What are the Characteristics of algae and fungi

general characteristics of algae and fungi, what does cyanobacteria mean what is cyanobacteria blue green algae, what do cyanobacteria use for energy production
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Published Date:02-08-2017
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Basic characteristics of the algae Phycology or algology is the study of the algae. The Structure of the algal cell word phycology is derived from the Greek word phykos, which means “seaweed.” The term algol- There are two basic types of cells in the algae, ogy, described in Webster’s dic tion ary as the study prokaryotic and eukaryotic. Prokaryotic cells lack of the algae, has fallen out of favor because it membrane-bounded organelles (plastids, mito- resembles the term algogenic which means “pro - chondria, nuclei, Golgi bodies, and flagella) and ducing pain.” The algae are thallophytes (plants occur in the cyanobacteria (Fig. 2.11). The remain- lacking roots, stems, and leaves) that have chloro - der of the algae are eukaryotic and have organelles. phyll a as their primary photo syn thetic pigment A eukaryotic cell (Fig. 1.1) is often surrounded and lack a sterile covering of cells around the by a cell wall composed of poly saccharides that are repro ductive cells. This definition encompasses a partially pro duced and secreted by the Golgi body. number of plant forms that are not necessarily The plasma membrane (plasmalemma) surrounds closely related, for example, the cyanobacteria the remaining part of the cell; this membrane is a which are closer in evolu tion to the bacteria than living structure responsible for controlling the to the rest of the algae. influx and outflow of sub stances in the proto - Algae most commonly occur in water, be it plasm. Locomotory organs, the flagella, propel the fresh water, marine, or brack ish. However, they can cell through the medium by their beating. The also be found in almost every other environ ment flagella are enclosed in the plasma membrane and on earth, from the algae growing in the snow of have a specific number and orienta tion of micro - some American mountains to algae living in tubules. The nucleus, which contains the genetic lichen associa tions on bare rocks, to uni cellular material of the cell, is surrounded by a double algae in desert soils, to algae living in hot springs. membrane with pores in it. The contents of the In most habitats they func tion as the primary pro - nucleus are a nucleolus, chromo somes, and the duc ers in the food chain, pro ducing organic background material or karyolymph. The chloro - mat erial from sun light, carbon dioxide, and water. plasts have membrane sacs called thylakoids t hat Besides forming the basic food source for these carry out the light reac tions of photo syn thesis. food chains, they also form the oxygen necessary The thylak oids are embedded in the stroma where for the metab olism of the consumer organ isms. In the dark reac tions of carbon fixation take place. such cases humans rarely directly consume the The stroma has small 70S ribo somes, DNA, and in algae as such, but harvest organ isms higher up in some cases the storage product. Chloroplasts are the food chain (i.e., fish, crustaceans, shellfish). surrounded by the two membranes of the chloro - Some algae, particularly the reds and browns, are plast envelope. Sometimes chloro plasts have a harvested and eaten as a vegetable, or the mucil - dense pro teinaceous area, the pyren oid, which ages are extracted from the thallus for use as is associated with storage-product forma tion. gelling and thickening ag ents.4INTRODUCTION Fig. 1.1 Drawing of a cell of the green alga Chlamydomonas microtubules, with all of the microtubules showing the organelles present in a eukaryotic algal cell. encased in the plasma membrane (Figs. 1.2, 1.3). (C) Chloroplast; (CV) contractile vacuole; (E.R.) endoplasmic On entering the cell body, the two central micro- reticulum; (F) flagella; (G) Golgi body; (M) mitochondrion; tubules end at a dense plate, whereas the nine (N) nucleus; (P) pyrenoid; (S) starch; (V) vacuole; (W) wall. peripheral doublets continue into the cell, usually picking up an additional structure that trans- Double-membrane-bounded mitochondria have forms them into triplets. The flagellum passes 70S ribo somes and DNA, and contain the respira- through a tunnel in the cell wall called the flag- tory apparatus. The Golgi body consists of a ellar collar. number of membrane sacs, called cisternae, The central pair of microtubules are single stacked on top of one another. The Golgi body microtubules with 13 protofilaments while the func tions in the pro duc tion and secre tion of poly - outer microtubules are doublets with the A- saccharides. The cyto plasm also contains large 80S tubule consisting of 13 protofilaments and the ribo somes and lipid bodies. B-tubule having 11 protofilaments. The central- pair microtubules resemble cytoplasmic micro- Flagella tubules, in that they are more labile than the The flagella of the green alga Chlamydomonas have outer doublet microtubules. The axoneme micro- been used as a model of flagellar structure. tubules are composed of - and -tubulin which Flagella structure has been highly conserved make up 70% of the protein mass of the axoneme throughout evolution, images from Chlamydo - (Dutcher, 1995). Radial spokes, each consisting of monas are virtually indistinguishable from flag- a thin stalk and head, project from the A-tubule of ella (or cilia – a term for a short flagellum) of the outer microtubule doublets (Figs. 1.2, 1.3). mammalian cells including human sperm and Inner and outer dynein arms attach to the A- certain epithelia (Johnson, 1995). Chlamydo monas tubule of the outer microtubule doublet and has been chosen because of the ease of growing extend to the B-tubule of the adjacent outer the organism and because the flagella can be microtubule doublet. Dynein is a mechanoen- detached from the cells by pH shock or blending. zyme that hydrolyzes ATP with the resulting Since the flagella are not essential for viability of energy used by dynein to move along the B-tubule the cell, it is relatively easy to isolate mutations of the adjacent outer microtubule doublet affecting flagella synthesis by the cells. (Fig. 1.3). In this action, the B-tubule is called A flagellum consists of an axoneme of nine the track while the A-tubule is called the cargo. doublet microtubules that surround two central The resulting displacement of outer microtubuleBASIC CHARACTERISTICS OF THE ALGAE 5 Fig. 1.2 The flagellar system in the green alga Chlamydomonas. (a) A diagrammatic drawing of a section of the flagellar system. The numbers refer to cross sections of the flagellar system in (b). (c) Diagrammatic drawing of the whole flagellar apparatus. The two flagella are joined by the proximal connecting fiber (PCF) and distal connecting fiber (DCF). (After Ringo, 1967.) Fig. 1.3 Chlamydomonas flagella. (a) Transmission electron asymmetric bending of the flagellum and propa- micrograph through the anterior region of a Chlamydomonas gation of flagellar waves (Johnson, 1995). reinhardtii cell including the cell wall (CW), double There are also other structures between the microtubules (DM), central pair microtubules (CP), plasma micro tubules in the basal region of the flagellum membrane (PM), transition zone (TZ), and basal body (BB). (basal body). Attached to the basal body there can (b) Thin section through an isolated demembranated flagellar be either micro tubular roots or stri ated fibrillar axoneme showing the main components. (c) Diagrams of roots. The former type of root consists of a group dyneins and related structures seen along the A-tubule of of micro tubules running from the basal body into each doublet. (From Mitchell, 2000.) the protoplasm (Figs. 1.2, 1.4), whereas the latter consists of groups of fibers that have striations doublets in relation to each other causes bending along their length (Figs. 1.4, 1.6) The gamete of of the flagellum (Mitchell, 2000). Kinesin proteins the green seaweed Ulva lactuca (sea lettuce) cause the central pair of microtubules to rotate has both types of flagellar roots (Fig. 1.5) within the axoneme (Fig. 1.4). As the central pair (Melkonian, 1980; Andersen et al., 1991). There are of microtubules rotates, the microtubules inter- four microtubular roots composed of micro - act with the individual radial spokes inducing tubules arranged in a cruciate pattern, and sliding between adjacent microtubule doublets, fibrous roots (rhizoplasts) composed of a bundle6INTRODUCTION Fig. 1.4 Bending of flagella occurs by the rotating central pair of microtubules activating dynein movement of specific outer doublet microtubules. Fig. 1.5 Schematic three-dimensional reconstruction of the flagellar apparatus of a female gamete of Ulva lactuca showing the four cruciately arranged microtubular roots and the fibrous contractile roots. (Adapted from Melkonian, 1980.)BASIC CHARACTERISTICS OF THE ALGAE 7 Fig. 1.6 Transmission electron micrographs of striated roots (rhizoplasts) in the green alga Scherffelia dubia (Chlorophyta). Arrow and arrowhead point to a striated root. (BB) Basal body; (C) chloroplast; (M) mitochondrion; (N) nucleus; (V) vacuole. (From Vierkotten et al., 2004.) 2Tubular flagellar hairs about 2 m long of filaments (Fig. 1.6). There are two types of fibrous roots: (1) system I fibrous roots composed composed of three regions: (1) a tapering basal of 2 nm filaments cross-striated with a period ic ity region 200 nm long attached to the flagellar of approximately 30 nm and (2) system II fibrous membrane, (2) a micotubular shaft 1 m long, and (3) a few 0.52 m-long terminal filaments roots composed of 4–8 nm filaments usually cross- striated with a period ic ity greater than 80 nm. (Andersen et al., 1991). System I fibrous roots are non-contractile while The bases of the hairs do not penetrate the flag- system II fibrous roots are contractile when appro- ellar membrane but are stuck to it. Development priately stimulated (Moestrup, 2000; Brugerolle of the tubular hairs begins in the space between and Mignot, 2003). the inner and outer membrane of the nuclear The flagellar membrane may have no hairs envelope (peri nuclear continuum) where the (mastigonemes) on its surface (whiplash or basal and micro tubular regions are assembled. acronematic flagellum) or it may have hairs on its These then pass to the Golgi apparatus, where surface (tinsel or hairy or pantonematic or the terminal filaments are added. Finally the hairs Flimmergeissel). There are two types of flagellar are carried to the plasma membrane in Golgi hair (Fig. 1.7): vesicles, where they are dis charged and attached 1Non-tubular flagellar hairs made up of solid to the flagellar membrane. Tripartite tubular fibrils 5–10 nm wide and 1–3 m long that are hairs occur in the Heterokontophyta. The term composed of glycoproteins. These hairs are stramenopile (straw hair) has been used to flexible and wrap around the flagellum include all protists with tubular hairs (van increasing the surface area and efficiency of der Auwera and deWachter, 1997). In addition propulsion. to the algae in the Heterokontophyta, the8INTRODUCTION Fig. 1.7 Drawings of the types of hairs on algal flagella. (a)Tripartite hairs (example Ascophyllum sperm). Each hair is composed of a basal region attached to the flagellar membrane, the microtubular shaft, and a terminal hair. (b) Non-tubular hairs (example Chlamydomonas gamete). ((a) adapted from Bouck, 1969; (b) from Snell, 1976.) Fig. 1.8 The sequence of flagellar transformation during cell division. st ramenopiles include the fungal oomycetes,divi sion,twonewflagellaappearnexttotheante - hyphochytrido mycetes, thraustochytrids, and the rior flagellum. These two new flagella elongate bicosoecids and labyrinthulids. whiletheoriginalante riorflagellummoves The remainder of the algae have non-tubular toward the posterior of the cell and loses its tubu- hairs if hairs occur on the flagella (Moestrup, lar hairs, to become the posterior smooth flagel- 1982). In addition to hairs, a number of different lum of one of the daughter cells. The two new scale types occur on the surface of the flagella. flagellaattheante riorendofthecellacquiretubu- These will be discussed in the chapters on the lar hairs and become the tinsel flagella of the individual algal groups. daughter cells. Thus, each daughter cell has one Flagella progress through a set of develop-newante riortinselflagellum,andoneposterior mental cycles during cell division (Fig. 1.8). A smooth whiplash flagellum that was originally a biflagellate cell with an anterior flagellum cov- flagellum in the parent cell (Beech and Wetherbee, ered with tubular hairs (tinsel flagellum), and a 1990; Melkonian et al., 1987). posterior smooth flagellum (whiplash flagellum), Algal cells can have different arrange ments of will be used as an example. Before the onset of cell flagella (Fig. 1.9). If the flagella are of equal length,BASIC CHARACTERISTICS OF THE ALGAE 9 Fig. 1.9 The shape of eukaryotic motile algal cells and their flag ellum is produced by an imbalance in the flagella. The drawings represent the common arrangement of assembly or disassembly of flagellar components flagella in the groups. There are a number of modifications in (Rosenbaum and Witman, 2002). Thus, disassem- structure that are not included here. (a)Cryptophyta; (b) bly occurs faster than assembly in flagellar retrac- most of the Heterokontophyta; (c)Bacillariophyceae of the Heterokontophyta; (d)Prymnesiophyta; (e) Chlorophyta; (f) tion. The opposite occurs during flagellar growth. Dinophyta; (g) Euglenophyta; (h) Eustigmatophyceae of the The differences in length of flagella arise from the Heterokontophyta; (i, j) Chlorophyta. shorter flagellum being delayed in the initial stages of construction. The assembly rate of the shorter flagellum is the same as the longer flagel- they are called isokont flagella; if they lum. There may be a gate at the base of the flagel- are of unequal length, they are called anisokont lum that regulates the passage of flagellar flagella; and if they form a ring at one end of precursors into the basal body and the flagellum the cell, they are called stephanokont flagella. (Schoppmeier and Lechtreck, 2003). Heterokont refers to an organ ism with a hairy and a smooth flagellum (Moestrup, 1982). Cell walls and mucilages Flagella can be of different length in the same In general, algal cell walls are made up of two cell. This is controlled by intraflagellar transport, components: (1) the fibrillar component, which defined as the bi-directional movement of particles forms the skele ton of the wall, and (2) the amor- along the length of the flagellum between the axoneme phous component, which forms a matrix within and the flagellar membrane (Beech, 2003). A mature which the fibrillar component is embedded. flagellum that is not elongating has a steady dis- The most common type of fibrillar component assembly of the flagellum that is countered by an is cellulose, a polymer of 1,4 linked -D-glucose. equally steady assembly provided by intraflagellar Cellulose is replaced by a mannan, a polymer of transport (Fig. 1.10). A change in length of the 1,4 linked -D-mannose, in some siphonaceous10 INTRODUCTION Fig. 1.10 (a) Intraflagellar transport results in more assembly of flagellar subunits than disassembly during flagellar growth. (b) A mature flagellum has an equal amount of assembly and disassembly of flagellar subunits. (c) There is more disassembly of flagellar subunits during flagellar retraction. Fig. 1.11 Structural units of alginic acid, fucoidin, and Phaeophyceae. Fucoidin (Fig. 1.11) also occurs in agarose. (After Percival and McDowell, 1967.) the Phaeophyceae and is a polymer of -1, 2, -1, 3, and -1, 4 linked residues of L-fucose sulfated at C- 4. In the Rhodophyta the amorphous component of the wall is composed of galactans or polymers of greens, and in Porphyra and Bangia in the Rhodophyta. In some siphonaceous green algae galactose, which are alternatively -1,3 and -1,4 and some Rhodophyta (Porphyra, Rhodochorton, linked. These galactans include agar (made up of agaropectin and agarose, Fig. 1.11) and carragee - Laurencia, and Rhodymenia), fibrillar xylans of nan (Fig. 4.15). different poly mers occur. The amorphous mucilaginous components occur in the great est amounts in the Phaeophyceae Plastids The basic type of plastid in the algae is a chloro- and Rhodophyta, the polysacc harides of which are plast, a plastid capable of photo syn thesis. commercially exploited. Alginic acid (Fig. 1.11) is apolymer composed mostly of -1,4 linked D- Chromoplast is syn onymous with chloro plast; in mannuronic acid residues with variable amounts the older literature a chloro plast that has a color other than green is often called a chromo plast. A of L-guluronic acid. Alginic acid is present in proplastid is a reduced plastid with few if any the intercellular spaces and cell walls of theBASIC CHARACTERISTICS OF THE ALGAE 11 Fig. 1.12 Types of chloroplast structure in eukaryotic algae. (a) One thylakoid per band , no chloroplast endoplasmic reticulum (Rhodophyta). (b) Two thylakoids per band, two membranes of chloroplast E.R. (Cryptophyta). (c)Three thylakoids per band, one membrane of chloroplast E.R. (Dinophyta, Euglenophyta). (d) Three thylakoids per band, two membranes of chloroplast E.R. (Prymnesiophyta and Heterokontophyta). (e) Two to six thylakoids per band, no chloroplast E.R. (Chlorophyta). thylak oids. A pro plastid will usually develop into to the chloroplasts in a secondary endosymbio- a chloroplast although in some hetero trophic sis. In the Euglenophyta and Dinophyta, there is one membrane of chloroplast E.R. (Fig. 1.12(c). In algae it remains a pro plastid. A leucoplast or amy- loplast is a colorless plastid that has become the Cryptophyta, Prymnesiophyta, and Heterokon - adapted for the accumula tion of storage product. tophyta, there are two membranes of chloroplast In the Rhodophyta and Chlorophyta, the E.R., with the outer membrane of chloroplast E.R. usually continuous with the outer membrane of chloro plasts are bounded by the double membrane of the chloro plast envelope (Fig. 1.12(a), (e)). In the the nuclear envelope, especially if the chloroplast other eukaryotic algae, the chloro plast envelope number is low (Fig. 1.12 (b), (d)). is surrounded by one of two membranes ofThebasicstructureofthephoto syn theticappa- ratus in a plastid consists of a series of flattened chloroplast endo plasmic reticulum(chloro plast E.R.), which has ribosomes attached to the outer membranous vesicles called thylakoids or discs, face of the membrane adjacent to the cytoplasm. and a surrounding matrix or stroma.Thethylak - The chloroplast E.R. is the remnant of the foodoidscontainthechloro phyllsandarethesites ofthephoto chem icalreac tions;carbondioxide vacuole membr ane and/or the plasma membrane involved in the original endosymbiosis leadingfixationoccursinthestroma.Thethylak oidscan12 INTRODUCTION be free from one another or grouped to form ribulose-1, 5-bisphosphate carboxylase/oxygenase thylakoid bands.Inthecyanobacteria and (Rubisco), the enzyme that fixes carbon dioxide Rhodophyta (Fig. 1.12(a)),thethylak oidsareusu- (Jenks and Gibbs, 2000; Nagasato et al., 2003). ally free from one another, with phycobilisomes Consequently, the size of the pyrenoid will vary (containing the phycobiliproteins) on the surface depending on how much Rubisco is present. ofthethylak oids.Thephycobi li somesonthesur- Rubisco exists in two forms (Jenks and Gibbs, face ofonethylak oidalternatewiththoseonthe 2000; Zhang and Lin, 2003): surfaceofanadjacentthylak oid.Thephycobi li - 1 Form I occurs in some bacteria, the somes appear as 35-nm granules when cyanobacteria, in all green plants and non- phycoerythinpre dominates,orasdiscswhenphy- green plants. Form I is composed of eight large cocyaninpre dominates.Inthemoreprimitive subunits and eight small subunits (Fig. 1.13). membersoftheRhodophytathethylak oidstermi- Form I has a high affinity for CO and a low 2 nateclosetothechloro plastenvelope,whereasin catalytic efficiency (low rate of CO fixation). 2 advanced members of the Rhodophyta peripheral In green algae, euglenoids, and green plants, thylak oidsarepresent,whichenclosetherestof the large subunit is coded by chloroplast DNA thethylak oids.IntheCryptophyta,thechloro - and the small subunit by nuclear DNA. In the plastscontainbandsoftwothylak oids(Fig. cyanelle (endosymbiotic cyanobacterium) of 1.12(b)); the phycobiliproteins are dis persed Cyanophora paradoxa and in some non-green withinthethylak oids.IntheEuglenophytaand algae, both subunits are coded by chloroplast Heterokontophyta the thylak oids are grouped DNA. in bands of three with a girdle or peripheral 2 Form II occurs in some eubacteria and in the bandrunningparalleltothechloro plastenve- dinoflagellates and is composed of two large lope. In the Dinophyta, Prymnesiophyta, and sub units. Form II has a low affinity for CO and 2 Eustigmatophyceae,thethylak oidsarealsoin a high catalytic efficiency. bands of three, but there is no girdle band (Fig. 1.12(c), (d)).IntheChlorophyta,thethylak oids The common ancestor of all ribulose-1,5-bisphos- occurinbandsoftwotosix,withthylak oidsrun- phate carboxylase was probably similar to Form II ning from one band to the next. The above group- and was adapted to the anaerobic condi tions and ingofalgalthylak oidsintobandsoccursunder high CO concentra tions prevailing in t he ancient 2 normalgrowthcondi tions.Abnormalgrowth earth (Haygood, 1996). Form I evolved as the condi tionscommonlycauselumpingofthylak - earth’s atmosphere became oxy gen ated, and CO 2 oids and other variations in structure. concentra tion declined and with it the need for a A pyrenoid (Fig. 1.12(b)) is a differentiated greater affinity for CO . The greater affinity for 2 region within the chloroplast that is denser than CO in Form I, however, came at the price of 2 the surrounding stroma and may or may not be tra- reduced catalytic efficiency. versed by thylakoids. A pyrenoid is frequently asso- Chloroplasts contain small (30–100 nm), spher- ciated with storage product. Pyrenoids contain ical lipid droplets between the thylakoids (Fig. 1.12 (c), (d)). These lipid droplets serve as a pool of lipid reserve within the chloroplast. Many motile algae have groups of tightly packed carotenoid lipid-globules that constitute an orange-red eyespot or stigma (Fig. 5.2) that is involved in response to light. Motile algae exhibit three types of responses to light (Kawai and Kreimer, 2000): phototaxis, photophobia, and glid- ing (Fig. 1.14). Fig. 1.13 The structure of Form I variation of Rubisco 1Phototaxis. In phototaxis, the orientation of showing the eight large subunits and eight small subunits. cell movement is effected by the direction andBASIC CHARACTERISTICS OF THE ALGAE 13 Fig. 1.14 Three types of flagellar orientation in Chlamydomonas. In phototaxis, the cells swim forward and rotate. Phototaxis requires that cells swim forward in a spiral path that causes rotation of the symmetrically placed eyespot. In photoshock, the cell has a transient avoidance response that causes the cell to swim backwards. In gliding, the leading flagellum and passive flagellum are 180° apart. intensity of light. The cells move toward the the trans flagellum is furthest from the light in positive phototaxis and away from the eyespot. The light is received by the light in negative phototaxis. The photoreceptor photoreceptor which controls the opening and in the green alga Chlamydo monas is closing of calcium channels, and the level of chlamyrhodopsin (Fig. 1.15) in the plasma intraflagellar calcium concentration. The membrane over the eyespot. Chlamyrhodopsin calcium concentration within the flagellum contains an all-trans, 6-S-trans retinal chromo - effects the interactions of the radial spokes phore that undergoes a 13-trans to cisisomeriz - with the central pair of microtubules ation during illumination (Hegemann, 1997). (Mitchell, 2000). When the plasma membrane The eyespot periodically shades the photo - of Chlamydomonas is made permeable, 8 receptor as the cell rotates during swimming. Chlamydomonas cells swim normally at 10 M The eyespot has a different structure in the calcium in the medium. Decreasing the 9 different groups of algae and will be covered in calcium to 10 M reduces the stroke velocity the appropriate chapters. Eyespots have certain of the trans flagellum, while increasing the 7 basic characteristics (Kawai and Kreimer, 2000): calcium to 10 M reduces the stroke velocity (1) Eyespots usually have carotenoid-rich lipid of the cis flagellum. globules packed in a highly ordered hexagonal 2Photophobia (photoshock). Photophobia is a arrangement. (2) Eyespots are usually single change in direction of movement of the cell structures in peripheral positions, most often caused by a rapid change in light intensity, oriented perpendicular to the axis of the irrespective of the direction of the light. swimming path. Swimming cells stop and change the beat Phototaxis in Chlamydomonas is controlled by pattern from the normal asymmetric flagellar the beating of each flagellum. The flagellum stroke to a symmetrical stroke that propels closest to the eyespot is the cis flagellum while the cell backward (Fig. 1.14). At the end of the photophobic response, the cells tumble and resume swimming in a new direction. Laboratory experiments with Chlamydomonas link photophobic responses 6 to increases in calcium above 10 M (Mitchell, 2000). Unlike phototaxis, interactions between radial spokes and central-pair microtubules are not necessary for a photophobic reaction. Fig. 1.15 The structure of chlamyrhodopsin, the 3Gliding (quiesence). In gliding, the flagella photoreceptor in Chlamydomonas. stop beating and adhere to a surface or an14 INTRODUCTION Fig. 1.16 Transmission electron micrograph of DNA in the chloroplast of the dinoflagellate Prorocentrum micans. (From Laatsch et al., 2004.) In the Chlorophyta (Fig. 5.2), Cryptophyta (Fig. 9.4) and most of the Heterokontophyta (Fig. 10.1), the eyespot occurs as lipid droplets in the chloro- plast. In the Euglenophyta (Fig. 6.2), Eustigmato - phyceae (Fig. 12.1), and Dinophyta (Figs. 7.21, 7.22, 7.23), the eyespot occurs as a group of membr ane-bounded lipid droplets, free of the chloroplast. Most chloroplasts contain prokaryotic DNA in an area of the chloroplast devoid of 70S ribo- somes (Figs. 1.16 and 1.17). The DNA is an evolu - tionary remnant of the cyanobacterium involved in the endosymbiosis leading to the chloroplast. The individual DNA microfibrils are circular, are attached to the chloro plast membranes, and lack basic pro teins (histones). The algae can be divided into two general groups according to the distri - bution of DNA in the plastids (Coleman, 1985). In the first group, the clumps of DNA (nucleoids) are scatt ered through out the plastids. This group includes the Cryptophyta, Dinophyta, Prymnesio - Fig. 1.17 Semidiagrammatic drawing of the two types of phyta, Eustigmatophyceae, Rhodophyta, and distribution of DNA in algal chloroplasts. Side and face views of the plastids are drawn. (Adapted from Coleman, 1985.) Chlorophyta. In the second group, the DNA occurs in a ring just within the girdle lamella. This group includes the Chrysophyceae, Bacillario phyceae, air/water interface (Mitchell, 2000). The cells Raphidophyceae, and Xanthophyceae (with the can glide over the surface with one flagellumexcep tion of Vaucheria and three genera known to actively leading and the other passively lack girdle lamellae – Bumilleria, Bumilleriopsis, and Pseudobumilleriopsis). The Euglenophyta fit into nei- trailing (Fig. 1.14). Cells may switch direction by changing which flagellum is active. Gliding ther group, showing a variable distribution of motility may be a common phenomenonchloro plast DNA. among organisms that live in the thin film of The photo syn thetic algae have chloro phyll in their chloro plasts. Chlorophyll is composed of a water on soil particles.BASIC CHARACTERISTICS OF THE ALGAE 15 Fig. 1.18 The structure of the chlorophylls. (From Meeks, 1974.) light reac tion) in all photo syn thetic algae and ranges from 0.3% to 3.0% of the dry weight. Chlorophyll a is insoluble in water and petroleum ether but soluble in alcohol, diethyl ether, ben- zene, and acetone. The pigment has two main absorp tion bands in vitro, one band in the red light region at 663 nm and the other at 430 nm (Fig. 1.19). Whereas chloro phyll a is found in all photo - syn thetic algae, the other algal chloro phylls have a more limited distribution and func tion as accessory photo syn thetic pig ments. Chlorophyll b is found in the Euglenophyta and Chlorophyta (Fig. 1.18). Chlorophyll bfunc tions photo syn thet - ically as a light-harvesting pigment trans ferring absorbed light energy to chloro phyll a. The ratio of chloro phyll a to chloro phyll b varies from 2:1 to 3:1. The solubil ity character istics of chloro phyll a are similar to chloro phyll b, and in vitro chloro - phyll b has two main absorp tion maxima in ace- Fig. 1.19 The absorption spectra of chlorophylls a, b, c, tone or methanol, one at 645 nm and the other at and d. 435 nm (Fig. 1.19). Chlorophyll c (Fig. 1.18) is found in the porphyrin-ring system that is very similar to that Dinophyta, Cryptophyta, and most of the of hemo globlin but has a magnesium atom Heterokontophyta. Chlorophyll c has two spec- instead of an iron atom (Fig. 1.18). The algae have trally different components: chloro phyll c and c . 1 2 four types of chloro phyll, a, b, c (c and c ), and d. Chlorophyll c is always present, but chloro phyll c 1 2 2 1 Chlorophyll a is the primary photo syn thetic pig- is absent in the Dinophyta and Cryptophyta. The ment (the light receptor in photo system I of the ratio of chloro phyll a to chloroph yll c ranges from16 INTRODUCTION 1.2:2 to 5.5:1. Chlorophyll c probably func tions com posed of three-membrane spanning helices as an accessory pigment to photo system II. The (Fig. 1.20). pigment is soluble in ether, acetone, methanol, 1 Green algae and higher plants use chlorophyll and ethyl acetate, but is insoluble in water and a/b binding proteins. petroleum ether. Extracted chloro phyll c has 1 2 Brown and golden-brown algae, (diatoms, main absorp tion maxima at 634, 583, and 440 nm chrysophytes, dinoflagellates, brown algae, and in methanol, whereas chloro phyll c has maxima 2 related groups) use a fucoxanthin chloro phyll at 635, 586, and 452 nm. a/c complex that is an integral part of the Chlorophyll d (Fig. 1.18) occurs in some thylakoid membr ane. The ratio of fucoxanthin cyanobacteria (Murakami et al., 2004). It has three to chlorop hyll in this complex is approximately main absorption bands at 696, 456, and 400 nm. 2 : 1 and the character istic brown or golden- The photo syn thet ically active pig ments of brown color of these algae is due to the high algae are gathered in dis crete pigment–protein level of fucoxanthin in these cells. Due to complexes which can be divided func tion ally into chloroph yll c and special xanthophylls, these two groups (Grossman et al., 1990): organ isms are especially suited to harvest blue 1 the photochemical reac tion center and green light, which are the most abundant containing chloro phyll a, where light energy at increasing ocean depths. This light- is converted into chem ical energy; harvesting complex also is composed of three 2 the light-harvesting complexes that serve as membrane-spanning helices and is closely antennae to collect and trans fer avail able light related to the light-harvesting complex in the energy to the reac tion center. first group (Caron et al., 1996). 3 Cyanobacteria, cryptophytes and red algae use The light-harvesting complexes use different the phycobi li some as the major light- antennae pigment complexes to capture light harvesting complex. energy. All of the light-harvesting complexes are Fig. 1.20 The basic structure of the light-harvesting complex in all eukaryotic plants. Three transmembrane helices traverse the membrane. The similarity of the light- harvesting complex in all eukaryotic plants is an argument for the chloroplast arising from a single endosymbiotic event. (Modified from Kuhlbrandt et al., 1994.)BASIC CHARACTERISTICS OF THE ALGAE 17 Carotenoidsareyellow,orange,orredpig ments ch loroplasts (Glazer, 1982). They are described as that usually occur inside theplastid but may be chromoproteins (colored pro teins) in which the outside in certain cases. In general, naturally occur- prosthetic group (non- pro tein part of the mole- ringcaroten oidscanbedividedintotwoclasses: cule) or chromophore is a tetra pyrole (bile pig- (1)oxygen-freehydro carbons,the carotenes;and ment) known as phycobilin. The prosthetic group (2)theiroxy gen atedderivatives,the xanthophylls. is tightly bound by covalent link ages to its Themostwide spreadcaroteneinthealgaeis apoprotein (protein part of the mole cule) (see -carotene (Fig. 1.21). There are a large number of Fig. 1.21). Because it is difficult to separat e the different xanthophylls, with the Chlorophyta pigment from the apoprotein, the term phyco - having xanthophylls that most closely resemble biliprotein is used. There are two different apo - those inhigherplants. Fucoxanthin (Fig. 1.21) is proteins,  and , which together form the basic the principal xanthophyll in the golden-brown unit of the phycobiliproteins. To either  or  are algae(Chrysophyceae,Bacillariophyceae,Prymne - attached the colored chromo phores. The major sio phyceae,andPhaeo phyceae),givingthesealgae “blue” chromo phore occurring in phycocyanin their character isticcolor.Likethechloro phylls,the and allophycocyanin is phycocyanobilin, and caroten oidsaresolubleinalcohols,benzene,and themajor “red” chromo phore occurring in phyco - acetone but insoluble in water. erythrin is phycoerythrobilin (Fig. 1.22). The cyanobacteria and chloroplasts of the The general classification of phycobiliproteins Rhodophyta and Cryptophyta have evolved mem- is based on their absorp tion spectra. There are brane-peripheral antenna complexes containing three types of phycoerythrin: R-phycoerythrin phycobiliproteins that transfer light energy to and B-phycoerythrin in the Rhodophyta, and C- photosytem II reaction centers. Like chlorophyll phycoerythrin in the Cyanophyta. There are also b/c/d, the phycobiliproteins expand the range of three types of phycocyanin: R-phycocyanin from light energy that can be utilized in photosyn - the Rhodophyta and C-phycocyanin and allophy- thesis. Light tends to become blue-green as it cocyanin from the Cyanophyta. In addi tion, in courses down the water column, and this light the Cryptophyta there are three spectral types is better absorbed by the biliproteins than of phycoerythrin and three spectral types of ch lorophyll a. phycocyanin. Phycobiliproteins are water-soluble blue or The basic subunit of a phycobilisome con- redpig ments located on (Cyanophyta, Rhodo - sists of apoproteins  and , each of which is phyta) or inside (Cryptophyta) thylak oids of algal attached to a chromophore (Anderson and Toole, Fig. 1.21 The structure of -carotene and fucoxanthin.18 INTRODUCTION Fig. 1.22 The structure of phycoerythrobilin. In intact cells, the overall efficiency of energy 1998; Samsonoff and MacColl, 2001) (Fig. 1.23). In the core of the phycobilisome  and  are trans fer from the phycobi li some to chloro phyll a attached to allophycocyanins, which are closest in the thylakoids ex ceeds 90% (Porter et al., 1978). Chromatic adapters c hange their pigment to chlorophyll intheenergy transfer pathway. components under different light wave lengths In the outer rods,  and areattachedtophy - cocyanin or phycocyanin. In the core of the (Fig. 1.24). For example, the cyanobacterium phycobilisome  and  are attached to allophy- Synechocystis grown in green light pro duces phyco- erythrin (red in color), phycocyanin (blue), and cocyanin. The , mole culesareassembledinto allophycocyanin (blue-green) in a molar ratio of hexa mers( ,  )cylindricalinshape.Thehexa - 1 1 mersthatmakeupthecoreofthephycobi li some about 2 : 2 : 1; when it is grown in red light, the areassembledinpairs,withthehexa mersof ratio is about 0.4 : 2 : 1. The phycobi li some struc- ture changes appropri ately, with the peripheral the rods radi atingfromthecore.Thehexa mers rods having more phycoerythrin hexa mers under are joined together bylinkerpoly pep tides.The linkerpoly pep tidesarebasicwhereasthehexa - green light, and less phycocyanin hexa mers. The mersareacidic;thissuggeststhatelectro static allophycocyanin core hexa mers stay the same. Depriving cells of nitro gen results in an inter ac tionsareimportantinassemblingphyco- ordered degrada tion of phycobi li somes (Fig. 1.25). biliproteins.Thereare high-molecular-weight poly pep tidesthatanchorthephycobi li some There is a pro gressive degrada tion of hexamer rod to the areaofthethylak oidmembranethat and linker poly pep tides followed by the core pep - tides. New phycobi li somes are rapidly syn thesized contains thereac tioncenterandassociated on the addi tion of nitro gen to the medium. chloroph ylls. The pathway of energy trans fer (Glazer et al., Phycobilisomes are, thus, an important source of 1985) is internal nitro gen and offer the algae that have phycoerythrin allophycocyanin B (  565) (  670) max max or → phycocyanin→ allophycocyanin→ or → chlorophyll a phycoerythrocyanin (  620–638) (  650) high-molecular- max max (  568) weight polypeptide max (  665) maxBASIC CHARACTERISTICS OF THE ALGAE 19 phycobi li somes (cyanobacteria, cryptophytes, and red algae) an important ecolog ical advantage in the open ocean, which is pre dominantly nitro gen limited (Vergara and Niell, 1993). Mitochondria and peroxisomes There are two types of mitochondria in algal cells (Leipe et al., 1994). Mitochondria with flat lamellae cristae occur in the red algae, green algae, euglen - oids, and cryptophytes (Fig. 1.26). Mitochondria with tubular cristae occur in hetero konts and hapt ophytes. Glycolate, the major sub strate of photo res - piration, can be broken down by either glycolate dehydrogenase in the mitochondria, or by glyco- late oxidase in peroxisomes, single membrane- bounded bodies in the cyto plasm (for the reac tions, Fig. 1.23 Drawing of a phycobilisome from the see the chapter on Chlorophyta). The distribution cyanobacterium Synechococcus. (Adapted from Grossman of the two enzymes is as follows (Betsche et al., et al., 1993.) 1992; Iwamoto et al., 1996): Fig. 1.24 Chromatic adaptation in a phycobilisome of a cyanobacterium. Fig. 1.25 Phycobilisome breakdown under conditions of nitrogen deprivation. (Adapted from Grossman et al., 1993.) Fig. 1.26 Drawings of the two types of mitochondria that occur in the algae. (a) Mitochondrion with flat lamellar cristae. (b) Mitochondrion with tubular cristae. (a) (b)20 INTRODUCTION 1 Glycolate dehydrogenase occurs in the ring contracts around the area of plastid fission cyanobacteria, cryptophytes, euglen oids, in association with GTPase proteins called diatoms, and the green algae with the excep - dynamins. The PD ring disappears after fission is tion of the Charophyceae. completed. 2 Glycolate oxidase occurs in the glaucophytes, red algae, brown algae, and the Charophyceae Storage products in the green algae and higher plants. The storage products that occur in the algae are as follows: Division of chloroplasts and mitochondria Chloroplasts and mitochondria divide by pinch- High-molecular-weight compounds ing in half to form two new organelles. A plastid- dividing (PD) ring or mitochondrion-dividing 1 -1,4 Linked glucans (MD) ring surrounds the organelle in the area a Floridean starch(Fig.1.28):Thissub stance of fission (Fig. 1.27) (Miyagishima et al., 2003; occurs in the Rhodophyta and is similar to Osteryoung and Nunnari, 2003). Each ring is the amylopectin of higher plants. It stains composed of two parts, an outer ring in the red-violet with iodine, giving a color similar protoplasm outside of the chloroplast and an to that of the stain reac tionofanimal inner ring in the stroma inside the inner mem- glycogen. Floridean starch occurs as bowl- brane of the chloroplast. These rings are also shaped grains from 0.5 to 25 moutside the called FtsZ (filamentous temperature-sensitive) chloroplast, inferring the host in the original rings after a counterpart that is present when bac- endosymbiosis took over formation of storage teria divide. The similarity is indicative of the product. This differs from the Chlorophyta endosymbiotic origin of chloroplasts and mito- where starchisproducedinthechloroplast. chondria from bacteria. The plastid-dividing ring Despite the differing locations of starch appears in the area of division and begins to con- synt hesis, the Rhodophyta and Chlorophyta tract after a microbody has migrated to the plas- use a common pathway in the synthesis of tid-dividing ring (Fig. 1.27). The plastid-dividing starch (Patron and Keeling, 2005). Fig. 1.27 Diagrammatic representation of the behavior of the plastid-dividing ring and mitochondrion-dividing ring in the unicellular red alga Cyanidioschyzon merolae.BASIC CHARACTERISTICS OF THE ALGAE 21 Fig. 1.28 The structure of floridean starch, inulin, laminarin, and floridoside. (After Percival and McDowell, 1967.) b Myxophycean starch: Found in the is intro duced by the number of 1→ 6 Cyanophyta, myxophycean starch has a linkag es, the degree of branching, and the similar s tructure to glycogen. This reserve occurrence of a terminal mannitol mole cule. product occurs as granules (-granules), The pres ence of a high pro por tion of C-6 the shape varying between species from inter residue link ages and of branch points rod-shaped granules to 25-nm particles to seems to determine the solubil ity of the elongate 31- to 67-nm bodies. poly saccharide in cold water: the greater c Starch: In the Chlorophyta, starch is com- thenumber of link ages, the higher the posed of amylose and amylopectin. It occurs solubil ity. Laminarin occurs as an oil-like inside the chloro plast in the form of starch liquid outside of the chloro plasts, commonly grains (Fig. 1.12(e)). In the Cryptophyta, in a vesicle surrounding the pyren oid. starch has an unusually high content of b Chrysolaminarin (leucosin): In the Chryso - amylose and occurs as grains between the phyceae, Prymnesio phyta, and Bacillario - chloro plast envelope and the chloro plast phyceae, chrysolaminarin consists of -1,3 E.R. (Fig. 1.12(b)). In the Dinophyta also, linked D-glucose residues with two 1→ 6 starch occurs in the cyto plasm outside of the gl ycosidic bonds per mole cule. Chrysola - chloro plast, but its structure is not known. minarin occurs in vesicles outside of the 2 -1,3 Linked glucanschloro plast and has more glucose residues a Laminarin (Fig. 1.28): In the Phaeophyceae, per mole cule than laminarin. laminarin consists of a related group of pre - c Paramylon: In the Euglenophyta, Xanthop - dominantly -1,3 linked glucans containing hyceae, and Prym nesiophyta 16 to 31 residues. Variation in the mole cule (Pavlova mesolychnon), paramylon occurs as22 INTRODUCTION wa ter-soluble, single-membrane-bounded the cell and contract (systole). The contractile vac- inclu sions of various shapes and dimen sions uole rhythmically repeats this pro cedure. If there outside of the chloro plast (Fig. 6.2). are two contractile vacuoles, they usually fill and Paramylon consists solely of -1,3 linked glu- empty alternately. Contractile vacuoles occur cose residues, and the mole cule is about as more frequently in fresh water than marine algae, large as that of chrysolaminarin. a phenomenon that gives credence to the theory 3Fructosans: Acetabularia (Chlorophyta) has an that the contractile vacuoles maintain a water inulin-like storage product consisting of a balance in the cells. The algal cells in fresh water series of 1,2 linked fructose units terminated have a higher concentra tion of dis solved sub - by a glucose end group (Fig. 1.28). stances in their proto plasm than in the surround- ing medium so that there is a net increase of Low-molecular-weight compounds water in the cells. The contractile vacuoles act to expel this excess water. An alternate theory on the 1Sugars: Chlorophyta and Euglenophyta form func tion of the contractile vacuoles is that they sucrose as a reserve product; trehalose is remove waste products from the cells. The found in the Cyanophyta and at low levels in Dinophyta have a structure similar to a contrac- the Rhodophyta. tile vacuole, called a pusule, which may have a 2Glycosides: The glyce rol glycosides, floridoside similar func tion but is more complex. (Fig. 1.28) and isofloridoside, are widely distrib - The contractile vacuoles of the Cryptophyta uted in the Rhodophyta. are character istic of the algae (Fig. 1.29). In the 3Polyols: Mannitol (Figs. 1.28, 4.4) occurs in Cryptophyta, the contractile vacuole occurs in a Rhodophyta and Phaeophyceae. It is also fixed ante rior posi tion next to the flagellar present in lower green algae, where it replaces depres sion (Patterson and Hausmann, 1981). At sucrose as a photo syn thetic product. Free the beginning of the filling phase (diastole), there glyce rol occurs widely in the algae and is an is no dis tinct contractile vacuole, only a region important photo syn thetic product in several filled with small (ca. 0.5-m diameter) contribu- zooxanthellae (endo symbiotic algae in tory vacuoles. These vacuoles fuse to form a large animals) and in some marine Volvocales, irregular vacuole which sub sequently rounds up. especially Dunaliella. The contributory vacuoles destined to form the next contractile vacuole now appear around the Contractile vacuoles rounded contractile vacuole. The contractile vac- The ability of algal cells to adjust to changes in the uole fuses with the plasma membrane of the flag- salin ityofthemediumisanimportantaspectof ellar pocket and dis charges its contents outside the physiology of these cells. In cells with walls, the cell. The area of the plasma membrane that this osmoregula tionisaccomplishedwiththe fuses with the contractile vacuole does not have a aid of turgor pressure, whereas in naked cells it periplast (special ized plates within the plasma is accomplished by means of contractile vacuoles membrane). This area is, instead, bounded by and/orregu la tionofthesolutespresentinthe micro tubules. The membrane of the contractile cells.Inthelattercase,cellsincreasetheinter nal vacuole is recovered by the cell as small vesicles con centra tionofosmot icallyactivemole culesand with an electron-dense coat, and the membrane ionswhentheconcentra tionofdis solvedsolutes components are reutilized by the cell. These vesi- increasesintheexternalmedium.Like wise,the cles plus the contractile vacuole occur in the inter nalconcentra tionofsuchmole cules spongiome or area around the contractile vac- decreaseswhentheconcentra tionofdis solvedsalts uole. In fresh water algae the contractile vacuole in the external medium decreases. cycle lasts for 4 to 16 seconds, whereas in marine Most algal flagellates have two contractile vac- species the cycle can last for up to 40 seconds. uoles in the ante rior end of a cell (Fig. 1.1). A con- Algal flagellates use a combina tion of contrac- tractile vacuole will fill with an aqueous solu tion tile vacuoles and osmoregula tion to control the (diastole) and then expel the solu tion outside of water content of their cells. In the chrysophyte

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