Transcript chapter 35 an introduction to flowering plants

CHAPTER 35
AN INTRODUCTION
TO FLOWERING
PLANTS
Prepared by
Brenda Leady, University of Toledo
Copyright (c) The McGraw-Hill
Companies, Inc. Permission required
for reproduction or display.
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Alternation of generations

Gametophyte (haploid)
 Microscopic
in flowering plants
 Produce gametes by mitosis

Sporophyte (diploid)
 Large
“plant” in flowering plants
 Produces spores by meiosis
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 Plant
embryo is a sporophyte that lies
dormant within a seed with a supply
of stored food and a seed coat
 May lay dormant for long periods until
conditions are favorable
 Embryo grows into seedling and then
mature plant
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Growth – increase in size or weight
 Development – increase in number or
organs, accompanied by differentiation
 Meristem – region of undifferentiated cells
producing new tissues by cell division
 Basic plant organs – roots, stems, and
leaves – contain several types of tissues

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Roots – provide anchorage in the soil and
foster efficient uptake of water and
minerals
 Stem – produce leaves and branches and
bear the reproductive structures
 Leaves – foliage leaves specialized for
photosynthesis
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
Radicle, embryonic root, first organ to
emerge from germinating seed
 Provides

water and minerals for growth
Hypocotyl produces cotyledons
– 2 seed leaves
 Monocots – 1 seed leaf
 Eudicots

Endosperm provides food for early embryo
growth
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Development

Shoot apical meristem (SAM)
 Rapidly dividing cells at
 Produces shoot system

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shoot apices
Stems, leaves and other organ systems
Root apical meristem (RAM)
 Also rapidly dividing cells
 Produces root system

Roots and root branches
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Vegetative growth
Production of tissues by SAM and RAM
and growth of mature plant
 Plant shoots produce vegetative buds –
miniature shoots having a dormant SAM
 Under favorable conditions, buds produce
new stems and leaves
 Indeterminate growth – SAMs
continuously produce new stem tissue and
leaves as long as conditions are favorable
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Reproductive development
Mature plants produce flowers, seeds and
fruits
 Flowers produced by determinate growth –
growth of limited duration
 Flower tissues enclose and protect tiny
male and female gametophytes
 Fruits enclose seeds and function in seed
dispersal
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Seed-to-seed lifetime
Annuals – plants that die after producing
seeds during their first year of life
 Biennials – plants that do not reproduce
the first year but may the following year
 Perennials – plants that live for more than
2 years, often producing seed each year
after maturity

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Plant growth and development

Four essential processes
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Cell division, growth, cell specialization, and apoptosis
Cell migration does not occur in plants unlike animals
Additional principles include
1.
2.
3.
4.
Development and maintenance of a distinctive
architecture throughout life
Increase in length by the activity of primary meristems
Maintenance of a population of ever-young stem cells
in meristems
Expansion of cells in controlled directions, by water
uptake
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1) Distinctive architecture

2 features
1.
Upper, apical pole and a lower, basal pole

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
2.
SAM at upper pole, RAM at basal pole
Apical-basal polarity
Originates during embryo development
Radial symmetry


Stem and root cylindrical
Leaves and flower parts in whorls or spirals
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2) Primary meristems
SAM and RAM produce additional
meristematic tissue that increases plant
length and produces new organs
 Primary meristems produce primary
tissues and organs of diverse types
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
SAM and RAM both produce
– generates dermal tissue
 Procambium – produces vascular tissues
 Ground meristem – produces ground tissues
defined by location
 Protoderm
Plant cell specialization and tissue
development do not depend much on the
lineage of a cell or tissue
 Chemical influences are much more
important
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Stem development and structure


New primary stem tissues arise by the cell
division activities of primary meristems located
near the bases of SAMs
Epidermis develops at the stem surface
 Produces

a waxy cuticle (reduces water loss)
Cortex – composed of parenchyma tissue
 Composed
of only one cell type, parenchyma cells
 Stores starch in plastids

Stem parenchyma also has the ability to
undergo cell division (meristematic capacity) to
heal damage
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
Stems also contain
 Collenchyma
tissue composed of
collenchyma cells
 Sclerechyma tissue composed of fibers and
sclerids
 Vascular tissue made of xylem and phloem
arranged in vascular bundles
Ring in eudicots
 Scattered in monocots
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Leaf development and structure

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Young leaves produced at the side of SAMs in leaf
primordia
Flattening expands surface area for light collection
Being thin helps shed excess heat
Bilaterally symmetrical
Upper adaxial (stem facing) side


Pallisade parenchyma absorbs sunlight efficiently
Lower abaxial (away from stem) side


More stomata
Spongy parenchyma has air spaces to foster gas exchange
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Root development and structure
Eudicots – taproot system with a main root
that produces branch roots
 Monocots – fibrous root system with
multiple roots
 Adventitious roots – produced on the
surface of stems of monocots and
eudicots
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3) Ever-young stem cells
Plant meristems include stem cells
 Term stem cell used for plant meristem
cells that remain undifferentiated but can
produce new tissues
 Plant stem cell divides to produce one cell
that remains unspecialized and another
cell that is capable of differentiating into
various types of specialized cells
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Plant Shoot Apical Meristem Size Is
Genetically Controlled
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Normal Arabidopsis SAM consists of several
hundred stem cells organized into at least three
distinct cell regions having different functions
Central zone consists of stem cells that divide but
remain undifferentiated
Normal growth depends on maintaining normal size
of central zone and SAM
Central zone cells make CLAVATA3 that controls
the size of the zone
Loss of CLAVATA3 causes peripheral zone cells to
become central zone cells
4) Plant cell expansion

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Growth includes producing new cells and cell
expansion
Extension occurs when water enters the central
vacuole by osmosis
Allows rapid plant growth
Expansions wedge cell wall polysaccharides
apart allowing enzymes to snip cross links
resulting in stretching
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Shoot system

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Includes all of a plant’s stems, branches
and leaves
Also produces flowers and fruits
Phytomere – shoot module
Stem node – leaves emerge
2. Internode – between adjacent nodes
3. Leaf
4. Axillary meristem – generate axillary buds for
lateral shoots
1.
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Hormones
Molecules that influence development at a
site distinct for production
 Auxin – controls production of leaf
primordia

 Accumulates
in particular apical region
increasing expansion gene expression

Gibberellic acid – produced by leaf
primordia not producing KNOX
 Stimulates
cell division and cell enlargement
so young leaves grow larger
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Leaf adaptations

Leaf form
leaves – only one blade, advantageous in
shade by providing maximal light absorption
 Complex or compound leaves – dissected into
leaflets, common in hot environments for heat
dissipation
 Simple

Leaf venation
 Eudicot leaves have pinnate or palmate venation
 Netted veins provide more support to the leaf
 Monocot
leaves have parallel venation
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
Leaf surface features
 Cuticle

on epidermis helps avoid desiccation
Filter UV radiation, reduce microbe and animal
attack, and self-cleaning
 Guard
cells regulate stomatal opening and
closing
 Trichomes offer protection from excessive
light, ultraviolet radiation, extreme air
temperature, or attack by herbivores
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Elle and Associates Investigated the Cost to Datura
wrightii of Producing Sticky Leaf Trichomes

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Some plants “sticky” – have glandular trichomes
Others “velvety” with similar nonglandular
trichomes
Sticky dominant to velvety
Sticky trichomes may deter certain herbivores but
may be costly when herbivores not present
Hypothesized that sticky plants might produce
fewer seeds than velvety plants, because plant
photosynthetic products are diverted from
reproduction
Data supported the initial hypothesis
Modified leaves
Most leaves function primarily in
photosynthesis
 Can be modified for other roles
 Tendrils
 Tough scales that protect buds
 Poinsetta “petals”
 Cactus spines
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Stem vascular tissue
Herbaceous plants produce mostly
primary vascular tissues
 Woody plants produce primary and
secondary vascular tissue

 Woody
plants begin as herbaceous seedling
with only primary vascular systems
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Primary vascular tissue
 Primary xylem

 Unspecialized parenchyma cells
 Stiff fibers for structural support
 Tracheids and vessel elements conduct
water
and dissolved minerals (not living cells)

Primary phloem
 Transports
organic compounds and certain
minerals
 Sieve elements (living cells)
 Companion cells aid seive element metabolism
 Parenchyma cells
 Supportive fibers
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Secondary vascular tissue
 Secondary xylem – wood
 Secondary phloem – inner bark
 Bark has both outer bark (mostly dead
cork cells) and inner bark (secondary
phloem)
 Secondary vascular tissues produced by
two types of secondary

 Vascular
cambium
 Cork cambium
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
Vascular cambium
 Produces
secondary xylem and secondary
phloem
 Secondary xylem conducts most of a woody
plant’s water and minerals may function
several years
 Usually only the current year’s production of
secondary phloem is active in food transport

Cork cambium
 Produces
cork
 Cork cells dead when mature and layered
with lignin and suberin
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Modified stems
Rhizomes- underground stems
 Potato tubers store food
 Grass stems grow as rhizomes or stolons

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Root system adaptations
Eudicots have taproots
 Monocots have fibrous roots
 Other types of roots

 Prop
roots
 Buttress roots
 Pneumatophores
 Fleshy storage roots – carrots, sugar beets
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Root growth

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15 distinct regions of cellular
specialization
3 major zones
Apical meristem producing root and root cap
2. Zone of elongation
3. Zone of maturation with specialized cells
1.
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
Root meristem and root cap
 RAM
contains stem cells, protoderm (epidermal
tissues), ground meristem (ground tissue), and
procambium (makes vascular tissue)
 Also produces protective root cap
 Root tips embedded in lubricating mucigel

Zone of elongation
 Cells

extend by water uptake
Zone of maturation
 Root
cell differentiation and tissue specialization
 Identified by presence of root hairs (water and mineral
uptake) absent from older regions
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Epidermis of mature roots encloses region
of ground parenchyma – root cortex
 Root cortex cells often rich in starch (food
storage site)
 Primary vascular system includes xylem
enclosed by phloem
 Pericycle encloses root vascular tissue

 Produces

lateral (branch) roots
Woody roots produce primary vascular
tissues followed by secondary vascular
tissues
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