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  • 1980-1984
  • 1965-1969  (2)
  • 1890-1899
  • 1968  (2)
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  • 1980-1984
  • 1965-1969  (2)
  • 1890-1899
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  • 1
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The possibility that 32PO 4 3- (32Pi) labeling of both chloroplast and non-chloroplast RNAs during light-induced chloroplast development in Euglena is due, in part, to the break-down of existing RNAs and their resynthesis into labeled RNAs has been examined by comparing the RNA content of dark-grown, non-dividing cells after completion of light-induced chloroplast development with that of identical cells maintained in darkness for the same period of time. The involvement of the photo-conversion of protochlorophyll to chlorophyll and other photoreceptor systems in the labeling of RNA during chloroplast development has been considered by comparing the labeling pattern obtained with wild-type cells with the patterns obtained with mutants of Euglena which either lack detectable amounts of protochlorophyll and chlorophyll or form only rudimentary chloroplasts upon light induction. No significant difference in RNA content between dark-grown, non-dividing cells containing fully developed chloroplasts and the same cells maintained in darkness for the development period can be detected. This observation is interpreted to mean that in non-dividing cells precursors for chloroplast-associated RNAs are derived from pools and pre-existing RNAs, including non-chloroplast RNAs, and that the matebolic entrapment of 32Pi involves a light-dependent turnover and DNA-directed RNA synthesis in wild-type cells. The RNA profiles on sucrose gradients of mutants of Euglena show no remarkable deviation from the profile established for wild-type cells. The labeling patterns obtained after 24 hours of incubation in light and in darkness differ from that obtained for wild-type cells in that all mutants show less of a light-minus-dark difference than wild-type and that mutants lacking plastid-associated DNA and detectable amounts of chlorophyll incorporate considerably more 32Pi into RNA in darkness than wild-type. One such mutant shows no significant difference in its light-dark labeling pattern. These observations indicate that cells possessing normal proplastids capable of forming functional chloroplasts regulate metabolism of RNA in darkness in a different manner than with either rudimentary chloroplasts or containing no detectable plastids structures. The possible involvement of more than one photoreceptor system in metabolic control is discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Since Euglena gracilis Klebs var. bacillaris Pringsheim contains a species of DNA unique to the chloroplast, an important question concerns the extent to which light unblocks the reading of the organelle's template to provide the informational RNA's necessary to construct the plastid proteins. Experiments with 32Pi labeling of chloroplast and nonchloroplast RNA's during light-induced chloroplast development show that both the RNA of the chloroplast and of the rest of the cell become labeled during this process, with the chloroplast RNA's displaying the higher specific activity. The fact that chloroplast RNA is not uniquely labeled indicates that process other than a simple reading of the chloroplast DNA are involved. If we are to preserve the concept of a reasonable degree of chloroplast informational autonomy, we may assume, from this and other data, that the light induction of chloroplast development involves not only the unblocking of chloroplast DNA to make information available, but also a concomitant unblocking of other sites of informational RNA synthesis (e.g., nuclear and mitochondrial DNA's). Such sites external to the developing chloroplast may be concerned with making available the building blocks and energy necessary for the synthesis of chloroplast constituents coded for by the chloroplast DNA. This model leads to the prediction that photosynthesis could be gratuitous for chloroplast development if these nonchloroplast sites were providing most of the building blocks and energy. Experiments are reported which show that chloroplast formation and the acquisition of photosynthetic competence can be achieved under conditions where photosynthesis is completely inhibited for the entire span of development by using the highly selective inhibitor 3, (3,4-dichlorophenyl) 1, 1-dimethyl urea (DCMU), in agreement with the proposed model. The fact that more than just the chloroplast responds to the inducing signals for chloroplast differentiation raises the problem of experimental measurement of interaction among cellular organelles. Since chloroplast development is usually carried out in resting cells to avoid complications due to cell division, we discuss the limitations imposed by turnover in such nondividing systems and present evidence that most of the RNA labeling observed, although actinomycin-D-sensitive, is due to turnover and/or the utilization of preexisting pools. Evidence obtained with mutants of Euglena that form only partial chloroplasts or that lack plastid DNA and plastid-related structures is reported. Such evidence indicates that the functional proplastid restrains overall RNA labeling in the uninduced cells and suggests that the proplastid might be the source of regulatory metabolic signals in the normal plastid-containing cells.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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