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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITIONJane B. Reece, Lisa A. Urry, Micae! L. Cain, "#e$en A. %asser&an, Pe#er '. Minors(y, Ro)er# B. Jac(son
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Lectures by
Erin Barley
Kathleen Fitzpatric
Plant Structure! "r#$th! an%
&e'el#p(ent
Chapter )*
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The Three Basic Plant Or+ans, R##ts!
Ste(s! an% Lea'es Basic morphology of vascular plants reflects their
evolution as organisms that draw nutrients from
below ground and above ground Plants take up water and minerals from below
ground
Plants take up CO2and light from above ground
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Three basic organs evolved: roots, stems, andleaves
They are organied into a root system and a
shoot system
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!igure "#$2Reproductive shoot (flower)
Apical bud
Node
Internode
Apical bud
Vegetative shoot
LeafBladeetiole
!tem
"aproot
Lateral (branch)roots
!hootsystem
Rootsystem
A#illary bud
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%oots rely on sugar produced byphotosynthesis in the shoot system, and shoots
rely on water and minerals absorbed by the root
system
&onocots and eudicots are the two ma'or
groups of angiosperms
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Roots
( root is an organ with important functions:)(nchoring the plant
)(bsorbing minerals and water
) *toring carbohydrates) +n most plants, absorption of water and minerals
occurs near the root hairs, where vast numbers of
tiny root hairs increase the surface area
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!igure "#$"
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&any plants have root adaptations withspecialied functions
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!igure "#$
rop roots
!torageroots
$!trangling%aerial roots
Buttressroots
neumatophores
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Stems
( stemis an organ consisting of)(n alternating system of nodes, the points at
which leaves are attached
) Internodes, the stem segments between nodes
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(n a#illary bud is a structure that has thepotential to form a lateral shoot, or branch
(n apical bud, or terminal bud, is located near the
shoot tip and causes elongation of a young shoot
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&any plants have modified stems -e$g$, rhiomes,bulbs, stolons, tubers.
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!igure "#$#Rhi&omes
Rhi&ome
Bulbs
!torage leaves
!tem
!tolons
"ubers
Root
!tolon
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Leaves
The leaf is the main photosynthetic organ of mostvascular plants
/eaves generally consist of a flattened blade and
a stalk called the petiole, which 'oins the leaf to a
node of the stem
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&onocots and eudicots differ in the arrangementof veins, the vascular tissue of leaves
) &ost monocots have parallel veins
)&ost eudicots have branching veins
+n classifying angiosperms, ta0onomists may use
leaf morphology as a criterion
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!igure "#$1
!imple leaf
A#illary
bud etiole
'ompound leaf
Leaflet
A#illary
bud etiole
oubly
compound leaf
A#illary
bud
etiole
Leaflet
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!igure "#$"endrils
!pines
!torageleaves
Reproductiveleaves
Bracts
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&er(al! -ascular! an% "r#un% Tissues
3ach plant organ has dermal, vascular, andground tissues
3ach of these three categories forms a tissue
system
3ach tissue system is continuous throughout the
plant
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!igure "#$4
ermaltissue
round
tissue
Vascular
tissue
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+n nonwoody plants, the dermal tissue systemconsists of the epidermis
( wa0y coating called the cuticle helps prevent
water loss from the epidermis
+n woody plants, protective tissues called
periderm replace the epidermis in older regions of
stems and roots
Trichomes are outgrowths of the shoot epidermisand can help with insect defense
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!igure "#$5
Very hairy pod
(*+ trichomes,mm-)
!lightly hairy pod
(- trichomes,mm-)
Bald pod
(no trichomes)
Very hairy pod.*+/ damage
!lightly hairy pod.-0/ damage
Bald pod.1+/ damage
232RI42N"
R2!5L"!
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The vascular tissue system carries out long6distance transport of materials between roots andshoots
The two vascular tissues are 0ylem and phloem
3ylem conveys water and dissolved mineralsupward from roots into the shoots
hloem transports organic nutrients from where
they are made to where they are needed
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Tissues that are neither dermal nor vascular arethe ground tissue system
7round tissue internal to the vascular tissue is
pith8 ground tissue e0ternal to the vascular tissue
is corte#
7round tissue includes cells specialied for
storage, photosynthesis, and support
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C#((#n Types #. Plant Cells
/ike any multicellular organism, a plant ischaracteried by cellular differentiation, the
specialiation of cells in structure and function
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The ma'or types of plant cells are:) Parenchyma
) Collenchyma
) *clerenchyma) 9ater6conducting cells of the 0ylem
) *ugar6conducting cells of the phloem
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arenchyma 'ells &ature parenchyma cells
ave thin and fle0ible primary walls
/ack secondary walls(re the least specialied
Perform the most metabolic functions
%etain the ability to divide and differentiate
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Biofli0: Tour of a Plant Cell
!igure "# ;
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!igure "#$;
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'ollenchyma 'ells 'ollenchyma cellsare grouped in strands and
help support young parts of the plant shoot
They have thicker and uneven cell walls They lack secondary walls
These cells provide fle0ible support without
restraining growth
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!igure "#$;
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!clerenchyma 'ells !clerenchyma cellsare rigid because of thick
secondary walls strengthened with lignin
They are dead at functional maturity There are two types:
) !clereids are short and irregular in shape and
have thick lignified secondary walls) 8ibers are long and slender and arranged in
threads
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!igure "#$;
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g
'ell wall
!clereid cells in pear (L4)
8iber cells (cross section from ash tree) (L4)
-0 m
0 m
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9ater:'onducting 'ells of the 3ylem The two types of water6conducting cells,
tracheids and vessel elements, are dead at
maturity
Tracheids are found in the 0ylem of all vascular
plants
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=essel elements are common to mostangiosperms and a few gymnosperms
=essel elements align end to end to form long
micropipes called vessels
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!igure "#$;
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gVessel "racheids *++ m
"racheids and vessels(colori&ed !24)
erforation
plate
Vesselelement
Vessel elements6 withperforated end walls
its
"racheids
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!ugar:'onducting 'ells of the hloem !ieve:tube elements are alive at functional
maturity, though they lack organelles
!ieve plates are the porous end walls that allowfluid to flow between cells along the sieve tube
3ach sieve6tube element has a companion cell
whose nucleus and ribosomes serve both cells
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!igure "#$;
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!ieve:tube element (left)and companion cell.cross section ("24)
!ieve:tube elements.
longitudinal view
!ieve plate
; m
'ompanioncells
!ieve:tubeelements
lasmodesma
!ieveplate
Nucleus ofcompanioncell
!ieve:tube elements.longitudinal view (L4)
;+ m
*0 m
!ieve plate with pores (L4)
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C#ncept )*/0, 1eriste(s +enerate cells .#r
pri(ary an% sec#n%ary +r#$th ( plant can grow throughout its life8 this is called
indeterminate growth
*ome plant organs cease to grow at a certain sie8this is called determinate growth
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4eristems are perpetually embryonic tissue andallow for indeterminate growth
Apical meristems are located at the tips of roots
and shoots and at the a0illary buds of shoots
(pical meristems elongate shoots and roots, a
process called primary growth
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Lateral meristems add thickness to woody plants,a process called secondary growth
There are two lateral meristems: the vascular
cambium and the cork cambium
The vascular cambium adds layers of vascular
tissue called secondary 0ylem -wood. and
secondary phloem
The cor< cambium replaces the epidermis withperiderm, which is thicker and tougher
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!igure "#$;;
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!hoot tip (shootapical meristemand young leaves)
A#illary budmeristem
Root apicalmeristems
Vascular cambium
'or@( via genetically altered bacteria
*tudying the genes and biochemical pathways
of Arabidopsiswill provide insights into plant
development, a ma'or goal of systems biology
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"r#$th, Cell &i'isi#n an% Cell E2pansi#n
By increasing cell number, cell division inmeristems increases the potential for growth
Cell e0pansion accounts for the actual increase in
plant sie
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The Plane and Symmetry of Cell Division
@ew cell walls form in a plane -direction.perpendicular to the main a0is of cell e0pansion
The plane in which a cell divides is determined
during late interphase
&icrotubules become concentrated into a ring
called the preprophase band that predicts the
future plane of cell division
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!igure "#$2#
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reprophase band
m
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/eaf growth results from a combination oftransverse and longitudinal cell divisions
+t was previously thought that the plane of cell
division determines leaf form
( mutation in the tangled-1gene that affects
longitudinal divisions does not affect leaf shape
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!igure "#$21
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Leaf epidermal cells ofwild:type mai&e
Leaf epidermal cells oftangled-1mai&e mutant
;+
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The symmetry of cell division, the distribution ofcytoplasm between daughter cells, determines cell
fate
(symmetrical cell division signals a key event in
development
) !or e0ample, the formation of guard cells involves
asymmetrical cell division and a change in the
plane of cell division
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!igure "#$2
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5nspeciali&edepidermal cell
Asymmetricalcell division
uard cell$mother cell%
evelopingguard cells
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olarityis the condition of having structural orchemical differences at opposite ends of an
organism
) !or e0ample, plants have a root end and a shoot
end
(symmetrical cell divisions play a role in
establishing polarity
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The first division of a plant ygote is normallyasymmetrical and initiates polariation into the
shoot and root
The gnommutant of Arabidopsisresults from a
symmetrical first division
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!igure "#$24
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Orientation of Cell Expansion
Plant cells grow rapidly and Acheaply by intakeand storage of water in vacuoles
Plant cells e0pand primarily along the plants main
a0is
Cellulose microfibrils in the cell wall restrict the
direction of cell elongation
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!igure "#$25
'ellulose
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'ellulosemicrofibrils
Nucleus
2longation
Vacuoles
0 m
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1#rph#+enesis an% Pattern F#r(ati#n
attern formation is the development of specificstructures in specific locations
Two types of hypotheses e0plain the fate of plantcells
) /ineage6based mechanisms propose that cell fateis determined early in development and passedon to daughter cells
) Position6based mechanisms propose that cell fate
is determined by final position
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30periments suggest that plant cell fate isestablished late in development and depends on
cell position
+n contrast, cell fate in animals is largely lineage6
dependent
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"ene E2pressi#n an% C#ntr#l #. Cell
&i..erentiati#n
Cells of a developing organism synthesie
different proteins and diverge in structure and
function even though they have a common
genome
Cellular differentiation depends on gene
e0pression, but is determined by position
Positional information is communicated throughcell interactions
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7ene activation or inactivation depends on cell6to6cell communication
) !or e0ample, Arabidopsisroot epidermis forms
root hairs or hairless cells depending on the
number of cortical cells it is touching
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'orticalcells
-+
m
GLABRA-2is e#pressed6 andthe cell remains hairless
"he root cap cells will be sloughed offbefore root hairs emerge
GLABRA-2is
not e#pressed6and the cellwill developa root hair
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Shi.ts in &e'el#p(ent, Phase Chan+es
Plants pass through developmental phases, calledphase changes, developing from a 'uvenile phase
to an adult phase
Phase changes occur within the shoot apical
meristem
The most obvious morphological changes typically
occur in leaf sie and shape
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Leaves producedby adult phaseof apical meristem
Leaves producedby Cuvenile phaseof apical meristem
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"enetic C#ntr#l #. Fl#$erin+
!lower formation involves a phase change fromvegetative growth to reproductive growth
+t is triggered by a combination of environmental
cues and internal signals
Transition from vegetative growth to flowering is
associated with the switching on of floral
meristem identity genes
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+n a developing flower, the order of eachprimordiums emergence determines its fate:
sepal, petal, stamen, or carpel
Plant biologists have identified several organ
identity genes-plant homeotic genes. thatregulate the development of floral pattern
These are MADS-boxgenes
( mutation in a plant organ identity gene cancause abnormal floral development
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(a) NormalArabidopsisflower
AbnormalArabidopsis
flower
(b)
'a
e
!t
!e
!e
!e
e
e
e
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%esearchers have identified three classes of floralorgan identity genes
The AB' hypothesis of flower formation identifies
how floral organ identity genes direct the formation
of the four types of floral organs
(n understanding of mutants of the organ identity
genes depicts how this model accounts for floral
phenotypes
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!epals
etals
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!tamens
'arpelsA
B'
A schematic diagram of the AB'hypothesis
(a)
'arpel
etal
!tamen
!epal
A Bgene
activity
B Cgene
activity
C geneactivity
A geneactivity
Activegenes.
9horls.
!tamen
'arpeletal
!epal
9ild type 4utant lac