Transcript Slide 1
About Plant Biology Chapter 1 Why Study Plant Biology? • Show interrelationships between plants and other fields of study • Prepare for careers in plant biology • Gain fundamental knowledge for upper division plant biology courses • Share expertise gained with nonbotanists What is a Plant? • An organism that is green and photosynthetic • Additional characteristics – Cell wall composed of cellulose – Multicellular body – Can control water loss – Have strengthening tissues – Can reproduce by means of microscopic, drought-resistant spores Ecologic Services • Sources of food, fabric, shelter, medicine • Produce atmospheric oxygen and organic nitrogen • Build new land • Inhibit erosion • Control atmospheric temperature • Decompose and cycle essential mineral nutrients Importance of Plants to Human Civilizations • Trees for lumber to make warships • Fuel to smelt metals, cure pottery, generate power and heat • Sources of wealth – spices • Sources of industrial products – Rubber – oil Natural Plant Losses • Plant losses occurring at a faster rate than ever before • Factors include – Agriculture – Urbanization – Overgrazing – Pollution – Extinction Environmental Laws • Described in 1961 by plant biologist Barry Commoner • Laws becoming more true every day • Four “environmental laws” – Everything is connected to everything else. – Everything must go somewhere. – Nature knows best. – There is no such thing as a free lunch. Scientific Method • Codefined and promoted in 17th century by Rene Decartes and Francis Bacon • Steps involved in scientific method – – – – – – Make observations Ask questions Make educated guesses about possible answers Base predictions on the guesses Devise ways to test predictions Draw conclusions Scientific Method • Hypothesis – “educated guess” based on observations and questioning • Predicted result occurs – hypothesis is most likely correct • Individuals using scientific method should be objective and unbiased Scientific Method Original Hypothesis Results support hypothesis Devise method to test hypothesis Results support hypothesis but suggest minor refinements Retest using minor refinements of process Analyze results Results do not support original hypothesis but fall within range that could be expected if original hypothesis is slightly modified Results are so unexpected that they do not support original hypothesis and require a new hypothesis Test using slightly modified hypothesis Test new hypotheses Studying Plants From Different Perspectives • Plant genetics – study of plant heredity • Plant systematics – study of plant evolution and classification • Plant ecology – study of how the environment affects plant organisms • Plant anatomy – study of a plant’s internal structure • Plant morphology – study of how a plant develops from a single cell into its diverse tissues and organs Study Plants from Taxonomic Classification • • • • Microbiology – study of bacteria Mycology – study of fungi Phycology – study of algae Bryology – study of mosses Interrelationships Among Several Plant Biology Disciplines Genes ENVIRONMENT Genetics Evolution METABOLISM Ecology Physiology Paleoecology Taxonomy & Systematics Biogeography PLANT TAXONOMIC GROUPS STRUCTURE Phycology Microbiology Mycology Bryology DEVELOPMENT Morphology Anatomy Plant Classification • Taxonomy • Linnaean system – Easy to use – Based on idea that species never changed – Grouped organisms according to arbitrary similarities – Fails to meet needs of modern biologists Linnaean Taxa Taxa Ending Kingdom Division -phyta Class -opsida Order -ales Family -aceae Genus No standard ending Species No standard ending Plant Classification Whittaker’s Five Kingdoms • Developed in 1969 by Robert Whittaker • Each kingdom assumed to be monophyletic group of species • Molecular biology techniques – Cladistics – Show five kingdom system also does not recognize evolutionary groups Whittaker’s Five Kingdoms Kingdom Monera Description Included bacteria Fungi Included molds, mildews, rusts, smuts, and mushrooms Protista Included simple organisms, some were photosynthetic, mostly aquatic organisms called algae Plantae Included more complex photosynthetic organisms that typically grew on land Animalia Included typically motile, multicellular, nonphotosynthetic organisms Plant Classification Cladistics • Based on evolutionary groups • Compare DNA base pair sequences of organisms to determine relatedness • Obtain percent similarity between organisms Plant Classification • Clades – evolutionary groups • Cladogram = phylogenetic tree – Branching diagram – Emphasizes shared features from common ancestor – Future discoveries may require modifications of cladogram Plant Classification • Domain – Neutral term – Groups of organisms as large or larger than a kingdom – Monophyletic • Three domains based on cladistics – Eukarya – Bacteria – Archaea Domain Eukarya • Made up of Whittaker’s plant, animal, and fungal kingdoms • Eukaryotic cells – Membrane-bounded organelles • Linear chromosomes • Protists – Not monophyletic – Controversy over where to place organisms Domain Bacteria • Organisms originally were placed in Whittaker’s Kingdom Monera • Microscopic • Prokaryotic cells – No membrane-bounded organelles – Circular chromosome • Sexual reproduction unknown • Found in every habitat on Earth Domain Bacteria Beneficial aspects • Decomposers • Some carry on photosynthesis – Cyanobacteria or blue-green algae • Nitrogen fixation – Convert inorganic N2 into ammonium for plant use – Cyanobacteria Domain Bacteria Detrimental effects • Pathogens – cause diseases • Human diseases – Botulism, bubonic plague, cholera, syphilis, tetanus, tuberculosis • Plant diseases Domain Archaea • Organisms originally were placed in Whittaker’s Kingdom Monera • Prokaryotic • Different cell structure and chemistry than organisms in Domain Bacteria Domain Archaea Divided into three groups based on habitat • Bacteria of sulfur-rich anaerobic hot springs and deep ocean hydrothermal vents • Bacteria of anaerobic swamps and termite intestines • Bacteria of extremely saline waters – Extreme halophiles – Photosynthetic – pigment bacteriorhodopsin Three Domains Domain Cell Type Description Eukaryotic Membrane bounded organelles, linear chromosomes Archaea Prokaryotic Found in extreme environments, cell structure and differ from members of Domain Bacteria Bacteria Prokaryotic Ordinary bacteria, found in every habitat on earth, play major role as decomposers Eukarya Kingdom Fungi • • • • Eukaryotic cells Typically microscopic and filamentous Rigid cell wall made of chitin Reproduce sexually in a variety of complex life cycles and spores • Widely distributed throughout world – mainly terrestrial Kingdom Fungi Economic importance • Decomposers • Form associations with roots of plants • Important foods for animals and humans – Mushrooms, morels • Decomposing action of yeast – Flavored cheeses, leavened bread, alcoholic beverages Kingdom Fungi Economic importance • Production of antibiotics – Penicillium • Pathogens – Invade both plant and animal tissue – Cause illnesses – Reduce crop yields Kingdom Protista • Eukaryotic cells • Reproduce both sexually and asexually • Catch-all group – Photosynthetic organisms – algae – Nonphotosynthetic organisms – slime molds, foraminiferans, protozoans Kingdom Protista Algae • Arrangements – Single cells, clusters, filaments, sheets, threedimensional packets of cells • Photosynthetic • Float in uppermost layers of all oceans and lakes Kingdom Protista • Phytoplankton – “grasses of the sea” – Microscopic algae – Form base of natural food chain – Produce 50% of all oxygen in atmosphere Kingdom Plantae • Included all organisms informally called plants • Bodies more complex than bacteria, fungi, or protists • Eukaryotic Kingdom Plantae • Unique biochemical traits of plants – Cell walls composed of cellulose – Accumulate starch as carbohydrate storage product – Special types of chlorophylls and other pigments Kingdom Plantae Ecologic and economic importance of plants • Form base of terrestrial food chains • Principal human crops • Provide building materials, clothing, cordage, medicines, and beverages Challenge for 21st Century While the human population increases, the major challenge of retaining natural biological diversity and developing a sustainable use of the world’s forests, grasslands, and cropland remains. As you study plant biology, think of the ways that you can contribute to this challenge. Proteins take on a variety of shapes, which enables specific interactions (function) with other molecules. Fig. 2.22 Stages in the formation of a functioning protein The Plant Cell and the Cell Cycle Chapter 3 Eucaryotic Cell structure • • • • • • • • • • • • Rough endoplasmic reticulum-site of secreted protein synthesis Smooth ER-site of fatty acid synthesis Ribosomes-site of protein synthesis Golgi apparatus- site of modification and sorting of secreted proteins Lysosomes-recycling of polymers and organelles Nucleus-double membrane structure confining the chromosomes Nucleolus-site of ribosomal RNA synthesis and assembly of ribosomes Peroxisome-site of fatty acid and amino acid degradation Flagella/Cilia- involved in motility Mitochondria-site of oxidative phosphorylation Chloroplast-site of photosynthesis Intermediate filaments- involved in cytoskeleton structure Plant vs Animal Cells • Plant cells have chloroplasts and perform photosynthesis • Outermost barrier in plant cells is the cell wall • Outermost barrier in animal cells is the plasma membrane Cell • Basic unit of plant structure and function • Robert Hooke – Looked at cork tissue under microscope – “little boxes or cells distinct from one another ….that perfectly enclosed air” • Nehemiah Grew – Recognized leaves as collections of cells filled with fluid and green inclusions Cell Theory Statement All plants and animals are composed of cells. Cells reproduce themselves. All cells arise by reproduction from previous cells. Year Contributor 1838 Matthias Schleiden and Theodor Schwann 1858 Rudolf Virchow 1858 Rudolf Virchow Basic Similarities of Cells • Cells possess basic characteristic of life – Movement – Metabolism – Ability to reproduce • Organelles – “little organs” – Carry out specialized functions within cells Light Microscope • View cells 20-200 µm in diameter • Can view living or stained specimens • Resolution (resolving power) – Ability to distinguish separate objects – Limited by lenses and wavelengths of light used – Smallest object that can be resolved is ~ 0.2 µm in diameter Confocal Microscope • Laser illumination • Detecting lens focuses on single point at a time – Scans entire sample to assemble picture • No reduction in contrast due to scattered light • Can generate 3-D images Transmission Electron Microscope • Responsible for discovery of most of smaller organelles in cell • Greater resolution • Uses beams of electrons rather than light • Magnets for lenses • Ultrathin section examined in vacuum • View image on fluorescent plate or photographic film Scanning Electron Microscope • Collected electrons used to form picture in television picture tube • High resolution view of surface structures • Requires vacuum • Recent refinements – Can operate in low vacuum – Can view live plant cells and insects Microscope Comparisons Source for Nature of illumination lenses Condition of specimen Image formation White light Living or killed stained specimen View directly through microscope Killed stained specimens Image analyzed on digital computer screen Ultrathin section of killed specimen contained within vacuum View on fluorescent plate or photographic film Surface view of killed specimen contained within vacuum, with low vacuum can view living cells Television picture tube Light microscope Confocal microscope Transmission electron microscope Scanning electron microscope Laser Electrons Electrons Glass Glass Magnets Magnets Generalized Plant Cell chloroplast vacuole nucleus cell wall mitochondrion Fig. 3-3 (b & c), p. 33 Boundaries Between Inside and Outside the Cell Plasma Membrane and Cell Wall Plasma Membrane • Surrounds cell • Controls transport into and out of cell • Selectively permeable Plasma Membrane • Composed of approximately half phospholipid and half protein, small amount of sterols – Phospholipid bilayer – Separates aqueous solution inside cell from aqueous layer outside cell – Prevents water-soluble compounds inside cell from leaking out – Prevents water-soluble compounds outside cell from diffusing in Plasma Membrane • Proteins in bilayer • Perform different functions – Ion pumps • Move ions from lower to higher concentration • Require ATP energy • Proton pump – moves H+ ions from inside to outside of cell • Ca+2 pump – moves Ca2+ to outside of cell – Channels – allow substances to diffuse across membrane Extracellular environment PHOSPHOLIPID BILAYER PUMPS AND CHANNELS Cytoplasm SENSORY PROTEINS RECEPTORS STEROL Fig. 3-4, p. 34 Plasma Membrane • Plasmodesmata – Connects plasma membranes of adjacent plant cells – Extends through cell wall – Allows materials to move from cytoplasm of one cell to cytoplasm of next cell • Symplast – name for continuous cytoplasm in set of cells E.R. lumen E.R. plasma membrane Cytoplasm Cell wall plasmodesmal proteins Cytoplasm Fig. 3-5, p. 35 Plasma Membrane • Apoplast – – Space outside cell – Next to plasma membrane within fibrils of cell wall – Area of considerable metabolic activity – Important space in plant but questionable as to whether it is part of the plant’s cells Cell Wall • Rigid structure made of cellulose microfibrils • Helps prevent cell rupture – – – – Process of osmosis allows water to enter cell Inflow of water expands cell Expansion forces cell membrane against cell wall Resistance of cell wall to expansion balances pressure of osmosis – Stops flow of water into cell – Keeps cell membrane from further expansion Cell Wall • Osmotic forces balanced by pressure exerted by cell wall – Creates turgor pressure – Causes cells to become stiff and incompressible – Able to support large plant organs – Loss of turgor pressure – plant wilts Fig. 3-6, p. 35 Cell Wall • Place cell in salt solution – Water leaves cytoplasm – Protoplast (space inside plasma membrane) shrinks – Plasma membrane pulls away from cell wall – Cell lacks turgor pressure - wilts PROTOPLAST SOLUTION Concentration 0.3 molar Pressure 0 megapascals Concentration 0.3 molar (Isotonic) Concentration 0.27 molar Pressure 0.66 megapascals Concentration 0.5 molar Pressure 0 megapascals Concentration 0 molar (Hypotonic) Concentration 0.5 molar (Hypertonic) Fig. 3-7 (a-c), p. 36 Fig. 3-7 (d), p. 36 Cell Wall Structure • Primary cell wall – Cell wall that forms while cell is growing • Secondary cell wall – Additional cell wall layer deposited between primary cell wall and plasma membrane – Generally contains cellulose microfibrils and water-impermeable lignin – Provides strength to wood Cell Wall Structure • Specialized types of cell walls – cutin covering cell wall or suberin imbedded in cell wall – Waxy substances impermeable to water – Cutinized cell walls • Found on surfaces of leaves and other organs exposed to air • Retard evaporation from cells • Barrier to potential pathogens Organelles of Protein Synthesis and Transport Nucleus, Ribosomes, Endoplasmic Reticulum, and Golgi Apparatus Nucleus • Ovoid or irregular in shape • Up to 25 µm in diameter • Easily stained for light or electron microscopy Nucleus • Surrounded by double membrane – nuclear envelope – Protein filaments of lamin line inner surface of envelope and stabilize it – Inner and outer membranes connect to form pores • Nucleoplasm – Portion of nucleus inside nuclear envelope one pore nuclear envelope 1 µm 0.2 µm lipid bilayer facing the nucleoplasm nuclear lipid bilayer facing envelope the cytoplasm pore complex that spans both bilayers Fig. 3-8, p. 37 Nucleus • Nucleoli (singular, nucleolus) – Densely staining region within nucleus – Accumulation of RNA-protein complexes (ribosomes) – Site where ribosomes are synthesized – Center of nucleoli • DNA templates • Guide synthesis of ribosomal RNA Nucleus • Chromosomes – Found in nucleoplasm – Contain DNA and protein – Each chromosome composed of long molecule of DNA wound around histone proteins forming a chain of nucleosome – Additional proteins form scaffolds to hold nucleosomes in place Fig. 3-9, p. 37 At times when a chromosome is most condensed, the chromosomal proteins interact, which packages loops of already coiled DNA into a “supercoiled” array. Fig. 3-9d, p. 37 At a deeper level of structural organization, the chromosomal proteins and DNA are organized as a cylindrical fiber. Fig. 3-9c, p. 37 Immerse a chromosome in saltwater and it loosens up to a beads-on-a-string organization. The “string” is one DNA molecule. Each “bead” is a nucleosome. Fig. 3-9b, p. 37 core of histone molecules A nucleosome consists of part of a DNA molecule looped twice around a core of histones. Fig. 3-9a, p. 37 Nucleus • DNA in chromosomes – Stores genetic information in nucleotide sequences – Information used to direct protein synthesis • Steps in protein synthesis – Transcription – DNA directs synthesis of RNA – Most RNA stays in nucleus or is quickly broken down – Small amount of RNA (mRNA) carries information from nucleus to cytoplasm Nuclear Components Component Structure and Function Nuclear envelope Double layered membrane, filaments of protein lamin line inner surface and stabilize structure, inner and outer membranes connect to form pores Nucleoplasm Portion inside the nuclear envelope Nucleoli Dark staining bodies within nucleus, site for ribosome synthesis Chromosomes Store genetic information in nucleotide sequences, each chromosome consists of chain of nucleosomes (long DNA molecule and associated histone proteins) Ribosomes • Small dense bodies formed from ribosomal RNA (rRNA) and proteins • Function in protein synthesis • Active ribosomes in clusters called polyribosomes – Attached to same mRNA – All ribosomes in one polyribosome make same type of protein Ribosomes • In living cell, ribosomes are not fixed – Move rapidly along mRNA – Read base sequence – Add amino acids to growing protein chain – At end of mRNA, ribosome falls off, releasing completed protein into cytoplasm mRNA ribosomes free polyribosomes attached polyribosomes Fig. 3-10, p. 38 mRNA ribosomes free polyribosomes attached polyribosomes Fig. 3-10a, p. 38 Endoplasmic Reticulum • • • • ER Branched, tubular structure Often found near edge of cell Function – Site where proteins are synthesized and packaged for transport to other locations in the cell – Proteins injected through membrane into lumen Endoplasmic Reticulum • Packaging of proteins by ER – Considered to be packaged when separated from cytoplasm by membrane – Sphere (vesicle) of membrane-containing proteins may bud off from ER – Vesicle carries proteins to other locations in cell Endoplasmic Reticulum • Types of ER – rough ER – ribosomes attached to surface – smooth ER – does not have attached ribosomes • Carbohydrate transport – Often attached to proteins in ER – Helps protect carbohydrate from breakdown by destructive enzymes Golgi Apparatus • Also called a dictyosome • Consists of stack of membranous, flattened bladders called cisternae 0.25 µm vesicles internal spaces cisternae Fig. 3-11, p. 38 Golgi Apparatus • Directs movements of proteins and other substances from ER to other parts of cell – Cell wall components (proteins, hemicellulose, pectin) pass through cisternae – Move to plasma membrane inside membranous sphere – Sphere joins with plasma membrane – Membrane of sphere becomes part of plasma membrane – Protein, hemicellulose, and pectin contents released to outside the cell Endomembrane System • Complex network that transports materials between Golgi apparatus, the ER, and other organelles of the cell • Movement – Rapid – Continuous Organelles of Energy Metabolism Plastids and Mitochondria Plastids • Found in every living plant cell – 20-50/cell – 2-10 µm in diameter • Surrounded by double membrane • Contain DNA and ribosomes – Protein-synthesizing system similar to but not identical to one in nucleus and cytoplasm two outer membranes thylakoids stroma Fig. 3-12 (a), p. 40 Plastids • Proplastids – Small plastids always found in dividing plant cells – Have short internal membranes and crystalline associations of membranous materials called prolamellar bodies – As cell matures, plastids develop • Prolamellar bodies reorganized • Combined with new lipids and proteins to form more extensive internal membranes Plastids • Types of plastids – Chloroplasts – Leukoplasts – Amyloplasts – Chromoplasts Fig. 3-12 (b-f), p. 40 Plastids • Chloroplasts – Thylakoids • Inner membranes • Have proteins that bind to chlorophyll – Chlorophyll • Green compound that gives green plant tissue its color – Stroma • Thick solution of enzymes surrounding thylakoids Plastids • Chloroplasts – Function • Convert light energy into chemical energy (photosynthesis) • Accomplished by proteins in thylakoids and stromal enzymes • Can store products of photosynthesis (carbohydrates) in form of starch grains Chloroplast Component Description Thylakoids Inner membranes of chloroplast, contain proteins that bind with chlorophyll Stroma Thick enzyme solution surrounding thylakoids Chlorophyll Green pigment that gives plant tissue its green color Storage form of carbohydrates produced Starch grains during photosynthesis Leukoplasts • leuko – “white” • Found in roots and some nongreen tissues in stems • No thylakoids • Store carbohydrates in form of starch • Microscopically appear as white, refractile, shiny particles Amyloplasts • amylo – “starch” • Leukoplast that contains large starch granules Chromoplasts • chromo – “color” • Found in some colored plant tissues – tomato fruits, carrot roots – High concentrations of specialized lipids – carotenes and xanthophylls – Give plant tissues orange-to-red color Plastids Prefix Meaning Function Chloroplast “chloro –” “yellowgreen” Photosynthesis, convert light energy into chemical energy, store carbohydrates as starch grains Leukoplast “leuko –” “white” Store carbohydrates in form of starch Amyloplast “amylo –” “starch” Leukoplasts that contain large granules of starch “color” Stores carotenes and xanthophylls, give orangeto-red color to certain plant tissues Chromoplast “chromo –” Mitochondria • Double-membrane structure • Contain DNA and ribosomes • Inner membrane infolded – Folds called cristae – Increase surface area available for chemical reactions outer compartment cristae inner compartment (matrix) inner membrane outer membrane Fig. 3-13, p. 41 Mitochondria • Matrix – Viscous solution of enzymes within cristae • Function – source of most ATP in any cell that is not actively photosynthesizing – Site of oxidative respiration – Release of ATP from organic molecules – ATP used to power chemical reactions in cell Other Cellular Structures Vacuoles, Vesicles, Peroxisomes, Glyoxysomes, Lysosomes, and Cytoskeleton Vacuoles • Large compartment surrounded by single membrane • Takes up large portion of cell volume • Tonoplast – Membrane surrounding vacuole – Has embedded protein pumps and channels that control flow of ions and molecules into and out of vacuole Vacuole • Functions – May accumulate ions which increase turgor pressure inside cell – Can store nutrients such as sucrose – Can store other nutritious chemicals – May accumulate compounds that are toxic to herbivores – May serve as a dump for wastes that cell cannot keep and cannot excrete Vesicles • Small, round bodies surrounded by single membrane – Peroxisomes and glyoxysomes • Compartments for enzymatic reactions that need to be separated from cytoplasm – Lysosomes • Contain enzymes that break down proteins, carbohydrates, and nucleic acids • May function in removing wastes within living cell • Can release enzymes that dissolve the entire cell Cytoskeleton • Collection of long, filamentous structures within cytoplasm • Functions – Keeps organelles in specific places – Sometimes directs movement of organelles around the cell • Cyclosis – cytoplasmic streaming Cytoskeleton • Structures in cytoskeleton – Microtubules – Motor proteins – Microfilaments • Specialized proteins connect microtubules and microfilaments to other organelles – Connections thought to coordinate many cell processes Microtubules • Relatively thick (0.024 µm in diameter) • Assembled from protein subunits called tubulin • Fairly rigid but can lengthen or shorten by adding or removing tubulin molecules Microtubules • Functions – Guide movement of organelles around cytoplasm – Key organelles in cell division – Form basis of cilia and flagella • Cilia and flagella never found in flowering plants • Important to some algae and to male gametes of lower plants Microfilaments • Thinner (0.007 µm in diameter) and more flexible than microtubules • Made of protein subunits called actin • Often found in bundles • Function – Serve as guides for movement of organelles Motor Proteins • Powered by ATP molecules • Microtubule motor proteins – Kinesins, dyneins – Move along microtubule making and breaking connections between tubulin subunits • Microfilament motor proteins – myosin Cytoskeleton Subunits Microtubules Microfilaments Tubulin (protein) Actin (protein) Motor proteins Function Kinesins, dyneins Key organelles in cell division, form basis of cilia and flagella, serve as guides for movement of organelles within cell Serve as guides for movement of organelles within cell Myosin The Organization of the Plant Body: Cells, Tissues, and Meristems Chapter 4 Organization of Plant Body Most vascular plants consist of: Shoot System Above ground part Below Root System ground part Stems, leaves, buds, flowers, fruit Main roots and branches Plant Cells and Tissues • Cell wall – surrounds each plant cell • Pectin – glues plant cells together • Meristems – Groups of specialized dividing cells – Sources of cells and tissues – Not tissues themselves • Plant organs – leaves, stems,roots, flower parts Fig. 4-CO, p. 49 Main Tissues of Plants Ground tissue system Most extensive in leaves (mesophyll) and young green stems (pith and cortex) Vascular tissue system Conducting tissues •Xylem – distributes water and solutes •Phloem – distributes sugars Dermal tissue system Covers and protects plant surfaces – epidermis and periderm Plant Tissues • Simple tissues – Composed of mostly one cell type – Workhorse cells of plant body – Functions • • • • • Conduct photosynthesis Load materials into and out of vascular system Hold plant upright Store things Help keep plant healthy and functioning Simple Plant Tissues Tissue type Parenchyma tissue Cell types Parenchyma cells Collenchyma tissue Collenchyma cells Sclerenchyma tissue Fibers, sclereids Table 4-1, p. 50 shoot tip xylem epidermis mesophyll bud flower phloem node internode Dermal tissues node pith xylem phloem cortex Vascular tissues leaf epidermis seeds (inside fruit) Ground tissues Shoot system Root system cortex xylem primary root lateral root root hairs phloem epidermis root tip root cap Fig. 4-1, p. 51 Parenchyma • Usually spherical or elongated • Thin primary cell wall • Perform basic metabolic functions of cells – Respiration – Photosynthesis – Storage – Secretion parenchyma cells Fig. 4-2a, p. 52 Parenchyma • Usually live 1-2 years • Crystals of calcium oxalate commonly found in vacuoles – May help regulate pH of cells • May aggregate to form parenchyma tissue in – Cortex and pith of stems – Cortex of roots – Mesophyll of leaves Parenchyma • Mature cells may be developmentally programmed to form different cell types – Wound healing – Transfer cells • Have numerous cell wall ingrowths • Improve transport of water and minerals over short distances • At ends of vascular cells help load and unload sugars and other substances parenchyma cell with lignified wall pit Fig. 4-2b, p. 52 Collenchyma • Specialized to support young stems and leaf petioles • Often outermost cells of cortex • Elongated cells • Often contain chloroplasts • Living at maturity collenchyma cell Fig. 4-6, p. 54 Collenchyma • Walls composed of alternating layers of pectin and cellulose • Can occur as aggregates forming collenchyma tissue – Form cylinder surrounding stem – Form strands • Make up ridges of celery stalk Sclerenchyma • Rigid cell walls • Function to support weight of plant organs • Two types of cells – Fibers – Sclereids • Both fibers and sclereids have thick, lignified secondary cell walls • Both fibers and sclereids are dead at maturity fiber Fig. 4-7a, p. 54 sclereid Fig. 4-7c, p. 54 Sclerenchyma • Fibers – Long, narrow cells with thick, pitted cell walls and tapered ends – Sometimes elastic (can snap back to original length) Sclerenchyma • Fibers – Arrangements • Aggregates that form continuous cylinder around stems • May connect end to end forming multicellular strands • May appear as individual cells or small groups of cells in vascular tissues Sclerenchyma • Sclereids – Many different shapes – Usually occur in small clusters or solitary cells – Cell walls often thicker than walls of fibers – Sometimes occur as sheets • Hard outer layer of some seed coats Complex Tissues Composed of groups of different cell types Complex tissue Cell types Xylem Vessel member, tracheid, fiber, parenchyma cell Phloem Sieve-tube member, sieve cell, companion cell, albuminous cell, fiber, sclereid, parenchyma cell Epidermis Guard cell, epidermal cell, subsidiary cell, trichome (hair) Periderm Phellem (cork) cell, phelloderm cell Secretory structures Trichome, laticifer collenchyma phloem xylem Fig. 4-8a, p. 56 secondary phloem secondary xylem Fig. 4-8b, p. 56 The Vascular System Xylem • Complex tissue • Transports water and dissolved minerals • Locations of primary xylem – In vascular bundles of leaves and young stems – At or near center of young root (vascular cylinder) Xylem Cell Types Cell Type Description •Water conducting cells Trachery element (tracheids •Not living at maturity and vessel members) •Before cell dies, cell wall becomes thickened with cellulose and lignin •Strength and support Fibers Parenchyma cells •Help load minerals in and out of vessel members and tracheids •Only living cells found in xylem Xylem • Secondary xylem – Forms later in development of stems and roots • Water exchanged between cells through tiny openings called pits – Simple pits • Occur in secondary walls of fibers and lignified parenchyma cells – Bordered pits • Occur in tracheids, vessel members, and some fibers parenchyma cells spiral annular reticulate scalariform pitted Fig. 4-9, p. 57 secondary cell wall nucleus pits primary cell wall cytoplasm secondary cell wall border primary cell wall Fig. 4-10 (a & b), p. 57 secondary cell wall border primary cell wall Fig. 4-10 (b), p. 57 Phloem • Complex tissue • Transports sugar through plant • Primary phloem – In vascular bundles near primary xylem in young stems – In vascular cylinder in roots Phloem • Cell types in angiosperm phloem – Sieve-tube members – Companion cells – Parenchyma – Fibers and/or sclereids sieve plate sieve-tube members parenchyma cells companion cell parenchyma cell sieve-tube plastids plasmodesmata parenchyma plastid Fig. 4-13, p. 59 Phloem • Sieve-tube members – Conducting elements of phloem – Join end-to-end to form long sieve tubes – Mature cell contains mass of dense material called P-protein • May help move materials through sieve tubes – Usually live and function from 1 to 3 years parenchyma cell sieve-tube member Fig. 4-14a, p. 59 Phloem • Sieve-tube members – mature sieve-tube members have aggregates of small pores called sieve areas • One or more sieve areas on end wall of sieve-tube member called a sieve-plate • Callose (carbohydrate) surrounds margins of pores – Forms rapidly in response to aging, wounding, other stresses – May limit loss of cell sap from injured cells Phloem • Companion cells – Connected by plasmodesmata to mature sieve-tube member – Contain nucleus and organelles – Thought to regulate metabolism of adjacent sieve-tube member – Play role in mechanism of loading and unloading phloem companion cell sieve-tube member Fig. 4-14b, p. 59 Phloem • Parenchyma – Usually living – Function in loading and unloading phloem sieve cell sieve area Fig. 4-14c, p. 59 Phloem • Fibers and/or sclereids – Long tapered cells – Lignified cell walls Phloem Gymnosperms and ferns • Sieve cells instead of sieve-tube members • Conducting elements in phloem • Long cells with tapered ends • Sieve areas but no sieve plates • Usually lack nuclei at maturity • Albuminous cells – Adjacent to sieve cells – Short, living cells – Act as companion cells to sieve cells The Outer Covering of the Plant Epidermis • Outer covering • Usually one cell layer thick – Epidermis of succulents may be 5-6 cell layers thick • Functions – Protects inner tissues from drying and from infection by some pathogens – Regulates movement of water and gases out of and into plant Epidermis • Cell types – Epidermal cells – Guard cells – Trichomes (hairs) Epidermis • Epidermal cells – Main cell type making up epidermis – Living, lack chloroplasts – Somewhat elongated shape – Cell walls with irregular contours – Outer wall coated with cutin to form cuticle • Cuticle found on all plant parts except tip of shoot apex and root cap • Cuticle often very thin in roots cuticle Fig. 4-17, p. 61 Epidermis • Guard cells – Found in epidermis of young stems, leaves, flower parts, and some roots – Specialized epidermal cells – Small opening or pore between each pair of guard cells • Allows gases to enter and leave underlying tissue – 2 guard cells + pore = 1 stoma (plural, stomata) guard cell Fig. 4-18a, p. 61 Epidermis • Guard cells – Differ from epidermal cells • Crescent shaped • Contain chloroplasts guard cell stoma pore subsidiary cell stoma apparatus epidermal cell Fig. 4-18b, p. 61 Epidermis • Subsidiary cell – Forms in close association with guard cells – Functions in stomatal opening and closing Epidermis • Trichomes – Epidermal outgrowths – Single cell or multicellular • Example: root hairs • Increase root surface area in contact with soil water Fig. 4-19, p. 62 Periderm • Protective layer that forms in older stems and roots • Secondary tissue • Several cell layers deep Periderm • Composed of – Phellem (cork) • On outside • Cells dead at maturity • Suberin embedded in cell walls – Phellogen (cork cambium) • Layer of dividing cells – Phelloderm • Toward inside • Parenchyma-like cells • Cells live longer than phellem cells Figure 3, p. 63 cuticle epidermis phellem cork cambium phelloderm cortex Fig. 4-20, p. 63 Periderm • Secretory structures – Primarily occur in leaves and stems – May be single-celled or complex multicellular structure – Examples • Trichomes – Could secrete materials out of plant to attract insect pollinators • Laticifers – Secrete latex which discourages herbivores from eating plant laticifer Fig. 4-21, p. 64 Table 4-2a, p. 65 Table 4-2b, p. 65 Table 4-2c, p. 66 Meristems Meristems • Special region in plant body where new cells form • Area where growth and differentiation are initiated – Growth • Irreversible increase in size that results from cell division and enlargement – Cell differentiation • Structural and biochemical changes a cell undergoes in order to perform a specialized function Meristems • Categories of meristems – Shoot and apical meristems • Ultimate source of all cells in a plant – Primary meristems • Originate in apical meristems • Differentiate into primary tissues – Secondary meristems • Produce secondary tissues SAM ground meristem Region of primary growth Primary meristems protoderm procambium cork cambium Secondary vascular meristems cambium Region of primary growth procambium ground Primary meristem meristems protoderm RAM Root system Fig. 4-22, p. 66 Root and Apical Meristems • • • • RAM – root apical meristem SAM – shoot apical meristem New cells produced by cell division Theoretically could divide forever – Does not occur • Scarcity of nutrients • Branch of plant can only carry so much weight • Genetic regulation of growth Primary Meristems • Functions – Form primary tissues – Elongate root and shoot Primary Meristems • Types of primary meristems – Protoderm • Cells differentiate into epidermis – Procambium • Cells differentiate into primary xylem and primary phloem – Ground meristem • Differentiates into cells of pith and cortex of stems and roots • Differentiates into mesophyll of leaves young leaf SAM protoderm ground meristem procambium Fig. 4-23b, p. 67 Fig. 4-23c, p. 67 ground meristem procambium protoderm RAM root cap Fig. 4-23d, p. 67 Secondary Meristems • Functions – Cell division – Initiation of cell differentiation – Lateral growth • Increases thickness and circumference of stems and roots Secondary Meristems • Not found in all plants – Lacking in plants that grow only one season – Leaves usually lack secondary growth • Types of secondary meristems – Vascular cambium • Differentiates into secondary xylem and secondary phloem – Cork cambium • Differentiates into periderm Additional Meristems • Intercalary meristems – In stems – Regulates stem elongation • Leaf specific meristems – Regulates leaf shapes • Repair of wounds • Formation of buds and roots in unusual places