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PubMed1992

Nodules Initiated by Rhizobium meliloti Exopolysaccharide Mutants Lack a Discrete, Persistent Nodule Meristem.

Infection of alfalfa with Rhizobium meliloti exo mutants deficient in exopolysaccharide results in abnormal root nodules that are devoid of bacteria and fail to fix nitrogen. Here we report further characterization of these abnormal nodules. Tightly curled root hairs or shepherd's crooks were found after inoculation with Rm 1021-derived exo mutants, but curling was delayed compared with wild-type Rm 1021. Infection threads were initiated in curled root hairs by mutants as well as by wild-type R. meliloti, but the exo mutant-induced threads aborted within the peripheral cells of the developing nodule. Also, nodules elicited by Rm 1021-derived exo mutants were more likely to develop on secondary roots than on the primary root. In contrast with wild-type R. meliloti-induced nodules, the exo mutant-induced nodules lacked a well defined apical meristem, presumably due to the abortion of the infection threads. The relationship of these findings to the physiology of nodule development is discussed.

Journal Article↗

PubMed1992

A 126 bp fragment of a plant histone gene promoter confers preferential expression in meristems of transgenic Arabidopsis.

The tissue-specific pattern of expression directed by the H4A748 Arabidopsis histone promoter was investigated by analysis of beta-glucuronidase (GUS) activity in transgenic Arabidopsis containing H4A748-GUS gene fusions. As determined by fluorimetric and histochemical tests, the H4A748 promoter directs preferential expression in meristems of young seedlings and adult plants. The low activity found in nonproliferating tissues may relate to basal constitutive expression of the histone promoter and/or to endoreduplication occurring in some tissues. The endogenous histone mRNA levels parallel the GUS activity found in different tissues. Analysis of the regulatory properties of 5' deleted promoters showed that multiple positive elements exist between -900 and -219 and that the proximal region of the promoter to -219 is sufficient to establish the full tissue-specific pattern of expression. Further deletion to -93 nearly abolished the promoter activity thus suggesting that the 126 bp fragment located between -219 and -93 contains the elements responsible for the specific expression pattern. The presence of several remarkable sequences within this fragment is discussed.

Agrobacterium tumefaciens↗

PubMed1997

GENETICS OF ANGIOSPERM SHOOT APICAL MERISTEM DEVELOPMENT.

Recent progress has been made in the genetic dissection of angiosperm shoot apical meristem (SAM) structure and function. Genes required for proper SAM development have been identified in a variety of species through the isolation of mutants. In addition, genes with expression patterns indicating they play a role in SAM function have been identified molecularly. The processes of SAM formation, self-renewal, and pattern formation within the SAM are examined with an emphasis on the contributions of recent classical and molecular genetic experiments to our understanding of this basic problem in plant developmental biology.

Journal Article↗

PubMed1982

An unusual arrangement of smooth membranes in the root meristem cells of Allium cepa L. following exposure to colchicine.

The unusual membranes in the root meristem cells of Allium cepa after exposure to colchicine are arranged in a closed multilayered structure consisting of a pair of double unit membranes enclosing a ground substance which consists essentially of ribosomes. The spaces between the unit membranes and between the pairs of unit membranes are uniform throughout the entire organelle. There is some indication of the association of this organelle with mitochondria.

Colchicine↗

PubMed2004

INCOMPOSITA: a MADS-box gene controlling prophyll development and floral meristem identity in Antirrhinum.

INCOMPOSITA (INCO) is a MADS-box transcription factor and member of the functionally diverse StMADS11 clade of the MADS-box family. The most conspicuous feature of inco mutant flowers are prophylls initiated prior to first whorl sepals at lateral positions of the flower primordium. The developing prophylls physically interfere with subsequent floral organ development that results in aberrant floral architecture. INCO, which is controlled by SQUAMOSA, prevents prophyll formation in the wild type, a role that is novel among MADS-box proteins, and we discuss evolutionary implications of this function. Overexpression of INCO or SVP, a structurally related Arabidopsis MADS-box gene involved in the negative control of Arabidopsis flowering time, conditions delayed flowering in transgenic plants, suggesting that SVP and INCO have functions in common. Enhanced flowering of squamosa mutants in the inco mutant background corroborates this potential role of INCO as a floral repressor in Antirrhinum. One further, hitherto hidden, role of INCO is the positive control of Antirrhinum floral meristem identity. This is revealed by genetic interactions between inco and mutants of FLORICAULA, a gene that controls the inflorescence to floral transition, together with SQUAMOSA. The complex regulatory and combinatorial relations between INCO, FLORICAULA and SQUAMOSA are summarised in a model that integrates observations from molecular studies as well as analyses of expression patterns and genetic interactions.

Alleles↗

PubMed1995

Transposon induced chimeras show that floricaula, a meristem identity gene, acts non-autonomously between cell layers.

Flower meristems comprise several distinct cell layers. To understand the role of cell interactions between and within these layers, we have generated plants chimeric for a key floral homeotic gene, floricaula (flo). These chimeras arose in Antirrhinum by excision of a transposon, restoring flo gene function. Activity of flo in a subset of cell layers gives fertile flowers with an abnormal morphology. This shows that flo can act non-autonomously between layers, although some aspects of its function are impaired. In addition, we show that flo exhibits some cell-autonomy within layers.

Cell Communication↗

PubMed1995

Expression of floricaula in single cell layers of periclinal chimeras activates downstream homeotic genes in all layers of floral meristems.

We show that the flowering sectors on plants mutant for floricaula (flo), a meristem identity gene in Antirrhinum majus, are periclinal chimeras expressing flo in either the L1, L2 or L3 cell layer. Flower morphology is almost normal in L1 chimeras, but altered in L2 and L3 chimeras. Expression of flo in any one cell layer results in the expression of organ identity genes, deficiens (def) and plena (ple) in all three cell layers of the chimeras, showing that flo acts inductively to promote gene transcription. The activation of both def and ple is delayed, and the expression domain of def is reduced, accounting for some of the phenotypic properties of the chimeras. Furthermore, we show that flo exhibits some cell-autonomy with respect to autoregulation.

Amino Acid Sequence↗

PubMedDate not supplied

[Circadian rhythm of cell division and mitosis duration in the root meristem of the common pea under normal conditions and under the influence of thyroxine].

Daily rhythms of the mitotic activity (MA) and mitosis duration were studied in meristem of the Pisum sativum L. primary roots. It is determined that MA increases in the day time. The daily rhythm of mitosis duration is absent. The germination of Pisum sativum seeds in solution with 1-thyroxine revealed that thyroxine increases average diurnal MA and results in formation of two-phases rhythm of mitosis number. The additional (night) increase of MA is connected with prolongation of mitosis.

Circadian Rhythm↗

PubMed2001

Evaluation of cytogenetic effects of isoproturon on the root meristem cells of Allium sativum.

OBJECTIVE: To validate the use of Allium sativum as a reliable test model for genotoxicity, isoproturon, a substituted phenylalkylurea herbicide, was evaluated on the root meristem cells by this plant system. METHOD: Test concentrations were selected by determining EC50 and root tips were exposed to various concentrations for 6 or 24 hr. EC50 concentration was calculated to be 70. 8 ppm for the root growth. In addition to root growth retardation exposure to isoproturon induced morphological changes like discolouration and stiffness of roots. RESULTS: Exposure to various experimental concentrations of isoproturon (35-280 ppm), including EC50, significantly and dose-dependently inhibited the mitotic index and induced chromosome breaks/mitotic aberrations at 6 or 24 hr. CONCLUSION: The frequency of aberrations was found to be decreased in a dose dependent manner at 24 or 48 hr post exposure, however in comparison of control cells the frequency of aberrations was considerably high which indicates genotoxicity potentials of isoproturon. Further, present study also suggests that Allium sativum is a sensitive, efficient, and reliable test system for measuring the genotoxicity potential of environmental chemicals.

Chromosome Aberrations↗

PubMed1975

Formative effects of morphactin on the shoot apical meristem of flax (linum usitatissimum L.).

The effect of a morphactin -- CF1 -- (2-chloro-9-hydroxyfluorene-9-carbocylic acid-methyl ester) on the morphogenesis of shoot apical meristem was studied on L. usitatissimum L. at three levels of supply. CF1 at 10 and 100 parts/10(6) induced repeated gamophylly resembling a concentric cupulate structure. GA3 superimposed at two levels viz. 10 and 100 parts/10(6) did not reverse this effect. The effect of CF1 is dose-dependent and reversal to normal behaviour occurs when the effect of CF1 wears off.

Carboxylic Acids↗

PubMed1976

[Cytotoxicity of cadmium : study on root meristems of Allium sativum L].

Cadmium nitrate, acetate and sulphate cause death of root meristems of Allium sativum at 5.10(-7) Mol/ml concentration for the two first ones and 10(-7) Mol/ml for the last one. Lower concentrations do not induce chromosomal aberrations. As to the cellular toxicity, cadmium salts are between phenyl-mercuric-hydroxid and lead nitrate, the first one being the most active.

Cadmium↗

PubMed2004

[Wheat germ agglutinin participates in regulation of cell division in apical root meristem of wheat seedlings].

A study was made of cell division activity and hormonal status in roots of 4 day old wheat seedling treated with wheat germ agglutinin (WGA). The revealed stimulating effect of WGA on mitotic index (MI) and cell area in root extension zone was specific for this lectin, because gliadin, taken as a control protein, caused no changes in growth parameters. Phytolectins (phytohemagglutinin and concanavalin A) possessing properties of mitogens rendered no such essential influence on cell growth of wheat. Immunoassay has shown that WGA-treatment leads to accumulation of auxins and cytokinins in roots. This suggest participation of WGA in regulation of MI of meristem cells in roots of seedlings during their interaction with phytohormones.

Cell Division↗

PubMedDate not supplied

[The cytogenetic effect of chronic irradiation revealed using an analysis of the first two mitoses in the root meristem of germinating seeds of Crepis tectorum from the 30-kilometer zone of the accident at the Chernobyl Nuclear Power Station].

Peculiarities of the appearance of C. tectorum rootlet in the course of seed germination have prompted the authors to use the method of continuous germination of seeds in 0.01% colchicine solution and to analyze chromosome aberrations in the first tetraploid cells derived from early dividing cells. Since it has been shown that cells of the embryo's root meristem of dormant Crepis tectorum seeds are at the G1 stage, the observed, by the method used, chromatid aberrations in the cells that early enter mitosis, are probably induced by the incorporated radioactive products at stages S and (or) G2 during seed germination.

Accidents↗

PubMed1989

The lack of correlation between the rate of rRNA transport from nucleoli into cytoplasm and the duration of G1 and G2 phases in root meristem cells.

In root meristems of 3 species (Secale cereale L., Vicia faba L. subsp. minor, Allium cepa L.) the durations of cell cycles and their phases were calculated using 3H-thymidine labelling. In the above species and in Helianthus annuus L. (parameters of the cell cycle determined earlier) the G1 and G2 phase durations were different: G1 + 1/2 M from 3 h to 6.1 h, G2 + 1/2 M from 1.1. h to 8.3 h, depending on the species. The rate of rRNA transport from nucleoli into cytoplasm during recovery after cold treatment was calculated from our data presented earlier. The results indicate that in 4 species studied there is no correlation (at P = 0.05) between the rate of rRNA transport and the duration of G1 and G2 phases.

Cell Cycle↗

PubMed1981

Coupling of replication, transcription and translation under two different steady state conditions in Allium cepa meristems.

Replication, transcription and translation rates have been analysed in root meristems of Allium cepa L. growing under two different steady conditions (10 and 25 degrees C). Cell size and the relative duration of cycle compartments are similar for both steady states, while cycle time is four times longer at the lower temperature. Though replication and translation rates per cycle are similar, at the lower temperature there is a doubling in the production of rRNA which coincides with the presence of enlarged nucleoli. There is some reduction in the maturation efficiency of this over-produced rRNA, and both the number and the efficiency of ribosomes in protein synthesis are also decreased. Hence, regulation in the post-transcriptional processes accounts for the similar protein production per genome in these two cycles.

Cell Cycle↗

PubMed1980

Observations on pre-prophase bands of microtubules in uniseriate hairs, stomatal complexes of sugar cane, and Cyperus root meristems.

Three aspects of the location and properties of pre-prophase bands of microtubules inplant tissues were examined. (i) Anatomical locations: Pre-prophase bands were found preceding mitosis in the basal meristematic cell of uniseriate hairs in Salvinia auriculata and in intercalary dividing cells in the uniseriate hairs of Tradescantia stamens. Previously they had only been found in 2- or 3-dimensional aggregates of cells. Other new locations were Tradescantia stamen filaments, and periclinal and anticlinal divisions in root and root cap meristems of Cuperus eragrostis. (ii) Prediction of the site of cytokinesis: Developing stomatal complexes of Saccharum officinarum were examined in view of recent reports that guard mother cells in this plant violate the otherwise general rule that the pre-prophase band predicts the line of fusion of the cell plate and the parental wall. The generality of the prediction phenomenon was upheld. (iii) Bisection of pre-prophase band sites: Evidence that the site of the pre-prophase band in the cell cortex is (at least approximately) bisected at cytokinesis was obtained for asymmetrical divisions in Cyperus roots, stomatal complexes of Saccharum, and Salvinia hairs, and symmetrical divisions in Tradescantia stamen hairs and Saccharum guard mother cells. The observations are discussed with particular reference to possible roles of the pre-prophase band site after its microtubules have disappeared at prophase.

Cell Cycle↗

PubMed1975

[Cytotoxicity of aurintricarboxylic acid: inhibition of cell proliferation and of protein synthesis in Allium sativum L. root meristems].

The inhibitory action of aurine-tricarboxylic acid (ATA) on protein synthesis, known in vitro, has been checked in vivo in Allium sativum L. root meristems. Parallel to this inhibition, ATA acts on cell proliferation, on the one hand by preventing the entering of cells into prophase and, on the other hand, by disturbing the process of mitosis.

Aurintricarboxylic Acid↗

PubMed1997

Monoclonal antibody raised against human mitotic cyclin B1, identifies cyclin B-like mitotic proteins in synchronized onion (Allium cepa L.) root meristem.

Cyclin B-like mitotic proteins have been detected in synchronized Allium cepa L. root tip cells by using mouse monoclonal anti-cyclin B1 antibody raised against human cyclin B1. Immunoblot shows two closely placed isoforms of cyclin B-like proteins having an apparent molecular weight around 54 kDa. In vivo [35S]-methionine labelling followed by immunoprecipitation and autoradiography indicates that cyclin B-like proteins are mainly synthesized in the G2 phase of the cell cycle and destroyed in late mitosis. Immunoblotting data depict that the level of cyclin B-like proteins reaches the maximum at the late G2 to early M phase; and it becomes degraded in the late hours of mitosis. Moreover, the cyclin B isoforms are stabilized in colchicine-arrested metaphase cells as already reported in animal cells.

Allium↗