Ectocarpus

MORPHOLOGY CELL STRUTURE REPRODUCTION LIFE CYCLE

1. Dr. Saurabh Kumar, HOD, Botany, KCMT Ectocarpus Occurrence It is a marine brown alga found throughout the world, particularly abundant along the Atlantic coast. A few species occur in fresh water. The plant grows attached to rocks and stones along coasts and consist of tufts of brownish, delicate highly branched filaments . Some species are epiphytes on other algae. Some of the common Indian species are E. coniferus, E. indicus, and E. arabicus. Ectocarpus fasciculatus grows on the fins of certain fishes.

2. Dr. Saurabh Kumar, HOD, Botany, KCMT Structure of thallus The thallus consists of profusely branched uniseriate filaments . Ectocarpus shows heterotrichous habit , consisting of a prostrate and erect system . The filaments of the erect system arise from the filaments of prostrate system. Prostate system: The prostrate system consists of creeping, irregularly branched filaments. These filaments are attached to the substratum with the help of rhizoids . Erect system: The erect system arises from the prostrate system. It consists of well branched filaments . Each branch arises beneath the septa. The main axis and the branches of the erect system are uniseriate . Branches terminate into an acute point to form a hair.

3. Dr. Saurabh Kumar, HOD, Botany, KCMT Cell Structure: Cells are cylindrical or rectangular and uninucleate . Cell wall is thick, composed of three layers of pectin and cellulose . Algin and fucoidan are also present in the cell wall. These are characteristic gelatinous substances present in the brown algae. The chromatophores may be ribbon-like with irregular outline or disc-shaped . The dominant pigment is fucoxanthin . It gives this algae golden brown color . The other photosynthetic pigments are chlorophyll a, c, beta-carotene and other xanthophylls .

4. Dr. Saurabh Kumar, HOD, Botany, KCMT Growth : In erect system growth is trichothallic. Intercalary meristem is present at the base of the hair. It is called trichothallic meristem . It increases the length of the terminal hair and vegetative cell of the branch. The growth in the prostrate system is apical.

5. Dr. Saurabh Kumar, HOD, Botany, KCMT Reproduction: In Ectocarpous the reproduction takes place by asexual and sexual methods. Asexual reproduction The asexual reproduction takes place by the formation of biflagellate zoospores. These zoospores may be haploid meiozoospore or gonozoospores produced in one- celled unilocular sporangia . Or they may be diploid formed in many- celled plurilocular sporangia. Both kinds of sporangia are present on the same diploid sporophyte plant. The sporangia are borne terminally and singly on lateral branches .

6. Dr. Saurabh Kumar, HOD, Botany, KCMT Unilocular Sporangia ( one-celled sporangia ) These are borne singly on lateral branches . Each sporangium is a stalked, globular, oval or pear- shaped structure having dense cytoplasm with many chromatophores and diploid nucleus . Diploid nucleus divides meiotically into many haploid nuclei (32-64), each of which changes into a zoospore. Each zoospore is small, pear-shaped and haploid structure with two laterally attached flagella . Zoospores develop into haploid sexual plant . Development of Unilocular Sporangium. The unilocular sporangia develop from the apical (terminal) cell of the lateral branches which increase considerably in size to take on a globose or ellipsoid shape and functions as a sporangial initial.

7. Dr. Saurabh Kumar, HOD, Botany, KCMT The number of chromatophores also increases within the developing sporangium. The diploid nucleus of the initial cell first undergoes meiosis, followed by several mitotic divisions to produce 32 to 64 haploid daughter nuclei . There is then cleavage of the cytoplasm to form as many uninucleate daughter protoplast units , with single chromatophores and haploid nuclei. Germination of meiozoospores After swimming for a while, each meiozoospore on contact with suitable substratum withdraw its flagella, becomes rounded and secretes a membrane around it. Within short time, a germ tube is formed , which divides many times and forms a prostrate filament. Some cells of the prostrate filament become active and form erect filaments. The plants developed on the germination of these haploid meiozoospores are gametophytes or sexual plants in the life cycle.

8. Dr. Saurabh Kumar, HOD, Botany, KCMT These are also formed on diploid plants at the ends of small branches. These are elongated cone-like structures , made up of many small cubical cells or compartments arranged in vertical rows . Diploid nucleus of each compartment changes into a single diploid zoospore which again gives rise to diploid plant on germination. Development of plurilocular sporangia: These are elongated, conical, multicellular bodies, developed singly on diploid (2n) or asexual (sporophytic) plants . They develop initially like unilocular sporangia at the tip of short lateral branches. The apical cell enlarges and functions as sporangial initial (mother cell). This sporangial initial becomes enlarged and contains numerous chromatophores . Plurilocular (neutral) Sporangium

9. Dr. Saurabh Kumar, HOD, Botany, KCMT It then undergoes repeated mitotic divisions , forming 6-12 cells in a vertical row. The cells than undergo several vertical divisions , as a result of which a multicellular cone-like structure , consisting of several hundred small cubical cells , arranged in 20-40 transverse tiers , is produced forming a plurilocular sporangium . Protoplast of each compartment metamorphoses into a single biflagellate zoospore. There is no reduction division during the formation of zoospore in plurilocular sporangium. So each small cubical cells of plurilocular sporangium contains a single diploid nucleus that metamorphoses into a single, uninucleate (2n) and biflagellate zoospore. The zoospores formed from plurilocular sporangia are similar to meiozoospores developed in unilocular sporangia, but are diploid. The zoospores from a sporangium liberate through an apical or lateral aperture, On germination each produces a sporophytic (2n) plant.

10. Dr. Saurabh Kumar, HOD, Botany, KCMT Sexual Reproduction Sexual reproduction in Ectocarpus takes place by isogamy or anisogamy. Majority of the species are isogamous and homothallic. Some species are anisogamous. Ectocarpus secundus is heterothallic and anisogamous. The gametes are produced in plurilocular gametangia . These gametangia are many-celled, elongated, and sessile or shortly stalked conical structures . Gametangia are produced on the haploid plants developing from the meiozoospores. The development of gametangia is similar to that of plurilocular sporangia . These develop from terminal cell of a lateral branch . The gametangial initial gets inflated. It divides mitotically by repeated transverse divisions . It produces a vertical row of flat cells . These cells undergo repeated vertical and transverse divisions . They form many hundred small cubical cells . These cells are arranged in 24-40 transverse rows. The protoplast of each cell metamorphoses into a single, pyriform, biflagellate, haploid gamete. The flagella are laterally attached . The zoospores and the gametes are similar in structure. But the gametes are relatively smaller in size . The gametes are liberated through an apical pore formed in the gametangium .

11. Dr. Saurabh Kumar, HOD, Botany, KCMT Isogamy Physiological anisogamy Morphological Anisogamy Isogamous species are E. pusilus and E. globifer etc. In these species, the fusion takes place between alike gametes . These gametes belong to the same plant or even to the same gametangium. It occurs in species like E. siliculosus. The fusing gametes are identical morphologically. But they show different sexual behavior . One is less active and is called female gamete . The other is more active and is called male gamete . The female gamete soon comes to rest . It settles on a substratum. It becomes surrounded by active male gametes . The male gametes attach themselves to the female gamete through their anterior flagella. The anchoring flagellum contracts, the body of one of the male gametes comes in contact with that of the female gamete and the fusion takes place. This phenomenon is called clump formation. It occurs in species like E. secundus. In this case, the two fusing gametes are dissimilar in size . They are produced in different gametangia: The smaller ones are produced in microgametangia. The larger ones are produced in megagametangia. Forms of Sexual Reproductions Fertilization: After fertilization diploid zygote is formed. There is no zygotic meiosis. The zygote germinates into a diploid sporophyte.

12. Dr. Saurabh Kumar, HOD, Botany, KCMT Isogamy Physiological anisogamy Morphological Anisogamy

13. Dr. Saurabh Kumar, HOD, Botany, KCMT Alternation of Generations: Ectocarpus shows isomorphic alternation of generations. There is alternation of morphologically similar gametophytic (haploid) and sporophytic (diploid) generations in its life cycle. ( Sporophyte: The sporophyte is diploid. It develops two types of sporangia. Zoospores are produced in these sporangia ) . Zoospores are produced by mitosis (mitozoospores) in plurilocular sporangia . The zoospores in unilocular sporangia are produced meiotically (meiozoospores ). The mitozoospores germinate into a diploid sporophyte . These spores cause reduplication of sporophyte generation. The meiozoospores germinate to give rise a haploid gametophyte plant . Gametophyte: It develops plurilocular gametangia. These gametophytes are similar to the sporophyte in morphology . Haploid gametes are produced in the gametangia . These gametes fuse to form a diploid zygote . Zygote germinates into a diploid sporophyte plant. In some species the gametophyte generation is also reduplicated by the parthenogenesis. In this case, the gametes from plurilocular sporangia form new gametophyte generation .)

14. DR.SAURABH KUMAR HOD, Department of Botany Khandelwal college of Management Science & Technology Bareilly. Dr. Saurabh Kumar, HOD, Botany, KCMT