Reproduction in Brown Algae

Asexual reproduction is accomplished by either fragmentation or spores. When cells divide, centrioles are apparent in the mitotic figure. This is significant because it is not ordinarily seen in plant cells. Sexual reproduction is of three types: isogamous, anisogamous, and oogamous. Three examples of life cycles are considered following.

Ectocarpus

We will use Ectocarpus to represent the isogamous form of sexual reproduction in brown algae. The center circle of figure 14-2 shows asexual reproduction while sexual reproduction is shown in the larger circle. Although the sporophyte is 2n and the gametophyte is n, the two generations look alike. Two types of sporangia are produced on the sporophyte: unilocular sporangia (having one compartment) and plurilocular sporangia (having many compartments). The unilocular sporangia each at first contain a single cell. This cell goes through repeated divisions, the first of which are meiotic and, thus, reduce the chromosome number. These first divisions are followed by a number of mitotic divisions, which generate a number of biflagellated haploid zoospores. The zoospores then grow into gametophytes. The gametophytes, of course, are haploid. Plurilocular gametangia are produced on the gametophytes. Biflagellated isogametes are produced in these gametangia by mitosis. The gametes fuse in pairs, thus producing zygotes that can then grow into new sporophyte plants.

While the preceding is clearly an example of alternation of generations, Ectocarpus can go through a reproductive cycle without alternation of generations. Look again at the sporophyte plants in figure 14-2 and note the plurilocular sporangia. These contain many cells that mature into diploid zoospores, which, instead of growing into gametophytes, become new sporo-phytes. Because there is no gametophyte generation in this sequence, alternation of generations is bypassed.

Some species of Ectocarpus are monoecious, having both plus and minus gametangia on the same plant. Other species are dioecious, requiring a fusion of gametes from different plants to form zygotes.

Phaeophyta: The Brown Algae • 145

Laminaria Asexual Unilocular Sporangia

Meiosis Occurs

Unilocular Form

O Mitotic . Divisions

Sexual Reproduction

Haploid Meiospores Released

Diploid Sporophyte May Produce a Plurilocular Sporangium

Asexual Reproduction

Gametophytes

Grow into New Sporophtes

New Sporophyte Plant

Gametes

Gametes Fuse

Figure 14-2 Ectocarpus life cycle. At right are sporophyte generations exhibiting two types of sporangia: (c) unilocular and (j) plurilocular. In the unilocular form, (a), meiosis occurs, (b), followed by mitotic divisions, (c). Haploid meiospores (d) are released, producing gametophytes, (e) and (f). Gametes fuse, (g), producing a zygote, (h), which grows into a new sporophyte plant, (i). The sporophyte at (i) is diploid and may produce a plurilocular sporangium (j). This sporangium produces diploid spores, (k), which grow to new sporophytes, (I), thus circumventing alternation of generations.

Laminaria

The sporophyte generation of Laminaria tends to reach considerable size and is differentiated into a rootlike holdfast, a stipe, and a flat blade. These plants attach with such firmness to rocks that when torn away, portions of the rock often come away also. Because the blade portion is much damaged by buffeting wave action, it is replaced by new growth in the spring. Each year, a zone of dividing (meristematic) cells where the stipe and the blade meet renew the

Ht Notes Ht blade. While the blade is annual, the stipe is perennial. When the plant is mature enough to produce sporangia, dark patches called son appear on the surface of the blade. Son are collections of sporangia. Meiosis takes place in the production of zoospores. These zoospores are minute, biflagellated cells of two types: those that produce male gametophytes and those that produce female gameto-phytes. One-half of the zoospores are of the one type, one-half are of the other.

The microscopically sized gametophytes actually evaded detection until 1916. Each gametophyte is composed of only a few cells. The antheridia that

Brown Algae Reproduction

Figure 14-3 Laminaria: at left, the conspicuous sporophyte generation consisting of (a) holdfast, (b) stipe, and (c) blade with (d) sporogenous tissue, (k) An enlargement of a sporangium intermingled with paraphyses. The spores at (e) are meiospores, which grow into microscopically sized gametophytes. The male gametophyte, (f), and the female gametophyte, (h). One egg cell, (i), is fertilized by the sperm, (g), to produce the zygote, (j), which grows into a new sporophyte.

Figure 14-3 Laminaria: at left, the conspicuous sporophyte generation consisting of (a) holdfast, (b) stipe, and (c) blade with (d) sporogenous tissue, (k) An enlargement of a sporangium intermingled with paraphyses. The spores at (e) are meiospores, which grow into microscopically sized gametophytes. The male gametophyte, (f), and the female gametophyte, (h). One egg cell, (i), is fertilized by the sperm, (g), to produce the zygote, (j), which grows into a new sporophyte.

Phaeophyta: The Brown Algae ♦ 147

are borne on the male gametophytes each produce a single sperm cell. # Notes * Likewise, the oogonia of the female plants each house a single egg. Sperm cells swim to the egg cell at the opening of the oogonium. The zygote thus formed grows into the familiar sporophyte plant.

Fucus

Fucus exists as a flat, dichotomously branching thallus bearing a short stipe and growing approximately one foot in length. The ends of certain branches become swollen; these swellings are called receptacles. The receptacles contain spherical o

Brown Algae Reproduction

Figure 14-4 Fucus. The plant is dichotomously branching with swollen receptacles, (a), having conceptacles, (b). The conceptacles are of two types: microsporangiate with microsporangia, (f), and paraphyses, (e); and megasporangiate with megasporangia, (d), and paraphyses, (c). The microspores develop directly into sperm cells (g), and the megaspores develop directly into egg cells (h). The zygote (i) grows into a new thallus. Because the spores develop directly into gametes, there is no alternation of generations.

Figure 14-4 Fucus. The plant is dichotomously branching with swollen receptacles, (a), having conceptacles, (b). The conceptacles are of two types: microsporangiate with microsporangia, (f), and paraphyses, (e); and megasporangiate with megasporangia, (d), and paraphyses, (c). The microspores develop directly into sperm cells (g), and the megaspores develop directly into egg cells (h). The zygote (i) grows into a new thallus. Because the spores develop directly into gametes, there is no alternation of generations.

it Notes Ht chambers called conceptacles, within which sporangia grow. The sporangia are of two types: microsporangia and megasporangia. In Fucus spiralis, both types of sporangia occur in the same conceptacle. In Fucus vesiculosis, the microsporangia and megasporangia are found on different plants. Microspores divide meiotically to form sperm cells, and megaspores produce egg cells by reduction divisions. Although both eggs and sperm are produced, no gametophytes are generated. The spores divide to produce gametes. The gametes are then released into the water, where fertilization occurs. The gametes are the only cells that have the haploid chromosome number. Although both spores and gametes are formed, it is not appropriate to label this alternation of generations.

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Responses

  • Raymond
    Are the spores in the sporangia produced by mitosis or meiosis?
    7 years ago
  • Iago
    What type of cell division occurs in unilocular sporangia?
    7 years ago
  • urho
    Do algae go thru alternation of generations?
    7 years ago
  • Stanislao
    What is the difference between the fucus receptacles and conceptacles?
    7 years ago
  • rebecca thompson
    Where are the spores produced on laminaria?
    7 years ago
  • Ralf
    What type of cell division is occurring ( mitosis or meiosis in laminaria?
    7 years ago
  • pinja lankila
    Is a paraphysis a gametophyte or sporophyte?
    7 years ago
  • madihah tesfalem
    What generation is the paraphysis?
    7 years ago
  • Sadoc
    Where is the receptacles on algae?
    7 years ago
  • kathrin
    How brown algae reproduce?
    7 years ago
  • Gimja
    What are paraphyses in brown alga?
    7 years ago
  • junior
    How a green algae goes through mitosis?
    6 years ago
  • bonacata
    Is brown algae sexual or asexual?
    5 years ago
  • arianna
    Does Laminaria grow dichotomously?
    5 years ago
  • amanuel
    How does phaeophyta exchange gases?
    5 years ago
  • kauko
    Do brown algae reproduce sexually?
    4 years ago
  • pertti
    What are unilocular sporangia where do they occur?
    4 years ago
  • teagan
    What type of sporangia produced only on sporophytic plant body in ectocarpus?
    3 years ago
  • Geronimo
    Does laminaria have paraphyses?
    3 years ago
  • LLOYD
    How we use ectocarpus in medicine production?
    3 years ago
  • kirsti
    What is the difference between unilocular and plurilocular sporangia of phaeophyta?
    3 years ago
  • aurelia lombardo
    What are the asexual spores produced by phaeophyta?
    3 years ago
  • cosimo sabbatini
    Which is asecual spore in brown algae?
    3 years ago
  • Biniam
    What is paraphyses in brown algae?
    3 years ago
  • Samantha
    What does unilocular sporangia produce?
    3 years ago
  • Gavino Genovesi
    Do green algae have unilocular spores?
    3 years ago
  • charley
    Does xanthophyta possess alternation of generation?
    3 years ago
  • natasha
    How does the plant body of ectocarpus differ from laminaria?
    3 years ago
  • lea
    What is reproduction and life cycle phaeophyta?
    3 years ago
  • virgilio
    What kind of reproduction is there in phaeophyta?
    3 years ago
  • Kerstin
    How to ectocarpus development of unlloculer sporangium?
    3 years ago
  • SVEN HOFFMANN
    What type of sexual reproduction occurs in fucus?
    3 years ago
  • Crispus
    Does brown algae also reproduce by zygotic meiosis?
    2 years ago
  • kelley
    Does laminaria have asexual reproduction?
    2 years ago
  • Brock
    Does laminaria reproduce asexually?
    2 years ago
  • brenda
    How does green algae reproduce sexually?
    2 years ago
  • zula
    Are the gametes of brown algae formed by meiosis or by mitosis?
    2 years ago
  • Quinto
    Does laminaria grow from a zygote?
    2 years ago
  • paladin
    What kind of reproduction occurs in brown and green algea?
    2 years ago
  • brigitte
    What is the asexual spore of phaeophyta?
    2 years ago
  • benigno
    Where reduction divisions occur in ectocarpus?
    2 years ago
  • cynthia
    Which type of meiosis is found in Fucus brown algae?
    2 years ago
  • meaza
    What is the type of production that takes place in brown algae?
    2 years ago
  • roosa pasanen
    Which type of asexul reproduction in green algae present?
    2 years ago
  • Enrica
    What are vegitative cells in brown algae?
    2 years ago
  • jose walter
    Why eutocarpus diploid spores are found in pleurilocular sporangium?
    2 years ago
  • Mandy Metzger
    How is sexual reproduction accomplished among algae?
    1 year ago
  • SETTIMIO
    Do brown algae fucus reproduce sexually?
    4 months ago
  • Yorda
    Do algae produce eggs and sperm?
    4 months ago
  • sebastian
    Which algae shows oogamous sexual reproduction?
    3 months ago

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