenville fine sandy loam (clayey, kaolinitic, thermic Rhodic Kandiudults), Tifton loamy sand, and a 4:1 coarse sand:fritted clay mixture (rhizotron), soil type was found to affect the percentage of roots having root hairs. Roots growing in the Tifton, sand:fritted clay mixture, and Greenville soils had 47, 17, and 14% root hairs, respectively. In all studies, the rosette form of root hair around lateral initiates was observed. Approximately 66% of the lateral initiates expressed rosette‐type root hairs. Mycorrhizal infection, though insufficient to significantly affect nutrient uptake, was greater with the rhizotron (18%) than the Greenville (6%) and Tifton soils (3%). There may be a possible interaction between root hair occurrence and mycorrhizae infection.