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  • 1
    ISSN: 1615-6102
    Keywords: Chlamydomonas reinhardtii ; Chloroplast nucleoidal destruction ; RNA synthesis ; UV interference
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The studies on the kinetics of nucleoid destruction reported here showed that destruction of chloroplast nucleoids (ct nucleoids) of male origin began to occur at about 30 minutes after mixing of male (mt−) and female (mt+) gametes. The timing of initiation of the destruction differed among zygotes but usually occurred during 50–120 minutes after mixing. About 10 minutes was required for complete digestion of the ct nucleoids. UV irradiation on young zygotes or addition of an RNA-synthesis inhibitor, actinomycin D, to the incubation medium during the first 0–30 minutes after mixing almost completely inhibited the incorporation of3H uridine into the cell nuclei and the preferential destruction without inhibiting cell nuclear fusion. These results suggest that soon after mating,de novo RNA synthesis is concerned for the preferential destruction of ct nucleoids. To determine in which of the two cell nuclei in the zygotes the RNA is synthesized, each gamete (mt−, mt+) was irradiated with UV and mated with unirradiated gametes of opposite mating type. This treatment of the male gametes had no effect on the incorporation of3H uridine into cell nuclei and the preferential destruction of ct nucleoids but UV irradiation of female gametes almost completely inhibited the incorporation of3H uridine into cell nuclei and the preferential destruction of ct nucleoids. Similar phenomena occurred in other crosses. The UV effect was photoreactivated in about 50% by white light, suggesting that the UV target is DNA. Thus, RNA synthesized in the cell nucleus of female origin soon after mating may be responsible for the preferential destruction of ct nucleoids of male origin
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Chloroplast nucleoid number ; Chloroplast DNA amount ; Preferential digestion ; Maternal inheritance ; Chlamydomonas reinhardtii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We studied the maternal chloroplast inheritance ofChlamydomonas reinhardtii by epifluorescence microscopy after staining with DNA specific fluorochrome DAPI and by genetic methods, using wild type cells and cells containing previously isolated mutation of cond-1 and cond-2. Wild type cells contained about 7 chloroplast (cp) nucleoids, while mutants, cond-1(+) and cond-2(+), contained about 14 and 23 cp nucleoids, respectively, after one week culture on agar plates. The total cpDNA contents were almost proportional to the numbers of cp nucleoids. When cells containing cond-1 or cond-2 mutation were used as a parental source to cross with wild type cells of the other parent, preferential digestion of cp nucleoids from male parent (mt−) origin occurred in the zygotes, although the frequencies of the digestion were slightly lower than that in the zygotes from the cross between wild type cells. Western blot analysis of the protein ofzyslB gene, which has been found related to preferential digestion of mt− origin cp-nucleoids DNA, showed that a high amount of this protein was detected with the initiation of preferential digestion of mt− cp nucleoids and disappeared with the completion of the digestion. Cp genetic markers for antibiotic resistance were maternally inherited in all crosses. These results showed that although the preferential digestion of cp nucleoids consisting of large number and large cpDNA amount requires a slightly longer period to complete, this high ploidy of the cp nucleoids does not disturb maternal inheritance.
    Type of Medium: Electronic Resource
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