Bop8e Chapter03 REVISED W16 Part 1

Ray F. Evert • Susan E. Eichhorn Raven Biology of Plants Eighth Edition

CHAPTER 3 The Plant Cell and the Cell Cycle

Powerhouse of the Plant Cell • The chloroplast is the site where light energy is used to produce the organic molecules required by the plant cell • In this image, the flattened and stacked membranes of the grana can be seen inside the chloroplast • Chlorophyll and other pigments embedded in the chloroplast membranes capture the sun's energy, the first step in the process essential to life—photosynthesis

Hooke's Microscope • The English microscopist Robert Hooke first used the term "cell" to refer to the small chambers he saw in magnified slices of cork • (a) One of Hooke's microscopes, made for him around 1670 • Light from an oil lamp (far left) was directed to the specimen through a water-filled glass globe that acted as a condenser • The specimen was mounted on a pin, just below the tip of the microscope • The microscope was focused by moving it up and down using a screw held to the stand by a clamp • (b) This drawing of two slices of cork appeared in Hooke's book, Micrographia, published in 1665

Chapter Overview • Prokaryotes and Eukaryotes • The Plant Cell: An Overview • Nucleus • Chloroplasts and Other Plastids • Mitochondria • Peroxisomes • Vacuoles • Endoplasmic Reticulum • Golgi Apparatus • Cytoskeleton • Flagella and Cilia • Cell Wall • The Cell Cycle • Interphase • Mitosis and Cytokinesis Main Points of this Chapter • The cell is the fundamental unit of life • Cells are of two fundamentally different types: prokaryotic and eukaryotic • Plant cells typically consist of a cell wall and a protoplast • The nucleus is surrounded by a nuclear envelope and contains nucleoplasm, chromatin, and one or more nucleoli • Ribosomes are the sites of protein synthesis • There are three main types of plastids: chloroplasts, chromoplasts, and leucoplasts • Mitochondria are the sites of respiration • Plastids and mitochondria share certain features with prokaryotic cells • Peroxisomes are surrounded by a single membrane Main Points of this Chapter, continued • Vacuoles perform a variety of functions • The endoplasmic reticulum is an extensive three-dimensional system of membranes with a variety of roles • The Golgi apparatus is a highly polarized membrane system involved in secretion • The cytoskeleton is composed of microtubules and actin filaments • The cell wall is the major distinguishing feature of the plant cell • Dividing eukaryotic cells pass through a regular sequence of events known as the cell cycle • During prophase, the duplicated chromosomes shorten and thicken • Metaphase, anaphase, and telophase followed by cytokinesis result in two daughter cells Prokaryotes and Eukaryotes Prokaryote (Escherichia coli) Prokaryote • Electron micrograph of cells of Escherichia coli, a bacterium that is a common, usually harmless inhabitant of the human digestive tract • However, some E. coli strains, which generally are acquired by ingestion of contaminated food or water, produce toxins that cause massive secretion of fluids into the intestine, resulting in vomiting and diarrhea • This heterotrophic (nonphotosynthetic) prokaryote is the most thoroughly studied of all living organisms Prokaryote, continued • Each rod-shaped cell has a cell wall, a plasma membrane, and cytoplasm • The genetic material (DNA) is found in the less granular area in the center of each cell • This region, known as the nucleoid, is not surrounded by a membrane • (In prokaryotes, nucleoid contains most or all of the cell's genetic material) • The densely granular appearance of the cytoplasm is largely due to the presence of numerous ribosomes, which are involved with protein synthesis • The two cells in the center have just divided but have not yet separated completely Photosynthetic Eukaryote Plasma Membrane Photosynthetic Eukaryote • Electron micrograph of a cell from the leaf of a maize (Zea mays) plant • The granular material within the nucleus is chromatin • It contains DNA associated with histone proteins • The nucleolus is the region within the nucleus where the RNA components of ribosomes are synthesized • Note the many mitochondria and chloroplasts, all bounded by membranes • (Mitochondria – sites of respiration involving conversion of energy-rich molecules to do cellular work and release of waste products; chloroplasts – sites of photosynthesis) • The vacuole, which is a fluid-filled region enclosed by a membrane, and the cell wall are characteristic of plant cells

Plasma Membrane (Eukaryote) • Under high magnification, cellular membranes often have a three-layered (dark-light-dark) appearance, as seen here (following slide) • This is a plasma membrane on either side of the common cell wall between two cells from an onion (Allium cepa) root tip • The numerous circular structures bordering the wall are microtubules Plasma Membrane The Plant Cell: An Overview

Nucleus Nuclear Aspects as considered in Selaginella kraussiana • Selaginella kraussiana (right) • (image: Wikipedia) Nucleus • Electron micrographs of nuclei in parenchyma cells of the seedless vascular plant Selaginella kraussiana show the nuclear pores (a, see arrow in following slide) Nuclear Pores in Selaginella kraussiana (surface view), a (arrow)

Note the polysomes (coils of ribosomes) on the surface of the nuclear envelope Nucleus • Electron micrographs of nuclei in parenchyma cells of the seedless vascular plant Selaginella kraussiana show the nuclear pores (b) in sectional view • The rough endoplasmic reticulum is seen paralleling the nuclear envelope in (b) • The nucleus is to the left Nuclear Pores in Selaginella Kraussiana (sectional view), b, rough endoplasmic reticulum (nucleus to the left of the arrows) Chromatin in Nicotiana tabacum Chromatin • Parenchyma cell from tobacco (Nicotiana tabacum) leaf, with its nucleus "suspended" in the middle of the cell by strands of cytoplasm (arrows) • The dense granular substance in the nucleus is chromatin, distinguishing it from the nucleoplasm • The less granular regions surrounding the nucleus are portions of a large central vacuole that merge beyond the plane of this cell section Nicotiana quadrivalvis (Indian tobacco) • Used by Native Americans from Oregon to British Columbia • (text & image: Wikipedia) Diagram of a Chloroplast- Containing Plant Cell Diagram of a Chloroplast-containing Plant Cell • Typically, the disk-shaped chloroplasts are located in the cytoplasm along the cell wall, with their broad surfaces facing the surface of the wall • Most of the volume of this cell is occupied by a vacuole (surrounded by the tonoplast), which is traversed by a few strands of cytoplasm • Tonoplast: membrane surrounding the vacuole • Cytosol, thick fluid that fills a cell • Cytoplasm: cytosol plus organelles • In this cell, the nucleus lies in the cytoplasm along the wall, although in some cells (see Figure 3—6) it might appear suspended by strands of cytoplasm in the center of the vacuole Ribosomes are formed in the cytosol and serve as the sites of protein synthesis Polysomes (or Polyribosomes), complexes of an mRNA molecule and two or more, that are formed during active translation

(mRNA involved in providing information translated in ribosomes indicating amino acid sequences to synthesize proteins in ribosomes) Polysomes • Numerous polysomes (clusters of ribosomes) are seen here on the surface of rough endoplasmic reticulum • The endoplasmic reticulum is a network of membranes extending throughout the cytosol of the eukaryotic cell, dividing it into compartments and providing surfaces on which chemical reactions can take place • Cytosol: part of the cell inside of the cell membrane, excluding the organelles • Polysomes are the sites at which amino acids are assembled into proteins • This electron micrograph shows a portion of a leaf cell from the fern Regnellidium diphyllum Regnellidium diphyllum • Regnellidium is a monotypic genus of ferns of family Marsileaceae • The single living species, Regnellidium diphyllum, the two-leaf water fern, is native to southeastern Brazil and adjacent regions of Argentina • It resembles its relatives from the genus Marsilea [M. vestita, water-clover, is native to WA] • (image and text: Wikipedia) Chloroplasts and Other Plastids Chloroplasts are the sites of photosynthesis Orientation of Chloroplasts Orientation of Chloroplasts • As shown in cross sections through the leaf of Arabadopsis thaliana, chloroplasts move to maximize or minimize their absorption of light, which is entering from the top of the micrographs • (a) Under dim light, chloroplasts (dark objects along the edges of the cells) move to the cell walls parallel to the leaf surface, thus maximizing light absorption for photosynthesis • (b) In bright light, chloroplasts migrate to the cell walls perpendicular to the light surface, thus minimizing light absorption and photodamage Internal Structure of a Chloroplast Internal Structure of a Chloroplast • (a) Section of a chloroplast of a maize (Zea mays) leaf showing grana and stroma thylakoids • The word thylakoid comes from the Greek word thylakos meaning "sac" or "pouch" • Grana Plastid DNA Nuclear and Plastid DNA • This photograph of a spinach (Spinacia oleracea) leaf mesophyll cell, stained with the fluorescent dye DAPI, shows the concentration of DNA (large white area) in the nucleus and the location of multiple copies of DNA (small white dots) in the chloroplasts • The chlorophyll molecules show red fluorescence Spinach (Spinacia oleracea) • (image: Wikipedia) Chromoplasts contain pigments other than chlorophyll Chromoplast Chromoplast • A chromoplast from a petal of Forsythia, a common garden shrub that is covered with yellow flowers in the early spring • The chromoplast contains numerous electron-dense oil bodies in which the yellow pigment is stored Forsythia (Forsythia) • (image: Wikipedia) Leucoplasts are nonpigmented plastids Leucoplasts Leucoplasts • Leucoplasts are small colorless plastids • [usually not located in photosynthesizing regions, but instead in other plant parts where they may be involved in food storage, e.g., as in amyloplasts, or in other processes] • Here they can be seen clustered around the nucleus in an epidermal cell of a leaf from the houseplant known as a wandering Jew (Tredescantia zebrina) • The purple color is due to anthocyanin pigments in vacuoles of the epidermal cells • [anthocyanins associated with flowers and fruits – pollination and dissemination, in leaves perhaps to screen out some light to help protect cells, etc.] Tradescantia zebrina (wandering jew) • (image: Wikipedia) Amyloplast Amyloplast • A type of leucoplast, this amyloplast is from the embryo sac of soybean (Glycine max) • The round, clear bodies are starch grains • The smaller, dark bodies are oil bodies • Amyloplasts are involved in the synthesis and long-term storage of starch in seeds and storage organs, such as potato tubers Glycine max (soybean) • (image: Wikipedia) Proplastids are the precursors of other plastids Plastid Developmental Cycle Plastid Developmental Cycle • (a) The central process shown here begins with the development of a chloroplast from a proplastid • Initially, the proplastid contains few or no internal membranes • (b) – (d) As the proplastid differentiates into a chloroplast, fattened vesicles develop from the inner membrane of the plastid envelope and eventually align themselves into grana and stroma thylakoids • (e) The thylakoid system of the mature chloroplast appears discontinuous with the envelope • (f), (g) Proplastids may also develop into chromoplasts and leucoplasts, such as the starch-synthesizing amyloplast shown here • Note that chromoplasts may be formed from proplastids, chloroplasts, or leucoplasts (for example, an amyloplast) • The various kinds of plastids can change from one type to another (dashed arrows) Etioplast Etioplast • An etioplast in a leaf cell of tobacco (Nicotiana tabacum) grown in the dark • [Etioplasts are chloroplasts that have not been exposed to light, including chloroplasts that may become etioplasts as result of light deficiency] • Note the semicrystalline prolamellar body (checkerboard pattern at the left) – this carries the precursor pigment for chlorophyll • When exposed to light, the tubular membranes of the prolamellar body develop into thylakoids, and grana also develop Mitochondria Mitochondria and chloroplasts evolved from bacteria Symbiogenesis • Symbiogenesis, or endosymbiotic theory, is an evolutionary theory that explains the origin of eukaryotic cells from prokarotes • Several key organelles of eykaryotes originated as a symbiosis between separate single-celled organisms • Mitochondria, plastids (e.g., chlorplasts), and possibly other organelles representing formerly free-living bacteria (prokaryotes) were taken inside another cell as endosymbionts around 1.5 billion years ago • Molecular and biochemical evidence suggest that mitochondria developed from proteobacteria (in particular, Rickettsiales) or close relatives) and chloroplasts from cyanobacteria (in particular, nitrogen- fixing filamentous cyanobacteria) • (Proteobacteria – large group of gram-negative bacteria, including pathogens such as Escherichia, Salmonella, etc., as well as bacteria involved in nitrogen fixation) • (great diversity of forms, and named after Proteus, a Greek god of the sea capable of assuming many different shapes) • (Wikipedia) Mitochondrion Mitochondrion • A mitochondrion in a leaf cell of spinach (Spinacia oleracea), in a plane of section revealing some strands of DNA in the nucleoid • (site of cellular respiration) • The envelope of the mitochondrion consists of two separate membranes • The inner membrane folds inward to form cristae, which are embedded in a dense matrix • The small particles in the matrix are ribosomes (sites of protein synthesis) Peroxisomes • Peroxisomes (also called microbodies) are organelles found in virtually all eukaryotic cells • Involved in many processes, including primary and secondary metabolism • E.g., in the breakdown of fatty acids, etc. (to yield energy, e.g., as required for the normal function of mammalian brains and lungs) and play a role in seed germination, etc. • (Hu et al., 2012; Wikipedia) Organelles in a leaf cell Organelles in a Leaf Cell • A peroxisome with a large crystalline inclusion and a single surrounding membrane may be contrasted wit the two mitochondria and the chloroplast, each of which has an envelope consisting of two membranes • (More on crystalline protein cell inclusions may be found in Heinze, Reichelt, Kleff, & Eising, 2000) • Due to the plane of the section, the double nature of the chloroplast envelope is apparent only in the lower portion of this electron micrograph • A single membrane, the tonoplast, separates the vacuole from the rest of the cytoplasm in this leaf cell of tobacco (Nicotiana tabacum) Cytoplasmic Components of a Plant Cell Cytoplasmic Components of a Plant Cell • Oil bodies are visible in this electron micrograph of a parenchyma cell from the thickened stem, or corm, of the quillwort (Isoetes muricata) • The dense material lining the vacuole is tannin • To the upper left of the mitochondrion, a cisterna of the endoplasmic reticulum is greatly distended • Some vacuoles are thought to arise from the endoplasmic reticulum in this way Calcium Oxalate Crystals Calcium Oxalate Crystals • Vacuoles can contain different forms of calcium oxalate crystals • (a) Druses or aggregates of crystals composed of calcium oxalate, from the vacuoles of epidermal cells of redbud (Cercis canadensis), as seen with a scanning electron microscope • (b) A bundle of raphides, or needlelike crystals of calcium oxalate, in a vacuole of a leaf cell of the snake plant (Sansevieria) • The tonoplast surrounding the vacuole is not discernible • The granular substance seen here is the cytoplasm Cercis canadensis (eastern redbud)

• Native Americans consumed redbud flowers raw or boiled, and ate the roasted seeds • (image and text: Wikipedia) Sansevieria spp. (snake plant)

• Ca. 70 species native to Africa, Madagascar and southern Asia • Ornamental and textile plants • Can remove atmospheric toxins • (image and text: Wikipedia) Calcium Oxalate Crystals Calcium Oxalate Crystals Endoplasmic Reticulum Golgi Body Cortical Endoplasmic Reticulum • A single epidermal cell of Nicotiana benthamiana showing cortical endoplasmic reticulum • [a network of membranous tubules within the cytoplasm of a eukaryotic cell, continuous with the nuclear membrane. It usually has ribosomes attached and is involved in protein and lipid synthesis (https://www.google.com/search?q=+endoplasmic+reticulum+&ie =utf-8&oe=utf-8)] • The cortical endoplasmic reticulum has been labeled with green fluorescent protein and photographed using confocal laser scanning microscopy • Tubular endoplasmic reticulum elements form a "cage" around each of the three chloroplasts (arrows) seen here • [

• North America, Europe, and northern Asia • Wetlands and riparian zones • Used as polishing material • (image and text: Wikipedia) Golgi Body Golgi Body Golgi Body The Endomembrane System The Endomembrane System • The endomembrane system consists of an interconnected network of the endoplasmic reticulum, the nuclear envelope, Golgi bodies with their transport and secretory vesicles, the plasma membrane, and vacuolar membranes • This diagram depicts the origin of new membranes rom the rough endoplasmic reticulum at the left • Transition vesicles pinch off a smooth-surfaced portion of the endoplasmic reticulum and carry membranes and enclosed substances to the forming (cis) face of the Golgi body • In this cell, cell wall substances are being transported stepwise across the Golgi stack to the trans-Golgi network by means of shuttle vesicles • Secretory vesicles derived from the trans-Golgi network then migrate to the plasma membrane and fuse with it, contributing new membrane to the plasma membrane and discharging their contents into the wall Coated Vesicles Coated Vesicles • These coated vesicles are surrounded by proteins, including clathrin • The three-pronged clathrin subunits are associated with one another to form cages around the vesicles • (vesicle coat serves to sculpt the curvature of a donor membrane, and to select specific proteins as cargo) The endoplasmic reticulum and Golgi apparatus are components of the endomembrane system