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  • 1
    ISSN: 1432-2048
    Keywords: Metosis (organelles) ; Organelles (during meiosis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this paper we have traced the evolution of the cytoplasmic organelles in the female germinal cell of Pisum sativum L., from the beginning of meiosis to the early stages of the maturing megaspore, in order to correlate the morphological changes with the physiological aspects of megasporogenesis. A process of intense cytoplasmic vacuolation takes place in the megaspore mother cell (MMC) during prophase I, probably proceeding from the smooth endoplasmic reticulum and dictyosomes; it results in the formation of big vacuoles, which play a role in MMC polarization. By means of this polarization most plastids and mitochondria are incorporated into the functional megaspore at the end of meiosis. There are plastid and mitochondria cycles which consist of dedifferentiation followed by redifferentiation, During these cycles a transient morphology appears, called a cup-shaped form, which we interpret as an expression of low organelle activity. The wall of the MMC thickens throughout megasporogenesis and loses its plasmodesmata during middle prophase I. The ribosome population is reduced during prophase I and then restored during the early stages of the megaspore maturing process, as shown by the quantitative study that we have carried out. The nucleolar cytoplasmic bodies play a part in this restoring process. These bodies have a special morphology and appear to be originated from the activity of the nucleolar organizing region (NOR) during nucleolar disorganization in prophase I. We think that this cytoplasmic evolution is a response to nuclear genic recombination, in order to provide the most adequate expression of the zygote genome.
    Type of Medium: Electronic Resource
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  • 2
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    Instituto Antartico Ecuatoriano
    Publication Date: 2021-05-19
    Description: Velocidades superficiales de las aguas fueron medidas en la Bahía chile en la Isla Greenwich, como parte de la Segunda Expedición Ecuatoriana a la Antártida, durante el verano del hemisferio sur, en 1990. Masas de hielo a la deriva desprendidas desde la costa fueron usadas como trazadores lagrangianos. Son comparadas corrientes superficiales y observaciones de vientos. La circulación superficial es determinada por los vientos cuando la velocidad de estos últimos exceden los 6 m/s. Los valores máximos y la dirección de la deriva superficial dependen exclusivamente del campo de viento prevaleciente. La velocidad de la corriente puede alcanzar valores de hasta 40 cm/s.
    Description: Surface water velocities have been measured at Chile Bay, Greenwich Island, as part of the Second Ecuadorian Antarctic Scientific Expedition, during the southern summer, 1990. Drifting ice floes broken from shore were used as a lagrangian tracer. Surface currents and wind observations are compared. Surface circulation is determined by winds, when the wind speed is higher than 6 m/s. Maximun values and direction of the surface drift current depend exclusively upon the actually prevailing wind field. Current speed may reach up to 40 cm/s.
    Description: Published
    Keywords: Surface water ; Surface water ; Ice drift ; Surface currents ; Surface drifters ; Polar waters ; Surface circulation
    Repository Name: AquaDocs
    Type: Journal Contribution , Non-Refereed , Article
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