RESUMO
After a stress treatment, in vitro-cultured pollen changes its normal gametophytic developmental pathway towards embryogenesis producing multicellular embryos from which, finally, haploid and double haploid plants develop. The architecture of the well-organized nuclear functional domains changes in response to DNA replication, RNA transcription, processing and transport dynamics. A number of subnuclear structures present in the interchromatin region (IR, the nuclear domain between chromosome territories) have been shown as involved, either directly or indirectly, in transcriptional regulation. These structures include the interchromatin granule clusters (IGCs), perichromatin fibrils (PFs), Cajal bodies (CBs) and perichromatin granules (PGs). In this work, we present a cytochemical, immunocytochemical, quantitative and morphometric analysis at the light, confocal and electron microscopy levels to characterize the changes in the functional architecture of the nuclear interchromatin domain during two developmental programs followed by the microspore: differentiation to mature pollen grains (transcriptionally inactive), and microspore embryogenesis involving proliferation in the first stages (highly engaged in transcription). Our results revealed characteristic changes in size, shape and distribution of the different interchromatin structures as a consequence of the reprogramming of the microspore, allowing us to relate the remodeling of the interchromatin domain to the variations in transcriptional activities during proliferation and differentiation events, and suggesting that RNA-associated structures could be a regulatory mechanism in the process. In addition, we document the presence of two structurally different types of CBs, and of IGC and CB-associated regions, similar to those present in animal cells, and not yet described in plants.
Assuntos
Brassica napus/genética , Brassica napus/fisiologia , Núcleo Celular/ultraestrutura , Brassica napus/embriologia , Brassica napus/ultraestrutura , Diferenciação Celular/genética , Diferenciação Celular/fisiologia , Núcleo Celular/genética , Núcleo Celular/fisiologia , Proliferação de Células , Cromatina/genética , Cromatina/ultraestrutura , Corpos Enovelados/genética , Corpos Enovelados/metabolismo , Corpos Enovelados/ultraestrutura , Secções Congeladas , Haploidia , Imuno-Histoquímica , Microscopia Confocal , Microscopia Imunoeletrônica , Modelos Biológicos , Pólen/genética , Pólen/fisiologia , Pólen/ultraestrutura , Processamento Pós-Transcricional do RNA/fisiologia , Esporos/genética , Esporos/fisiologia , Esporos/ultraestrutura , Estresse FisiológicoRESUMO
The formation of haploid gametes in organisms with sexual reproduction requires regular bivalent chromosome pairing in meiosis. In many species, homologous chromosomes occupy separate territories at the onset of meiosis. To be paired at metaphase I, they need to be brought into a close proximity for interactions that include homology recognition and the establishment of some form of bonds. How homologues find each other is one of the least understood meiotic events. Plant species with large or medium sized genomes, such as wheat or maize, are excellent materials for the cytological analysis of chromosome dynamics at early meiosis, but genes that control meiosis have been identified mainly in small genome species such as Arabidopsis thaliana. This review is focused on the contribution studies on plants are providing to the knowledge of the initial steps of the meiotic process.
Assuntos
Cromossomos de Plantas/genética , Meiose/genética , Células Vegetais , Plantas/genética , Arabidopsis/citologia , Arabidopsis/genética , Núcleo Celular/genética , Centrômero/genética , Pareamento Cromossômico/genética , Citogenética , DNA de Plantas/genética , Modelos Genéticos , Secale/citologia , Secale/genética , Triticum/citologia , Triticum/genética , Zea mays/citologia , Zea mays/genéticaRESUMO
BACKGROUND AND AIMS: The great potential of using nanodevices as delivery systems to specific targets in living organisms was first explored for medical uses. In plants, the same principles can be applied for a broad range of uses, in particular to tackle infections. Nanoparticles tagged to agrochemicals or other substances could reduce the damage to other plant tissues and the amount of chemicals released into the environment. To explore the benefits of applying nanotechnology to agriculture, the first stage is to work out the correct penetration and transport of the nanoparticles into plants. This research is aimed (a) to put forward a number of tools for the detection and analysis of core-shell magnetic nanoparticles introduced into plants and (b) to assess the use of such magnetic nanoparticles for their concentration in selected plant tissues by magnetic field gradients. METHODS: Cucurbita pepo plants were cultivated in vitro and treated with carbon-coated Fe nanoparticles. Different microscopy techniques were used for the detection and analysis of these magnetic nanoparticles, ranging from conventional light microscopy to confocal and electron microscopy. KEY RESULTS: Penetration and translocation of magnetic nanoparticles in whole living plants and into plant cells were determined. The magnetic character allowed nanoparticles to be positioned in the desired plant tissue by applying a magnetic field gradient there; also the graphitic shell made good visualization possible using different microscopy techniques. CONCLUSIONS: The results open a wide range of possibilities for using magnetic nanoparticles in general plant research and agronomy. The nanoparticles can be charged with different substances, introduced within the plants and, if necessary, concentrated into localized areas by using magnets. Also simple or more complex microscopical techniques can be used in localization studies.
Assuntos
Cucurbita/metabolismo , Nanopartículas Metálicas/análise , Microscopia Confocal/métodos , Microscopia Eletrônica de Transmissão/métodos , Microscopia de Fluorescência/métodos , Transporte Biológico , Cucurbita/citologia , Cucurbita/ultraestrutura , Ferro/química , MagnetismoRESUMO
The arrangement of chromosome pairs 5RL and 7R added to the wild type and the ph1b mutant line of hexaploid wheat are analyzed in 2N somatic root tip cells during the cell cycle relative to the arrangement that chromosomes 5RL show in 4N tapetal cells produced after colchicine treatment. Both homologous chromosome pairs are identified at interphase and mitosis by fluorescence in situ hybridization. In nuclei at interphase, chromosomes appear as discrete domains that show the Rabl orientation. Homologous chromosomes are predominantly non-associated and their positioning seems not to be influenced by the Ph1 gene that suppresses homoeologous meiotic pairing. This pattern of arrangement contrasts with the high level of somatic pairing that sister chromosomes show in the interphase that follows chromosome duplication induced by colchicine. Disruption of pairing observed in some 4N nuclei is produced at c-anaphase which suggests no topological redistribution of homologues during conformation of the new nucleus. Homologous chromosomes show no predominant arrangement in ellipsoidal metaphase plates, which contrasts with the preferential opposite location of homologues in human prometaphase rosettes. Differences between chromosomes in the variation of the length through the cell cycle and in the chromatin morphology when the Ph1 is absent suggest different patterns of chromatin condensation in both chromosomes.
