CaСl2 Salt Signaling in Primary Root Architecture and Lateral Root Emergence in Arabidopsis thaliana

Russian Journal of Plant Physiology - Plant root architecture modulates during developmental stages and adjusts with the environmental condition. The cytosolic calcium which is a ubiquitous...     

Ameloblastin in Hertwig’s Epithelial Root Sheath Regulates Tooth Root Formation and Development

Tooth root formation begins after the completion of crown morphogenesis. At the end edge of the tooth crown, inner and outer enamel epithelia form Hertwig’s epithelial root sheath (HERS). HERS extends along with dental follicular tissue for root formation. Ameloblastin (AMBN) is an enamel matrix protein secreted by ameloblasts and HERS derived cells. A number of enamel proteins are eliminated in root formation, except for AMBN. AMBN may be related to tooth root formation; however, its role in this process remains unclear. In this study, we found AMBN in the basal portion of HERS of lower first molar in mice, but not at the tip. We designed and synthesized small interfering RNA (siRNA) targeting AMBN based on the mouse sequence. When AMBN siRNA was injected into a prospective mandibular first molar of postnatal day 10 mice, the root became shorter 10 days later. Furthermore, HERS in these mice revealed a multilayered appearance and 5-bromo-2′-deoxyuridine (BrdU) positive cells increased in the outer layers. In vitro experiments, when cells were compared with and without transiently expressing AMBN mRNA, expression of growth suppressor genes such as p21^Cip1 and p27^Kip1 was enhanced without AMBN and BrdU incorporation increased. Thus, AMBN may regulate differentiation state of HERS derived cells. Moreover, our results suggest that the expression of AMBN in HERS functions as a trigger for normal root formation.     

Root growth in biopores—evaluation with in situ endoscopy

Background and aims

The significance of biopores for nutrient acquisition from the subsoil depends on root-soil contact, which in turn is influenced by root architecture. The aim of this study was to detect differences regarding the architecture and root-soil contact of homorhizous barley roots (Hordeum vulgare L.) and allorhizous oilseed rape roots (Brassica napus L.) growing in biopores.

Methods

In situ endoscopy was used as a technique that allows non-destructive display of pore wall characteristics and root morphology inside large biopores under field conditions.

Results

For both crops, about 85 % of all roots did establish contact to the pore wall. However, according to their different root architecture, the two crops varied in their strategy of resource acquisition: While barley was characterized by thin vertical or ingrowing roots, most of them in direct contact to the pore wall, oilseed rape established contact to the pore wall predominantly via lateral roots.

Conclusions

Root morphological and pore wall assessment with in situ endoscopy in combination with detailed studies of soil biochemical and soil physical parameters of the pore wall is considered an essential prerequisite for more precise future modelling of nutrient acquisition and uptake.     

Is there a Root effect in Xenopus hemoglobin?

The reaction of Xenopus hemoglobin with oxygen and carbon monoxide has been reinvestigated over the pH range 8.5-6.0, in the absence and presence of organic phosphates (2,3-diphosphoglycerate or inositol hexakisphosphate), to establish if the tetramer can be stabilized in a T-quaternary state by protons and polyphosphate; the equilibrium and kinetic data indicate that Xenopus hemoglobin does exhibit a Root effect. These new results are discussed with reference to those reported by Bridges et al. [(1985) Resp. Physiol. 61, 125-136] on Xenopus blood and, more generally, to the molecular definition and the structural basis of the Root effect as an extreme form of the Bohr effect.     

Notes from the Underground： Receptor-Like Kinases in Arabidopsis Root Development

During plant development, the frequency and context of cell division must be controlled, and cells must differentiate properly to perform their mature functions. In addition, stem cell niches need to be maintained as a reservoir for new cells. All of these processes require intercellular signaling, whether it is a cell relaying its position to other cells, or more mature cells signaling to the stem cell niche to regulate the rate of growth. Receptor-like kinases have emerged as a major component in these diverse roles, especially within the Arabidopsis root. In this review, the functions of receptor-like kinase signaling in regulating Arabidopsis root development will be examined in theareas of root apical meristem maintenance, regulation of epidermal cell fate, lateral root development and vascular differentiation.     

Root taxa identification in plant mixtures – current techniques and future challenges

Background

Studying root biomass, root system distribution and belowground interactions is essential for understanding the composition of plant communities, the impact of global change, and terrestrial biogeochemistry. Most soil samples and minirhizotron pictures hold roots of more than one species or plant individual. The identification of taxa by their roots would allow species-specific questions to be posed; information about root affiliation to plant individuals could be used to determine intra-specific competition.

Scope

Researchers need to be able to discern plant taxa by roots as well as to quantify abundances in mixed root samples. However, roots show less distinctive features that permit identification than aboveground organs. This review discusses the primary use of available methods, outlining applications, shortcomings and future developments.

Conclusion

Methods are either non-destructive, e.g. visual examination of root morphological criteria in situ, or require excavated and excised root samples. Among the destructive methods are anatomical keys, chemotaxonomic approaches and molecular markers. While some methods allow for discerning the root systems of individual plants, others can distinguish roots on the functional group or plant taxa level; methods such as IR spectroscopy and qPCR allow for quantifying the root biomass proportion of species without manual sorting.     

Unusual Fine Root Distributions of Two Deciduous Tree Species in Southern France: What Consequences for Modelling of Tree Root Dynamics?

The spatial distribution of fine roots of two deciduous tree species was investigated in contrasting growing conditions in southern France. Hybrid walnut trees (Juglans regia×nigra cv. NG23) and hybrid poplars (Populus euramericana cv. I214) were both cultivated with or without annual winter intercrops for 10 years on deep alluvial soils. Soil samples for measuring the fine root distribution of both trees and crops were obtained by soil coring down to 3-m depth at several distances and orientations from the tree trunk. The distribution of live fine roots from walnut and poplar trees was patchy and sometimes unexpected. In the tree-only stands, fine root profiles followed the expected pattern, as fine root density decreased with increasing depth and distance from the tree trunk. However, many fine root profiles under intercropped trees were uniform with depth, and some inverse profiles were observed. These distributions may result from a high degree of plasticity of tree root systems to sense and adapt to fluctuating and heterogeneous soil conditions. The distortion of the tree root system was more pronounced for the walnut trees that only partially explored the soil volume: in the tree-only stand, the walnut rooting pattern was very superficial, but in the intercropped stand walnut trees developed a deep and dense fine root network below the crop rooting zone. The larger poplars explored the whole available soil volume, but the intercrop significantly displaced the root density from the topsoil to layers below 1 m depth. Most tree root growth models assume a decreasing fine root density with depth and distance from the tree stem. These models would not predict correctly tree–tree and tree–understorey competition for water and nutrients in 3D heterogeneous soil conditions that prevail under low-density tree stands. To account for the integrated response of tree root systems to such transient gradients in soils, we need a dynamic model that would allow for both genotypic plasticity and transient environmental local soil conditions.     

Root distribution,standing crop biomass and belowground productivity in a semidesert in México

In a semidesert community in México (Zapotitlán de las Salinas, Puebla) the vertical distribution of roots and root biomass was estimated at 0–100 cm depth on two sampling dates, November 1995 (wet season) and January 1998 (dry season). Root productivity at 7 to 14.5 cm depth was estimated with the in-growth core technique every two months from March 1996 to February 1998. The relationship between environmental factors and seasonal root productivity was analyzed. Finally, we tested the effect of an irrigation equivalent to 20 mm of rain on root production. Seventy four percent of the total number of roots were found at 0-40 cm depth. Very fine roots (<1 mm diameter) were found throughout the soil profile (0-100 cm). In contrast, fine roots (1-3 mm diameter) were found only from 0–90 cm depth, and coarse roots (>3 mm diameter) from 0–60 cm depth. The root biomass was 971.5 g m^–2 (S.D. = 557.39), the very fine and fine roots representing 62.9% of the total. Total root productivity, as estimated with the ingrowth core technique, was 0.031 Mg ha^–1 over the dry season and 0.315 Mg ha^–1 over the wet season. Only very fine roots were obtained at all sampling dates. Rainfall was significantly correlated with very fine root production. The difference between fine root production in non-watered (0.054 g m^–2) and watered (0.429 g m^–2) treatments was significant. The last value was the same as that predicted for a rain of 20 mm, according to the exponential model describing the relation between the production of very fine roots and rainfall at the site.     

When Does the Self-Regulatory Response Elicited in Soybean Root after Inoculation Occur?

The inoculation of soybean (Glycine max L.) roots with Bradyrhizobium japonicum produces a regulatory response that inhibits nodulation in the younger regions of the roots. By exposing the soybean roots to live homologous bacteria for only a short period of time, the question of whether or not early interactions of rhizobia with root cells, prior to infection, elicit this regulatory response has been explored. B. japonicum cells mixed with infective bacteriophages were applied to the roots and then 6 or 24 hours later roots were again inoculated with phage-resistant rhizobia. Mixing of the rhizobia and bacteriophages caused bacterial lysis in 6 to 8 hours and allowed the bacteria to act as live symbionts on the root for only a few hours. However, the interaction of live homologous bacteria with the soybean roots for a few hours did not cause inhibition of nodulation in the younger regions of the roots. Results of these experiments indicate that the self-regulatory response in soybean is not rapidly produced by the early, pre-infection, interactions between rhizobia and the root cells.     

Root (wilt) disease of coconut palms in South Asia – an overview

Root (wilt) disease (RWD) caused by phytoplasma is one of the most devasting diseases of coconut palms. The major symptoms of the disease in leaves are wilting and drooping and flaccidity; ribbing, paling/yellowing and necrosis of leaflets are typical symptoms of foliar diseases. Unopened pale yellow leaflets of spindle leaves are more susceptible to leaf rot disease, which is caused by Exerohilum rostratum and Colletotrichum gloeosporioides. RWD is caused by phytoplasmas, the cell wall-less prokaryotes that are bounded by a “unit” membrane. In ultrathin sections, they appear as a complex multi-branched, beaded, filamentous or spheroidal pleomorphic bodies. The disease was transmitted by plant hoppers (Proutista moesta) and lace wing bug (Stephanitis typica). Phytoplasmas are generally present in the phloem sieve tubes and in the salivary glands of these insect vectors. Phytoplasmas cannot be cultured in vitro, and hence it is very difficult to identify them. Using polymerase chain reaction technique, group-specific primers have been applied to detect mixed-phytoplasma infections in a single host. RWD, is a non-lethal, debilitating disease, and hence an integrated approach for the management of this disease in coconut palms has been discussed in this study.     

Root distribution in an Amazonian seasonal forest as derived from δ13C profiles

Carbon isotope ratios of the main stem in trees, saplings, and seedlings were correlated with their main stem diameter in an Amazonian seasonal forest. This correlation became the basis of using carbon isotope ratios of roots from various levels of the soil profile in order to determine root distribution from emergent, canopy and subcanopy trees, saplings and herbaceous understorey plants. It was observed that the distribution of roots in the soil profile is horizontally and vertically heterogeneous. Pockets of roots from saplings or herbaceous understorey plants were found as deep as 4 m and pockets of roots from emergent trees were found as shallow as 1 m depth.     

A Galacturonic Acid–Containing Xyloglucan Is Involved in Arabidopsis Root Hair Tip Growth

Root hairs provide a model system to study plant cell growth, yet little is known about the polysaccharide compositions of their walls or the role of these polysaccharides in wall expansion. We report that Arabidopsis thaliana root hair walls contain a previously unidentified xyloglucan that is composed of both neutral and galacturonic acid–containing subunits, the latter containing the β-d-galactosyluronic acid-(1→2)-α-d-xylosyl-(1→ and/or α-l-fucosyl-(1→2)-β-d-galactosyluronic acid-(1→2)-α-d-xylosyl-(1→) side chains. Arabidopsis mutants lacking root hairs have no acidic xyloglucan. A loss-of-function mutation in At1g63450, a root hair–specific gene encoding a family GT47 glycosyltransferase, results in the synthesis of xyloglucan that lacks galacturonic acid. The root hairs of this mutant are shorter than those of the wild type. This mutant phenotype and the absence of galacturonic acid in the root xyloglucan are complemented by At1g63450. The leaf and stem cell walls of wild-type Arabidopsis contain no acidic xyloglucan. However, overexpression of At1g63450 led to the synthesis of galacturonic acid–containing xyloglucan in these tissues. We propose that At1g63450 encodes XYLOGLUCAN-SPECIFIC GALACTURONOSYLTRANSFERASE1, which catalyzes the formation of the galactosyluronic acid-(1→2)-α-d-xylopyranosyl linkage and that the acidic xyloglucan is present only in root hair cell walls. The role of the acidic xyloglucan in root hair tip growth is discussed.     

Genetic Analysis of Root Growth in Rice Seedlings Under Different Water Supply Conditions

To understand the genetic background of root growth of rice (Oryza sativa L.) seedlings under different water supply conditions, quantitative trait loci (QTLs) and epistatic effect on seminal root length, maximum adventitious root length, adventitious root number, total root dry weight and ratio of root to shoot were detected using molecular map including 103 restriction fragment length polymorphism (RFLP) markers and 104 amplified fragment length polymorphism (AFLP) markers mapped on a recombinant inbred line (RIL) population with 150 lines derived from a cross between an lowland rice IR1552 and an upland rice Azucena in both solution culture (lowland condition) and paper culture (upland condition). Six QTLs and twenty-two pairs of epistatic loci for the four parameters were detected. Three QTLs detected for maximum adventitious root length in solution culture (MARLS), total root dry weight in both solution culture and paper culture (TRDWS and TRDWP) accounted for about 20%, 23% and 13% of the total variations, respectively. Only epistatic loci were found for maximum adventitious root length and adventitious root number in paper culture (MARLP and ARNP), and for ratio of root to shoot in both paper and solution culture (R/SP and R/SS), which accounted for about 12%-61% of the total variations in the parameters, respectively. No identical QTL or epistatic loci were found for the parameters in both solution and paper culture. The results indicate that there is a different genetic system responsible to root growth of rice seedlings under lowland and upland conditions and epistasis might be the major genetic basis for MARLP, ARNP, R/SP and R/SS.     

Root–shoot allometry of tropical forest trees determined in a large-scale aeroponic system

Background and Aims

This study is a first step in a multi-stage project aimed at determining allometric relationships among the tropical tree organs, and carbon fluxes between the various tree parts and their environment. Information on canopy–root interrelationships is needed to improve understanding of above- and below-ground processes and for modelling of the regional and global carbon cycle. Allometric relationships between the sizes of different plant parts will be determined.

Methods

Two tropical forest species were used in this study: Ceiba pentandra (kapok), a fast-growing tree native to South and Central America and to Western Africa, and Khaya anthotheca (African mahogany), a slower-growing tree native to Central and Eastern Africa. Growth and allometric parameters of 12-month-old saplings grown in a large-scale aeroponic system and in 50-L soil containers were compared. The main advantage of growing plants in aeroponics is that their root systems are fully accessible throughout the plant life, and can be fully recovered for harvesting.

Key Results

The expected differences in shoot and root size between the fast-growing C. pentandra and the slower-growing K. anthotheca were evident in both growth systems. Roots were recovered from the aeroponically grown saplings only, and their distribution among various diameter classes followed the patterns expected from the literature. Stem, branch and leaf allometric parameters were similar for saplings of each species grown in the two systems.

Conclusions

The aeroponic tree growth system can be utilized for determining the basic allometric relationships between root and shoot components of these trees, and hence can be used to study carbon allocation and fluxes of whole above- and below-ground tree parts.     

Root or shoot nitrate assimilation in terrestrial vascular plants – does it matter?

Plant and Soil - Most terrestrial vascular plants can assimilate soil obtained NO3- in their root and shoot. Data from the literature are collated and analysed with respect to genotype and...     

Are Root Hydraulic Conductivity Responses to Salinity Controlled by Aquaporins in Broccoli Plants?

Broccoli (Brassica oleracea L. var. Italica) is a recognised health-promoting vegetable, which is moderately sensitive to salinity. In this study, the primary response of broccoli plants (cv. Marathon) to salinity has been characterised. For this, leaf water relations, nutrient composition, root hydraulic conductivity (L ₀) and the effect of mercury (an aquaporin blocker) on L ₀ were determined for plants grown with 0, 20, 40, 60, 80 or 100 mM NaCl for 2 weeks. During the 2 weeks of treatment, the plants showed a two-phase growth response to salinity. During the first phase (1 week), growth reduction was high, probably related to water stress as no osmotic adjustment occurred and reductions of L ₀, the mercury effect and Gs were observed. After 2 weeks, the growth reduction could have resulted from internal injury caused by Na⁺ or Cl⁻, since osmotic adjustment was achieved and water relations plus the mercury effect were re-established to a high degree, indicating high aquaporin functionality. The fact that aquaporin functionality fits well with the overall water relations response is very relevant, since the two-phase adaptation to salinity may imply two types of aquaporin regulation.