BIO 4320 marine algers systematikk og kologi
Division HETEROKONTOPHYTA ClassBACILLARIOPHYCEAE KISELALGER DIATOMEER/DIATOMS Klasse Bacillariophyceae
in Division Heterokonto-phyta (= Ochrophyta) Phylogeny Based on molecular biology Fossile record
Early Cretaceous (kritt-tiden) ca 180 million years ago [centrics] Pennate forms ca 70 mya Prominence Miocene 24 mya Figur 12.14 Cell division Cells enlarge (duplication of organelles) Mitosis
Cytokinesis (division of cytoplasma) Wall formation Cells separate open mitosis (kjernedeling)
Polar plate Polar plate kinetochore Interphase: nucleus moves just beneth the spindle, microtubule radiate over nucleus from Microtubule center Prophase: prophase spindle forms between polar plates, micrtotubule center disintegrates, Nuclear membran still present Metaphase: nuclear membrane broken down (open mitosis), chromatin at center. Spindel microtubule overlap in center. Chromatin attached to chromatid microtubule by kinethocores and are being pulled apart Anaphase the chromatids have separeted and the cytokinese may preseed chromatids interphase prophase metaphase anaphase from van den Hoek et al. 1995 Dividing diatom daughter cells TEM-section D.Klaveness from
Norsk kystplanktonflora Amphipleura pellucida
Dividing cell New epitheca New hypotheca New epitheca Growth in diatoms Single celled species grow, divide and separate
The cell volume increase rapidly just prior to division Cell division takes place during a short interval of time e.g. Ditylum brightwellii ;53 minutes Navicula pelliculosa ;2-3 hours Wall formation Cytokinesis Si(OH)4-uptake Frustule formation Cell wall formation in Amphipleura (pennate diatom) Growth of the new valva in a pennate diatom
Primary central band Young central nodule Raphe rib Extension of secondary arms Recurving of primary band at poles Nacent transapical rib Extension of secondary arms from center Nacent raphe Developing connections between raphe ribs Extension of primary central bands are approaching and fusing with secondary arms Raphe slit is enclosed and ribs completed Growth of the new valva in a pennate diatom size-reduction 10 cell divisions = 1024 celler
1 cell keep the original size 1023 cells will get a smaller diameter asexual/vegetativ propagation
Cells divide 0,5 1 2 x pr day Colony size will increase rapidly Disruption cells limit colony size auxospores Re-establishing maximal cell size
Usually part of the sexual life cycle May also be produced asexually Sexual reproduction When cells reach about 1/3 of maximum size
Oogamy in centric diatoms Isogamy anisogamy in pennate Vegetative cells are diplontic Gametic lifesycle Life cycle in centric diatoms
oogamy from Syvertsen 1990 male gamete from centric diatom
NB! Flagellum without central microtubuli in the axoneme Flagellum basal body with microtubule doublets only from van den Hoek et al. 1995 Life cycle in centric diatoms; example Chaetoceros didymus
after Cupp 1943 Life cycle in centric diatoms
Vegetativ cells Oogonia Gametangia Auxospore Resting spore Several of the meiotic products die Chaetoceros didymus Life cycle in Chaetoceros didymus
Vegetativ cells Gamete production Oogonium and gametes Syngamy Auxospore formation Resting spore formation after von Stosch et al. 1973 Life cycle in pennate diatoms
iso- or anisogamy non-flagellated gametes Gametangia (pairing of parental cells within enclosing mucus) Life cycle in pennate diatoms
- isogami, anisogami Unequal cytokinese follows first meiotic division and the two smaller cells die. Frustules open. Protoplasts emerge as second meiotic division complete and one haploid nucleus in each protoplast die. Result; post meiotic protoplasts have one haploid nucleus Sexual events may be synchronized related to rich or poor nutrient conditions
Sexual events may occur irregularly during the growth season Changes in temerature, day length, nutrient availability, the presence of a mate may trigger sexual reproduction Auxospores and resting spores
Auxospores makes it possible for the species to regain maximal cell size Most often zygotic Resting spores are thick walled and facilitate survival in non productive periods Produced asexually Sinking/floating Counteracted by reducing the sinking velocity:
Specific weight of silica = 2,07 Counteracted by reducing the sinking velocity: Chain formed colonies Setae Shape Reducing the weight of the cell: Ion composition of the cell vacuole sap Cell motility Centric diatoms - cell vacuole content adjusted to match the density of sea water Pennate diatoms - raphid cells moving over substratum. Raphid movment Some centric and araphids have slow movement where excretion of mucus from labiate process is involved flotation Vacuoles up to 90-98% of cell volume
Vacuoles with increased Na+, Mg++, reduced K+ og Ca++ (diatoms) Raphe in Navicula Raphe tverr-snitt /cross section
actin filaments anchors cellmembran to frustule IPM invaginated part of the plasmalemma PM plasma membrane /plasmalemma MF microfilaments actin filaments VFP vesicle with fibrous polysaccharid content Slimstav/mucilage rod Raphe tverr-snitt /cross section Raphe associated microtubules and attached motor proteins (kinesin/dynein) motor source that drags the polysaccharide rods external movement in pennate diatom
Possible action of kinesin and/or dynein 0,2-50 m.sec-1 mucilage rods i.e. up to cm.hour-1 Nutrition Diatoms have chloroplasts and most are photosynthetic (eg as plankton utilising inorganic nutrients) Many occur in low light/high DOM habitats (e.g. polar sea ice, beaches, sediments) utilising organic nutrients Many can grow in the dark if organic substrates are supplied Some do not photosynthesize (e.g. Nitzschia alba) Vertical migration in sand
Hantzschia virgata tidal rythm on intertidal sand and mud flats at low tide golden brown patches on the surface of intertidal sandflats at high tide up to 2 cm below the sediment surface. Surf zone diatoms Solide line floating cells
Dashed line mucus coating Dotted line - dividing cells Predators; Donax and Emerita Troen, France Attheya important class characteristics
organization; coccoids with silica wall flagellum only present in male gametes (order Biddulphiales) general characteristics of Bacillariophyceae
Non-motile single cells enclosed in a silica wall consisting of two parts 250 slekter/genera arter/species Distributed in marine and freshwater