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 MethodOriginal Hypothesis Devise method to

test hypothesisAnalyze results

Results support

hypothesis

Results support

hypothesis but suggest minor refinements

Results are so unexpected that

they do not support original hypothesis and require a new

hypothesis

Results do not support original

hypothesis but fall within range that

could be expected if original

hypothesis is slightly modified

Retest using minor

refinements of process

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

GenesGenetics

Evolution

Taxonomy & Systematics

METABOLISMPhysiology

ENVIRONMENTEcology

Paleoecology

Biogeography

TAXONOMIC GROUPS

DEVELOPMENT

STRUCTUREPhycology

Microbiology

Mycology

Bryology

Morphology

Anatomy

PLANT

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 KingdomsKingdom Description

MoneraIncluded bacteria

FungiIncluded molds, mildews, rusts, smuts, and mushrooms

ProtistaIncluded simple organisms, some were photosynthetic, mostly aquatic organisms called algae

PlantaeIncluded more complex photosynthetic organisms that typically grew on land

AnimaliaIncluded 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

Eukarya EukaryoticMembrane bounded organelles, linear chromosomes

Archaea ProkaryoticFound in extreme environments, cell structure and differ from members of Domain Bacteria

Bacteria ProkaryoticOrdinary bacteria, found in every habitat on earth, play major role as decomposers

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

Economic importance

• Production of antibiotics– Penicillium

• Pathogens– Invade both plant and animal tissue– Cause illnesses– Reduce crop yields

Kingdom Fungi

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, three-

dimensional 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

• 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

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 Year Contributor

All plants and animals are composed of cells. 1838

Matthias Schleiden and Theodor Schwann

Cells reproduce themselves. 1858 Rudolf Virchow

All cells arise by reproduction from previous cells.

1858Rudolf 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 ComparisonsSource for illumination

Nature of lenses

Condition of specimen

Image formation

Light microscopeWhite light Glass

Living or killed stained specimen

View directly through microscope

Confocal microscope

Laser Glass

Killed stained specimens

Image analyzed on digital computer screen

Transmission electron microscope Electrons Magnets

Ultrathin section of killed specimen contained within vacuum

View on fluorescent plate or photographic film

Scanning electron microscope Electrons Magnets

Surface view of killed specimen contained within vacuum, with low vacuum can view living cells

Television picture tube

Generalized Plant Cell

Fig. 3-3 (b & c), p. 33

chloroplast

cell wall

mitochondrion

nucleus

vacuole

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

Fig. 3-4, p. 34

Extracellular environment

PUMPS ANDCHANNELS

SENSORY PROTEINSRECEPTORS

CytoplasmSTEROL

PHOSPHOLIPIDBILAYER

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

Fig. 3-5, p. 35

E.R. lumen

E.R. Cytoplasm

Cell wall

plasmodesmalproteins

plasmamembrane

Cytoplasm

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

Fig. 3-7 (a-c), p. 36

PROTOPLAST SOLUTION

Concentration0.3 molar(Isotonic)

Concentration0 molar(Hypotonic)

Concentration0.27 molar

Pressure0.66 megapascals

Concentration0.5 molar(Hypertonic)

Concentration0.3 molar

Pressure0 megapascals

Concentration0.5 molar

Pressure0 megapascals

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

Fig. 3-8, p. 37

0.2 µm1 µmnuclear envelope

one pore

lipid bilayer facingthe nucleoplasm

nuclearenvelope

lipid bilayer facingthe cytoplasm

pore complex thatspans both bilayers

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

Fig. 3-9d, p. 37

At times when a chromosome is mostcondensed, the chromosomal proteinsinteract, which packages loops of alreadycoiled DNA into a “supercoiled” array.

Fig. 3-9c, p. 37

At a deeperlevel of structuralorganization, thechromosomalproteins and DNAare organized asa cylindrical fiber.

Fig. 3-9b, p. 37

Immerse achromosome insaltwater and itloosens up to abeads-on-a-stringorganization. The“string” is oneDNA molecule.Each “bead” isa nucleosome.

Fig. 3-9a, p. 37

A nucleosomeconsists of part ofa DNA moleculelooped twicearound a coreof histones.

core ofhistonemolecules

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 envelopeDouble 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

NucleoliDark 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

Fig. 3-10, p. 38

mRNA

ribosomes

freepolyribosomes

attachedpolyribosomes

Fig. 3-10a, p. 38

mRNA

ribosomes

freepolyribosomes

attachedpolyribosomes

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

Fig. 3-11, p. 38

vesicles internal spaces

0.25 µm

cisternae

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

Fig. 3-12 (a), p. 40

two outermembranes

thylakoids

stroma

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

ThylakoidsInner membranes of chloroplast, contain proteins that bind with chlorophyll

StromaThick enzyme solution surrounding thylakoids

ChlorophyllGreen pigment that gives plant tissue its green color

Starch grainsStorage form of carbohydrates produced 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

PlastidsPrefix Meaning Function

Chloroplast “chloro –”“yellow-green”

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

Chromoplast “chromo –” “color”

Stores carotenes and xanthophylls, give orange-to-red color to certain plant tissues

Mitochondria

• Double-membrane structure

• Contain DNA and ribosomes

• Inner membrane infolded– Folds called cristae– Increase surface area available for chemical

reactions

Fig. 3-13, p. 41

(matrix)

innercompartment

outermembrane

cristae

outercompartment

innermembrane

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

SubunitsMotor proteins

Function

MicrotubulesTubulin (protein)

Kinesins, dyneins

Key organelles in cell division, form basis of cilia and flagella, serve as guides for movement of organelles within cell

MicrofilamentsActin (protein)

Myosin

Serve as guides for movement of organelles within cell

The Organization of the Plant Body: Cells, Tissues, and

MeristemsChapter 4

Organization of Plant Body

Most vascular plants consist of:

Shoot System

Above ground part

Stems, leaves, buds, flowers, fruit

Root SystemBelow ground part

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 Cell types

Parenchyma tissue Parenchyma cells

Collenchyma tissue Collenchyma cells

Sclerenchyma tissue Fibers, sclereids

Table 4-1, p. 50

Fig. 4-1, p. 51

phloem

xylemcortex

cortexphloemxylem

pith

mesophyll

epidermis

Shoot systemRoot system

xylem

epidermis

epidermis

phloem

node

node

Vascular tissues

Ground tissues

internode Dermal tissues

root caproot tip

root hairslateral root

primary root

seeds (inside fruit)

leaf

flowerbud

shoot tip

Parenchyma

• Usually spherical or elongated

• Thin primary cell wall

• Perform basic metabolic functions of cells– Respiration – Photosynthesis– Storage– Secretion

Fig. 4-2a, p. 52

parenchymacells

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

Fig. 4-2b, p. 52

pitparenchyma cell with lignified wall

Collenchyma

• Specialized to support young stems and leaf petioles

• Often outermost cells of cortex

• Elongated cells

• Often contain chloroplasts

• Living at maturity

Fig. 4-6, p. 54

collenchyma cell

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

Fig. 4-7a, p. 54

fiber

Fig. 4-7c, p. 54

sclereid

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

XylemVessel member, tracheid, fiber, parenchyma cell

PhloemSieve-tube member, sieve cell, companion cell, albuminous cell, fiber, sclereid, parenchyma cell

EpidermisGuard cell, epidermal cell, subsidiary cell, trichome (hair)

Periderm Phellem (cork) cell, phelloderm cell

Secretory structures Trichome, laticifer

Fig. 4-8a, p. 56

collenchyma

phloem

xylem

Fig. 4-8b, p. 56

secondary xylem

secondary phloem

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

Trachery element (tracheids and vessel members)

•Water conducting cells

•Not living at maturity

•Before cell dies, cell wall becomes thickened with cellulose and lignin

Fibers

•Strength and support

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

Fig. 4-9, p. 57

pitted

parenchyma cells

annularspiral

scalariform

reticulate

Fig. 4-10 (a & b), p. 57

primarycell wall

secondarycell wall

nucleus

pits

primarycell wall

secondarycell wall

cytoplasm

border

Fig. 4-10 (b), p. 57

primarycell wall

secondarycell wall

border

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

Fig. 4-13, p. 59

plasmodesmata

sieve plate sieve-tube members

parenchyma cell

sieve-tube plastids

parenchyma plastid

parenchyma cells

companion cell

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

Fig. 4-14a, p. 59

sieve-tube memberparenchyma cell

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

Fig. 4-14b, p. 59

sieve-tube membercompanion cell

Phloem

• Parenchyma– Usually living– Function in loading and unloading phloem

Fig. 4-14c, p. 59

sieve areasieve cell

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

Fig. 4-17, p. 61

cuticle

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)

Fig. 4-18a, p. 61

guard cell

Epidermis

• Guard cells– Differ from epidermal cells

• Crescent shaped• Contain chloroplasts

Fig. 4-18b, p. 61

guard cell

porestoma

stomaapparatus

subsidiarycell

epidermal cell

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

Fig. 4-20, p. 63

cuticle

cortex

epidermis

phellem

cork cambium

phelloderm

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

Fig. 4-21, p. 64

laticifer

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

Fig. 4-22, p. 66

Region ofprimary growth

SAM

Region ofprimary growth

Root system

Primarymeristems

Secondarymeristems

Primarymeristems

RAM

groundmeristem

protodermprocambium

corkcambium

vascularcambium

procambiumgroundmeristemprotoderm

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

Fig. 4-23b, p. 67

procambium

young leaf SAM

protoderm

groundmeristem

Fig. 4-23c, p. 67

Fig. 4-23d, p. 67

ground meristem

procambium protoderm

RAM

root cap

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