RESUMEN
Although many molecular regulators of morphogenesis have been identified in plants, it remains largely unknown how the molecular networks influence local cell shape and how cell growth, form, and position are coordinated during tissue and organ formations. So far, analyses of gene function in morphogenesis have mainly focused on the qualitative analysis of phenotypes, often providing limited mechanistic insight into how particular factors act. For this reason, there has been a growing interest in mathematical and computational models to formalize and test hypotheses. These require much more rigorous, quantitative approaches; in parallel, new quantitative and correlative imaging pipelines have been developed to study morphogenesis. Here, we describe a number of such methods, focusing on live imaging.
Asunto(s)
Biología Computacional/métodos , Morfogénesis/genética , Células Vegetales , Desarrollo de la Planta/genética , Forma de la Célula/genética , Pared Celular/genética , Modelos TeóricosRESUMEN
Microtubules are highly dynamic structures that play a major role in a wide range of processes, including cell morphogenesis, cell division, intracellular transport and signaling. The recent identification in plants of proteins involved in microtubule organization has begun to reveal how cytoskeleton dynamics are controlled.
Asunto(s)
Magnoliopsida/fisiología , Proteínas Asociadas a Microtúbulos/fisiología , Microtúbulos/fisiología , Calcio/metabolismo , División Celular , Citoesqueleto/fisiología , Magnoliopsida/genética , Magnoliopsida/metabolismo , Proteínas Asociadas a Microtúbulos/genética , Centro Organizador de los Microtúbulos/fisiología , Microtúbulos/genética , Proteínas Motoras Moleculares , Morfogénesis , Transducción de Señal , Tubulina (Proteína)/genética , Tubulina (Proteína)/fisiologíaRESUMEN
Shoot apical meristems are composed of proliferating, embryonic type cells, that generate tissues and organs throughout the life of the plant. This review covers the cell biology of the higher plant shoot apical meristem (SAM). The first section describes the molecular basis of plant cell growth and division. The genetic mechanisms, that operate in meristem function and the identification of several key regulators of meristem behavior are described in the second section, and intercellular communication and coordination of cellular behavior in the third part. Finally, we discuss some recent results that indicate interaction between the cellular regulators, such as the cell cycle control genes and developmental regulators.
Asunto(s)
Regulación de la Expresión Génica de las Plantas/fisiología , Meristema/crecimiento & desarrollo , Brotes de la Planta/crecimiento & desarrollo , Diferenciación Celular/fisiología , División Celular/fisiología , Pared Celular/metabolismo , Ciclinas/metabolismo , Meristema/metabolismo , Meristema/ultraestructura , Reguladores del Crecimiento de las Plantas/metabolismo , Brotes de la Planta/metabolismo , Brotes de la Planta/ultraestructuraRESUMEN
The KNAT2 (for KNOTTED-like from Arabidopsis thaliana 2) homeobox gene is expressed in the vegetative apical meristem. It is also active during flower development, suggesting a function in the structuring of flowers. To investigate its role, we used a DEXAMETHASONE (DEX)-inducible system to generate transgenic plants that overexpressed a fusion of KNAT2 with the hormone binding domain of the glucocorticoid receptor. DEX-induced plants were similar to plants overexpressing the closely related KNAT1 gene, indicating overlapping functions, although we observed differences as well. In particular, KNAT2-GR activation induced ectopic carpel features. First, KNAT2 induced the homeotic conversion of nucellus into carpel-like structures. Second, KNAT2 induced stigmatic papillae on rosette leaves in the ap2-5 background. Third, ectopic expression of the carpel identity gene AGAMOUS (AG) was observed in carpels and ovules. Interestingly, the homeotic conversion was not dependent on AG activity, because it was maintained in the ag-1 ap2-5 double mutant. Therefore, our data indicate that KNAT2 also must activate other carpel regulators. Together, these results suggest that KNAT2 plays a role in carpel development.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis/genética , Proteínas de Homeodominio/genética , Proteínas de Plantas/genética , Arabidopsis/crecimiento & desarrollo , Arabidopsis/ultraestructura , Dexametasona/farmacología , Regulación de la Expresión Génica de las Plantas , Microscopía Confocal , Microscopía Electrónica de Rastreo , Datos de Secuencia Molecular , Estructuras de las Plantas/crecimiento & desarrollo , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Plantas Modificadas Genéticamente/ultraestructura , beta-Galactosidasa/genéticaRESUMEN
The shoot apical meristem is a group of rapidly dividing cells that generate all aerial parts of the plant. It is a highly organised structure, which can be divided into functionally distinct domains, characterised by specific proliferation rates of the individual cells. Genetic studies have enabled the identification of regulators of meristem function. These factors are involved in the formation and maintenance of the meristem, as well as in the formation of the primordia. Somehow, they must also govern cell proliferation rates within the shoot apex. Possible links between meristem regulators and the cell cycle machinery will be discussed. In order to analyse the role of cell proliferation in development, cell cycle gene expression has been perturbed using transgenic approaches and mutation. The effect of these alterations on growth and development at the shoot apex will be presented. Together, these studies give a first insight into the regulatory networks controlling the cell cycle and into the significance of cell proliferation in plant development.
Asunto(s)
Genes de Plantas , Células Vegetales , Brotes de la Planta/citología , División Celular , Regulación del Desarrollo de la Expresión Génica , Meristema/citología , Meristema/genética , Mutación , Desarrollo de la Planta , Brotes de la Planta/genética , Plantas/genéticaRESUMEN
The process of organ positioning has been addressed, using the pin-formed 1 (pin1) mutant as a tool. PIN1 is a transmembrane protein involved in auxin transport in Arabidopsis. Loss of function severely affects organ initiation, and pin1 mutants are characterised by an inflorescence meristem that does not initiate any flowers, resulting in the formation of a naked inflorescence stem. This phenotype, combined with the proposed role of PIN1 in hormone transport, makes the mutant an ideal tool to study organ formation and phyllotaxis, and here we present a detailed analysis of the molecular modifications at the shoot apex caused by the mutation. We show that meristem structure and function are not severely affected in the mutant. Major alterations, however, are observed at the periphery of the pin1 meristem, where organ initiation should occur. Although two very early markers of organ initiation, LEAFY and AINTEGUMENTA, are expressed at the periphery of the mutant meristem, the cells are not recruited into distinct primordia. Instead a ring-like domain expressing those primordium specific genes is observed around the meristem. This ring-like domain also expresses a boundary marker, CUP-SHAPED COTYLEDON 2, involved in organ separation, showing that the zone at the meristem periphery has a hybrid identity. This implies that PIN1 is not only involved in organ outgrowth, but that it is also necessary for organ separation and positioning. A model is presented in which PIN1 and the local distribution of auxin control phyllotaxis.
Asunto(s)
Proteínas de Arabidopsis , Proteínas Portadoras/fisiología , Proteínas de la Membrana/fisiología , Proteínas de Transporte de Membrana , Proteínas de Plantas/fisiología , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Arabidopsis/fisiología , Proteínas Portadoras/genética , Diferenciación Celular , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Proteínas de la Membrana/genética , Meristema , Mutagénesis , Proteínas de Plantas/genética , Brotes de la Planta , Regulación hacia ArribaRESUMEN
We have previously shown that endoreduplication levels in hypocotyls of Arabidopsis thaliana (L.) Heynh. are under negative control of phytochromes. In this study, the hormonal regulation of this process was analysed using a collection of A. thaliana mutants. The results show that two hormones in particular, gibberellin (GA) and ethylene, play distinct roles. Hypocotyl cells of the GA-deficient mutant ga1-11 grown in the dark did not elongate and showed a greatly reduced endoreduplication. Normal endoreduplication could be restored by supplying 10(-9) M of the gibberellin GA(4+7), whereas the restoration of normal cell growth required 100-fold higher concentrations. The GA-insensitive mutant gai showed reduced cell elongation but normal ploidy levels. We conclude that (i) GA(4+7) has a global positive effect on endoreduplication and (ii) that endoreduplication is more sensitive to GA(4+7) than cell elongation. Ethylene had a completely different effect. It induced an extra round of endoreduplication both in light- and dark-grown seedlings and acted mainly on discrete steps rather than having a global effect on endoreduplication. The genes EIN2 and CTR1, components of the ethylene signal transduction pathway were both involved in this process.
Asunto(s)
Arabidopsis/fisiología , Etilenos/metabolismo , Giberelinas/metabolismo , Hipocótilo/fisiología , Arabidopsis/crecimiento & desarrollo , ADN/análisis , ADN/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Etilenos/farmacología , Citometría de Flujo , Genes de Plantas , Giberelinas/farmacología , Hipocótilo/crecimiento & desarrollo , Luz , Fenómenos Fisiológicos de las PlantasRESUMEN
T-DNA integration in the nuclear plant genome may lead to rearrangements of the plant target site. Here we present evidence for a chromosomal inversion of 26 cM bordered by two T-DNAs in direct orientation, which is linked to the mgoun2 mutation. The integration sites of the T-DNAs map at positions 80 and 106 of chromosome I and we show that each T-DNA is bordered by plant sequences from positions 80 and 106, respectively. Although the T-DNAs are physically distant, they are genetically closely linked. In addition, three markers located on the chromosome segment between the two T-DNA integration sites show no recombination with the mgo2 mutation. We show that the inversion cannot be a consequence of a recombination event between the two T-DNAs, but that the integration of the T-DNAs and the inversion were two temporally linked events. T-DNA integration mechanisms that could have led to this inversion are discussed.
Asunto(s)
Arabidopsis/genética , Inversión Cromosómica , Cromosomas , ADN Bacteriano/genética , Ligamiento Genético , Marcadores Genéticos , Heterocigoto , Mutación , Proteínas de Plantas/genética , Recombinación GenéticaRESUMEN
The shoot apical meristem (SAM) is a small group of dividing cells that generate all of the aerial parts of the plant. With the goal of providing a framework for the analysis of Arabidopsis meristems at the cellular level, we performed a detailed morphometric study of actively growing inflorescence apices of the Landsberg erecta and Wassilewskija ecotypes. For this purpose, cell size, spatial distribution of mitotic cells, and the mitotic index were determined in a series of optical sections made with a confocal laser scanning microscope. The results allowed us to identify zones within the inflorescence SAM with different cell proliferation rates. In particular, we were able to define a central area that was four to six cells wide and had a low mitotic index. We used this technique to compare the meristem of the wild type with the enlarged meristems of two mutants, clavata3-1 (clv3-1) and mgoun2 (mgo2). One of the proposed functions of the CLV genes is to limit cell division rates in the center of the meristem. Our data allowed us to reject this hypothesis, because the mitotic index was reduced in the inflorescence meristem of the clv3-1 mutant. We also observed a large zone of slowly dividing cells in meristems of clv3-1 seedlings. This zone was not detectable in the wild type. These results suggest that the central area is increased in size in the mutant meristem, which is in line with the hypothesis that the CLV3 gene is necessary for the transition of cells from the central to the peripheral zone. Genetic and microscopic analyses suggest that mgo2 is impaired in the production of primordia, and we previously proposed that the increased size of the mgo2 meristem could be due to an accumulation of cells at the periphery. Our morphometric analysis showed that mgo2 meristems, in contrast to those of clv3-1, have an enlarged periphery with high cell proliferation rates. This confirms that clv3-1 and mgo2 lead to meristem overgrowth by affecting different aspects of meristem function.
Asunto(s)
Arabidopsis/citología , Meristema/citología , Arabidopsis/ultraestructura , Meristema/ultraestructura , Microscopía Electrónica de Rastreo , MitosisRESUMEN
A majority of the cells in the Arabidopsis hypocotyl undergo endoreduplication. The number of endocycles in this organ is partially controlled by light. Up to two cycles occur in light-grown hypocotyls, whereas in the dark about 30% of the cells go through a third cycle. Is the inhibition of the third endocycle in the light an indirect result of the reduced cell size in the light-grown hypocotyl, or is it under independent light control? To address this question, the authors examined the temporal and spacial patterns of endoreduplication in light- or dark-grown plants and report here on the following observations: (i) during germination two endocycles take place prior to any significant cell expansion; (ii) in the dark the third cycle is completed very early during cell growth; and (iii) a mutation that dramatically reduces cell size does not interfere with the third endocycle. The authors then used mutants to study the way light controls the third endocycle and found that the third endocycle is completely suppressed in far red light through the action of phytochrome A and, to a lesser extent, in red light by phytochrome B. Furthermore, no 16C nuclei were observed in dark-grown constitutive photomorphogenic 1 seedlings. And, finally the hypocotyl of the cryptochrome mutant, hy4, grown in blue light was about three times longer than that of the wild-type without a significant difference in ploidy levels. Together, the results support the view that the inhibition of the third endocycle in light-grown hypocotyls is not the consequence of a simple feed-back mechanism coupling the number of cycles to the cell volume, but an integral part of the phytochrome-controlled photomorphogenic program.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis/genética , Arabidopsis/fisiología , Fitocromo/fisiología , Ubiquitina-Proteína Ligasas , Arabidopsis/citología , Proteínas Portadoras/genética , Proteínas Portadoras/fisiología , Citocromos/genética , Citocromos/fisiología , ADN de Plantas/genética , Oscuridad , Retroalimentación , Amplificación de Genes , Genoma de Planta , Hipocótilo/citología , Hipocótilo/genética , Hipocótilo/fisiología , Luz , Mutación , Fitocromo/genética , Proteínas de Plantas/genética , Proteínas de Plantas/fisiología , PloidiasRESUMEN
We report two new recessive mutations in Arabidopsis, mgoun1 and mgoun2 which cause a reduction in the number of leaves and floral organs, larger meristems and fasciation of the inflorescence stem. Although meristem structure is affected in the mutants, we provide evidence that its overall organisation is normal, as shown by the expression patterns of two meristem markers. Microscopical analyses suggest that both mutations affect organ primordia production. mgo1 strongly inhibits leaf production in a weak allele of shoot meristemless, stm-2. In addition, mgo1 and 2 severely reduce the ability of the fasciata1 and 2 mutants to initiate organs, although meristem formation per se was not inhibited. The strong allele, stm-5, is epistatic to mgo1, showing that the presence of meristematic cells is essential for MGO1 function. These results suggest a role for the MGO genes in primordia initiation although a more general role in meristem function can not be excluded. We describe a form of fasciation which is radically different from that described for clavata, which is thought to have an increased size of the meristem centre. Instead of one enlarged central meristem mgo1 and 2 show a continuous fragmentation of the shoot apex into multiple meristems, which leads to the formation of many extra branches. The phenotype of mgo1 clv3 and mgo2 clv3 double mutants suggest that the MGO and CLV genes are involved in different events. In conclusion, our results reveal two new components of the regulatory network controlling meristem function and primordia formation. A model for MGO genes is discussed.
Asunto(s)
Arabidopsis/genética , Regulación del Desarrollo de la Expresión Génica/genética , Genes de Plantas/genética , Meristema/crecimiento & desarrollo , Regulación de la Expresión Génica de las Plantas , Genes Recesivos/genética , Microscopía Confocal , Microscopía Electrónica de Rastreo , Mutación/genética , Fenotipo , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/ultraestructuraRESUMEN
Endoreduplication, a strategy to amplify nuclear DNA without cell division, is very common but poorly understood in plants. Recent findings in Drosophila provide a first picture of the molecular mechanism, which appears to be conserved between plants and animals. In Arabidopsis, the study of trichomes, leaf epidermis and hypocotyl cells sheds new light on the developmental regulation of this process, and its relation to cell expansion.
Asunto(s)
Arabidopsis/genética , Replicación del ADN , Drosophila/genética , Mitosis/genética , Animales , Arabidopsis/citología , Arabidopsis/crecimiento & desarrollo , Drosophila/citología , Drosophila/crecimiento & desarrollo , PloidiasRESUMEN
The Arabidopsis thaliana hypocotyl is widely used to study the effects of light and plant growth factors on cell elongation. To provide a framework for the molecular-genetic analysis of cell elongation in this organ, here we describe, at the cellular level, its morphology and growth and identify a number of characteristic, developmental differences between light-grown and dark-grown hypocotyls. First, in the light epidermal cells show a characteristic differentiation that is not observed in the dark. Second, elongation growth of this organ does not involve significant cortical or epidermal cell divisions. However, endoreduplication occurs, as revealed by the presence of 4C and 8C nuclei. In addition, 16C nuclei were found specifically in dark-grown seedlings. Third, in the dark epidermal cells elongate along a steep, acropetal spatial and temporal gradient along the hypocotyl. In contrast, in the light all epidermal cells elongated continuously during the entire growth period. These morphological and physiological differences, in combination with previously reported genetic data (T. Desnos, V. Orbovic, C. Bellini, J. Kronenberger, M. Caboche, J. Traas, H. Höfte [1996] Development 122: 683-693), illustrate that light does not simply inhibit hypocotyl growth in a cell-autonomous fashion, but that the observed growth response to light is a part of an integrated developmental change throughout the elongating organ.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Arabidopsis/citología , Arabidopsis/efectos de la radiación , Diferenciación Celular/efectos de la radiación , División Celular/efectos de la radiación , Cotiledón/citología , Cotiledón/crecimiento & desarrollo , Cotiledón/efectos de la radiación , Oscuridad , Cinética , Luz , Microscopía Electrónica de RastreoRESUMEN
A polyclonal antiserum against the p34cdc2 homologue of Arabidopsis thaliana, CDC2aAt, was used in parallel with a polyclonal antiserum against the PSTAIRE motif to study the subcellular localization of CDC2 during the cell cycle of isolated root tip cells of Medicago sativa. During interphase, CDC2 was located in the nucleus and in the cytoplasm. The cytoplasmic localization persisted during the complete cell cycle, whereas the nuclear signal disappeared at nuclear envelope breakdown. At the beginning of anaphase, the anti-CDC2aAt antibody transiently co-localized with condensed chromosomes. The chromosomal co-localization disappeared as anaphase continued and remained excluded from the separated chromosomes until cytokinesis, when CDC2 re-located to the newly forming nuclei. We also observed a co-localization of CDC2 with three microtubular structures, the pre-prophase band, the spindle, and the phragmoplast.
Asunto(s)
Arabidopsis/enzimología , Proteína Quinasa CDC2/metabolismo , Proteínas de Plantas/metabolismo , Arabidopsis/citología , Ciclo Celular , CromosomasRESUMEN
We report here the isolation and characterization of the nucMs1 alfalfa cDNA, whose predicted amino acid sequence structurally resembles the yeast Nsr1 protein and animal nucleolins. These proteins consist of an N-terminal acidic domain, centrally located RNA recognition motifs (RRMs), and a C-terminal glycine- and arginine-rich domain. In comparison with animal nucleolins that contain four RRMs, NucMs1 more closely resembles the yeast Nsr1 protein, which contains only two RRMs. A NucMs1 C-terminal peptide antibody specifically recognized a 95-kD nucleolar protein in alfalfa cells that changed its localization in a cell cycle-dependent manner. The nucMs1 transcript and p95nucMs1 protein levels correlated with cell proliferation, and nucMs1 gene expression was found to be induced in the G1 phase upon mitogenic stimulation of G0-arrested leaf cells. In situ hybridization analysis of different alfalfa organs during various developmental stages showed that nucMs1 gene expression is highest in root meristematic cells, but it is also found in other meristematic cells of the plant body. nucMs1 expression is tightly linked to cell proliferation but does not depend on a particular cell cycle phase. No nucMs1 expression was observed in cells that had exited the cell cycle and were undergoing differentiation or polar growth, indicating that nucMs1 may not be necessary for processes other than cell proliferation.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Ciclo Celular/fisiología , Proteínas Fúngicas/metabolismo , Medicago sativa/fisiología , Proteínas Nucleares/metabolismo , Fosfoproteínas/metabolismo , Proteínas de Plantas/metabolismo , Proteínas de Unión al ARN , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/fisiología , Animales , Secuencia de Bases , Proteínas de Ciclo Celular/biosíntesis , División Celular , Nucléolo Celular/fisiología , Biblioteca de Genes , Homeostasis , Mamíferos , Medicago sativa/genética , Datos de Secuencia Molecular , Proteínas Nucleares/biosíntesis , Oligodesoxirribonucleótidos , Fosfoproteínas/biosíntesis , Proteínas de Plantas/biosíntesis , Saccharomyces cerevisiae/genética , Transcripción Genética , NucleolinaRESUMEN
Plant morphogenesis is dependent on a tight control of cell division and expansion. Cell elongation during post-embryonic hypocotyl growth is under the control of a light-regulated developmental switch. Light is generally believed to exert its effects on hypocotyl elongation through a phytochrome-and blue-light receptor-mediated inhibitory action on a so far unknown cell elongation mechanism. We describe here a new class of allelic mutants in Arabidopsis, at the locus PROCUSTE1 (prc1-1 to -4), which have a hypocotyl elongation defect specifically associated with the dark-grown development program. Normal hypocotyl elongation is restored in plants grown in white, blue or red light. In agreement with this, the constitutive photomorphogenic mutation cop1-6, which induces a de-etiolated phenotype in the dark, is epistatic to prc1-2 for the hypocotyl phenotype. Epistasis analyses in red and blue light respectively, indicate that phytochrome B but not the blue light receptor HY4, is required for the switch from PRC1-dependent to PRC1-independent elongation. The conditional hypocotyl growth defect is associated with a deformation of the hypocotyl surface due to an uncontrolled swelling of epidermal, cortical or endodermal cells, suggesting a defect in the structure of the expanding cell wall. A similar phenotype was observed in elongating roots, which was however, independent of the light conditions. The aerial part of mature mutant plants grown in the light was indistinguishable from the wild type. prc1 mutants provide a means of distinguishing, for the first time, two genetic pathways regulating hypocotyl cell elongation respectively in dark- and light-grown seedlings, whereby light not only inhibits hypocotyl growth, but also activates a PRC1-independent cell elongation program.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Arabidopsis/genética , Genes de Plantas , Alelos , Arabidopsis/ultraestructura , Cruzamientos Genéticos , Oscuridad , Prueba de Complementación Genética , Homocigoto , Hipocótilo/ultraestructura , Luz , Microscopía Electrónica de Rastreo , Morfogénesis , Mutación , FenotipoRESUMEN
We have identified an Arabidopsis thaliana CDC48 gene which, unlike the putative mammalian homologue vasolin-containing protein (VCP), functionally complements Saccharomyces cerevisiae cdc48 mutants. CDC48 is an essential gene in S. cerevisiae and genetic studies suggest a role in spindle pole body separation. Biochemical studies link VCP function to membrane trafficking and signal transduction. We have described the AtCDC48 expression pattern in a multicellular eukaryote; the zones of cell division, expansion and differentiation are physically separated in higher plants, thus allowing the analysis of in situ expression patterns with respect to the state of cell proliferation. AtCDC48 is highly expressed in the proliferating cells of the vegetative shoot, root, floral inflorescence and flowers, and in rapidly growing cells. AtCDC48 mRNA and the encoded protein are up-regulated in the developing microspores and ovules. AtCDC48 expression is down-regulated in most differentiated cell types. AtCDC48p was primarily localized to the nucleus and, during cytokinesis, to the phragmoplast, a site where membrane vesicles are targeted in the deposition of new cell wall materials. This study shows that the essential cell division function of CDC48 has been conserved by, at least, some multicellular eukaryotes and suggests that in higher plants, CDC48 functions in cell division and growth processes.
Asunto(s)
Arabidopsis/genética , Proteínas de Ciclo Celular/genética , Proteínas de Plantas/genética , Adenosina Trifosfatasas , Secuencia de Aminoácidos , Animales , Arabidopsis/citología , Arabidopsis/metabolismo , Secuencia de Bases , Proteínas de Ciclo Celular/química , Proteínas de Ciclo Celular/metabolismo , División Celular/genética , ADN de Plantas , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Immunoblotting , Datos de Secuencia Molecular , Proteínas de Plantas/metabolismo , Proteínas de Saccharomyces cerevisiae , Homología de Secuencia de Aminoácido , Proteína que Contiene ValosinaRESUMEN
Type 1 protein phosphatases are very highly conserved throughout eukaryotes where they regulate a number of key metabolic and morphogenetic processes. A cDNA, AtPP1bg, representing a new member of the type 1 protein phosphatase gene family in Arabidopsis has been isolated on the basis of hybridization with the Aspergillus bimG protein phosphatase gene. The AtPP1bg gene potentially encodes a 37 kDa protein very closely related to PP1 but with divergent N- and C-termini. The predicted amino acid sequence shows 71% identity to the ORF of the bimG gene. When expressed in Aspergillus under the alcA promoter, this phosphatase complements the temperature-sensitive bimG11 mutation allowing nearly normal vegetative growth at 37 degrees C (but not at 42 degrees C). Notably, the plant PP1 does not support morphogenesis (conidiation) at 37 degrees C. This may indicate that conidophore formation has particular phosphatase requirement(s) which the plant PP1 cannot supply. The pattern of expression of the AtPP1bg transcript has been studied during development of the plant. In situ hybridization of Arabidopsis with antisense probes shows that this phosphatase gene is expressed at a low level throughout the plant, but is strongly upregulated within developing flowers, especially in the tapetum, the developing and mature pollen and in the ovaries. This implies that the AtPP1bg either has a specialized role in the formation of these organs, or that there is an increased requirement for protein phosphatase 1 at these stages. It was found that the level of AtPP1bg transcript, as judged by the relative intensity of staining in different cells within the floral meristems, did not vary during the cell cycle.
Asunto(s)
Arabidopsis/enzimología , Aspergillus/genética , Ciclo Celular/genética , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Fosfoproteínas Fosfatasas/biosíntesis , Proteínas de Plantas/biosíntesis , Proteínas Recombinantes de Fusión/metabolismo , Secuencia de Aminoácidos , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Aspergillus/crecimiento & desarrollo , Secuencia de Bases , ADN Complementario/genética , ADN de Plantas/genética , Inducción Enzimática , Proteínas Fúngicas/genética , Prueba de Complementación Genética , Hibridación in Situ , Datos de Secuencia Molecular , Oocitos/metabolismo , Fosfoproteínas Fosfatasas/genética , Proteínas de Plantas/genética , Polen/metabolismo , Proteína Fosfatasa 1 , Alineación de Secuencia , Homología de Secuencia de Aminoácido , TemperaturaRESUMEN
We have studied the F-actin network in cycling suspension culture cells of carrot (Daucus carota L.) using rhodaminyl lysine phallotoxin (RLP). In addition to conventional fixation with formaldehyde, we have used two different nonfixation methods before adding RLP: extracting cells in a stabilizing buffer; inducing transient pores in the plasma membrane with pulses of direct current (electroporation). These alternative methods for introducing RLP revealed additional features of the actin network not seen in aldehyde-fixed cells. The three-dimensional organization of this network in nonflattened cells was demonstrated by projecting stereopairs derived from through-focal series of computer-enhanced images. F-actin is present in interphase cells in four interconnected configurations: a meshwork surrounding the nucleus; thick cables in transvacuolar strands and deep in the cytoplasm; a finer network of bundles within the cortical cytoplasm; even finer filaments that run in ordered transverse array around the cell periphery. The actin network is organized differently during division but it does not disappear as do the cortical microtubules. RLP stains a central filamentous cortical band as the chromatin begins to condense (preprophase); it stains the mitotic spindle (as recently shown by Seagull et al. [Seagull, R. W., M. Falconer, and C. A. Weerdenburg, 1987, J. Cell Biol., 104:995-1004] for aldehyde fixed suspension cells) and the cytokinetic apparatus (as shown by Clayton, L., and C. W. Lloyd, 1985, Exp. Cell Res., 156:231-238). However, it is now shown that an additional network of F-actin persists in the cytoplasm throughout division associating in turn with the preprophase band, the mitotic spindle, and the cytokinetic phragmoplast.
Asunto(s)
Citoesqueleto de Actina/ultraestructura , Actinas/metabolismo , Núcleo Celular/ultraestructura , Citoplasma/ultraestructura , Citoesqueleto/ultraestructura , Citoesqueleto de Actina/efectos de los fármacos , Ciclo Celular , Células Cultivadas , Citocalasina D , Citocalasinas/farmacología , Fijadores/farmacología , Formaldehído/farmacología , Técnicas Histológicas , Faloidina/análogos & derivados , Células Vegetales , Rodaminas , Coloración y EtiquetadoRESUMEN
A method is described for localizing microtubules using gold-labeled antibodies in combination with anti-tubulin. Cortex cells of Equisetum hyemale are broken open while still in buffer, after initially being attached to poly-L-lysine-coated grids. Thus, the cytoplasm becomes accessible to the antibodies. After application of the antibodies, the cleaved cells are post-fixed, stained, dehydrated, and critical point-dried. Different fixation procedures are compared: fixation in paraformaldehyde, in glutaraldehyde, and in glutaraldehyde followed by a sodium borohydride reduction step. All three methods result in good labeling of the microtubules, with low backgrounds. However, organization of the cytoplasm is best preserved in cells fixed in glutaraldehyde without sodium borohydride treatment. The method is highly suitable for studying the membrane-bound cytoskeleton because detergent extraction and/or embedding are avoided.