Role Of Roots Research Articles

Root hydraulics: The forgotten side of roots in drought adaptation

Roots have long been proposed as a major avenue of research to improve crop adaptation to water limitations. The simple assumption is that deeper and more profuse root systems could tap extra water from the soil profile and alleviate drought effects. However, after decades of research, success in breeding cultivars with improved root systems is lagging behind. Here, we attempt to analyze the possible reasons for this, and re-focus on what root traits might provide the most promising avenues for drought adaptation. We approach the root system from the angle of water extraction, using data from a lysimetric system that allows monitoring and comparing plant water use over the entire crop life cycle and yield, and analyze whether and how differences in water extraction lead to improved yield across different crops. The main message from that analysis is that water extraction during reproduction and grain filling is critical and comes from a number of traits that influence the rate at which plant use the available water before and during stress. Roots may have an effect on this, not from the traditionally thought density or depth, but rather from their hydraulic characteristics. Plants can indeed control water use by controlling leaf area development and this is a “long term” control. Plants also control water losses by controlling stomata opening under high vapor pressure deficit (VPD) conditions, in a transient manner. Both processes (leaf development and stomata opening) are mostly controlled by hydraulic processes. The role of roots in drought adaptation could be there, along with the soil, in setting an hydraulic environment that allow plants to use water in a way that allow maximizing water use for these critical stages.

Enhanced rhizosphere colonization of beneficialBacillus amyloliquefaciensSQR9 by pathogen infection

Root exudates play important roles in root-soil microorganism interactions and can mediate tripartite interactions of beneficial microorganisms-plant-pathogen in the rhizosphere. However, the roles of organic acid components in this process have not been well studied. In this study the colonization of a plant growth-promoting rhizobacterium, Bacillus amyloliquefaciens SQR9, on cucumber root infected by Fusarium oxysporum f. sp. cucumerinum J. H. Owen (FOC) was investigated. Chemotaxis and biofilm formation response of SQR9 to root exudates and their organic acid components were analysed. Infection of FOC on cucumber had a positive effect (3.30-fold increase) on the root colonization of SQR9 compared with controls. Root secretion of citric acid (2.3±0.2μM) and fumaric acid (5.7±0.5μM) was enhanced in FOC-infected cucumber plants. Bacillus amyloliquefaciens SQR9 exhibited enhanced chemotaxis to root exudates of FOC-infected cucumber seedlings. Further experiments demonstrated that citric acid acts as a chemoattractant and fumaric acid as a stimulator of biofilm formation in this process. These results suggest that root exudates mediate the interaction of cucumber root and rhizosphere strain B.amyloliquefaciens SQR9 and enhance its root colonization.

How do heavy metal ATPases contribute to hyperaccumulation?

AbstractPlants contain metal chelators and transporters that regulate metal homeostasis. The HMA3 and HMA4 genes encode proteins belonging to the PIB‐type. Recently, some studies on the characterization of the HMA2 gene from several plants for potential application in phytoremediation have been reported. This ATPase family of integral membrane transporter proteins that transport transition metals are probably involved in mediating metal‐resistant and metal‐hyperaccumulating traits. While HMA3 may contribute to metal detoxification by sequestering Cd into the vacuole, HMA4 acts as a physiological master switch during the process of metal hyperaccumulation, and HMA2 and HMA4 play roles in root to shoot metal translocation. The focus of this review is the discussion on the different functions of HMA3, HMA4, and HMA2 in various plant species. It is hypothesized that a refined distinction and description of the roles of several types of these metal transporters in plants will be essential for the development of schemes to genetically modify plants that accumulate specific metals, with subsequent use in either phytoremediation or in improving human nutrition. Enhanced expression of HMA3 and HMA4 is a prerequisite for hyperaccumulation and hyperresistance in hyperaccumulators. Through genetic engineering, these genes are able to generate nontoxic, metal‐free crops to produce safe food.

The Tomato 14-3-3 Protein TFT4 Modulates H+ Efflux, Basipetal Auxin Transport, and the PKS5-J3 Pathway in the Root Growth Response to Alkaline Stress

Alkaline stress is a common environmental stress, in particular in salinized soils. Plant roots respond to a variety of soil stresses by regulating their growth, but the nature of the regulatory pathways engaged in the alkaline stress response (ASR) is not yet understood. Previous studies show that PIN-FORMED2, an auxin (indole-3-acetic acid [IAA]) efflux transporter, PKS5, a protein kinase, and DNAJ HOMOLOG3 (J3), a chaperone, play key roles in root H(+) secretion by regulating plasma membrane (PM) H(+)-ATPases directly or by targeting 14-3-3 proteins. Here, we investigated the expression of all 14-3-3 gene family members (TOMATO 14-3-3 PROTEIN1 [TFT1]-TFT12) in tomato (Solanum lycopersicum) under ASR, showing the involvement of four of them, TFT1, TFT4, TFT6, and TFT7. When these genes were separately introduced into Arabidopsis (Arabidopsis thaliana) and overexpressed, only the growth of TFT4 overexpressors was significantly enhanced when compared with the wild type under stress. H(+) efflux and the activity of PM H(+)-ATPase were significantly enhanced in the root tips of TFT4 overexpressors. Microarray analysis and pharmacological examination of the overexpressor and mutant plants revealed that overexpression of TFT4 maintains primary root elongation by modulating PM H(+)-ATPase-mediated H(+) efflux and basipetal IAA transport in root tips under alkaline stress. TFT4 further plays important roles in the PKS5-J3 signaling pathway. Our study demonstrates that TFT4 acts as a regulator in the integration of H(+) efflux, basipetal IAA transport, and the PKS5-J3 pathway in the ASR of roots and coordinates root apex responses to alkaline stress for the maintenance of primary root elongation.

Shoot Induction, Biochemical Changes During in vitro Rooting in Paeonia lactiflora Pall 'Hortensis'

Background: Peony is an ornamental as well as medicinal plant which is difficult to propagate in vitro . Its major problem during in vitro culture is leaching out of phenols in the medium. It causes hindrance in growth and development. Rooting is a complex process and main step for vegetative propagation. The main objective is to propagate this plant and produce multiple copies and understand rooting phenomenon which is usually complicated. Methods: The underground rhizomatous buds of Paeonia lactiflora Pall. ‘Hortensis’ were selected as the explants. In vitro micropropagation was carried out along with biochemical studies during rooting process. Results: Shoot induction, axillary shoot proliferation and rooting were established. The best initial medium for ‘hortensis’ was the half-strength Murashige and Skoog (MS) medium (double-strength Ca ) supplemented with 1 mg L N +2 1 6 benzyl-adenine (BA) and 0.5 mg L Gibberellic Acid (GA ). Shoot induction was 100% with 6.2 shoots per explant. 1 3 Rooting was also observed on the half-strength MS medium supplemented with 1.0 mg L Indole-3-butyric Acid 1 (IBA) and indole-3-acetic acid (IAA). The highest percentage of rooting (15%) was observed when in vitro shoots were dipped in the full-strength liquid MS medium supplemented with 10.0 mg L IBA without agar for five days and then 1 transferred to the quarter strength MS medium without any Plant Growth Regulator (PGR). Conclusion: The cultivar P. lactiflora hortensis is hard to root in vitro. The activities of peroxidase, indole acetic oxidase, polyphenolic oxidase and phenolic content have been estimated prior to and after rooting. These enzyme activities and phenolics have been reported to play a major role in rooting.

Study of The Enhance The Role of Roots on Soil Shear Strength

Study of The Enhance The Role of Roots on Soil Shear Strength

HvHMA2, a P1B-ATPase from Barley, Is Highly Conserved among Cereals and Functions in Zn and Cd Transport

Manipulation of crops to improve their nutritional value (biofortification) and optimisation of plants for removal of toxic metals from contaminated soils (phytoremediation) are major goals. Identification of membrane transporters with roles in zinc and cadmium transport would be useful for both aspects. The P1B-ATPases play important roles in heavy metal allocation and detoxification in Arabidopsis and it is now important to elucidate their roles in monocots. We identified nine P1B-ATPases in barley and this study focuses on the functional characterization of HvHMA2, providing evidence for its role in heavy metal transport. HvHMA2 was cloned using information from EST analysis and 5′ RACE. It possesses the conserved aspartate that is phosphorylated during the reaction cycle of P-type pumps and has motifs and key residues characteristic of P1B-ATPases, falling into the P1B-2 subclass. Homologous sequences occur in three major sub-families of the Poaceae (Gramineae). Heterologous expression in Saccharomyces cerevisiae demonstrates that HvHMA2 functions as a Zn and Cd pump. Mutagenesis studies show that proposed cation coordination sites of the P1B-2 pumps are crucial for the metal responses conferred by HvHMA2 in yeast. HvHMA2 expression suppresses the Zn-deficient phenotype of the Arabidopsis hma2hma4 mutant indicating that HvHMA2 functions as a Zn pump in planta and could play a role in root to shoot Zn transport. When expressed in Arabidopsis, HvHMA2 localises predominantly to the plasma membrane.

The role of roots in the resource economics spectrum

The role of roots in the resource economics spectrum

COLD ACCLIMATION INFLUENCE POST-HARVEST NEEDLE RETENTION IN ROOT DETACHED BALSAM FIR (ABIES BALSAMEA (L.) MILL.)

This study investigated the influence of cold acclimation on post-harvest needle retention in balsam fir (Abies balsamea (L.) Mill.) and explored certain physiological roles of roots and low temperature. In a controlled environment study, 18 month old seedlings with either detached or intact roots were exposed to a range of temperatures (-20 to 20°C) for different durations and selected physiological responses were measured. Cold acclimation of seedlings with intact roots resulted in 36% less needle loss, 76% lower fresh weight losses and 45% less water consumption when compared to those exposed to cold acclimation with no roots. A temperature of 5°C registered the lowest average daily water use of 0.16 ml/g/day, lowest needle loss of 7.1 mg/g and a positive weight gain (4%) when compared to -20, -5, 0 or 20°C. An acclimation temperature of -20°C reduced leaf chlorophyll content by 9x when compared to 5°C. Xylem pressure potential did not relate to needle loss. We hypothesize that roots play a key role in cold acclimation and needle retention by increasing membrane stability, preserving stomatal functions and maintaining chlorophyll content through yet unknown signals.

Disruption of the Arabidopsis thaliana Inward-Rectifier K+ Channel AKT1 Improves Plant Responses to Water Stress

The Arabidopsis thaliana inward-rectifier K(+) channel AKT1 plays an important role in root K(+) uptake. Recent results show that the calcineurin B-like (CBL)-interacting protein kinase (CIPK) 23-CBL1/9 complex activates AKT1 in the root to enhance K(+) uptake. In addition, this CIPK-CBL complex has been demonstrated to regulate stomatal movements and plant transpiration. However, a role for AKT1 in plant transpiration has not yet been demonstrated. Here we show that disruption of AKT1 conferred an enhanced response to water stress in plants. Experiments performed in hydroponics showed that, when water potential was diminished by adding polyethylene glycol, akt1 adult plants lost less water than wild-type (WT) plants. Under long-term water stress in soil, adult akt1 plants displayed lower transpiration and less water consumption than WT plants. Finally, akt1 stomata closed more efficiently in response to ABA. Such results were also observed in cipk23 plants. The similar responses shown by cipk23 and akt1 plants to water stress denote that the regulation of AKT1 by CIPK23 may also take place in stomata and has a negative impact on plant performance under water stress conditions.

Monosaccharide Absorption Activity of Arabidopsis Roots Depends on Expression Profiles of Transporter Genes under High Salinity Conditions

Plant roots are able to absorb sugars from the rhizosphere but also release sugars and other metabolites that are critical for growth and environmental signaling. Reabsorption of released sugar molecules could help reduce the loss of photosynthetically fixed carbon through the roots. Although biochemical analyses have revealed monosaccharide uptake mechanisms in roots, the transporters that are involved in this process have not yet been fully characterized. In the present study we demonstrate that Arabidopsis STP1 and STP13 play important roles in roots during the absorption of monosaccharides from the rhizosphere. Among 14 STP transporter genes, we found that STP1 had the highest transcript level and that STP1 was a major contributor for monosaccharide uptake under normal conditions. In contrast, STP13 was found to be induced by abiotic stress, with low expression under normal conditions. We analyzed the role of STP13 in roots under high salinity conditions where membranes of the epidermal cells were damaged, and we detected an increase in the amount of STP13-dependent glucose uptake. Furthermore, the amount of glucose efflux from stp13 mutants was higher than that from wild type plants under high salinity conditions. These results indicate that STP13 can reabsorb the monosaccharides that are released by damaged cells under high salinity conditions. Overall, our data indicate that sugar uptake capacity in Arabidopsis roots changes in response to environmental stresses and that this activity is dependent on the expression pattern of sugar transporters.

Molecular characterization and expression analysis of phosphate transporter gene TaPT2-1 in wheat (Triticum aestivum L.)

A transcript-derived fragment (TDF) showing up-regulated expression under low Pi stress and being identical to an uncharacterized phosphate transporter gene TaPT2-1 was cloned in wheat. TaPT2-1 was 2075 bp in length and encoded a 568-aa polypeptide. Transmembrane prediction analysis suggested that TaPT2-1 had 13 conserved transmembrane domains. TaPT2-1 shared much higher similarities to other four homologs from Arabidopsis thaliana, Solanum tuberosum, Capsicum frutescens, and Solanum melongena. The expression of TaPT2-1 was root specific and low Pi inducible, suggesting that it plays roles in roots and is involved in the Pi acquisition under Pi-starved condition. The promoter region of TaPT2-1 was cloned based on genome walk analysis. Several types of cis-regulatory elements, such as low Pi responding and tissue specific, were identified in TaPT2-1 promoter. The transgenic tobacco plants with the integrated TaPT2-1 promoter GUS were generated, and GUS histochemical staining analysis in the roots and leaves of the transgenic plants was performed. The results of GUS staining in roots and leaves under various Pi supply conditions were in accordance with the TaPT2-1 transcripts detected based on RT-PCR analysis. Taken together, the distinct expression of low Pi-induced and root-specific TaPT2-1 suggested that it could be used as the potential gene resource on generation of elite crop germplasms with high Pi use efficiency in the future.

Linking water and nutrients through the vadose zone: a fungal interface between the soil and plant systems

Plant water availability, use, and management have largely focused on physical processes of infiltration and the role of roots in uptake and transpiration. However, roots and mycorrhizal fungi redistribute water in complex patterns. Here I describe some of our observations and experiments showing that mycorrhizal fungi play key roles in moving water for both transpiration and to facilitate nutrient acquisition under dry conditions. Mycorrhizal fungal hyphae grow from both surface and deep roots even into bedrock to help extract water under dry conditions. In both deep and surface roots, mycorrhizal fungi acquire water from pores too small for roots and root hairs to access, and at distances from roots and root hairs. Mycorrhizal fungi are also able to utilize hydraulic-lifted water from plants to obtain nutrients in extremely dry surface soils. The importance of these root symbionts in water and nutrient dy- namics, and as integrators of surface and deeper water dynamics need further investigation. Predicting water use by irrigated crops in mesic lands has become relatively accurate, facilitating manipula- tion of water application and for predicting crop growth and production. However, these models are largely based on the relatively even distribution of soil structural elements through the root zone, coupled with an understanding in the vertical spatial distribu- tion of water inputs. Even then, however, water movement within the soil profile is chaotic, resulting in complex patterns of water movement under unsatu- rated conditions. Much of the research on water movement and use has been undertaken as a physical process, but here I discuss the role of mycorrhizal fungi in redistributing soil moisture for plant use and for plant re-allocation to mycorrhizal fungi to acquire surface nutrients. Water and nutrients are tightly coupled in regulating ecosystem processes including productivity and de- composition. However, in arid land soils, water and nutrients are spatially segregated. Most of the nutrients are applied (as fertilizers) or continually cycled in the upper soil layers and the highest nutrient availability is generally in a thin organic layer between the litter and the mineral soils, and in the upper mineral soil. In

Numeral-Incorporating Roots in Numeral Systems: A Comparative Analysis of Two Sign Languages

Numeral-incorporating roots in the numeral systems of Argentine Sign Language (LSA) and Catalan Sign Language (LSC), as well as the main features of the number systems of both languages, are described and compared. Informants discussed the use of numerals and roots in both languages (in most cases in natural contexts). Ten informants took part in the LSC data collection, and six in the LSA data collection. The data were corroborated by analyzing the videos available at www.youtube.com/confargsordos (for LSA) and by videos and books provided by the ILLESCAT Foundation (for LSC), as well as by previous research. A general inventory of roots in both languages and specifically of roots in both numerals systems was carried out. The role of roots in the formation of ordinals and cardinals and the main features of both number systems are described. The data suggest that numeral-incorporating roots in these number systems are formed only from numerals that do not derive from manual counting. This assumption is discussed, and further research about this point is emphasized.

Changes of Antioxidative Enzymes and Lipid Peroxidation in Leaves and Roots of Waterlogging-Tolerant and Waterlogging-Sensitive Maize Genotypes at Seedling Stage

To better understand the physiological and biochemical mechanisms of waterlogging tolerance, waterlogging effects on lipid peroxidation and the activity of antioxidative enzymes were investigated in leaves and roots of two maize genotypes, HZ32 (waterlogging-tolerant) and K12 (waterlogging-sensitive). Potted maize plants were waterlogged at the second leaf stage under glasshouse conditions. Leaves and roots were harvested 1 d before and 2, 4, 6, 8 and 10 d after the start of waterlogging treatment. Through comparing the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), catalase (CAT) and guaiacol peroxidase (POD) between waterlogging-tolerant and waterlogging-sensitive genotype, we deduced that CAT was the most important H 2O 2 scavenging enzyme in leaves, while APX seemed to play a key role in roots. POD, APX, GR and CAT activities in conjunction with SOD seem to play an essential protective role in the O 2 T and H 2O 2 scavenging process. Lipid peroxidation was enhanced significantly only in K12 ( P < 0.001) and there was no difference ( P > 0.05) in HZ32 up to 6 d after waterlogging stress. These results indicated that oxidative stress may play an important role in waterlogging-stressed maize plants and that the greater protection of HZ32 leaves and roots from waterlogging-induced oxidative damage results, at least in part, through the maintenance of increased antioxidant enzyme activity.

10.1007/s11183-008-1001-8

The review considers the roles of root and shoot tissues in transport and accumulation of heavy metals in plants of two contrast groups, i.e., excluders and hyperaccumulators. The regularities in distribution of cadmium, lead, nickel, and strontium are summarized. Effects of other cations, calcium in particular, on accumulation and distribution of heavy metals are analyzed. Specific patterns of metal distribution in hyperaccumulator plants are discussed together with morphological and functional features underlying the ability of plants to accumulate heavy metals in the aboveground organs. Based on the data available, the root and shoot tissues are classified according to their roles in transport and distribution of the metals examined.

Stimulation of nonselective amino acid export by glutamine dumper proteins.

Phloem and xylem transport of amino acids involves two steps: export from one cell type to the apoplasm, and subsequent import into adjacent cells. High-affinity import is mediated by proton/amino acid cotransporters, while the mechanism of export remains unclear. Enhanced expression of the plant-specific type I membrane protein Glutamine Dumper1 (GDU1) has previously been shown to induce the secretion of glutamine from hydathodes and increased amino acid content in leaf apoplasm and xylem sap. In this work, tolerance to low concentrations of amino acids and transport analyses using radiolabeled amino acids demonstrate that net amino acid uptake is reduced in the glutamine-secreting GDU1 overexpressor gdu1-1D. The net uptake rate of phenylalanine decreased over time, and amino acid net efflux was increased in gdu1-1D compared with the wild type, indicating increased amino acid export from cells. Independence of the export from proton gradients and ATP suggests that overexpression of GDU1 affects a passive export system. Each of the seven Arabidopsis (Arabidopsis thaliana) GDU genes led to similar phenotypes, including increased efflux of a wide spectrum of amino acids. Differences in expression profiles and functional properties suggested that the GDU genes fulfill different roles in roots, vasculature, and reproductive organs. Taken together, the GDUs appear to stimulate amino acid export by activating nonselective amino acid facilitators.

Wool-waste as organic nutrient source for container-grown plants

A container experiment was conducted to test the hypothesis that uncomposted wool wastes could be used as nutrient source and growth medium constituent for container-grown plants. The treatments were: (1) rate of wool-waste application (0 or unamended control, 20, 40, 80, and 120 g of wool per 8-in. pot), (2) growth medium constituents [(2.1) wool plus perlite, (2.2) wool plus peat, and (2.3) wool plus peat plus perlite], and (3) plant species (basil and Swiss chard). A single addition of 20, 40, 80, or 120 g of wool-waste to Swiss chard (Beta vulgaris L.) and basil (Ocimum basilicum L.) in pots with growth medium provided four harvests of Swiss chard and five harvests of basil. Total basil yield from the five harvests was 1.6-5 times greater than the total yield from the unamended control, while total Swiss chard yield from the four harvests was 2-5 times greater relative to the respective unamended control. The addition of wool-waste to the growth medium increased Swiss chard and basil tissue N, and NO(3)-N and NH(4)-N in growth medium relative to the unamended control. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) microanalysis of wool fibers sampled at the end of the experiments indicated various levels of decomposition, with some fibers retaining their original surface structure. Furthermore, most of the wool fibers' surfaces contained significant concentrations of S and much less N, P, or K. SEM/EDX revealed that some plant roots grow directly on wool-waste fibers suggesting either (1) root directional growth towards sites with greater nutrient concentration and/or (2) a possible role for roots or root exudates in wool decomposition. Results from this study suggest that uncomposted wool wastes can be used as soil amendment, growth medium constituent, and nutrient source for container-grown plants.

Rhizosphere: biophysics, biogeochemistry and ecological relevance

Life on Earth is sustained by a small volume of soil surrounding roots, called the rhizosphere. The soil is where most of the biodiversity on Earth exists, and the rhizosphere probably represents the most dynamic habitat on Earth; and certainly is the most important zone in terms of defining the quality and quantity of the Human terrestrial food resource. Despite its central importance to all life, we know very little about rhizosphere functioning, and have an extraordinary ignorance about how best we can manipulate it to our advantage. A major issue in research on rhizosphere processes is the intimate connection between the biology, physics and chemistry of the system which exhibits astonishing spatial and temporal heterogeneities. This review considers the unique biophysical and biogeochemical properties of the rhizosphere and draws some connections between them. Particular emphasis is put on how underlying processes affect rhizosphere ecology, to generate highly heterogeneous microenvironments. Rhizosphere ecology is driven by a combination of the physical architecture of the soil matrix, coupled with the spatial and temporal distribution of rhizodeposits, protons, gases, and the role of roots as sinks for water and nutrients. Consequences for plant growth and whole-system ecology are considered. The first sections address the physical architecture and soil strength of the rhizosphere, drawing their relationship with key functions such as the movement and storage of elements and water as well as the ability of roots to explore the soil and the definition of diverse habitats for soil microorganisms. The distribution of water and its accessibility in the rhizosphere is considered in detail, with a special emphasis on spatial and temporal dynamics and heterogeneities. The physical architecture and water content play a key role in determining the biogeochemical ambience of the rhizosphere, via their effect on partial pressures of O2 and CO2, and thereby on redox potential and pH of the rhizosphere, respectively. We address the various mechanisms by which roots and associated microorganisms alter these major drivers of soil biogeochemistry. Finally, we consider the distribution of nutrients, their accessibility in the rhizosphere, and their functional relevance for plant and microbial ecology. Gradients of nutrients in the rhizosphere, and their spatial patterns or temporal dynamics are discussed in the light of current knowledge of rhizosphere biophysics and biogeochemistry. Priorities for future research are identified as well as new methodological developments which might help to advance a comprehensive understanding of the co-occurring processes in the rhizosphere.

The underestimated role of roots in leaf defenses against herbivores

The underestimated role of roots in leaf defenses against herbivores