Which Algal Group Has Chloroplasts Much Like Those Of Green Plants In Structure And Pigment Makeup

5.iii.iii: Red and Green Algae

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• Yuba Higher, College of the Redwoods, & Ventura Higher via ASCCC Open Educational Resources Initiative

Learning Objectives

• Distinguish betwixt unlike groups of algae using life cycle, morphological features, and cellular composition.
• Connect adaptations in the cherry and dark-green algae to habitat characteristics and ecology.
• Identify structures and phases in the Polysiphonia and Spirogyra life cycles; know the ploidy of these structures.

Ruddy algae and green algae are included in the supergroup Archaeplastida. It was from a common ancestor of these protists that the land plants evolved, since their closest relatives are found in this group. Molecular evidence supports that all Archaeplastida are descendants of an endosymbiotic relationship between a heterotrophic protist and a cyanobacterium. This primary endosymbiosis resulted in the chloroplasts of all photosynthetic eukaryotes discussed in this book! The red and light-green algae include unicellular, multicellular, and colonial forms.

Glaucophyta

Glaucophytes are unicellular, phototrophic eukaryotics institute in freshwater ecosystems. Glaucophytes are likely an ancestral branch in the Archaeplastida and are often used every bit prove of the cyanobacterial origin of chloroplasts. They accept chloroplast-similar organelles, called cyanelles or muroplasts, that have peptidoglycan between the two membranes. They accept the same pigments as blue-green alga and reddish algae: chlorophyll a and phycobilins. Much like the cyanobacteria, they announced blue-greenish due to the interaction of chlorophyll and phycocyanins (glauco- comes from the Greek glaukos significant blue-green). Non-motile cells have a rigid cell wall composed of cellulose. Motile cells have two whiplash flagella. Sexual reproduction has even so to exist documented in this grouping.

Figure \(\PageIndex{1}\): A nonmotile glaucophyte cell asexually reproducing. 2 daughter cells are produced within the cell wall of the mother cell. Each daughter prison cell has a distinct cell wall and is filled with green cyanelles. Photograph by James Tran, CC BY 2.0, via Wikimedia Eatables

Figure \(\PageIndex{2}\): A motile cell (zoospore) of Cyanophora paradoxa. The green structures within this cell are cyanelles. Two flagella can be distinguished on the correct side. Scale bar indicates x µm. From algae civilization of University Duisburg-Essen (Germany), pictures were taken with Zeiss Axioplan and Canon 600D, CC BY-NC. Retrieved from EOL.org.

Rhodophyta

Ruby-red algae descended from the same endosymbiotic upshot every bit the Glaucophyta. The scarlet algae are about exclusively marine. Some are unicellular but most are multicellular. Approximately 6,000 species accept been identified. They have true chloroplasts with ii membranes (no remnant peptidoglycan) containing chlorophyll a. Like the cyanobacteria, they use phycobilins every bit antenna pigments - phycoerythrin (which makes them red) and phycocyanin. Cerise paint allows the red algae to photosynthesize at deeper depths than the greenish or brown algae, harnessing more of the blueish light waves that penetrate deeper into the water cavalcade. Unlike green algae and plants, cerise algae store carbohydrates equally Floridean starch in the cytosol. Some are used as food in coastal regions of Asia. Agar, the base of operations for culturing bacteria and other microorganisms, is extracted from a cherry-red alga.

Selection Pressures and Drivers

An important aspect of understanding the life history traits of the Rhodophyta is understanding the challenges of living in a marine environment.

1. Admission to sunlight: Most colors of light cannot penetrate into deeper water, as they are scattered by water molecules. The wavelengths of light that reach deepest into the ocean are blue and green. Many fish that live in the deep bounding main are cherry-red. Because red light does not penetrate to the depths where they alive, this makes them almost undetectable by sight. Remember, we encounter things because of the light that bounces off of them. Cherry pigments reflect ruddy light, so no red light, no reflected light. Red algae are using a similar strategy--absorb the wavelengths of light that are not cerise--with a different goal: to use that absorbed light to make food. The phycoerythrin in their chloroplasts reflects reddish light, giving them a cerise advent, and absorbs the blueish light that is able to penetrate to deeper areas in the water column.
2. Fertilization: The sea is an expansive surroundings, oft with large areas of open space betwixt populations of organisms. In this surround, successful fertilization of an egg by a nonmotile sperm--red algae lack flagella--presents a challenge. Having multicellular haploid and diploid phases provides red algae more opportunities to produce gametes and spores. A diploid stage that clones the zygote, the carposporophyte, provides more opportunities to practise meiosis from each fertilization outcome.
3. Salinity: Marine environments are relatively high in salinity. A possible adaptation for this is to have sulfated polysaccharides in the prison cell wall, such equally the galactans nowadays in Rhodophyta. This is a strategy present in (potentially all) marine algae and is inferred to be an adaptation for salinity-tolerance. See this open-access article for farther information.

Effigy \(\PageIndex{3}\): The red algae are a fascinating grouping that accept evolved a diversity of morphologies and strategies. This red alga, Asterocolax gardneri, is a parasite on other cherry algae. Note that it lacks the color feature of the Rhodophyta. Considering it feeds off other algae, it does not need to make its own food via photosynthesis and and so does not crave photosynthetic pigments. Photo by Chloe and Trevor, CC-Past-NC.

Morphology

Cerise algae accept a various range of morphologies. Unicellular forms may live solitarily or as colonies just, unlike other members of the Archaeplastida, lack flagella. Flagella are absent from the Rhodophyta, lost at some point in their evolutionary history. Multicellular forms can exist filamentous, leafy, canvass-similar, coralloid, or even crust-similar (some examples in Figure \(\PageIndex{4}\) and Figure \(\PageIndex{5}\)). The strange coralline crimson algae have calcerous deposits in the cell walls that make the thallus difficult, like a coral. These can take a variety of forms and are able to live at depths other algae cannot (over 500 feet deep for some!).

Effigy \(\PageIndex{4}\): These images are all of multicellular blood-red algae, which can range from filamentous (offset image) to "leafy" (2nd image, left) to sheet-like (second image, right). The red color is due to an abundance of the cerise pigment phycoerythrin, which gives this grouping crimson chloroplasts. First image by Melissa Ha CC-BY-NC. Second image past Maria Morrow CC-Past-NC.

Effigy \(\PageIndex{5}\): Examples of coralline red algae.The first epitome shows the thallus of a Calliarthon tuberculosum alga that has washed up on the beach. Having lost its characteristic pink color, the white, calcerous walls are more than obvious. The 2d photo shows a crustose coralline ruddy alga (species unknown to the writer) forming pink blotches on a rock. There are a pair of forceps pointing at one of these blotches. First photo past Jennifer Rycenga, CC-BY-NC. Second photo past past Gsaunders, CC-BY-NC

Cells of multicellular species are connected via incomplete cytokinesis, resulting in pit connections (Figure \(\PageIndex{6}\)).

Figure \(\PageIndex{6}\): A pit connection between Polysiphonia cells. The images shows a channel (pit connection) connecting two adjacent cells, indicated by an arrow. This pit connection passes through the cell walls of both cells, every bit well equally the middle lamellae. Photo by Maria Morrow CC-Past-NC.

Polysiphonia Life Cycle

Red algae take a haplodiplontic (alternation of generations) life cycle that has an actress diploid stage: the carposporophyte. Polysiphonia is the model organism for the Rhodophyta life cycle. The gametophytes of Polysiphonia are isomorphic (iso- meaning same, morph- meaning form), meaning they have the same basic morphology. Any divergence y'all see in coloration of the images in this section is due to staining. They would all announced a deep red color in an unstained slide.

Figure \(\PageIndex{7}\): All stages of the Polysiphonia life bicycle accept the same bones morphology. If you were to run into them without magnification, they would all look more or less similar this: a small-scale, blood-red, finely branching thallus. The reproductive structures are used to differentiate the life stages: presence of spermatangia, cystocarps, or tetrasporangia. Photo by Gsaunders, CC-BY-NC.

Male Gametophyte

The male gametophyte has elongated structures that emerge from the tips of the thallus branches. These are spermatangia, where spermatia are produced past mitosis.

Figure \(\PageIndex{8}\): A Polysiphonia male person gametophyte. In the first image, branches of the male gametophyte each terminate with several elongated structures that look virtually like ears of corn. Each of these structures is a spermatangium. In the 2nd image, a spermatangium is shown by itself, detached from the gametophyte. Cells in the spermatangum undergo mitosis to produce haploid, non-motile, unicellular gametes called spermatia. The image is not clear enough to distinguish individual spermatia. Photos by Maria Morrow, CC-Past-NC.

Female person Gametophyte and Carposporophyte

The female gametophyte produces an egg that is independent within a construction called the carpogonium. This structure has a long, sparse projection called a trichogyne (trich- meaning hair, -gyne meaning female). During fertilization, a spermatium fuses with the trichogyne and the nucleus of the spermatium travels down the tube to the egg. When the nucleus of the spermatium fuses with the egg, a zygote is produced. This zygote is retained and nourished by the female gametophyte as information technology grows.

The globose structures you see growing from the female gametophyte thallus are chosen cystocarps. A cystocarp is composed of both female gametophyte tissue (north) and carposporophyte tissue (2n). The outer layer of the cystocarp, the pericarp (peri- meaning around) is derived from the female person gametophyte and is haploid. The interior of the cystocarp consists of the carposporophyte, which is diploid, and produces structures called carposporangia, inside of which it produces carpospores past mitosis. All of these--carposporophyte, carposporangia, and carpospores--are diploid.

Figure \(\PageIndex{9}\): The image shows branches of the female gametophyte thallus on the left side. In the center, a globose cystocarp emerges from i of those branches. The cystocarp is equanimous of a haploid pericarp that forms the exterior of the structure. The cells of the pericarp expect blocky, almost scale-like. Within the pericarp, the tissues are diploid and vest to the carposporophyte. The carposporophyte is composed of many elongated carposporangia. Photos by Maria Morrow, CC-BY-NC.

Tetrasporophyte

The diploid carpospores are released into the bounding main waters, where they will be carried on currents to some other location. If a carpospore lands in an appropriate environment, it will grow by mitosis into a tetrasporophyte (2n). The tetrasporophyte produces tetrasporangia (2n) within the branches of the thallus. Each tetrasporangium produces four unique, haploid tetraspores past meiosis. Tetraspores (n) are released and volition grow by mitosis into either male or female person gametophytes, completing the life cycle.

Figure \(\PageIndex{10}\): The epitome shows branches of the tetrasporophyte. Each of the compartments within the branches is filled with a globose tetrasporangium. In most of these, articulate delineations can be seen where the tetrasporangium is dividing past meiosis into four distinct cells. These cells are haploid tetraspores. Photo by Maria Morrow, CC-BY-NC.

Total Life Wheel Diagram

Effigy \(\PageIndex{11}\): The alternation of generations life cycle of Polysiphonia. On the left side, in the center, there are four haploid tetraspores. These tetraspores grow by mitosis into haploid gametophytes, either "male" or "female". The male person gametophyte produces spermatangia at the tips of its branches and these spermatangia produce haploid spermatia by mitosis. The female person gametophyte produces carpogonial branches, which have an egg at the base of operations and a long filament chosen a trichogyne that extends from the egg chamber. A spermatium fuses with a trichogyne and its nucleus travels down the trichogyne to fertilize the egg, making a diploid zygote. The zygote grows, still fastened to the gametophyte, inside a structure chosen the cystocarp. The cystocarp has an external layer called the pericarp that is formed from the female gametophyte's tissue (meaning it is haploid). Within the pericarp, the zygote has grown by mitosis into a carposporophyte making elongated carposporangia. Within each carposporangium, diploid carpospores are produced by mitosis. Carpospores are released and grow by mitosis into tetrasporophytes. Within the branches of the tetrasporophyte, tetrasporangia are formed and undergo meiosis to produce four haploid tetraspores each. These tetraspores are released and we go far back where we started. Diagram by Nikki Harris CC-By-NC with labels added by Maria Morrow.

Summary of Characteristics for Blood-red Algae

• Morphology: Unicellular to multicellular, no flagellated stages. Cells of multicellular species are connected via incomplete cytokinesis, resulting in pit connections.
• Cell wall composition: Cellulose and galactans
• Chloroplasts: 2 membranes, pigments are chlorophyll a and phycobilins (primarily phycoerythrin, providing their red color)
• Storage carbohydrate: Floridean starch
• Life cycle: Alternation of generations with an extra diploid stage, the carposporophyte
• Ecology: Primarily marine (97% of species)

Green Algae

The most arable group of algae is the light-green algae. The nature of the evolutionary relationships between the green algae are still up for debate. Equally of 2019, genetic data supports splitting the greenish algae into two major lineages: chlorophytes and streptophytes. The streptophytes include several lineages of green algae (such as the charophytes) and all country plants. Streptophytes and chlorophytes represent a monophyletic group called Viridiplantae (literally "dark-green plants"). The green algae exhibit similar features to the state plants, specially in terms of chloroplast structure. They have chlorophyll a and b, have lost phycobilins but gained carotenoids, and store carbohydrates as starch inside plastids. Although some of the multicellular forms are large, they never develop more a few types of differentiated cells and their fertilized eggs do not develop into an embryo.

Greenish algae are an important source of food for many aquatic animals. When lakes and ponds are "fertilized" with phosphates and nitrates (e.grand., from sewage and the runoff from fertilized fields and lawns), dark-green algae ofttimes grade extensive algal "blooms". Members of this group tin be constitute in freshwater and marine habitats, and many have adapted to life on state, either inside of lichens or costless-living (come across Figure \(\PageIndex{12}\)).

Figure \(\PageIndex{12}\): Trentepohlia is a genus of green algae that is found in terrestrial environments. It forms fluffy orange colonies on trees and is a photobiont in many lichens. Ane might non know they were looking at a green algae, due to the orange pigmentation. Still, green algae have carotenoids. These terrestrial green algae produce an affluence of carotenoids, maybe for protection from dominicus harm. Photograph by Scott Loarie, CC0.

Choice Pressures and Drivers

1. Sun Harm. Green algae represent a diverse group of organisms with diverse life history traits, many of which are shared with country plants. The development of carotenoids-- yellow, orange, and cerise pigments that deed in both light harvesting and sun protection--offers this group increased access to sunlight while simultaneously protecting against UV impairment. UV rays do not penetrate very far into the water column, and so organisms moving into shallower waters or terrestrial environments would need to deal with this new challenge. Many terrestrial species of dark-green algae appear orangish, rather than greenish, due to the production of large amounts of carotenoids.

Morphology

These algae exhibit great multifariousness of grade and part. Like to ruby algae, light-green algae can be unicellular or multicellular. Many unicellular species grade colonies and some green algae be as big, multinucleate, single cells. Green algae primarily inhabit freshwater and damp soil, and are a mutual component of plankton. Chlamydomonas is a elementary, unicellular chlorophyte with a pear-shaped morphology and 2 opposing, anterior flagella that guide it toward lite sensed by its eyespot (Figure \(\PageIndex{xiii}\)). More circuitous species exhibit haploid gametes and spores that resemble Chlamydomonas.

Effigy \(\PageIndex{13}\): This image shows two unicellular green algae from the genus Chlamydomonas. They appear green due to the loss of phycobilins and development of chlorophyll b. They each have two whiplash flagella, though these are but visible on one of them in the picture. Photo by Melissa Ha, CC-BY-NC.

The alga Volvox is ane of a colonial organism, which behaves in some means similar a collection of individual cells, but in other ways like the specialized cells of a multicellular organism (Effigy \(\PageIndex{14}\)). Volvox colonies comprise 500 to 60,000 cells, each with two flagella, independent within a hollow, spherical matrix composed of a gelatinous glycoprotein secretion. Individual Volvox cells movement in a coordinated fashion and are interconnected by cytoplasmic bridges. But a few of the cells reproduce to create daughter colonies, an instance of basic cell specialization in this organism.

Figure \(\PageIndex{xiv}\): Volvox aureus is a light-green alga in the supergroup Archaeplastida. This species exists every bit a colony, consisting of cells immersed in a gel-similar matrix and intertwined with each other via pilus-like cytoplasmic extensions. Descriptive text: The micrograph on the left shows a sphere about 400 microns across with round green cells nearly 50 microns across inside. The middle micrograph shows a similar view at college magnification. The micrograph on the correct shows a broken sphere that has released some of the cells, while other cells remain within. (credit: Dr. Ralf Wagner)

Volvox can reproduce both asexually and sexually. In asexual reproduction, the gonidia develop into new organisms that suspension out of the parent (which then dies). In sexual reproduction, the presence of an inducing chemical causes the following:

• The gonidia of the males to develop into clusters of sperm.
• The gonidia of the females to develop into new spheres each of whose own gonidia develops into a pair of eggs.
• The sperm break out of the male parent and swim to the female where they fertilize her eggs.
• The zygotes course a resting stage that enables Volvox to survive harsh conditions (Figure \(\PageIndex{xv}\)).

Figure \(\PageIndex{fifteen}\): Volvox thick-walled, desiccation-resistant zygote. There is a larger sphere composed of many individuals (shown as bluish dots). Inside that larger sphere, there are several smaller spheres with thick, warty walls. Photo by Maria Morrow, CC-BY-NC.

Video \(\PageIndex{one}\): This video shows how sexual reproduction occurs in the colonial green alga Volvox. Sourced from YouTube.

The genome of Volvox carteri consists of 14,560 protein-encoding genes - merely 4 more genes than in the unmarried-celled Chlamydomonas reinhardtii! Most of its genes are also plant in Chlamydomonas. The few that are not encode the proteins needed to form the massive extracellular matrix of Volvox.

Species in the genus Caulerpa exhibit flattened fern-similar foliage and can reach lengths of 3 meters (Effigy \(\PageIndex{16}\)). Caulerpa species undergo nuclear division, simply their cells exercise non complete cytokinesis, remaining instead every bit massive and elaborate single cells.

Effigy \(\PageIndex{16}\): Caulerpa taxifolia is a chlorophyte consisting of a single cell containing potentially thousands of nuclei, much like a plasmodial slime mold. (credit: NOAA)

Truthful multicellular organisms, such every bit the body of water lettuce, Ulva, are also represented amongst the green algae (Figure \(\PageIndex{17}\) and Figure \(\PageIndex{18}\)).

Figure \(\PageIndex{17}\): Ulva is a genus of multicellular marine green algae that forms apartment sheets of cells. In the image on the left, at that place is a pressed sample of an Ulva expansa thallus that is serving as an herbarium specimen. In the image on the correct, a piece of an Ulva thallus is existence viewed through a microscope. Each cell contains green chloroplasts and a big nucleus, two of which are labeled in the epitome. Photos by Maria Morrow, CC-Past-NC.

Figure \(\PageIndex{xviii}\): Chaetomorpha coliformis, a marine green alga formed from chains of cylindrical cells (commonly called ocean emeralds). Photograph by Svenjah Heesch, (CC-By-NC).

Spirogyra Life Wheel

Though green algae display a diversity of life cycles, many have a haplontic life bicycle. A model organism for the dark-green algae is Spirogyra (Figure \(\PageIndex{19}\)). Spirogyra is a unicellular green algae that grows in long, filamentous colonies, making it appear to exist a multicellular organism. Even though it is technically unicellular, its colonial nature allows u.s.a. to classify its life cycle as haplontic. In the haploid vegetative cells of the colony, the chloroplasts are arranged in spirals, containing darkened regions chosen pyrenoids where carbon fixation happens. Each haploid jail cell in the filament is an private, which makes sexual reproduction between colonies an interesting procedure.

Figure \(\PageIndex{nineteen}\): A vegetative prison cell in a Spirogyra colony. The nucleus is visible in the center of the cell, including a large, dark nucleolus. The chloroplasts are arranged in spirals effectually the cell and have dark regions chosen pyrenoids where carbon dioxide is fixed. Photo by Maria Morrow, CC-BY-NC.

When two colonies of Spirogyra see that are of a complementary mating blazon (+/-), sexual reproduction occurs. The two colonies marshal, each jail cell across from a complementary jail cell on the other filament. A conjugation tube extends from each cell in ane colony (Figure \(\PageIndex{xx}\)), inducing formation of a tube on the cells in the other colony. The conjugation tubes from each colony fuse together.

Figure \(\PageIndex{20}\): Spirogyra forming conjugation tubes. In that location are ii vegetative colonies that are about to interact. The colony on the right has chemically sensed the presence of the colony on the correct and has started to abound projections in the cell walls of each jail cell in the colony, extending them toward the other colony. These are the beginnings of conjugation tubes. Photo by Maria Morrow, CC-BY-NC.

The contents of one cell will move through the conjugation tube and fuse with the contents of the complementary prison cell, resulting in a diploid zygote (Figure \(\PageIndex{21}\)). The zygote appears as a large, egg-like structure contained within the complementary jail cell. Information technology has a thick wall that provides resistance to desiccation and cold, assuasive colonies of Spirogyra to overwinter, when needed. The other colony is now a filament of empty cells that will be broken down by some decomposer. When atmospheric condition are right, the zygote undergoes meiosis to produce another vegetative colony of haploid cells.

Figure \(\PageIndex{21}\): Cells in diverse stages of conjugation. Of the cells that have formed conjugation tubes and connected, the ane farthest to the left has simply recently finished the transfer and fusion of its cytoplasm, just the zygote hasn't fully formed yet. In the cell on the far right, there is a fully formed zygote. It is night in color and has thick walls. The chloroplasts are non individually distinguishable within information technology. Photo past Maria Morrow, CC-BY-NC.

Full Life Cycle Diagram

Figure \(\PageIndex{22}\): The haplontic life bike of Spirogyra. Starting from the upper left corner and moving right, there is a single haploid vegetative colony of Spirogyra. The chloroplasts are drawn in as a unmarried ribbon with circles representing pyrenoids. Each cell has a large, dark nucleus. Moving to the correct, two colonies of complementary mating types begin to interact with each other through chemical signals and outset forming conjugation tubes. In the next frame, the conjugation tubes have connected and the contents of one cell begins to transfer through the conjugation tube into a jail cell in the other colony. This is plasmogamy. Karyogamy occurs when the ii nuclei fuse together and the diploid zygote is formed. This zygote waits for appropriate conditions to germinate, undergo meiosis, and form a new haploid colony. Diagram by Nikki Harris, CC BY-NC with labels added by Maria Morrow.

Summary of Characteristics for Green Algae

• Morphology: Unicellular to multicellular; ii whiplash flagella on motile cells
• Jail cell wall composition: Cellulose
• Chloroplasts: 2 membranes, pigments are chlorophyll a, chlorophyll b, and carotenoids
• Storage carbohydrate: Starch
• Life cycle: Varies, but primarily haplontic. Some marine species have alternation of generations.
• Ecology: Freshwater, marine, and terrestrial species

Summary

Glaucophytes, red algae, and green algae are part of the Archaeplastida. These organisms are descended from the same primary endosymbiosis event. Glaucophytes are thought to be one of the earliest lineages to diverge due to the presence of remnant peptidoglycan between the membranes of its chloroplast-like cyanelles. Unsurprisingly, glaucophytes and red algae share the aforementioned pigments as Cyanobacteria.

Red algae (phylum Rhodophyta) are united by several synapomorphies (shared derived characteristics). They lack flagella, accept pit connections betwixt cells, and store carbohydrates equally Floridean starch. The sulfated galactans in their prison cell walls allows them increased fitness in marine environments, while the pigment phycoerythrin allows them to photosynthesize deeper in the h2o column. They have an alternation of generations life wheel with an actress diploid stage, the carposporophyte, that clones the zygote. These characteristics tin exist continued to the ecology stressors presented by the marine habitats most cerise algae are found in.

Green algae correspond several distinct lineages. Similar plants, they store carbohydrates equally starch within their plastids and have the pigments chlorophyll a and b, every bit well as carotenoids. Organisms in this group take haplontic (e.g. Spirogyra) or haplodiplontic (e.g. Ulva) life cycles. Many green algae are unicellular, forming complex colonies. Green algae can be institute in marine, freshwater, and terrestrial environments (including within lichens!).

Source: https://bio.libretexts.org/Bookshelves/Botany/Botany_(Ha_Morrow_and_Algiers)/Unit_1%3A_Biodiversity_(Organismal_Groups)/05%3A_Protists/5.03%3A_Photosynthetic_Protists/5.3.03%3A_Red_and_Green_Algae

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