General Characters of Rhodophyceae & Life Cycle of Polysiphonia SMG

General Characters of Rhodophyceae and description of the life cycle of Polysiphonia

1. GENERAL CHARACTERS OF RHODOPHYCEAE & LIFE CYCLE OF POLYSIPHONIA Dr. Saji Mariam George Associate Professor Assumption College Autonomous Changanacherry

2. CLASS RHODOPHYCEAE (RED ALGAE ): GENERAL CHARACTERS Habitat : Most of the species are marine( Polysiphonia , Corallina ) . A few (about 200 ) are freshwater forms ( e.g. Batrachospermum , Lemanea etc. ) Some are t errestrial in moist soil. Most Red algae are Lithophytes- attached to rocks Some are Epiphytes – e.g. Polysiphonia . Some are Parasites – e.g. Harveyella mirabilis , H . pachyderma Some are semi-parasites.(e.g. Polysiphonia fastigiata )

3. RED ALGAE Corallina (Marine ) Polysiphonia (Marine)

4. RED ALGAE Lemanea (Fresh water) Batrachospermum (Fresh water)

5. Habit / Thallus organization / Range of Thallus structure i ) In some species, the thallus is Unicellular e.g . Porphyridium

6. ii ) Majority are multicellular – Palmelloid (e.g. Asterocystis ) , filamentous (e.g. Goniotrichum ), Parenchymatous ( Porphyra , Bangia ) or pseudoparenchymatous (e.g. Dumonita , Helminthocladia ) In most multicellular forms , vegetative cells are interconnected by pit connections called plasmodesmata . The thallus is extremely delicate, feathery and beautifully coloured Thallus may be Uniaxial or Multiaxial

7. Uniaxial Thallus H as an axial or central and usually corticated filament which bears branched laterals ( e.g. Achrochaetium ) In some cases, the laterals may be organized to form a uniaxial , pseudoparenchymatous thallus . (e.g. Grimelia , Dalesseria , Batrachospermum ) Multiaxial Thallus H as a tuft or bundle of axial or central filaments which give radiating laterals to the margin . In some cases, the central filaments and the laterals collectively form a pseudoparenchymatous thallus ( e.g. Polysiphonia )

8. Parenchymatous thallus - Porphyra Parenchymatous thallus – Bangia

9. Pseudoparenchymatous thallus Helminthocladia Pseudoparenchymatous thallus Dumonita

10. Palmelloid thallus Asterocystis (Syn. Chroodactylon ornatum ) Filamentous thallus - Goniotrichum

11. Uniaxial Thallus - Achrochaetium Uniaxial Thallus – Pseudoparenchymatous - Dalesseria

12. Uniaxial Thallus - Batrachospermum Multiaxial Thallus - Polysiphonia

13. Cell structure : Cell wall & Protoplast Cell wall is bilayered Outer layer is composed of pectic compounds and polysulphate esters. In some cases, the outer layer has a mucilagenous coating composed of sulphated galactans such as Agar, Carrageenin , Furcellaran and Porphyran . In some cases, outer layer is impregnated with Calcium carbonate. The inner layer is made up of Cellulose.

14. Protoplast Consists of Plasma membrane, cytoplasm. Cytoplasm is located in the peripheral position due to a large central vauole Cytoplasm contains cell organelles, a single stellate or axile or several, discoid and parietal chromatophores . Each chromatophore is a double - layered , fluid – filled bag containing the matrix called stroma which contain photosynthetic lamellae containing photosynthetic pigments - Chlorophylls a, d, alpha & beta carotene, blue Phycocyanin & Allophycocyanin , red Phycoerythrin ( Phycobilins ), Leutein , Violaxanthin , Zeaxanthin , Flavoxanthin etc. The red colour of the algae is due to the predominanance of the red pigment Phycoerythrin and Phycocyanin . Despite   their name, not all Rhodophyceae are red. Some of them have very little Phycoerythrin and appear green or bluish.

15. Reserve food Floridean starch, Floridosides , Mannoglycerate , Maltose, Sucrose, Trehalose , Isofloridosides and very small amounts of Alcohols & Fats. Nucleus one or multinucleate e.g . In Griffithsia , 3000 – 4000 nuclei per cell Griffithsia

16. Reproduction Methods : Vegetative , Asexual, Sexual i ) Vegetative Reproduction Common among unicellular forms. Simple fission or cell division – e.g. Porphyridium Fragmentation in multicellular forms ii ) Asexual Reproduction by Spores a ) Monospores Large 4-nucleate Aplanospores Produced singly in a monosporangium e.g . Batrachospermum , Compsopogen . Compsopogen

17. b ) Neutral Spores Non –motile asexual spores produced by the direct transformation of vegetative cells e.g . Bangia c) Carpospores Rounded, uninucleate and non-motile asexual spores formed from the direct or indirect division of the zygote e.g . Polysiphonia d ) Tetraspores Uninucleate and haploid spores formed in tetrasporangia by meiosis e.g . Polysiphonia

18. iii) Sexual Reproduction Oogamy Both male and female gametes are non - motile Male sex organ – Antheridium or Spermatangium - male gamete spermatium . Female sex organ – Carpogonium – has a receptive , hair - like trichogyne – female gamete egg or ovum Some sps . Are monoecious Some are dioecious

19. During fertilization, a spermatium is carried to the carpogonium by water current and gets attached to the trichogyne - the point of contact dissolves – the spermatium nucleus passes down to the egg located in the base of the carpogonium – fertilization – zygote Zygote - Gonimoblast filaments – terminal cell of each filament matures to a carposporangium . The urn – shaped structure consisting of carpogonium , gonimoblast filaments and carposporangia is called Cystocarp ( Carposporophyte ) - Carpospore - Tetrasporophyte – Tetraspores .

20. Life cycle 1. Haplobiontic life cycle. Three Phases in the Life cycle. Two haploid phases and one diploid phase (Zygote) e.g. Batrachospermum 2. Diplo biontic life cycle. Three phases in the life cycle Two diploid phases and one haploid phase. e.g. Polysiphonia

21. POLYSIPHONIA Systematic Position Division : Rhodophyta Class : Rhodophyceae Sub Class : Floridae Order : Ceramiales Family : Rhodomelaceae Common Indian Sps . Polysiphonia elongata P . p latycarpa P . u rceolata P. vaiegata

22. Habitat/ Occurrence A marine alga A lithophyte Some are semi-parasite Some are epiphytes Cosmopolitan in distribution

23. Habit/ Thallus Structure Multiaxial thallus Form violet – red thick tufts Heterotrichous habit – prostrate and erect system Prostrate system creeps over the substratum- well developed and multiaxial -e.g. P. nigrescens , P. urceolata and gives rise to rhizoids In some species, multiaxial prostrate system is absent and instead the basal cells of erect aerial branches form massive attachment discs. ( P. elongata and P. violacea )

24. POLYSIPHONIA …..

25. Prostrate system gives off many multiaxial aerial branches The main axis of the long aerial branches consists of a central (axial)siphon of elongated cylindrical cells, surrounded by smaller pericentral cells or siphons. Cells of central and pericentral siphons are interconnected through pit connections . In the older portions of the main axis, pericentral cells become corticated by one or more layers of small cortical cells.

26. Main axis has - i ) Short branches of limited growth or Trichoblasts Arise from the main axis in a spiral manner. Uniaxial and lack pericentral siphon Cells contain very few chromatophores Fertile t richoblasts bear male and female reproductive structures. ii ) Long branches of unlimited growth. Basal part is polysiphonous , but distal part is monosiphonous . Do not bear reproductive structures.

27. Cell Structure Cells of the central and pericentral siphons are long and cylindrical Cell wall is two layered - outer pectin and polysulphate esters and inner cellulose Internal to the cell wall is the cell membrane Cytoplasm forms a lining layer – contains a single nucleus, several discoid chromatophores which contain photosynthetic pigments – Chlorophylls a and d , carotene, xanthophylls, blue Phycocyanin , red Phycoerythrin ( Phycobilins ) . Pyrenoids are absent The reserve food is Floridian starch A large central vacuole Pit connections occur between adjacent cells.

28. POLYSIPHONIA

29. Growth Takes place by the activity of the dome-shaped apical cell. Reproduction Asexual and Sexual Polysiphonia is heterothallic. It exhibit triphasic alternation of generations. Three kinds of thalli are present in the life cycle of Polysiphonia . i ) The Gametophyte The thallus is haploid , free living and dioecious . There are separate male gametophyte which bear the male sex organ Spermatangium and female gametophyte which bear the female sex organ, Carpogonium .

30. ii ) The Carposporophyte These are diploid thallus which develop from the zygote. They produce carposporangia which produce diploid carpospores. iii ) The Tetrasporophyte Formed by the germination of diploid carpospore . It is diploid and produces tetrasporangia which produce haploid t etraspores which on germination produce male and female gametophytes.

31. i ) The Gametophytes The gametophytes are concerned with sexual reproduction which is Oogamous . Polysiphonia is heterothallic or dioecious – the male sex organs and the female sex organs are borne on different gametophytes. Male gametophyte produces male sex organ Spermatangium Female gametophyte produces female sex organ Carpogonium . Both male and female gametophytic plants are morphologically similar.

32. Male Gametophyte It bears the male sex organs Spermatangia which are borne in dense clusters and are closely packed forming a compact cone –shaped structure on the upper branch of dichotomously branched male trichoblasts . In some species, both the branches of the trichoblasts become fertile. The two basal cells of the trichoblast functions as the stalk. Other cells cut off pericentral cells. Thus the fertile portion of this branch becomes polysiphonous The pericentral cells may divide once or twice producing a large number of spermatangial mother cells which are arranged in the form of a compact layer external to the central siphon.

33. Each spermatangial mother cell gives rise to 2 to 4 spermatangia or antheridia. The spermatangia are spherrical or oblong unicellular structures The contents of each spermatangium produce a single , non – motile spherical male gamete or spermatium . Spermatia are liberated by the formation of a narrow slit in the spermatangial wall and are carried by water currents to the vicinity of the female sex organ.

34. Female Gametophyte It bears the female sex organ , Carpogonium . The female trichoblast initial arises from the central siphon 3 or 4 cells behind the apical cell. It divides repeatedly to form a reduced female trichoblast 5 to 7 cells in height. The 3 lowermost cells of the female trichoblast divide vertically to form an ensheathing layer of pericentral cells which are arranged in three tiers one above the other. One of the pericentral cells in the middle tier on the adaxial side becomes the supporting cell. The latter cuts off a small initial cell at its free end known as the procarp initial. The initial cell divides and redivides to form a small, curved four – celled branch called the carpogonial filament or procarp .

35. The terminal cell of the carpogonial filament functions as the carpogonium mother cell which gets modified into the carpogonium . The carpogonium has a basal swollen portion in which the egg or female gamete is present and a terminal slender portion called trichogyne . In the mean time, the supporting cell cuts off two sterile cells, one towards its base called the basal sterile filament initial and another on one side called the lateral sterile filament initial . The latter divides immediately to form a two – celled lateral sterile filament. At this stage, the carpogonium is ready for fertilization.

36. Fertilization The spermatia , liberated from the male gametophytic plants are carried by the water currents to the carpogonium . When a spermatium adheres to the trichogyne of the carpogonium , the point of attachment dissolves and the male nucleus enters into the trichogyne . The male nucleus then enters the trichogyne and moves down and reaches the swollen base of the carpogonium and fuses with the female gamete to form the zygote. The formation of zygote represents the end point of the haploid gametophytic generation and the starting point of the diploid carposporophyte .

37. Post – Fertilization changes The post – fertilization changes in Polysiphonia include the following events. The 2 celled lateral sterile filament becomes 4 to 10 celled. The basal sterile filament initial divides to form a 2 – celled filament. The sterile filaments are nutritive in function. The supporting cell buds off an Auxiliary cell at its upper end. It has a haploid nucleus and lies close to the carpogonium . The auxiliary cell establishes a tubular connection with the base of the carpogonium . The diploid nucleus of the carpogonium divides mitotically into 2 daughter nuclei and one of these nuclei migrates into the auxiliary cell through the tubular connection. The haploid nucleus of the auxiliary cell now degenerates leaving behind only the diploid nucleus.

38. The carpogonial branch gradually begin to shrivel. The outgrowths of the pericentral cells adjacent to the supporting cells start producing an envelope around the developing carposporophyte . Now, many initials called Gonimoblast initials are produced from the Auxiliary cells. The diploid nucleus of the auxiliary cell divides mitotically and each daughter nucleus migrates into the gonimoblast initial. Thus each gonimoblast initial contains a diploid nucleus. Each gonimoblast initial divides and redivides to form a short gonimoblast filament. The terminal cell of the gonimoblast filament develop into an elongated , pear-shaped carposporangia . The contents of each carposporangium differentiate into a single diploid carpospore .

39. Polysiphonia : Post – Fertilization changes

40. By this time, the supporting cell, auxiliary cell, carpogonial filament and the sterile filaments fuse to form an irregularly shaped nutritive cell called the placental cell. ii ) The Carposporophyte or Cystocarp This is the second individual formed in the life cycle of Polysiphonia . The whole structure consisting of gonimoblast filaments, carposporangia , carpospores and placental cell gets completely enveloped by the developing young vegetative filaments which form an urn-shaped body called the cystocarp or the carposporophyte The wall of the cystocarp is called Pericarp and the opening is called Ostiole . The cystocarp or the carposporophyte is dependent on the female gametophytic plant . The carpospores are liberated through the ostiole and are carried by water currents.

41. iii ) The Tetrasporophytes The diploid carpospore on germination produce new diploid plants called tetrasporophytes which resemble gametophytic plants in morphology - It consists of the central siphon encircled by the pericentral siphons. The thallus is laterally branched. The tetrasporophyte is a free living diploid plant They produce sac like tetrasporangia from small – sized pericentral cells. Each pericentral cell divides vertically into an outer cell and an inner cell . The outer cell divides and forms two or more cover cells , where as the inner cell functions as the sporangial mother cell.

42. The sporangial mother cell divides transversely into a lower stalk cell and an upper tetrasporangial cell. The tetrasporangial cell functions as the tetrasporangium . The diploid nucleus of each tetrasporangium divides meiotically to form 4 haploid nuclei and form 4 tetraspores which are arranged tetrahedrally . Tetraspores are liberated by the rupturing of the sporangial wall. Tetraspores germinate and produce haploid gametophytic plants . Out of the 4 tetraspores , 2 develop into male gametophytes and the other 2 develop into female gametophytes.

43. Polysiphonia : Tetrasporophyte

44. Polysiphonia : Post – Fertilization changes

45. Polysiphonia : Life Cycle The life cycle of Polysiphonia is triphasic and haplo-diplobiontic . Three different phases in the life cycle : i ) Haploid phase represented by the male and female gametophytes ii ) Diploid phase represented by carposporophyte ( Cystocarp ) iii ) Diploid phase represented by tetrasporophyte . i ) Haploid phase The gametophytes reproduce sexually - The male gametophyte produce spermatangia which produce the non - motile male gametes spermatia . The female gametophyte produce the female gamete. The fusion of the male gamete spermatium and the female gamete results in the formation of diploid zygote.

46. ii ) Diploid phase R epresented by carposporophyte S econd phase in the life cycle of Polysiphonia . This phase is developed from the diploid zygote. Post fertilization events include the development of gonimoblast initials, carposporangium and the diploid carpospore . These whole structures and the placental cell is protected by a two layered pericarp . This phase is dependent on the female gametophyte .

47. iii ) Diploid phase R epresented by tetrasporophyte . The diploid carpospore develops into the diploid tetrasporophyte . It is a free living plant and is morphologically similar to the gametophytic plants . The diploid tetrasporophyte produce tetrasporangium which undergoes meiosis and form 4 haploid tetraspores . The germination of haploid tetraspores produce haploid gametophytic plants. Thus in the life cycle of Polysiphonia , there are one haploid phase represented by the gametophytic plants and two diploid phase represented by the carposporophyte ( c ystocarp ) and the tetrasporophyte . Hence the life cycle is said to be triphasic and haplo-diplobiontic type.

48. Polysiphonia : Life Cycle