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At least 73 records · Page 4Linked to original sources
PubMed1986

A Structural Comparison of the Acidic Extracellular Polysaccharides from Rhizobium trifolii Mutants Affected in Root Hair Infection.

The structures of the acidic extracellular polysaccharides (EPSs) from several R. trifolii mutants were compared by examining their compositions and their sugar linkages as determined by methylation analysis. These mutant strains were derived from the wild-type R. trifolii ANU843 and were unable to induce normal root hair curling (Hac- phenotype) or nodulation response (Nod- phenotype) in clover plants. These strains included several transposon Tn5-induced Nod-mutants, strain ANU871, which possesses a 40 to 50 kilobase deletion of the resident Sym plasmid, and strain ANU845 which is missing the Sym plasmid (pSym-). Strains ANU845(pSym-) containing either plasmid pRt150 or pBR1AN were also used. The recombinant plasmid pRt150 restores only root hair curling capacity to ANU845 while plasmid pBR1AN (an R. trifolii pSym) restores both root hair curling and nodulation capacity to this strain. Our composition and methylation results show that the EPSs from all these strains have the same glycosyl and pyruvyl linkages. Thus we suggest that neither the nod genes involved in root hair curling nor the entire pSym encodes for the arrangement of glycosyl or pyruvyl residues in these EPSs. Whether or not the nod genes dictate the location of acetyl or beta-hydroxybutyrate substituent groups remains to be determined.

Journal Article↗
PubMed1989

A non-nodulating alfalfa mutant displays neither root hair curling nor early cell division in response to Rhizobium meliloti.

The early events in the alfalfa-Rhizobium meliloti symbiosis include deformation of epidermal root hairs and the approximately concurrent stimulation of cell dedifferentiation and cell division in the root inner cortex. These early steps have been studied previously by analysis of R. meliloti mutants. Bacterial strains mutated in nodABC, for example, fail to stimulate either root hair curling or cell division events in the plant host, whereas exopolysaccharide (exo) mutants of R. meliloti stimulate host cell division but the resulting nodules are uninfected. As a further approach to understanding early symbiotic interactions, we have investigated the phenotype of a non-nodulating alfalfa mutant, MnNC-1008 (NN) (referred to as MN-1008). Nodulating and non-nodulating plants were inoculated with wild-type R. meliloti and scored for root hair curling and cell divisions. MN-1008 was found to be defective in both responses. Mutant plants inoculated with Exo- bacteria also showed no cell division response. Therefore, the genetic function mutated in MN-1008 is required for both root hair curling and cell division, as is true for the R. meliloti nodABC genes. These observations support the model that the distinct cellular processes of root hair curling and cell division are triggered by related mechanisms or components, or are causally linked.

Cell Division↗
PubMed2004

nip, a symbiotic Medicago truncatula mutant that forms root nodules with aberrant infection threads and plant defense-like response.

To investigate the legume-Rhizobium symbiosis, we isolated and studied a novel symbiotic mutant of the model legume Medicago truncatula, designated nip (numerous infections and polyphenolics). When grown on nitrogen-free media in the presence of the compatible bacterium Sinorhizobium meliloti, the nip mutant showed nitrogen deficiency symptoms. The mutant failed to form pink nitrogen-fixing nodules that occur in the wild-type symbiosis, but instead developed small bump-like nodules on its roots that were blocked at an early stage of development. Examination of the nip nodules by light microscopy after staining with X-Gal for S. meliloti expressing a constitutive GUS gene, by confocal microscopy following staining with SYTO-13, and by electron microscopy revealed that nip initiated symbiotic interactions and formed nodule primordia and infection threads. The infection threads in nip proliferated abnormally and very rarely deposited rhizobia into plant host cells; rhizobia failed to differentiate further in these cases. nip nodules contained autofluorescent cells and accumulated a brown pigment. Histochemical staining of nip nodules revealed this pigment to be polyphenolic accumulation. RNA blot analyses demonstrated that nip nodules expressed only a subset of genes associated with nodule organogenesis, as well as elevated expression of a host defense-associated phenylalanine ammonia lyase gene. nip plants were observed to have abnormal lateral roots. nip plant root growth and nodulation responded normally to ethylene inhibitors and precursors. Allelism tests showed that nip complements 14 other M. truncatula nodulation mutants but not latd, a mutant with a more severe nodulation phenotype as well as primary and lateral root defects. Thus, the nip mutant defines a new locus, NIP, required for appropriate infection thread development during invasion of the nascent nodule by rhizobia, normal lateral root elongation, and normal regulation of host defense-like responses during symbiotic interactions.

Alleles↗
PubMed2005

Does the presence of arbuscular mycorrhizal fungi influence growth and nutrient uptake of a wild-type tomato cultivar and a mycorrhiza-defective mutant, cultivated with roots sharing the same soil volume?

We investigated the growth and nutrient uptake of the Lycopersicon esculentum symbiosis mycorrhiza-defective plant mutant rmc, challenged with arbuscular mycorrhiza (AM) fungal propagules, in the presence or absence of roots of the commercial wild-type tomato cv. Golden Queen (GQ). Two plants shared the middle (combi) compartment of a horizontal three-compartment split-root pot with one part of their root system; the other part was grown separately in an outer (solo) pot. Combinations of rmc and GQ plants were grown together in soil that was either mycorrhiza-free (-M) or prepared with AM fungal inoculum (+M). Surface colonization of rmc roots was strongly increased in the presence of (+M) GQ roots. AM fungal inoculation increased phosphorus uptake of GQ plants, but decreased growth and P uptake of rmc plants. Growth and P uptake of (+M) GQ plants were reduced when plants were grown in combination with rmc rather than another GQ plant. AM fungi in the (combi) compartment may have preferentially formed hyphae spreading infection rather than functioning in P uptake in (+M) GQ plants grown in combination with rmc. Surface colonization of (+M) rmc roots, in the presence of GQ roots, was probably established at the expense of carbohydrates from associated GQ plants. Possible reasons for a decreased P uptake of rmc plants in response to AM fungal inoculation are proposed.

Solanum lycopersicum↗
PubMed1983

The central-peripheral transition zone of cervical spinal nerve roots in Jimpy mutant and normal mice. Light- and electron-microscopic study.

Comparative morphological and ultrastructural investigations on the cervical dorsal and ventral central-peripheral transition zones (CPTZs) of Jimpys and control mice have been performed at early and advanced myelination stages. After postnatal development a characteristic cone-shaped glial outgrowth extends into the proximal part of the dorsal roots, while the ventral roots exhibit short Schwann cell and peripheral nervous tissue invaginations into the spinal cord at the ventral root-spinal cord junction in both animal groups. In Jimpys, although there is marked central myelin deficiency and absence of oligodendroglial development on the CNS side, the normal general aspect of the CPTZs is maintained. Previously postulated astrocytic and neuroaxonal abnormalities in the mutants do not alter the central-peripheral borderline, and Schwann cell migration from the spinal nerve roots into the cord does not occur.

Animals↗
PubMed1987

Effects of Rhizobium meliloti nif and fix mutants on alfalfa root nodule development.

Ineffective alfalfa nodules were examined at the light and electron microscope level after inoculation with Rhizobium meliloti strains with mutations in nif and fix genes. All the mutant strains induced nodules that contained elongated bacteroids within the host cells, but the bacteroids quickly senesced. The nodules were small and numerous, and the host cells also exhibited symptoms of an ineffective symbiosis. nifB, fixA, and fixB bacteroids appeared to be completely differentiated (by ultrastructural criteria), i.e., as bacteroids developed, they increased in diameter and length and their cytoplasm underwent a change from homogeneous and electron dense to heterogeneous and electron transparent after enlargement. In contrast, nifA bacteroids rarely matured to this state. The bacteroids degenerated at an earlier stage of development and did not become electron transparent.

Medicago sativa↗
PubMed2004

Expression of KT/KUP genes in Arabidopsis and the role of root hairs in K+ uptake.

Potassium (K(+)) is the most abundant cation in plants and is required for plant growth. To ensure an adequate supply of K(+), plants have multiple mechanisms for uptake and translocation. However, relatively little is known about the physiological role of proteins encoded by a family of 13 genes, named AtKT/KUP, that are involved in K(+) transport and translocation. To begin to understand where and under what conditions these transporters function, we used reverse transcription-PCR to determine the spatial and temporal expression patterns of each AtKT/KUP gene across a range of organs and tested whether selected AtKT/KUP cDNAs function as K(+) transporters in Escherichia coli. Many AtKT/KUPs were expressed in roots, leaves, siliques, and flowers of plants grown under K(+)-sufficient conditions (1.75 mm KCl) in hydroponic culture. AtHAK5 was the only gene in this family that was up-regulated upon K(+) deprivation and rapidly down-regulated with resupply of K(+). Ten AtKT/KUPs were expressed in root hairs, but only five were expressed in root tip cells. This suggests an important role for root hairs in K(+) uptake. The growth and rubidium (Rb(+)) uptake of two root hair mutants, trh1-1 (tiny root hairs) and rhd6 (root hair defective), were studied to determine the contribution of root hairs to whole-plant K(+) status. Whole-plant biomass decreased in the root hair mutants only when K(+) concentrations were low; Rb(+) (used as a tracer for K(+)) uptake rates were lower in the mutants at all Rb(+) concentrations. Seven genes encoding AtKUP transporters were expressed in E. coli (AtKT3/KUP4, AtKT/KUP5, AtKT/KUP6, AtKT/KUP7, AtKT/KUP10, AtKT/KUP11, and AtHAK5), and their K(+) transport function was demonstrated.

Arabidopsis↗
PubMed1989

Reduced gravitropic sensitivity in roots of a starch-deficient mutant of Nicotiana sylvestris.

Gravitropism was studied in seedlings of Nicotiana sylvestris Speg. et Comes wild-type (WT) and mutant NS 458 which has a defective plastid phosphoglucomutase (EC 2.7.5.1.). Starch was greatly reduced in NS 458 compared to the WT, but small amounts of starch were detected in rootcap columella cells in NS 458 by light and electron microscopy. The roots of WT are more sensitive to gravity than mutant NS 458 roots since: (1) in mutant roots, curvature was reduced and delayed in the time course of curvature; (2) curvature of mutant roots was 24-56% that of WT roots over the range of induction periods tested; (3) in intermittent-stimulation experiments, curvature of mutant roots was 37% or less than that of WT roots in all treatments tested. The perception time, determined by intermittent-stimulation experiments, was < or = 5 s for WT roots and 30-60 s for mutant roots. The growth rates for WT and NS 458 roots were essentially equal. These results and our previous results with WT and starchless mutant Arabidopsis roots (Kiss et al. 1989, Planta 177, 198-206) support the conclusions that a full complement of starch is necessary for full gravitropic sensitivity and that amyloplasts function in gravity perception. Since a presumed relatively small increase in plastid buoyant mass (N. sylvestris mutant versus Arabidopsis mutant) significantly improves the orientation of the N. sylvestris mutant roots, we suggest that plastids are the likeliest candidates to be triggering gravity perception in roots of both mutants.

Gravitropism↗
PubMed1996

The effects of asymmetric calcium application on primary root curvature of ageotropum pea mutant.

Recent studies indicate that roots of ageotropum seedlings can be used to study the hydrotropic response of roots independent of physiological events related to the gravity response of roots. There is evidence that Ca2+ ions are important in both the gravitropic and hydrotropic response of roots. In this study, we have compared three fully graviresponsive pea cultivars and the ageotropum mutant with regard to: 1) general root anatomy, 2) the effects of unilateral Ca application to both the root cap and DEZ region on root curvature, and 4) effects of unilateral application of EGTA to the DEZ region.

Calcium↗
PubMed1984

Ultrastructure and movements of cell organelles in the root cap of agravitropic mutants and normal seedlings of Arabidopsis thaliana.

The root anatomy and ultrastructure of the agravitropic Arobidopsis thaliana L. mutants Dwf and aux-1 were compared with the gravitropic mutant aux-2 and the wild type (WT) in an attempt to find an explanation for the lack of response to gravity. No differences were found in the organization of the root cap. The central part of the cap (columella) contains 5 storeys of developing, functioning and degenerating statocytes. Their ultrastructure is very similar in all four types of plant. Particular attention was paid to the distribution of rough endoplasmic reticulum (ER). Both in the WT and the mutants the ER is concentrated in the distal part at the "floor" of the cell. Light micrographs were used to compare the sedimentation rates of movable cell structures in normal and agravitropic root statocytes. A longitudinal movement of amyloplasts and nuclei was observed when the roots were inverted. In WT and aux-2 the rates were on average 6.3 micrometers h-1 (amyloplasts) and 2.1 micrometers h-1 (nucleus). In aux-1 the sedimentation rates were significantly lower: 2.4 and 0.6 micrometers h-1, respectively. Based on magnified electron micrographs of normal and inverted statocytes a morphometrical analysis of the distribution and redistribution of amyloplasts, nuclei, mitochondria, vacuoles and ER was made. The only significant difference was found in the redistribution of amyloplasts between aux-1 and the gravitropical normal types.

Arabidopsis↗
PubMed1988

Molecular Studies on the Role of a Root Surface Agglutinin in Adherence and Colonization by Pseudomonas putida.

Pseudomonas putida aggressively colonizes root surfaces and is agglutinated by a root surface glycoprotein. Mutants of P. putida derived chemically or by Tn5 insertion demonstrated enhanced or decreased agglutinability. Two nonagglutinable Tn5 mutants (Agg) and two mutants with enhanced agglutinability (Agg) possessed Tn5 in unique restriction sites. Agg mutants colonized root surfaces of seedlings grown from inoculated seeds, but at levels lower than those observed with the Agg parent. In short-term binding studies, Agg cells adhered at levels that were 20- to 30-fold less than those for Agg parental cells. These data suggest that the agglutination interaction plays a role in the attachment of P. putida to root surfaces.

Journal Article↗
PubMed2002

Root, root hair, and symbiotic mutants of the model legume Lotus japonicus.

To gain an overview of plant factors controlling nodule number and organogenesis, an extensive screening using model legume Lotus japonicus was carried out. This screening involved 40,000 M2 seeds, and 32 stable mutant lines were isolated. From these, 16 mutant lines maintaining the phenotypic variation were selected and genetically analyzed. With respect to nodule number, four loci were identified, Ljsym77, Ljsym78, slippery root (slp), and radial organization1 (rdo1). The former two mutants have an increased number of nodules, while the latter two have a decreased number. Ljsym78-1 and Ljsym78-2 are hypernodulating mutants with a branched root system and were found to be allelic to Ljsym16. The phenotype of the Ljsym77 mutant was highly pleiotropic, being deficient in light and gravity responses. The slp mutant was isolated as a low-nodulating mutant lacking root hairs. Concerning nodule organogenesis, nine symbiotic loci were identified, including the two loci alb1 and fen1. Mutants affecting the developmental process of nodule organogenesis were placed in three phenotypic categories: Nod- (Ljsym70 to Ljsym73), Hist- (alb1-1, alb1-2, and Ljsym79), and Fix- (fen1, Ljsym75, and Ljsym81).

Ethyl Methanesulfonate↗
PubMed1970

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: I. Root Effect and Kinetin-like Activity.

The wilty tomato mutant, flacca, and the normal variety, Rheinlands Ruhm, were compared for kinetin-like activity in ontogeny. The mutant wilts easily because its stomata resist closure. This stomatal resistance decreases with age. The occurrence of a root factor which induces stomatal opening was inferred from grafting experiments. It was hypothesized that the excessive stomatal openings in the mutant may result from excess of kinetin-like activity in the leaf of that plant. In addition, it was suggested that the closure of stomata in the aging mutant is due to a decrease of kinetin-like activity with age. Kinetin-like activity in the leaf was determined by incorporation of labeled leucine. The concentration of cytokinins in root exudate and leaf extract was determined by the soybean callus assay. Evidence was presented of higher kinetin-like activity in the leaves of the mutant and higher cytokinin concentration in its root exudate. Cytokinin concentration in the shoot was found to be only slightly higher in the mutant than in the normal plants. Kinetin-like activity in the leaf and cytokinin concentration of root exudate decreased with age in both mutant and normal plants. Kinetin-like activity in the leaves of mutant plants, which phenocopy the normal variety as a result of continuous application of abscisic acid, was lower than in control mutant plants. The significance of these findings per se and in connection with stomatal behavior is discussed.

Journal Article↗
PubMed2007

Dissecting the biosynthetic pathway for the bypass1 root-derived signal.

The Arabidopsis BYPASS1 (BPS1) gene is required for normal root and shoot development. In bps1 mutants, grafting and root excision experiments have shown that mutant roots produce a transmissible signal that is capable of arresting shoot development. In addition, we previously showed that growth of bps1 mutants on the carotenoid biosynthesis inhibitor fluridone resulted in partial rescue of both leaf and root defects. These observations suggest that a single mobile carotenoid-derived signal affects both root and shoot development. Here, we describe further characterization of the bps1 root-derived signal using genetic and biosynthetic inhibitor approaches. We characterized leaf and root development in double mutants that combined the bps1 mutant with mutants that have known defects in genes encoding carotenoid processing enzymes or defects in responses to carotenoid-derived abscisic acid. Our studies indicate that the mobile signal is neither abscisic acid nor the MAX-dependent hormone that regulates shoot branching, and that production of the signal does not require the activity of any single carotenoid cleavage dioxygenase. In addition, our studies with CPTA, a lycopene cyclase inhibitor, show that signal production requires synthesis of beta-carotene and its derivatives. Furthermore, we show a direct requirement for carotenoids as signal precursors, as the GUN plastid-to-nucleus signaling pathway is not required for phenotypic rescue. Together, our results suggest that bps1 roots produce a novel mobile carotenoid-derived signaling compound.

Abscisic Acid↗
PubMed2002

The IRE gene encodes a protein kinase homologue and modulates root hair growth in Arabidopsis.

We identified an Arabidopsis mutant, incomplete root hair elongation (ire), whose root hairs are about 40% shorter than the wild type owing to the early cessation of their growth. In contrast, the hy5 mutant has root hairs about twice as long as the wild type, possibly because of delayed cessation of growth. Thus IRE and HY5 are likely to modify the duration of growth of root hairs. We cloned the IRE locus using the T-DNA tagged line. The IRE locus encodes a protein that includes a serine/threonine protein kinase domain. The primary structure of this kinase domain shows significant similarity to a group of protein kinases among various eukaryotes. In the Arabidopsis genome there are at least three genes that are closely related to IRE. The IRE transcript was detected in every organ examined. However, the IRE promoter-GUS fusion gene was strongly expressed in the elongating root hair cells, suggesting the cell-autonomous function of IRE in root hairs. GUS activity was also detected in pollen grains, which develop by tip growth, suggesting that IRE has a common role in the tip growth of plant cells.

Alleles↗
PubMed1998

Root-growth behavior of the Arabidopsis mutant rgr1. Roles of gravitropism and circumnutation in the waving/coiling phenomenon.

In this study we investigated the kinetics of the gravitropic response of the Arabidopsis mutant rgr1 (reduced root gravitropism). Although the rate of curvature in rgr1, which is allelic to axr4, was smaller than in the wild type (ecotype Wassilewskija), curvature was initiated in the same region of the root, the distal elongation zone. The time lag for the response was unaffected in the mutant; however, the gravitropic response of rgr1 contained a feature not found in the wild type: when roots growing along the surface of an agar plate were gravistimulated, there was often an upward curvature that initiated in the central elongation zone. Because this response was dependent on the tactile environment of the root, it most likely resulted from the superposition of the waving/coiling phenomenon onto the gravitropic response. We found that the frequency of the waving pattern and circumnutation, a cyclic endogenous pattern of root growth, was the same in rgr1 and in the wild type, so the waving/coiling phenomenon is likely governed by circumnutation patterns. The amplitudes of these oscillations may then be selectively amplified by tactile stimulation to provide a directional preference to the slanting.

Arabidopsis↗
PubMed1982

Quantitative light and electron microscopic studies on the ventral roots of the wobbler mutant mouse.

In wobbler mutant mice and normal litter-mates the numbers of axons have been counted in cervical and lumbar ventral roots and the dimensions of nerve fibres measured in the fifth cervical, C5, and third lumbar, L3, roots. In wobbler cervical ventral roots C5, C7 and C8 and lumbar roots L4 and L5 the number of axons was reduced. Abnormal features were seen in all mutant cervical ventral roots but not in the lumbar roots. The histogram of fibre size was shifted to the left in the wobbler C5 roots where axon loss was considerable, particularly amongst the large diameter axons, and in L3 roots where, although there was no over-all loss of axons, there were fewer ventral root fibres of large diameter. Abnormal features were also observed in a few dorsal root ganglion cells.

Animals↗