RESUMO
Epithelial cell dynamics can be difficult to study in intact animals or tissues. Here we use the medusa form of the hydrozoan Clytia hemisphaerica, which is covered with a monolayer of epithelial cells, to test the efficacy of an orientation-independent differential interference contrast microscope for in vivo imaging of wound healing. Orientation-independent differential interference contrast provides an unprecedented resolution phase image of epithelial cells closing a wound in a live, nontransgenic animal model. In particular, the orientation-independent differential interference contrast microscope equipped with a 40x/0.75NA objective lens and using the illumination light with wavelength 546 nm demonstrated a resolution of 460 nm. The repair of individual cells, the adhesion of cells to close a gap, and the concomitant contraction of these cells during closure is clearly visualized.
Assuntos
Movimento Celular , Células Epiteliais/citologia , Células Epiteliais/fisiologia , Hidrozoários/citologia , Microscopia Intravital/métodos , Microscopia de Interferência/métodos , Cicatrização , Animais , Microscopia Intravital/instrumentação , Microscopia de Interferência/instrumentaçãoRESUMO
Root system development is an important agronomic trait. The right architecture in a given environment allows plants to survive periods of water of nutrient deficit, and compete effectively for resources. Root systems also provide an optimal system for studying developmental plasticity, a characteristic feature of plant growth. This review proposes a framework for describing the pathways regulating the development of complex structures such as root systems: intrinsic pathways determine the characteristic architecture of the root system in a given plant species, and define the limits for plasticity in that species. Response pathways co-ordinate environmental cues with development by modulating intrinsic pathways. The current literature describing the regulation of root system development is summarized here within this framework. Regulatory pathways are also organized based on their specific developmental effect in the root system. All the pathways affect lateral root formation, but some specifically target initiation of the lateral root, while others target the development and activation of the lateral root primordium, or the elongation of the lateral root. Finally, we discuss emerging approaches for understanding the regulation of root system architecture.
Assuntos
Meio Ambiente , Reguladores de Crescimento de Plantas/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/fisiologia , Transdução de Sinais/fisiologia , Ciclo Celular/fisiologia , Genes de Plantas/fisiologia , Fenômenos Fisiológicos Vegetais , Raízes de Plantas/citologia , Raízes de Plantas/genética , Transdução de Sinais/genéticaRESUMO
Plant morphology is dramatically influenced by environmental signals. The growth and development of the root system is an excellent example of this developmental plasticity. Both the number and placement of lateral roots are highly responsive to nutritional cues. This indicates that there must be a signal transduction pathway that interprets complex environmental conditions and makes the "decision" to form a lateral root at a particular time and place. Lateral roots originate from differentiated cells in adult tissues. These cells must reenter the cell cycle, proliferate, and redifferentiate to produce all of the cell types that make up a new organ. Almost nothing is known about how lateral root initiation is regulated or coordinated with growth conditions. Here, we report a novel growth assay that allows this regulatory mechanism to be dissected in Arabidopsis. When Arabidopsis seedlings are grown on nutrient media with a high sucrose to nitrogen ratio, lateral root initiation is dramatically repressed. Auxin localization appears to be a key factor in this nutrient-mediated repression of lateral root initiation. We have isolated a mutant, lateral root initiation 1 (lin1), that overcomes the repressive conditions. This mutant produces a highly branched root system on media with high sucrose to nitrogen ratios. The lin1 phenotype is specific to these growth conditions, suggesting that the lin1 gene is involved in coordinating lateral root initiation with nutritional cues. Therefore, these studies provide novel insights into the mechanisms that regulate the earliest steps in lateral root initiation and that coordinate plant development with the environment.
Assuntos
Arabidopsis/crescimento & desenvolvimento , Raízes de Plantas/crescimento & desenvolvimento , Antocianinas/metabolismo , Arabidopsis/fisiologia , Ciclo Celular , Diferenciação Celular , Dimetil Sulfóxido/metabolismo , Meio Ambiente , Ácidos Indolacéticos/fisiologia , Mutação , Ácidos Naftalenoacéticos/farmacologia , Nitrogênio/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/fisiologia , Plantas Geneticamente Modificadas , Transdução de Sinais , Sacarose/metabolismoRESUMO
Mutation of the SCARECROW (SCR) gene results in a radial pattern defect, loss of a ground tissue layer, in the root. Analysis of the shoot phenotype of scr mutants revealed that both hypocotyl and shoot inflorescence also have a radial pattern defect, loss of a normal starch sheath layer, and consequently are unable to sense gravity in the shoot. Analogous to its expression in the endodermis of the root, SCR is expressed in the starch sheath of the hypocotyl and inflorescence stem. The SCR expression pattern in leaf bundle sheath cells and root quiescent center cells led to the identification of additional phenotypic defects in these tissues. SCR expression in a pin-formed mutant background suggested the possible origins of the starch sheath in the shoot inflorescence. Analysis of SCR expression and the mutant phenotype from the earliest stages of embryogenesis revealed a tight correlation between defective cell divisions and SCR expression in cells that contribute to ground tissue radial patterning in both embryonic root and shoot. Our data provides evidence that the same molecular mechanism regulates the radial patterning of ground tissue in both root and shoot during embryogenesis as well as postembryonically.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/fisiologia , Proteínas de Plantas/fisiologia , Arabidopsis/citologia , Arabidopsis/genética , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Zíper de Leucina , Folhas de Planta/citologia , Folhas de Planta/fisiologia , Proteínas de Plantas/genética , Raízes de Plantas/citologia , Raízes de Plantas/fisiologia , Caules de Planta/citologia , Caules de Planta/fisiologia , Sementes/fisiologiaRESUMO
Lateral root formation in plants involves the stimulation of mature pericycle cells to proliferate and redifferentiate to create a new organ. The simple organization of the root of Arabidopsis thaliana allows the development of lateral root primordia to be characterized histologically. We have divided the process of lateral root development into 8 stages defined by specific anatomical characteristics and cell divisions. To identify the cell types in the developing primordium we have generated a collection of marker lines that express beta-glucuronidase in a tissue- or cell type-specific manner in the root. Using these tools we have constructed a model describing the lineage of each cell type in the lateral root. These studies show that organization and cell differentiation in the lateral root primordia precede the appearance of a lateral root meristem, with differential gene expression apparent after the first set of divisions of the pericycle.
Assuntos
Arabidopsis/crescimento & desenvolvimento , Arabidopsis/citologia , Diferenciação Celular , Divisão Celular , Meristema , Raízes de Plantas , SementesRESUMO
Although the introduction of foreign genes into Arabidopsis has become routine, the production of transgenic Arabidopsis plants still requires several months. A transgene expression system (TES) has been developed that allows characterization of gene expression patterns and the effects of foreign genes in the Arabidopsis root in 2-4 weeks. The method is based on regeneration of stably transformed roots directly from callus tissue. TES has been used to study the expression of the SCARECROW gene, which is involved in establishing radial patterning in the root. The 2.5 kb region directly upstream of the SCARECROW coding region was found to be sufficient to confer cell-type specific expression. Furthermore, this promoter is active in the scr mutant background, indicating that factors essential for cell-type specific expression are present even in the absence of correct radial patterning. Finally, TES was used to demonstrate that the SCARECROW gene under control of this promoter complements the root organization defect of the scr mutant. These experiments demonstrate the utility of the TES system for studying gene expression in roots in wild-type and mutant backgrounds and for molecular complementation of root mutant phenotypes. It is possible that the method will also be applicable to other organs.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Zíper de Leucina/genética , Proteínas de Plantas/genética , Raízes de Plantas/genética , Plantas Geneticamente Modificadas , Teste de Complementação Genética , Mutagênese , Reação em Cadeia da Polimerase , Regiões Promotoras GenéticasRESUMO
In the Arabidopsis root meristem, initial cells undergo asymmetric divisions to generate the cell lineages of the root. The scarecrow mutation results in roots that are missing one cell layer owing to the disruption of an asymmetric division that normally generates cortex and endodermis. Tissue-specific markers indicate that a heterogeneous cell type is formed in the mutant. The deduced amino acid sequence of SCARECROW (SCR) suggests that it is a member of a novel family of putative transcription factors. SCR is expressed in the cortex/endodermal initial cells and in the endodermal cell lineage. Tissue-specific expression is regulated at the transcriptional level. These results indicate a key role for SCR in regulating the radial organization of the root.