Give illustrated account of life history of Ectocarpus

It is marine Algae remains attached to substratum by rhizoids. Some species may be parasitic or may occur on higher members like of order fucales. Plant body is branched and has brown filaments which are slender. Plant body is made up of two parts, a creeping portion which serves as holdfast and a number of branches which arise from it. Filaments are made up of single row of cells. Each cell is uninucleate small and rectangular and has many chromatophores containing brown pigment. Pyrenoids are also present in chromatophores. Growth of filament is intercalary. Plant is autotrophic in nutrition.

Reproduction: Ectocarpus reproduces by Asexual and Sexual method.

Asexual Reproduction: (A) This takes place by biflagellate zoospores produced in unicellular sporangia which are borne by diploid asexual plant. They start as simple globular cells filled with Protoplasm. Nucleus undergoes single reduction division followed by simple division.

Around each daughter nucleus protoplasm collects to form zoospore. Each zoospore is haploid structure bearing two flagella at its lateral side. On liberation zoospore swims and settles down and grows into haploid plant.

(B) Asexual Reproduction may also take place by formation of diploid biflagellate zoospore produced in plurilocular or Neutral sporangia. These are formed by terminal cells on the short lateral branches. Contents of these undergo repeated divisions followed by wall formation. As a result a number of cubical chambers of almost equal are formed. As there is no reduction division at any stage, so the zoospores form diploid plants on germination these zoospores form diploid plants.

(2) Sexual Reproduction: It takes place from isogamy to an isogamy. Fusing of motile gametes may be of equal size of they may be of unequal size.

They are produced inside the plurilocular sporangia borne on haploid thalli. Such sporangia which are borne of haploid thalli are known as gametangia. They produce gametes which are haploid in nature. Plants are usually monoecious. Isogametes or amisogametes on liberation from same or different plants unite and form a diploid zygote. This zygote gives rise to diploid plant which in turn may bear neutral or unilocular sporangia.

Alteration of Generation:

In Ectocarpus gametophytes and sporophytes are similar morphologically and both are capable of asexual reproduction by zoospores. Some plants are haplonts others diplonts and still others show a regular alternation of generation of gametophytes and sporophytes.

Reproduction:

It takes place by vegetative or sexual method.

1.         Vegetative Reproduction:

It takes place by fragmentation. During this process little adventitious hoots formed either as a resut of injury to the thallus or by activity of meristem, get separated from the parent plant and develop into new thatti.

2.         Sexual Reproduction:

It is ooganous type. Sex organs like antheridia and oogonia are borne within spherical or conical chambers called conceptables in the swollen tips of branches called receptacles. Species of Fucus may be homo or heterothallic. In homothallic species the antheridia and oogonia may develop in same conceptacle eg: Ficis furcantus or different conceptacles of the same plant eg: Ficis spiralis. Conceptacles open outside by small opening called ostoile.

The oogonuim (female reproductive organs) develops from the superficial cell of conceptacle. Cell divides into a basal and oogonial initial cell. The basal cell does not divide further and forms a stalk while oofonial initial cell is fertile and forms the oogonium. The nucleus of oogonium then undergoes successive divisions to form eight daughter nuclei. First two nuclear divisions constitute meiosis. Cytoplasm undergoes cleavage to form eight uni-nucleate parts. Each uni-nucleate daughter protoplast rounds on. Eight spherical eggs or oospores are thus formed. At maturity the oogonial wall thickens and becomes differentiated into three layers. They are inner most endochite, middle mesochite and outer most exochite. Exochite ruphures in water. Oognoia are still enclosed by inner two layers. These are set free as a package through the ostiole into surrounding water. Sea water causes mesochite to ruphire at its apex and unvaginate. This exposes endochite. Endochite also takes water and finally dissolves. The eggs float away as passive or non-motile.

The antheriduim (male reproduction organ) is produced on the ultimate tips of branched paraphysis of male conceptacles.

Each Antheriduim is small oval or spherical uni-nucleate cell borne on the tip of much branched paraphysis. Any cell of the wall functions as antheridial initial cell and it divides into a stalk cell and antheriduim proper cell. It enlarges to form a terminal antheriduim. The stalk cell usually produces a branch which pushes the antheriduim to one side and itself gives rise to a second. Antheriduim by the repetition of this process are formed branched prophysis. The nucleus of the antheridial cell divides into two, four, eight, sixteen, thirty two and sixty four nuclei. Each nucleus surrounded by bit of protoplasm is metamorphosed into biflagellate pyriform antherozoid or sperm. It has two laterally attached flagella and an eyespot. Outer wall of antheriduim ruptures and all the sperms enclosed by mucilaginous wall come out.

This inner layer of mucilage is softened and sperms are released. Sometimes whole f the antheriduim comes out of the conceptacle and releases the sperms.

Fertilization: It takes place inside the water. Several sperms surround an egg but only one fuses with egg and results in formation of zygote which diploid in nature.

Germination of Zygote: The zygote or oospore germinates to produce new Fucus Plant.