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Diatoms, Dinoflagellates, Lichen

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  2. Introduction • The diatoms are unicellular, sometimes colonial algae found in almost every aquatic habitat as free-living photosynthetic autotrophs, colorless heterotrophs, or photosynthetic symbiotes • Phytoplakton • Evolve early Jurassic (~185 Ma ago) • Photo synthetic algae (Mostly) • 20% producer of food chain • More than 200000 sp.
  3. • Cell wall is made up of Silicone cell wall (silic acid)-(pectin+silica) • Silicate is any of the ionized forms of monosilicic acid [Si(OH)4] • Huge depositor of silicone • Cell size 2 um to 500um (majority)
  4. Cell wall • It is constructed of two almost equal halves, the smaller fitting into the larger like a Petri dish • The outer of the two half-walls is the epitheca and the inner the hypotheca • Each theca is composed of two parts, the valve, a more or less flattened plate, and the connecting band • The cells are surrounded by a rigid two-part box-like cell wall composed of silica, called the frustule
  5. • Two connecting bands, one attached to each valve, are called the girdle • Sometimes the connecting bands themselves are called girdle bands • there are one or more additional bands between the valve and the girdle, which are called intercalary bands • the edge of the valve is bent inward, this portion is called the mantle or valve jacket
  6. • The siliceous material of the frustule is laid down in certain regular patterns that leave the wall ornamented are four basic types 1. Centric and radial, where the structure is arranged according to a central point 2. Trellisoid, where the structure is arranged uniformly over the surface without reference to a point or line 3. Gonoid, where the structure is dominated by angles 4. Pennate, where the structure is symmetrically arranged upon either side of a central line
  7. • Some pennate diatoms have a raphe system composed of the raphe (a longitudinal slot in the theca), divided into two parts by the central nodule • Besides the raphe, there are basically two types of wall perforations within the Bacillariophyceae: the simple pore or hole, and the more complex loculus or areola
  8. • Special pores (mucilage or slime pores) through which mucilage is secreted • In the pennate diatoms, these pores usually occur singly near one or both poles of the valve and generally occupy thickenings in the walls. • The frustule is composed of quartzite or hydrated amorphous silica and small amounts of aluminum, magnesium, iron, and titanium mixed with it • Diatom frustules from marine plankton contain 96.5% SiO2 and 1.5% Al2O3 or Fe2O3
  9. Vegetative reproduction • Epithecas of the daughter cells with each daughter cell producing new hypotheca • Daughter cells is of then same size as the parent cell, and the other is smaller • Cellular energy for silicification and transport comes from aerobic respiration without any direct involvement of photosynthetic energy
  10. • Diatoms have an absolute requirement for silicon if cell division is to take place. In water, solid silica dissociates to produce undissociated silicic acid Si(OH)4: • SiO2 (solid) 2 H2O-----> Si(OH)4
  11. • Although silicon is the second most abundant element in the Earth’s crust, its availability is limited by its solubility in water. • The Si(OH)4 in marine waters is about 6 ppm. In the global ocean, about 97% of the dissolved Si is present as Si(OH)4 • Prior to cell division, the cell elongates, pushing the epitheca away from the hypotheca, and the nucleus divides. After the protoplasm has divided into two by the invagination of the plasmalemma
  12. Motility • Some diatoms are able to glide over the surface of a substrate, leaving a mucilaginous trail in their wake. 1. The Navicula type, with a straight movement; 2. The Amphora type, in which the path is usually curved 3. The Nitzschia type, which always exhibits curved pathways with two different radii • The observed rates of gliding in diatoms vary from 2 to 14 m s-1 at room temperature
  13. • Diatoms can glide only when the valve containing a raphe is in contact with the surface • the diatom secretes a mucilaginous tether from the portion of the raphe near the central nodule • The tether attaches to the substratum and the cell pulls itself onto a valve containing a raphe using the tether • Those pennate diatoms that glide have bundles of actin microfilaments running parallel to the raphe
  14. Plastids and storage products • The chloroplasts contain chlorophylls a, c1, and c2 • Fucoxanthin is the principal carotenoid, giving the cells their golden-brown color • Fucoxanthin is an efficient carotenoid in the transfer of energy to chlorophyll a (PS II) • The storage product is chrysolaminarin, which is located in vesicles in the cell Note: (Chrysolaminarin is a linear polymer of β(1→3) and β(1→6) linked glucose units in a ratio of 11:1)
  15. Resting spores and resting cells • Some diatom cells form thick, ornamented walls at different times in their life cycle and become resting spores • Resting spores are formed after the diatom cells have been subjected to a stress shock like light, temperature, and salinity. • Nutrient depletion that trigger resting spore formation • due to the loss of vacuoles and their contents it becomes small
  16. Auxospores • The auxospores are formed by the fusion of two gametes • In the centric and gonoid diatoms, the male gamete is motile • In the pennate and trellisoid diatoms, both gametes are non- flagellated • Depending on the species, auxospores develop in one of three different ways
  17. Reproduction • Vegetative cells of diatoms are diploid (2N) and so meiosis can take place, producing male and female gametes which then fuse to form the zygote. • The zygote sheds its silica theca and grows into a large sphere covered by an organic membrane, the auxospore
  18. Dinoflagellates
  19. • Living dinoflagellates are one of the most important components in plankton. • Marine as well as in fresh water also 1700 sp marine and 220 sp freshwater dinoflagellates • Spiraling motion propelled by dimorphic flagella • Phototrophs and mixotrophs (phagotrophs and autotrophs) • Some species are endosymbionts of marine animals and play an important part in the biology of coral reefs
  20. • 90% of all dinoflagellates are marine plankton • majority are microscopic, the largest, dinoflagellates as large as 2 mm in diameter • Some dinoflagellates produce resting stages, called dinoflagellate cysts or dinocysts, as part of their life cycles. • They make most of the worlds oxygen • Chlorophylls a and c2 are present in the chloroplasts, with peridinin and neoperidinin being the main carotenoids.
  21. • First described by Henry Baker in 1753 “Animalcules which cause the Sparkling Light in Sea Water” • Dinoflagellates are protists which have been classified using both the International Code of Botanical Nomenclature (ICBN, now renamed as ICN) and the International Code of Zoological Nomenclature (ICZN). • In the 1830s, the German microscopist Christian Gottfried Ehrenberg examined many water and plankton samples and proposed several dinoflagellate genera
  22. Dinoflagellate, Gonyaulax polyedra Dinoflagellates exhibit two flagella which permit movement Groove Theca One flagella is located within the groove and the other is located at the lower end (not visible).
  23. Cell envelop • Dinoflagellates have a complex cell covering called an amphiesma or cortex, composed of a series of membrances, flattened vesicles called alveolae and related structures
  24. • peculiar form of nucleus, called a dinokaryon, the chromosomes are attached to the nuclear membrane, lack histone • Remain condensed throughout interphase rather than just during mitosis • The nuclei of the more advanced dinoflagellates are striking cytologically in that they have their chromatin condensed into 2.5 nm fibrils
  25. • phototrophy, mixotrophy and heterotrophy. • Some free living dinoflagellates do not have chloroplasts but host a phototrophic endosymbiont • Thecate and nonthecate dinoflagellates draw prey to the sulcal • region of the cell (either via water currents set up by the flagella or via pseudopodial extensions) and ingest the prey through the sulcus. • Pseudopodial engulf called pallium
  26. • both fresh and marine waters, although a much greater variety of forms is found in marine members • A typical motile dinoflagellate consists of an epicone and hypocone divided by the transverse girdle or cingulum
  27. • Epicone and hypocone are normally divided into a number of Thecal plates (Number can vary from genera to genera) • longitudinal sulcus running perpendicular to the girdle • longitudinal and transverse flagella emerge through the thecal plates in the area where the girdle and sulcus meet
  28. • Chloroplast covered three layered and chl a, chl c2, carotenoid, xanthophylls • A group of xanthophylls that appears to be unique to dinoflagellates, typically peridinin, dinoxanthin, and diadinoxanthin. These pigments give many dinoflagellates their typical golden brown color • All other organelles rough and smooth endoplasmic reticulum, Golgi apparatus, mitochondria, lipid and starch grains, and food vacuoles
  29. • Chlorophylls a and c2 are present in the chloroplasts, with peridinin and neoperidinin being the main carotenoids • The storage product is starch, similar to the starch of higher plants • The nucleus has permanently condensed chromosomes and is called a dinokaryotic or mesokaryotic nucleus • Amphiesma is the term used to specify the outermost layers of the dinoflagellate cell and includes all of the thecal plates
  30. Cell structure Fig. 7.2 Light and electron the features of the class. (C) Chromosome; (CE) chloroplast envelope; (CER) chloroplast endoplasmic reticulum; (E) epicone; (G) Golgi apparatus; (Gr) girdle; (H) hypocone; (L) lipid globule; (LF) longitudinal flagellum; (Nu) nucleolus; (P) trichocyst pore; (S) starch; (T) trichocyst; (TF) transverse
  31. • Dinophyceae consists of an outer plasmalemma beneath which lies a single layer of flattened vesicles • These vesicles, which normally contain cellulosic plates
  32. • Transverse and longitudinal flagella. Transverse flagella beats to the cell left and longitudinal flagellum, that beats posteriorly. • The flagella lie in surface grooves: the transverse one in the cingulum and the longitudinal one in the sulcus
  33. • Generally, dinoflagellates have a transverse flagellum that fits into the transverse girdle and a longitudinal flagellum that projects out from the longitudinal sulcus • The longitudinal flagellum usually has a wide basal portion and a thinner apical portion • Mechanical stimulus of cells causes the longitudinal flagellum to be retracted and folded so that the flagellum lies along the sulcus • Dinoflagellates swim from 200 to 500 µm s-1
  34. • The transverse flagellum is about two to three times as long as the longitudinal flagellum and has a helical shape • The transverse flagellum consists of 1. Axoneme whose form approximates a helix 2. striated strand that runs parallel to the longitudinal axis of the axoneme 3. Flagellar sheath
  35. Vegetative cell with a relaxed longitudinal flagellum (LF) at full length. (b) A cell with the longitudinal flagellum (LF) fully contracted and folded in the sulcus. (TF) transverse flagellum. (c) Schematic drawing of a retracted flagellum showing the contracted Rfiber (R) and the axoneme (A). (B) Basal body; (M) plasma membrane.
  36. Pusule • A pusule is a sac-like structure that opens by means of a pore into the flagellar canal and probably has an osmoregulatory function similar to that of a contractile vacuole
  37. Chloroplasts and pigments • photosynthetic dinoflagellates originated from a secondary endosymbiosis with a red alga • Contain chlorophyll a and c, and peridinin
  38. Phototaxis and eyespots • The action spectra for phototaxis is the same in all dinoflagellates that have been studied, with maximum phototaxis obtained at a wavelength of 450 nm • An eyespot is not necessary for a phototactic response, indicating that the phototactic machinery was carried in the host organisms in the endosymbiosis leading to photosynthetic dinoflagellates
  39. Resting spores or cysts • The Resting spore or cyst of most dinoflagellates is morphologically distinct from the parent cell. They are 30 to 70 µm in diameter with smooth or spinose bodies • Ten times more carbohydrate and 1.5% the respiratory rate of vegetative cells • Highly resistant to decay and contain dinosporin, a chemical similar to sporopollenin in the pollen of higher plants
  40. • The process of encystment or resting spore formation is regulated by a complex interaction of day length, temperature, and nutrient concentration
  41. Toxins • Some Dinophyceae have the ability to produce very potent toxins which cause the death of fish and shellfish during red tides when there are dinoflagellate blooms that color the water red • Produce toxins contain chloroplasts, indicating that the ability to produce toxins may have been derived from endosymbiotic cyanobacteria
  42. Kinds of poisoning 1. Diarrhetic shellfish poisoning dinophysistoxin-4 2. Ciguatera fish poisoning gambieric acids, ciguatoxins, and maitotoxins 3. Paralytic shellfish poisoning saxitoxin
  43. Bioluminescence • There are two types of light emission in living • organisms: (1) bioluminescence (chemiluminescence) in which energy from an exergonic chemical reaction is transformed into light energy (2) photoluminescence, which is dependent on the prior absorption of light
  44. • marine bioluminescence, emitting a bluish-green (maximum wavelength at 474 nm) flash of light of 0.1-second duration when the cells are stimulated. • The compound responsible for bioluminescence is luciferin , which is oxidized with the aid of the enzyme luciferase
  45. • In the basic reaction of bioluminescence a luciferin is oxidized by a luciferase, resulting in an electronically excited product (P)* which emits a photon (h) on decomposition:
  46. possible partial structure of dinoflagellate luciferin. (After Dunlap and Hastings, 1981; Hastings, 1986.) Tetra pyrol ring
  47. • Dinoflagellates can emit light in three modes: (1) they can flash when stimulated mechanically, chemically, or electrically (2) they can flash spontaneously; (3) late at night they can glow dimly
  48. Heterotrophic dinoflagellates • An estimated half of the more than 2000 living dinoflagellate species lack chloroplasts and are exclusively heterotrophic • many dinoflagellates that contain chloroplasts are capable of mixotrophy where a portion of their nutrients is obtained heterotrophically • The different modes of heterotrophy are: (1) Phagotrophy through the direct engulfment of prey (2) Pallium feeding where the prey is engulfed
  49. Direct engulfment of prey • 300-um-long food-gathering tentacle that is covered with a slimy exudate • Two wing-like extensions of the cells form an oral pouch at the base of the tentacle • At the bottom of the oral pouch is a cytosome that opens like a slit during ingestion of food organisms
  50. Drawing of the ingestion of food organisms (other algae, bacteria) by Noctiluca. (a) The tentacle (T) is in an extended configuration. Any food organisms (FO) that collide with the mucus-covered tentacle tip, stick to the tentacle. (N) Nucleus; (OP) oral pouch. (b) The tentacle bends back toward the oral pouch. (c) The cytosome (C) at the base of the oral pouch opens, the tentacle tip is inserted into the cytosome, and the food organisms are swept into a food vacuole.
  51. Pallium feeding • feeding veil, the pallium • Occur from flagellar pore • A thin filament of cytoplasm (about 1 µm in diameter) emerges from the sulcal pore and attaches to the prey
  52. • prey protoplasm is digested by enzymes released into the pallium, and the digestion products are transported into the feeding cell
  53. Peduncle feeding • projection of cytoplasm full of microtubules, in the epicone just above the intersection of the sulcus and cingulum • The peduncle can extend from 8 to 12 um to attach to, and make a hole into, the prey • The cytoplasm of the prey moves through the peduncle to the dinoflagellate cytoplasm
  54. Endosymbionts • All Zooxanthellae are dinoflagellates and most of them are members within the genus Symbiodinium • inhabit in invertebrates and protists • sea anemones, jellyfish and several species of radiolarians • dinoflagellates are parasites
  55. Reproduction • Asexual reproduction by binary fission • Sexual reproduction by fussion • This takes place by fusion of two individuals to form a zygote, which may remain mobile in typical dinoflagellate fashion and is then called a planozygote. • This zygote may later form a resting stage or hypnozygote, which are called dinoflagellate cyst or dinocyst. • After (or before) germination of the cyst, the hatchling undergoes meiosis to produce new haploid cells called planomeiocyte
  56. Harmful algal bloom • Aggregate millions of cell and produced a toxin is capable to kill shellfish and fish • This phenomenon is called a red tide, form colour impact on water. • They contain dinoflagellate luciferase involved in dinoflagellate bioluminescence, and luciferin, a chlorophyll-derived tetrapyrrole ring that acts as the substrate to the light-producing reaction.
  57. Classification • The diatoms into three classes on the basis of structural morphology 1. Centric diatoms (Coscinodiscophyceae), 2. pennate diatoms without a raphe (Fragilariophyceae), 3. Pennate diatoms with a raphe (Bacillariophyceae)
  58. • The first recognizable fossils are centric diatoms with pennate diatoms being recorded late • The first pennate diatom fossils were araphid (no raphe) with raphid diatoms appearing • The Bacillariophyceae can be divided into two orders as follows:
  59. • Order 1: Biddulphiales • Radial or gonoid ornamentation; • Many chloroplasts; • No raphe; • resting spores formed; • motile spermatozoids with a single tinsel flagellum; • oogamous sexual reproduction.
  60. • Order 2: Bacillariales • pennate or trellisoid ornamentation • One or two chloroplasts • Raphes possibly present with gliding • No flagellated spermatozoids • Sexual reproduction by conjugation
  61. CLASSIFICATION • There is a single class in the Dinophyta, the Dinophyceae • Four orders are considered here Order 1 Prorocentrales: Cell wall divided vertically into two halves; No girdle; Two flagella borne at cell apex.
  62. Order 2 Dinophysiales: Cell wall divided vertically into two halves, Cells with elaborate extensions of the theca
  63. Order 3 Peridiniales: Motile cells with an epicone and hypocone separated by a girdle, Relatively thick theca
  64. Order 4 Gymnodiniales: Motile cells with an epicone and hypocone separated by a girdle; Theca thin or reduced to empty vesicles.
  65. lichen Prepared by: Dharmesh Sherathia, Assistant Professor, CCSIT, Junagadh
  66. • Firstly discovered by tulasne in 1852 • Association of fungi and algae or cyanobacteria • Living inside the filaments of fungi • Widely distributed – grow on soil, rocks, trees, marine or intertidal • Variety of habitats – cold to hot, arid to moist • Withstand environmental extremes • Bush like or leafy structure of lichen called macrolichen and all other lichen are microlichen
  67. • Generally three types of structure in lichen • 1. Fruticose 2.Foliose 3. Crustose • Fruticose: growing up like a tuft or multiply branched leafless mini-shrub, or hanging down in strands or tassles • Foliose: growing in 2-dimensional, flat, leaflike lobes that lift up from the surface • Crustose: crust-like, adhering tightly to a surface (substrate) like a thick coat of paint
  68. • Fruticose – branched, strap shaped or threadlike thallus, upright or hanging
  69. • Foliose – flattened branching lobes loosely attached to the substratum, leaflike • Have upper and lower surfaces
  70. • Crustose – flattened, scalelike, • No lower surface, tightly bound to substratum
  71. • Squamulose – intermediate between foliose and crustose • Scales, lobes smaller than in foliose • Intermediates exist
  72. Fungal symbiont • Most lichenized fungi are Ascomycota – most form apothecia, some form perithecia and pseudothecia • 12 orders include mostly lichenized members • Some are Basidiomycota – Aphyllophorales, few Agaricales • Some are Deuteromycota
  73. Classification • On the nature of fungi, lichen classified into two main group Ascolichen and basidiolichen • Ascolichen may further devide in two group 1. Discolichens: cup shaped apothecia 2. Pyrenolichens: flask shaped perithecia • There are three genera of basidiolichen a) Cora b) Corella c) Dictyonema
  74. Internal structure
  75. Autotrophic symbionts • Green algae – Trebouxia is a common genus, found in 75% of lichens in temperate zone • Cyanobacteria – Nostoc is a common genus • 26 genera of algae and cyanobacteria found in lichens, 90% of lichens contain Trebouxia, Nostoc or one other genus • Autotroph may be free living • Blue- green algae, green algae
  76. Internal structure Gonidial layer
  77. Internal structure
  78. Reproduction • Vegetative reproduction by soredia, isidia, cephalodia, oidia, fragmentation • Asexually reproduction by pycnodium • Spore germinate on thallus and send hyphae in diff. direction. If algal cell comes in contact. Hyphe covered and formed protuberance like structure • In some case protuberance discharge
  79. Reproduction • Sexual reproduction – characteristic of fungal symbiont • Ascospores are discharged, algal cells are not discharged with them • Thought that after ascospores germinate, they make contact with algal cell
  80. Vegetative reproduction • Specialized structures • Soredia - algal cells enveloped by hyphae, no cortex, form powdery masses on surface of thallus, detach from thallus • Isidia – column like structures with cortex
  81. Isidia
  82. Cephalodia • Dark swelling on surface • Unfortunately this one is foreign body • discharge and formed abnormal body Oidia • Small segment of hyphae Fragmentation • Long or short fragment of thallus grow on parental thallus, branch broken up by wind
  83. Physiology • Autotrophic associations – algal cells carry out photosynthesis, lichen depends on net production of organic compounds by photosynthesis • Most of the photosynthate (70-80%) produced by alga is incorporated into the fungus • Green algae secrete polyalcohols like ribitol, cyanobacteria secrete glucose • Photobiont becomes leaky of carbohydrates when associated with fungus – not so when grown alone
  84. Growth • Exhibit low growth rates – many grow at rates of 1-4 mm/yr, up to 9 cm/yr • Makes studies difficult Factors affecting growth: • Light – variable – some prefer low light intensities, others high • Temperature – variable • Moisture – appears to be an important variable, do not have water absorbing organs, depend on moisture in air • Some aquatic lichen life is more than4500 years
  85. Moisture • When lichen thallus is wetted, absorbs water quickly by gelatinous matrix in the cortex • Starts growth process • As thallus dries, growth process slows and stops • Dew and humidity are important sources of moisture • Thalli are inactive when dry – only grow when wetted – may be responsible for slow growth rate
  86. Separation of symbionts • Fungal symbionts grown in culture exhibit slow growth rates (1-2 mm/yr) • Many exhibit requirements for vitamins • Algae also grow slowly in culture, Trebouxia prefers organic N and low light
  87. Symbiotic association • Traditionally been classified as a mutualistic symbiosis where both symbionts benefit • Fungus appears to be chief benefactor, receives • Organic compounds as C and energy source • With cyanobacteria, N fixation may occur so that the fungus also receives N source
  88. Symbiotic association • Benefits for autotrophic symbiont are less clear-cut • Fungus produces substances that absorb water which is provided to alga • Fungus takes up inorganic nutrients from atmosphere • Protects algal cells from mechanical injury, predation, and high light intensities • Association allows alga to achieve a wider distribution than if free-living
  89. Air pollution • Even though lichens are very resistant to natural environmental extremes – they are extremely sensitive to air pollution – particularly SO2 • Obtain nutrients from atmosphere, not soil • Both species composition and numbers of thalli decline from edge to center of industrialized areas • Some are useful as indicator species
  90. Use of lichen • Food • Dyes (litmus paper, Harris tweed) • Essential oils for perfumes, soaps • Bioactive compounds (antiviral, antibacterial) • Nesting/bedding material • Poisons