Dieter G. Müller

Generationswechsel, Kernphasenwechsel und Sexualität der Braunalge Ectocarpus siliculosus im Kulturversuch

SummaryThe life cycle of Ectocarpus siliculosus from Naples (Italy) was investigated, using well defined cultured material. Gametophytes and sporophytes differ morphologically and functionally. The gametophytes are dioecious, with genotypic determination of their sex. Sporophytes exist in the haploid, diploid and tetraploid phase. All sporophytes can form unilocular sporangia. In tetraploid and diploid sporophytes the formation of unilocular sporangia is connected with meiosis. Certain motile cells of haploid plants may spontaneously give rise to diploid or tetraploid sporophytes which are homozygous. Gametophytes can only be formed together with sporophytes form the swarmers of unilocular sporangia (heteroblasty). Meiosis in tetraploid sporophytes resulted in diploid gametophytes, the gametes of which fused with haploid female gametes. All observed nuclear phases and growth forms are connected with each other by meiosis, heteroblasty, fusion of gametes and spontaneous increase in chromosome number.ZusammenfassungDer Entwicklungscyclus von Ectocarpus siliculosus wurde unter Kulturbedingungen untersucht. Gametophyten und Sporophyten können morphologisch und funktionell unterschieden werden. Die Gametophyten sind diöcisch, die Geschlechtsbestimmung erfolgt genotypisch. Sporophyten können in der haploiden, diploiden und tetraploiden Phase vorliegen. Sporophyten aller Kernphasen können unilokuläre Sporangien ausbilden, tetraploide und diploide Sporophyten führen dabei eine Reduktionsteilung durch. Schwärmer haploider Gametophyten und Sporophyten können sich spontan zu diploiden oder tetraploiden homozygoten Sporophyten entwickleln. Gametophyten können nur zusammen mit Sporophyten aus Schwärmern unilokulärer Sporangien entstehen (Heteroblastie). Aus der Reduktionsteilung tetraploider Sporophyten gingen diploide männliche Gametophyten hervor, deren Gameten mit normalen weiblichen Gameten kopulierten. Die verschiedenen Kernphasen und Wuchsformen stehen durch Reduktionsteilungen, Heteroblastie, Kopulation und spontane Aufregulierung der Chromosomenzahl miteinander in Verbindung.The life cycle of Ectocarpus siliculosus from Naples (Italy) was investigated, using well defined cultured material. Gametophytes and sporophytes differ morphologically and functionally. The gametophytes are dioecious, with genotypic determination of their sex. Sporophytes exist in the haploid, diploid and tetraploid phase. All sporophytes can form unilocular sporangia. In tetraploid and diploid sporophytes the formation of unilocular sporangia is connected with meiosis. Certain motile cells of haploid plants may spontaneously give rise to diploid or tetraploid sporophytes which are homozygous. Gametophytes can only be formed together with sporophytes form the swarmers of unilocular sporangia (heteroblasty). Meiosis in tetraploid sporophytes resulted in diploid gametophytes, the gametes of which fused with haploid female gametes. All observed nuclear phases and growth forms are connected with each other by meiosis, heteroblasty, fusion of gametes and spontaneous increase in chromosome number.

Flagellar structure of the gametes of Ectocarpus siliculosus (Phaeophyta) as revealed by negative staining

SummaryFrom light microscopic observations of the mating reaction in the marine brown alga Ectocarpus siliculosus it can be deduced that the foremost part of the front flagellum of the male gamete plays an important role in establishing initial sexual contact. The flagellar apparatus of both male and female isogametes of this organism has been studied electron microscopically using negative staining technique, with special attention focused onto the whiplash tips (“acronema”). The fine structure of this terminal flagellar appendage, which is very long (about 10 μm) and extremely sensitive to mechanical stress, is identical in structure in both, the tinsel and the smooth (hind) flagellum. It is characterized by a continuation of only the two central microtubules of the flagellar shaft which appear cross-bridged to each other and are ensheathed by the plasma membrane. Although the two types of gametes are different in their functions, differences in the fine structure of their flagellar apparatus were not detected.

Untersuchungen zur Entwicklungsgeschichte der Braunalge Ectocarpus siliculosus Aus Neapel

Culture experiments and cytological studies were carried out under well-defined conditions. The haploid chromosome number is between 18 and 31. There are two morphological types of plants: the well-branched gametophyte resembling the plants found in nature, and the unbranched sporophytic form which may be haploid or diploid, found only in cultures. Meiosis takes place in the unilocular sporangia on diploid sporophytes. Haploid sporophytes form unilocular sporangia without reduction of the chromosome number. The spores from unilocular sporangia both on diploid and haploid sporophytes give rise to plants with either sporophytic or gamethophytic growth. The gametophytes are homothallic, the gametes forming motile zygotes with four flagella. Parthenogenetic development of gametes exclusively results in the formation of haploid sporophytes. Both the haploid and diploid sporophytes can propagate by means of zoids from plurilocular sporangia. Several observations reported here disagree with the findings of other workers.SummaryCulture experiments and cytological studies were carried out under well-defined conditions. The haploid chromosome number is between 18 and 31. There are two morphological types of plants: the well-branched gametophyte resembling the plants found in nature, and the unbranched sporophytic form which may be haploid or diploid, found only in cultures. Meiosis takes place in the unilocular sporangia on diploid sporophytes. Haploid sporophytes form unilocular sporangia without reduction of the chromosome number. The spores from unilocular sporangia both on diploid and haploid sporophytes give rise to plants with either sporophytic or gamethophytic growth. The gametophytes are homothallic, the gametes forming motile zygotes with four flagella. Parthenogenetic development of gametes exclusively results in the formation of haploid sporophytes. Both the haploid and diploid sporophytes can propagate by means of zoids from plurilocular sporangia. Several observations reported here disagree with the findings of other workers.ZusammenfassungKulturversuche und cytologische Untersuchungen an Ectocarpus siliculosus aus dem Mittelmeer (Neapel) führten zu folgenden Ergebnissen: die haploide Chromosomenzahl liegt zwischen 18 und 31. Es sind zwei morphologisch verschiedene Wuchsformen vorhanden, die dem Freilandmaterial gleichenden haploiden Gametophyten und die nur in Kultur beobachteten Sporophyten. Letztere können sowohl in der Haplophase als auch in der Diplophase vorliegen und bilden in jedem Fall neben pluriloculären auch uniloculäre Fortpflanzungsorgane aus. In den uniloculären Sporangien der diploiden Sporophyten findet die Reduktionsteilung statt, während sie in denselben Sporangien auf haploiden Pflanzen unterbleibt. Unter den Schwärmern aus den Gametangien der Geschlechtspflanzen finden sich viergeißlige bewegliche Zygoten. Unter den Nachkommen eines Gemisches von unkopulierten Schwärmern und Zygoten wurden haploide und diploide Sporophyten gefunden. Unter den Nachkommen aus uniloculären Sporangien haploider und diploider Pflanzen sind fast stets Vertreter beider Wuchsformen zu finden. Einige der hier mitgeteilten Beobachtungen stimmen nicht mit den Angaben früherer Autoren überein.

Relative sexuality in Ectocarpus siliculosus

Abstract181 plants of the marine brown alga Ectocarpus siliculosus were collected at Naples, Italy, and clonal cultures established. 94 female and 82 male gametophytes were identified. 5 plants were asexual, although they had the characteristic morphological appearance of gametophytes. There is very clear and stable sexual bipolarity and no indication of “relative sexuality” as described by Hartmann. Examination of Hartmanns publications and observations on the cultured material showed several possible ways how his misinterpretations may have originated.

Versuche zur Charakterisierung eines Sexual-Lockstoffes bei der Braunalge Ectocarpus siliculosus

Female gametes of the brown alga Ectocarpus siliculosus produce a sexual attractant which is highly volatile and has a characteristic odor. Two biological test reactions have been worked out for its detection: chemokinesis and positive chemotaxis of the male gametes. The substance can be collected by passing a stream of air through suspensions of female gametes, and can be condensed in a cold trap at-83°C. The substance can be detected by gas chromatography; it is represented by a single peak.SummaryFemale gametes of the brown alga Ectocarpus siliculosus produce a sexual attractant which is highly volatile and has a characteristic odor. Two biological test reactions have been worked out for its detection: chemokinesis and positive chemotaxis of the male gametes. The substance can be collected by passing a stream of air through suspensions of female gametes, and can be condensed in a cold trap at-83°C. The substance can be detected by gas chromatography; it is represented by a single peak.ZusammenfassungWeibliche Gameten der Braunalge Ectocarpus siliculosus bilden einen Sexuallockstoff, der sehr stark flüchtig ist und einen charakteristischen Geruch besitzt. Er kann durch zwei biologische Testreaktionen nachgewiesen werden: Chemokinesis und positive Chemotaxis der männlichen Gameten. Das Gamon kann durch einen Luftstrom gesammelt und in einer Kältefalle bei-83°C ausgefroren werden. Das Gamon läßt sich gaschromatographisch nachweisen, es ist nach den bisherigen Beobachtungen eine homogene Fraktion.

Ein leicht flüchtiges Gyno-Gamon der BraunalgeEctocarpus siliculosus

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