Root Growth Responses Research Articles

Mechanisms of thaxtomin A-induced root toxicity revealed by a thaxtomin A sensitive Arabidopsis mutant (ucu2-2/gi-2).

The Arabidopsis mutant ( ucu2 - 2/gi - 2 ) is thaxtomin A, isoxaben and NPA-sensitive indicated by root growth and ion flux responses providing new insights into these compounds mode of action and interactions. Thaxtomin A (TA) is a cellulose biosynthetic inhibitor (CBI) that promotes plant cell hypertrophy and cell death. Electrophysiological analysis of steady-state K(+) and Ca(2+) fluxes in Arabidopsis thaliana roots pretreated with TA for 24 h indicated a disturbance in the regulation of ion movement across the plant cell membrane. The observed inability to control solute movement, recorded in rapidly growing meristematic and elongation root zones, may partly explain typical root toxicity responses to TA treatment. Of note, the TA-sensitive mutant (ucu2-2/gi-2) was more susceptible with K(+) and Ca(2+) fluxes altered between 1.3 and eightfold compared to the wild-type control where fluxes altered between 1.2 and threefold. Root growth inhibition assays showed that the ucu2-2/gi-2 mutant had an increased sensitivity to the auxin 2,4-D, but not IAA or NAA; it also had increased sensitivity to the auxin efflux transport inhibitor, 1-naphthylphthalamic acid (NPA), but not 2,3,5- Triiodobenzoic acid (TIBA), when compared to the WT. The NPA sensitivity data were supported by electrophysiological analysis of H(+) fluxes in the mature (but not elongation) root zone. Increased sensitivity to the CBI, isoxaben (IXB), but not dichlobenil was recorded. Increased sensitivity to both TA and IXB corresponded with higher levels of accumulation of these toxins in the root tissue, compared to the WT. Further root growth inhibition assays showed no altered sensitivity of ucu2-2/gi-2 to two other plant pathogen toxins, alternariol and fusaric acid. Identification of a TA-sensitive Arabidopsis mutant provides further insight into how this CBI toxin interacts with plant cells.

Effects of low-energy N+-beam implantation on root growth in Arabidopsis seedlings

The effects of ion implantation on the morphology changes and biological responses of plants are dependent on implantation doses. Previous studies mainly focus on the application of ion-beam technology in genetic mutation. Our knowledge regarding the mechanism underlying the plant growth inhibition induced by ion implantation remains limited. In this study, we explore the responses of root growth to low-energy N+-beam implantation using implanted Arabidopsis seeds. Our results showed that the root and root tip length were obviously reduced by implantation with large doses of low-energy N+ beam. The analysis of confocal images showed that ion implantation reduced the cell viability and cell division activity in root meristem. The production rate of superoxide radical (O2•-) and contents of hydrogen peroxide (H2O2) in roots under ion implantation were markedly higher than those of controls. Transcriptional expression analysis of selected genes revealed that Arabidopsis RBOH genes associated with reactive oxygen species (ROS) production were significantly up-regulated in roots in response to ion implantation. The activities of antioxidant enzymes were also induced by ion implantation. Moreover, ROS scavenging obviously enhanced cell viability and cell division in response to ion implantation and alleviated the root growth inhibition of the implanted seedlings. Our results suggest that the overproduction of ROS induced by ion implantation is involved in the inhibitory effect of low-energy ion beam on root growth by affecting the cell viability and cell division of root meristem in Arabidopsis seedlings.

Responses of root growth and antioxidative systems of paddy rice exposed to antimony and selenium

Antimony (Sb) is a toxic element for plant; however, its toxic mechanisms, in particular for its toxicity to plant root growth, are unclear. Selenium (Se) can detoxify Sb, but its associated detoxification mechanisms have not been fully clarified. The aim of the present study was to investigate the effects of Sb alone, or accompanying with Se, on the root growth, antioxidative systems and the uptake of Se and Sb in paddy rice. Two nested hydroponic experiments were performed based on a two-factor, five-level central composite design. The results showed that Sb and Se could each reduce the contents of the other in both the shoots and roots. With 0.8mgL−1 Se in the solution, increasing Sb levels from 1 to 9mgL−1 significantly reduced the shoot biomass but enhanced the root biomass; however, in the presence of 5mgL−1 Sb in the solution, the opposite results were observed with increased Se levels from 0.1 to 1.5mgL−1. In the presence of 0.8mgL−1 Se, the addition of Sb increased the values of most root growth parameters, such as root length, root area, root forks, and the numbers of fine roots, medium roots and thick roots, suggesting a counteracting effect on root growth already negatively affected by 0.8mgL−1 Se. However, the increased values of the root growth parameters cannot explain the significantly inhibited Se uptake in both the shoots and roots, suggesting an unknown mechanism in this respect. The addition of Se counteracted the negative effects of Sb on the cell membrane lipids and shoot biomass, but reduced the values of the root growth parameters. Thus, the enzymes SOD, APX and CAT might play important roles in rebalancing the excess ROS resulting from exposure to Se and/or Sb. These results support the hypothesis that Se affects the root growth to inhibit Sb uptake and simultaneously regulate the antioxidant systems to reduce oxidative stress.

Abscisic Acid: Hidden Architect of Root System Structure.

Plants modulate root growth in response to changes in the local environment, guided by intrinsic developmental genetic programs. The hormone Abscisic Acid (ABA) mediates responses to different environmental factors, such as the presence of nitrate in the soil, water stress and salt, shaping the structure of the root system by regulating the production of lateral roots as well as controlling root elongation by modulating cell division and elongation. Curiously, ABA controls different aspects of root architecture in different plant species, perhaps providing some insight into the great diversity of root architecture in different plants, both from different taxa and from different environments. ABA is an ancient signaling pathway, acquired well before the diversification of land plants. Nonetheless, how this ancient signaling module is implemented or interacts within a larger signaling network appears to vary in different species. This review will examine the role of ABA in the control of root architecture, focusing on the regulation of lateral root formation in three plant species, Arabidopsis thaliana, Medicago truncatula and Oryza sativa. We will consider how the implementation of the ABA signaling module might be a target of natural selection, to help contribute to the diversity of root architecture in nature.

Nitric oxide is required for the auxin-induced activation of NADPH-dependent thioredoxin reductase and protein denitrosylation during root growth responses in arabidopsis.

Auxin is the main phytohormone controlling root development in plants. This study uses pharmacological and genetic approaches to examine the role of auxin and nitric oxide (NO) in the activation of NADPH-dependent thioredoxin reductase (NTR), and the effect that this activity has on root growth responses in Arabidopsis thaliana. Arabidopsis seedlings were treated with auxin with or without the NTR inhibitors auranofin (ANF) and 1-chloro-2, 4-dinitrobenzene (DNCB). NTR activity, lateral root (LR) formation and S-nitrosothiol content were measured in roots. Protein S-nitrosylation was analysed by the biotin switch method in wild-type arabidopsis and in the double mutant ntra ntrb. The auxin-mediated induction of NTR activity is inhibited by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (CPTIO), suggesting that NO is downstream of auxin in this regulatory pathway. The NTR inhibitors ANF and DNCB prevent auxin-mediated activation of NTR and LR formation. Moreover, ANF and DNCB also inhibit auxin-induced DR5 : : GUS and BA3 : : GUS gene expression, suggesting that the auxin signalling pathway is compromised without full NTR activity. Treatment of roots with ANF and DNCB increases total nitrosothiols (SNO) content and protein S-nitrosylation, suggesting a role of the NTR-thioredoxin (Trx)-redox system in protein denitrosylation. In agreement with these results, the level of S-nitrosylated proteins is increased in the arabidopsis double mutant ntra ntrb as compared with the wild-type. The results support for the idea that NTR is involved in protein denitrosylation during auxin-mediated root development. The fact that a high NO concentration induces NTR activity suggests that a feedback mechanism to control massive and unregulated protein S-nitrosylation could be operating in plant cells.

The soluble ABA receptor PYL8 regulates drought resistance by controlling ABA signaling in Arabidopsis

The phytohormone abscisic acid (ABA) mediates plant responses to environmental stresses, including drought stress. Recent identification of a family of soluble ABA receptors has expanded our understanding of ABA signaling in plants. Here, we examined the function of PYL8, which encodes a soluble ABA receptor. Plants overexpressing PYL8 (PYL8ox) showed lower germination rates and more inhibition of root growth than wild-type plants in response to ABA; PYL8ox plants also showed enhanced drought tolerance. By contrast, PYL8-silenced (PYL8i) plants showed less inhibition of root growth in response to ABA; PYL8i plants also showed decreased drought tolerance, compared with wild-type plants. The PYL8ox plants showed higher transcript levels of ABA-responsive genes and PYL8i plants showed lower transcript levels of these genes. Altered expression of PYL8 did not affect expression of other PYL family members. We also found that subcellular localization of PYL8 changed in response to ABA. These results suggest that PYL8 plays an essential role in ABA-mediated developmental processes and drought responses.

Simultaneous effects of leaf irradiance and soil moisture on growth and root system architecture of novel wheat genotypes: implications for phenotyping.

Plants in the field are exposed to varying light and moisture. Agronomic improvement requires knowledge of whole-plant phenotypes expressed in response to simultaneous variation in these essential resources. Most phenotypes, however, have been described from experiments where resources are varied singularly. To test the importance of varying shoot and root resources for phenotyping studies, sister pre-breeding lines of wheat were phenotyped in response to independent or simultaneous exposure to two light levels and soil moisture profiles. The distribution and architecture of the root systems depended strongly on the moisture of the deeper soil layer. For one genotype, roots, specifically lateral roots, were stimulated to grow into moist soil when the upper zone was well-watered and were inhibited by drier deep zones. In contrast, the other genotype showed much less plasticity and responsiveness to upper moist soil, but maintained deeper penetration of roots into the dry layer. The sum of shoot and root responses was greater when treated simultaneously to low light and low soil water, compared to each treatment alone, suggesting the value of whole plant phenotyping in response to multiple conditions for agronomic improvement. The results suggest that canopy management for increased irradiation of leaves would encourage root growth into deeper drier soil, and that genetic variation within closely related breeding lines may exist to favour surface root growth in response to irrigation or in-season rainfall.

Tricho- and atrichoblast cell files show distinct PIN2 auxin efflux carrier exploitations and are jointly required for defined auxin-dependent root organ growth.

The phytohormone auxin is a vital growth regulator in plants. In the root epidermis auxin steers root organ growth. However, the mechanisms that allow adjacent tissues to integrate growth are largely unknown. Here, the focus is on neighbouring epidermal root tissues to assess the integration of auxin-related growth responses. The pharmacologic, genetic, and live-cell imaging approaches reveal that PIN2 auxin efflux carriers are differentially controlled in tricho- and atrichoblast cells. PIN2 proteins show lower abundance at the plasma membrane of trichoblast cells, despite showing higher rates of intracellular trafficking in these cells. The data suggest that PIN2 proteins display distinct cell-type-dependent trafficking rates to the lytic vacuole for degradation. Based on this insight, it is hypothesized that auxin-dependent processes are distinct in tricho- and atrichoblast cells. Moreover, genetic interference with epidermal patterning supports this assumption and suggests that tricho- and atrichoblasts have distinct importance for auxin-sensitive root growth and gravitropic responses.

Cd accumulation potential as a marker for heavy metal tolerance in soybean

Plants have a potential for the uptake and accumulation of essential and non-essential trace elements. The ability to take up and tolerate metals varies between and within species as well as between metals. For most metals, the mechanisms involved in plant tolerance, uptake and accumulation are still not fully known and it is not known to what extent the plant response is metal-specific rather than a general stress response. In the present study, the growth response of soybean to Cd, As, Al and NaCl was compared and contrasted to simple sequence repeat (SSR) marker analysis results for Cda1, a dominant gene located in a major quantitative trait locus that regulates Cd accumulation in soybean, to evaluate the hypothesis that general effect patterns are induced by the individual metals. Principal component analysis revealed that the root growth response was most diverse for Al exposure and decreased in the order of Al > As > Cd > NaCl. NaCl did not exert a differentiating effect, indicating response mechanisms similar, at least partially, to metal exposure. The applied stressors yielded a distinguishable pattern of root responses, indicating the potential of such screens to identify agents acting similarly or differently. The SSR marker analysis also facilitated characterization of the Cd accumulation potential of the 22 soybean cultivars studied, and thereby identification of cultivars with potential health risk under cultivation in Cd-contaminated soils.

Two Hydroxyproline Galactosyltransferases, GALT5 and GALT2, Function in Arabinogalactan-Protein Glycosylation, Growth and Development in Arabidopsis.

Hydroxyproline-O-galactosyltransferase (GALT) initiates O-glycosylation of arabinogalactan-proteins (AGPs). We previously characterized GALT2 (At4g21060), and now report on functional characterization of GALT5 (At1g74800). GALT5 was identified using heterologous expression in Pichia and an in vitro GALT assay. Product characterization showed GALT5 specifically adds galactose to hydroxyproline in AGP protein backbones. Functions of GALT2 and GALT5 were elucidated by phenotypic analysis of single and double mutant plants. Allelic galt5 and galt2 mutants, and particularly galt2 galt5 double mutants, demonstrated lower GALT activities and reductions in β-Yariv-precipitated AGPs compared to wild type. Mutant plants showed pleiotropic growth and development phenotypes (defects in root hair growth, root elongation, pollen tube growth, flowering time, leaf development, silique length, and inflorescence growth), which were most severe in the double mutants. Conditional mutant phenotypes were also observed, including salt-hypersensitive root growth and root tip swelling as well as reduced inhibition of pollen tube growth and root growth in response to β-Yariv reagent. These mutants also phenocopy mutants for an AGP, SOS5, and two cell wall receptor-like kinases, FEI1 and FEI2, which exist in a genetic signaling pathway. In summary, GALT5 and GALT2 function as redundant GALTs that control AGP O-glycosylation, which is essential for normal growth and development.

Chromosome-anchored QTL conferring aluminum tolerance in hexaploid oat

Aluminum (Al) toxicity is a major constraint on crop production in acid soils around the world. Hexaploid oat (Avena sativa L.) possesses significant Al tolerance making it a good candidate for production in these environments. Genetic improvement for Al tolerance in oat has traditionally been achieved through conventional plant breeding and could be enhanced by marker-assisted selection. The objectives of this study were to develop a chromosome-anchored genetic map for an oat recombinant inbred population and to identify SNP markers linked to quantitative trait loci (QTL) affecting root growth response to Al. Three QTL on chromosomes 7C-17A, 13A, and 19A conferring Al tolerance were identified using primary root regrowth of recombinant inbred lines derived from the cross between UFRGS 17 (Al tolerant) and UFRGS 930598-6 (Al sensitive). Localization of each QTL onto the sequenced rice genome revealed the genetic region on chromosome 13A might be associated with a putative malate transporter locus (LOC_Os06g15779). Studies of root apex tissue indicated that exudation of malate was increased in the Al-tolerant parent UFRGS17 and not in the sensitive parent. Based on these data, the malate transporter might be a candidate gene responsible for one of the Al tolerance QTL identified in this study.

Phosphorus and magnesium interactively modulate the elongation and directional growth of primary roots in Arabidopsis thaliana (L.) Heynh.

A balanced supply of essential nutrients is an important factor influencing root architecture in many plants, yet data related to the interactive effects of two nutrients on root growth are limited. Here, we investigated the interactive effect between phosphorus (P) and magnesium (Mg) on root growth of Arabidopsis grown in pH-buffered agar medium at different P and Mg levels. The results showed that elongation and deviation of primary roots were directly correlated with the amount of P added to the medium but could be modified by the Mg level, which was related to the root meristem activity and stem-cell division. High P enhanced while low P decreased the tip-focused fluorescence signal of auxin biosynthesis, transport, and redistribution during elongation of primary roots; these effects were greater under low Mg than under high Mg. The altered root growth in response to P and Mg supply was correlated with AUX1, PIN2, and PIN3 mRNA abundance and expression and the accumulation of the protein. Application of either auxin influx inhibitor or efflux inhibitor inhibited the elongation and increased the deviation angle of primary roots, and decreased auxin level in root tips. Furthermore, the auxin-transport mutants aux1-22 and eir1-1 displayed reduced root growth and increased the deviation angle. Our data suggest a profound effect of the combined supply of P and Mg on the development of root morphology in Arabidopsis through auxin signals that modulate the elongation and directional growth of primary root and the expression of root differentiation and development genes.

임간재배 시 광조절과 부엽토 처리에 따른 삽주의 생육 및 광합성 특성

This study was carried out to determine the effects of light controls and leaf mold on root growth and physiological responses of Atractylodes japonica growing in forest farming. The experiment was performed by light controls (100%, 62.5%, 40.3% and 19.7% of full sunlight) and application of leaf mold to soil. Height, stem diameter, number of flower buds and root collar diameter were the highest in leaf mold within 62.5% of full sunlight (relative light intensity 62.5%). And these were the higher in leaf mold within each light level. As the shading level increased, light saturation point and maximum photosynthesis rate decreased. As the light level decreased, SPAD value increased in control and leaf mold. As a result of surveying the whole experiment, A. japonica was judged worse root growth under the lower light level. It was concluded that the light level was one of the most important factors to produce A. japonica. Also, producing high-quality of A. japonica with the price competitiveness by using leaf mold like the experiment can be an effective way to increase incomes for farmers.

Assessing the progress of colonization by arbuscular mycorrhiza of four plant species under different temperature regimes

AbstractTo capitalize on the benefits offered by arbuscular mycorrhizal fungi (AMF) in agricultural systems, the effect of low soil temperature has to be taken into consideration over large areas of the planet. However, the effect of suboptimal root‐zone temperatures on AMF colonization is poorly understood. It has been suggested that it depends on the host plant species. We hypothesized that this interdependence is a function of the parameter used to assess the presence of AMF in the roots. In a pot experiment with non‐sterilized soil, we investigated the influence of three soil temperatures (10, 15, and 20°C) on the progress of root colonization of four host plant species (Ornithopus compressus, Lolium rigidum, Triticum aestivum, and Zea mays) by indigenous AMF. Plant root density, arbuscular colonization rate (AC) and colonized root density (CRD) were assessed 14, 28, and 42 d after sowing. Based on CRD, the effect of temperature on the progress of root colonization by AMF was independent of the host plant species. The apparent influence of the host plant species was only due to the species‐specific effect of soil temperature on root growth and therefore on AC. The host plant species only determined the minimum temperature for the AM colonization initiation, possibly due to species‐specific response of root growth and exudation to cool temperatures.

Water-deficit treatment followed by re-watering stimulates seminal root growth associated with hormone balance and photosynthesis in wheat (Triticum aestivum L.) seedlings

Elucidating the growth responses of roots to water status will reveal physiological mechanisms underlying drought tolerance and water conservation in plants. Hydroponic experiments were conducted using two winter wheat cultivars, Wangshuibai (drought-sensitive) and Luohan 7 (drought-tolerant), and a water deficit was induced using a 20 % (m/v) aqueous solution of polyethylene glycol 6000 (−0.6 MPa). The lack of water significantly reduced the plant dry weight, leaf area, total root length (TRL) and surface area in seminal (SRs) and nodal roots (NRs), but the effects were less pronounced in Luohan 7 than in Wangshuibai. After re-watering, leaf area, TRL and surface area of Luohan 7 increased significantly, as compared to the controls, due to rapid compensatory growth of SRs, while those of Wangshuibai were still significantly reduced. Under water-deficit conditions, the concentrations of indole-3-acetic acid (IAA) and cytokinin (CTK) and their ratio (IAA/CTK) in SRs and NRs of both cultivars were significantly lower than those of controls, but increased after re-watering. However, Luohan 7 showed significantly increases in IAA/CTK of SRs as compared to the control. Net photosynthetic rate was much lower during water deficit in both cultivars, but it was enhanced significantly after re-watering, especially for Luohan 7. Moreover, sucrose content was significantly increased in leaves while reduced in roots under water-deficit conditions. After re-watering, sucrose content in leaves of both cultivars and in roots of Wangshuibai was severely reduced, while the values in roots of Luohan 7 were significantly increased as compared to the control. These results indicate that the drought-tolerant cultivar has a greater ability to maintain plant growth under water deficit and greater compensatory growth in SRs associated with higher IAA/CTK and photosynthetic products supply after re-watering.

Response of cotton root growth and yield to root restriction under various water and nitrogen regimes

AbstractWater and nitrogen (N) are two major factors limiting cotton growth and yield. The ability of plants to absorb water and nutrients is closely related to the size of the root system and the rooting space. Better understanding of the physiological mechanisms by which cotton (Gossypium hirsutum L.) adapts to water and N supply when rooting volume is restricted would be useful for improving cotton yield. In this study, cotton was grown in soil columns to control rooting depth to either 60 cm (root‐restriction treatment) or 120 cm (no‐root‐restriction treatment). Four water–N combinations were applied to the plants: (1) deficit irrigation and no N fertilizer (W0N0), (2) deficit irrigation and moderate N fertilizer rate (W0N1), (3) moderate irrigation and no N fertilizer (W1N0), and (4) moderate irrigation and moderate N fertilizer rate (W1N1). Results revealed that root restriction reduced root length density (RLD), root volume density (RVD), root mass density (RMD), superoxide dismutase (SOD) activity, nitrate reductase (NR) activity, total plant biomass, and root : shoot ratio. In contrast, root restriction increased aboveground biomass and yield. The RLD, RVD, RMD, and root : shoot ratio decreased in the order W0N0 > W1N0 > W0N1 > W1N1 in both the root‐restriction and no‐root‐restriction treatments. However, the opposite order (i.e., W1N1 > W0N1 > W1N0 > W0N0) was observed for SOD activity, NR activity, aboveground biomass, and seed yield. Our results suggest that, when N and water supplies are adequate, root restriction increases both root activity and the availability of photosynthates to aboveground plant parts. This increases shoot growth, the shoot : root ratio, and yield.

AtNIGT1/HRS1 integrates nitrate and phosphate signals at the Arabidopsis root tip.

Nitrogen and phosphorus are among the most widely used fertilizers worldwide. Nitrate (NO3−) and phosphate (PO43−) are also signaling molecules whose respective transduction pathways are being intensively studied. However, plants are continuously challenged with combined nutritional deficiencies, yet very little is known about how these signaling pathways are integrated. Here we report the identification of a highly NO3−-inducible NRT1.1-controlled GARP transcription factor, HRS1, document its genome-wide transcriptional targets, and validate its cis-regulatory-elements. We demonstrate that this transcription factor and a close homolog repress primary root growth in response to P deficiency conditions, but only when NO3− is present. This system defines a molecular logic gate integrating P and N signals. We propose that NO3− and P signaling converge via double transcriptional and post-transcriptional control of the same protein, HRS1

Soybean root development under water stress in eroded soils

Root growth is affected by soil features that could change after erosion. The goal of this study was to understand how root growth responded to water stress resulting from erosion. For this purpose a pot experiment was conducted combining three eroded soils (lightly, moderately, severely) and four soil water levels (relative to field capacity of 100%, 80%, 60%, 40%) using nondisturbed Luvic Phaeozem soil from field by electric drill. The results showed that the response of soybean root growth to soil water was different for the three eroded soils and varied with growth stages of the plant. Under an optimal water supply, roots grew best in moderately eroded soils. Response of soybean root growth to water stress degree was similar under deficit water situation for three eroded soils, and under excess water stress situation, the root growth of lightly eroded soils was restricted more seriously than that of moderately and severely eroded soils during the initial branching stage. Root growth was restricted only seriously to the lack of water conditions for moderately and severely eroded soils; however, root growth of lightly eroded soils was restricted still seriously to both excess and a lack of water supply, and root growth of lightly eroded soils was restricted more seriously to water stress than that of moderately and severely eroded soils from the branching to maturing stages. The root distributions with depths were not different among three eroded soils under optimal water supply, but root growth of lightly eroded soils was restricted more seriously to water stress than moderately and severely eroded soils for three soil layers, and water stress degree of root weight increased with depths. The study results could provide theoretical basis of improving land productivity for different eroded soils.

Root Growth Responses to Soil Amendment in an Urban Brownfield

Root Growth Responses to Soil Amendment in an Urban Brownfield

Changes in Moisture Contents of Rice-hull Based Root Media and Growth Responses of ‘Seolhyang’ Strawberry during Vegetative Propagation

Changes in Moisture Contents of Rice-hull Based Root Media and Growth Responses of ‘Seolhyang’ Strawberry during Vegetative Propagation