Transcript Botany Part II Plant Structure and Growth

1
Monocots and Eudicots = Phylum ANTHOPHYTA
Both are MONOPHYLETIC = ONE common ancestor
2
- Plants need resources from both the
air and soil, so the ROOT system
(ground) needs to work with the
SHOOT system (air)…they depend
on each other
Tissue  a group of cells,
consisting of one or more types,
which perform a specific function
(ex. ground tissue, vascular tissue,
etc)
Organ  several types of tissues
that work together to carry out
particular functions (3 main organs
in plants = roots, stems, leaves)
3
Roots
- Function → anchor, absorb
water, store food
-Monocots = fibrous roots
-Dicots = taproots
- Roots may have root hairs to
increase the surface area and take
up water
- Adventitious roots are above
ground roots
-Have epidermal tissue but no
waxy cuticle
Adventitious Roots
of Ficus
Root
Hairs
Taproot – Ex. Carrot
Fibrous Root – Ex. Onion
4
Shoots
-Stems and Leaves
- Can be:
-Vegetative (leaves)
- Reproductive (flowers)
5
Stems
-Alternating system of nodes
(leaf attachments) and
internodes (between leaves)
- Axillary bud (angle at
leaf/stem) have potential to
bud
-Terminal bud → concentrated
growth; this inhibits the axillary
buds = APICAL DOMINANCE
The presence of a terminal bud is
responsible for inhibiting the
growth of axillary buds. If the
terminal bud gets removed
(pruning), then the axillary bud
will start to grow. Sometimes
gardeners cut the terminal bud off
so that the axillary buds will grow
and the plant will become fuller.
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COPY THIS INTO YOUR
NOTES!!!
Mesophyll Tissue 
- VERY photosynthetic
- Divided into spongy and
palisades mesophyll
-
Leaves
Main photosynthetic
organ in plants
Flattened blade and
petiole (stalk)
Waxy cuticle (helps
prevent water loss)
Some have special
functions
7
3 Types of Plant Tissues:
- Dermal → outer layer;
“epidermis”
- Vascular → transport;
xylem and phloem
- Ground →
photosynthetic;
storage; support
8
Dermal Tissue
-The dermal tissue is the
epidermis of the plant; it is
called the “skin of the plant”
- It is the outside layer of the
plant
- It is a single layer of cells
that are tightly packed
together
- It can secrete a waxy cuticle
(prevent dehydration)
Note the upper
and lower
epidermis
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Vascular Tissue
- Organized into veins
- Transports materials between
the roots and the shoots
- The vascular tissue of the root
or stem is called the stele
- 2 main parts:
- Xylem → transports water
“up”
- Phloem → transports food
to roots and nonphotosynthetic parts of the
plant; from “source to sink”;
transports up and down
In this picture,
the “S” stands
for phloem
(sieve tube
elements)
10
Ground Tissue
- Neither dermal nor vascular
- Functions in photosynthesis,
storage, and structural support
- In eudicots (where the vascular
bundles are arranged in a ring)
it is divided into:
-Pith (internal to the vascular
tissue)
- Cortex (external to the
vascular tissue)
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There are 3 basic types of plant cells:
1. Parenchyma
2. Collenchyma
3. Sclerenchyma
Each cell type has structural adaptations in the cell contents (protoplast) and in the cell
wall.
Terms to know:
- Plasmodesmata → channels connecting cells
- Middle lamella → cements adjacent cell walls
- Primary wall → made as the cell grows
- Secondary wall → made after the growth stops
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Parenchyma
-Thin, flexible primary walls
- Most lack secondary walls
- “Typical cell” → generally the LEAST
specialized (all cells start out as parenchyma)
-Can dedifferentiate for plant tissue cultures
-Photosynthetic!!
- Perform most metabolic functions
-Do not usually do cell division (unless in
meristems), but retain the ability to divide and
differentiate
13
Collenchyma
-Thicker, but uneven primary cell
walls
- Grouped together to support
young parts of shoots
-LACK secondary walls
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Sclerenchyma
-Function as SUPPORT
ELEMENTS in plants
- They have thick secondary walls
strengthened with lignin
-More rigid than collenchyma
-Mature cells cannot elongate
(b/c of rigid cell walls), so they
are present in cells that have
stopped growing
15
Xylem
-Transports water and
dissolved materials “up”
from the roots
- There are two types of
water conducting
elements:
-Tracheids → long
and thin; their
secondary cell walls
have hardened with
lignin; they have pits
where water flows
through
-Vessel Elements →
wider and shorter;
thinner walls and
linked together
forming long tubes
(called xylem vessels)
-The cells that make up
xylem are DEAD at
maturity
Xylem
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Phloem
-Transports food to roots and
other non-photosynthetic parts
of the plant
- Moves sucrose and other
organic molecules through tubes
formed by chains of cells called
sieve tube elements →
- These sieve tube elements
are ALIVE at maturity
- The end of each element
has a sieve plate, which
has pores to allow
substances through
- They are associated with
non-conducting
companion cells that help
them move the materials
(via plasmodesmata)
- Used in
TRANSLOCATION (Bulk
Flow Movement)
Phloem =
Blue
(in this
picture)
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Meristems
-Perpetual embryonic tissue
in growth areas (makes more
cells!)
- Pattern of growth depends
on the locations of the
meristems
- There are 2 main types of
meristems:
-Apical Meristems
-Lateral Meristems
Meristems allow for
LIFELONG GROWTH!!!
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Apical meristems
are found at the tips
of roots and at the
buds of shoots.
These are for
PRIMARY growth
(LENGTH). They
give rise to the
primary plant body.
They allow roots to
extend through the
soil and the shoots
to increase their
exposure to light
and carbon dioxide.
19
Lateral meristems are cylinders that run along the root/
shoot. They provide SECONDARY growth (THICKNESS) .
They add girth to the plant by making secondary vascular
tissue and periderm. These meristems are very important in
woody plants (trees, etc).
- There are two types of
lateral meristems: the
vascular cambium and the
cork cambium.
- The vascular cambium adds
layers of vascular tissue
called secondary xylem
(wood) and secondary
phloem.
- Plants with vascular
cambium with lignified
cell walls are called
woody plants (not
herbaceous)
- The cork cambium replaces
the epidermis with thicker,
tougher periderm.
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- Annuals  complete their life
cycle—from germination to
flowering to seed production
to death—in a single year or
less.
- Biennials  span two years,
with flowering and fruiting in
the second year
- Perennials  plants such as
trees, shrubs, and some
grasses that live many years
21
- Roots show mostly PRIMARY GROWTH and produce the
epidermis, ground tissue, and vascular tissue.
- Water and minerals absorbed from the soil must enter the
plant through the epidermis, a single layer of cells covering
the root.
- Root hairs greatly increase the surface area of the epidermis.
- In angiosperm roots, the stele is a vascular cylinder with a
solid core of xylem and phloem.
- The ground tissue of roots consists of parenchyma cells.
- When plant stems are cut, roots will develop at the cut end
which is opposite the apical bud.
Root Cap →
protects meristem
Zone of cell
division → apical
meristem and its
derivatives
Quiescent Center
→ Cells that divide
more slowly than
meristem cells;
resistant to damage
Zone of elongation
→ cells elongate;
responsible for
pushing the root tip
Zone of
differentiation (aka
zone of maturation)
→ specialization;
complete
differentiation and
become distinct cell
types
22
Stele – vascular bundle in the center of roots; produced by the procambium
There are 3 Primary
Meristems:
Protoderm – forms
the dermal tissue
(epidermis)
Procambium –
forms the stele
(vascular tissue in
the center of roots –
primary
xylem/phloem)
Ground – forms
ground tissue
23
Secondary Growth –
Thickness
- Occurs in stems and
sometimes in roots, but rarely
in leaves
- TWO LATERAL MERISTEMS:
-Vascular Cambium →
makes secondary xylem
(WOOD) and secondary
phloem
-Cork Cambium → Makes
the tough covering for roots
and stems which replaces the
epidermis
-Periderm → layers of cork and
cork cambium
- Bark → refers to all tissue
external to vascular cambium
(secondary phloem, cork, cork
cambium)
IF there is
secondary
growth, the
plant is
considered to
be “woody”
not
“herbaceous”
KNOW THIS PICTURE AND THESE DEFINITIONS!!
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One of the major differences between plants and
animals is TOTIPOTENCY!
For plants growth and development is NOT
restricted to the embryonic/ juvenile
period but occurs throughout the life of the
plant; can develop into any part of the
plant; to get features from the juvenile
form, must take cuttings from areas formed
in that period
Growth = increase in size
Development = changes that
elaborate an organisms body
Plant Life Cycle:
Germ → Flower →Seed → Death
RECALL:
Annual = 1 year or less
Biennial = 2 years
Perennial = Lives many years
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Processes that are important to the development of plants:
1. Morphogenesis → development of body form and organization;
depends on pattern formation (specific structure in specific
location)
2. Differentiation → specialization of cells; depends on control of gene
expression (regulating transcription and translation)
3. Growth → includes both:
- Cell Division (can be symmetrical or asymmetrical)
- Cell Expansion (water accounts for 90% of expansion – fills
vacuoles)
Both of these contribute to plant form
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Terms to Know:
- Stomata
- Guard Cells
- Palisades Mesophyll
- Spongy Mesophyll
-Mycorrhizae (symbiotic fungus on
roots to help get water)
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29
Mycorrhizae is a fungus that grows
in association with the roots of a
plant in a symbiotic or mildly
pathogenic relationship. It helps the
plant absorb water from the
surrounding soil and in turn has
access to the carbohydrates (sugars)
of the plant.
30
Symplastic → Continuum of cytosolic
compartments; requires only one
crossing of the membrane; once it is in
the cell, it moves from cell to cell via
plasmodesmata; (therefore the PM
can regulate what can and cannot be
shared through the plant)
Apoplastic → Continuum of cell walls
and extracellular spaces without
actually entering the cell (when it
wants to cross into the cellular
compartment, it also has to pass
through the PM to be “checked”)
Transmembrane - water and solutes
move out of one cell, across the cell
wall, and into the neighboring cell, and
keep moving following this pattern; this
route requires repeated crossings of
plasma membranes
It is important to pass through the PM so
that the materials can get checked and the
vascular system does not spread harmful
things to the rest of the plant
31
Hydrogen ions (H+) play the primary
role in basic transport processes in
plant cells. The membrane potential
is established mainly through the
pumping of H+ by proton pumps.
During cotransport, plant cells use
the energy in the H+ gradient and
membrane potential to drive the
active transport of many different
solutes.
For instance, cotransport with H+ is
responsible for absorption of neutral
solutes, such as sucrose, by phloem
cells and other plant cells.
An H+/sucrose cotransporter
couples movement of sucrose against
its concentration gradient with
movement of H+ down its
electrochemical gradient.
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Determines the direction and
movement of water in plants!
WATER POTENTIAL   = S + P
-Water potential depends on two
things:
-1. Solute concentration
-Adding SOLUTES LOWERS
ψ
-2. Physical pressure
- adding PRESSURE
INCREASES ψ
- Water moves from HIGH ψ to LOW
ψ
- Pure water → ψ = 0
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




Bulk flow functions in long-distance transport.
Diffusion is efficient for transport within a cell or between cells.
However, diffusion is much too slow for long-distance
transport within a plant, such as the movement of water and
minerals from roots to leaves.
Water and solutes move through xylem vessels and sieve tubes
by bulk flow, the movement of a fluid driven by a pressure
gradient.
Phloem transport moves by bulk flow.
34
Bulk Flow → movement of
water and solutes by pressure
Root Hairs → increase SA to
increase absorption
Mycorrhizae → RECALL: a
fungus that has a symbiotic
relationship with plant roots;
absorbs water
Endodermis → surrounds the
stele (center where the
vascular tissue is); contains
the casparian strip
Casparian Strip → waxy layer
made of suberin that is
impervious to water; ensures
that materials from the
apoplastic pathway have to
cross a PM to get “checked”;
everything must pass through
a cell before entering the stele
See Next Slide…
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36
Sap = water and
dissolved minerals
The sap moves through
the plant by 2 forces:
1. Root Pressure →
“PUSH”
2. Transpiration/
Cohesion/
Adhesion →
“PULL”
37
Root Pressure = PUSH
-Minerals accumulate in the stele;
this DECREASES Ψ …therefore
water flows INTO the root cortex
which creates a pressure that forces
the fluid up the xylem
-Guttation → if more water is
“pushed up” than is transpired
(lost/evaporated), water is forced
out of the leaves (occurs at night
and when there is high humidity)
- This is NOT the major mechanism
38
Xylem sap transport is SOLAR POWERED! Most of the movement of xylem is due
to the evaporation of water through stomata!!
Transpiration/ Cohesion/ Adhesion =
PULL
- Water is lost by transpiration (loss of
water vapor from leaves); therefore
water is drawn from other cells by
osmosis
- Cohesion – water sticking to water
- Adhesion – water sticking to cell walls
***Both of these factors are due to Hbonding***
- This is the MAJOR MECHANISM of
xylem sap
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

The transpiration-cohesiontension mechanism
transports xylem sap against
gravity.
Long-distance transport of
water from roots to leaves
occurs by bulk flow, with
the movement of fluid
driven by a water potential
difference at opposite ends
of xylem tissue.
40
The BENEFIT of transpiration is
evaporative cooling. If the
temperature of the plant stays
down, the enzymes for
photosynthesis and respiration
will not denature.
Stomata open and close (via guard cells) by
changing shape. If the plant has enough
water, the vacuoles will be full and the guard
cells will be turgid/ swollen and therefore
OPEN. If there is little water available, the
guard cells are flaccid and the stomata will
be CLOSED…which means no gas exchange
for PS!
Guard cells control
stomatal opening on a
moment-to-moment
basis, reacting to a
cloud or transient
shaft of sunlight.
In general,
transpiration is
greatest on sunny,
warm, dry, and windy
days because these
environmental factors
increase evaporation
41
Lots of K+ = ↓Ψ (adding solutes decreases water potential) = Osmosis (H2O IN) =
turgid = stomata open
Little K+ = ↑Ψ = Osmosis (H2O OUT) = flaccid = stomata closed
Stomata are
usually open at
night to decrease
transpiration.
CAM plants have
the stomata open
at night. Then the
CO2 is converted
into an organic
acid, which
releases CO2 for
Calvin Cycle
during the day.
42
- Translocation = movement of food
via phloem; utilizes sieve tube
cells
- Usually the “food” is the
disaccharide sucrose (SUGAR!!)
- Sugar “source” = WHERE the
sugar is MADE (usually leaves)
- Sugar “sink” = consumer/ storer
of sugar (growing roots, shoots,
fruits, apical meristems)
- Movement is always:
SOURCE to SINK
- The sugar may go up or down
depending on where the source
and sink are in relation to one
another
- Requires active transport (moves
by bulk flow which is driven by
pressure)…needs ENERGY!!
43
44
A plant goes
through 2
different
generations:
- Gametophyte =
produces
gametes by
mitosis; haploid
- Sporophyte =
produces haploid
spores by
meiosis; diploid;
usually the
dominant phase
The diploid plant, the sporophyte, makes haploid spores by
meiosis. These spores divide by mitosis to form gametophytes,
multicellular male and female haploid plants that produce
gametes (eggs and sperm). Fertilization results in diploid
zygotes, which divide by mitosis to form new sporophytes.
45
-Non-reproductive parts = sepal and petals
- Reproductive parts:
- Male = Stamen (anther makes pollen)
- Female = Carpel (stigma, style, ovary)
- Complete flower = have all 4 organs; all
bisexual (have both male and female)
- Incomplete flower = lacking one or more
floral parts; unisexual
46
-In sporangia (pollen sacs) are diploid cells (called microsporocytes) that do
meiosis to form haploid microspores, which gives rise to pollen (male
gametophyte)
- Two cells:
- Generative cell = produces sperm
- Tube cell = produces pollen tube
-Pollen = 2 sperm cells
Microsporocyte
47
Ovary → Ovule → Megasporocyte → Megaspores
- The megasporocyte goes through MEIOSIS to form the megaspores
- Only 1 of the 4 megaspores survive
- The surviving megaspore divides 3 times without cytokinesis to give one cell
with 8 haploid nuclei
- 3 antipodal cells  unknown function
- 2 polar nuclei  combines with a sperm to form the 3n endosperm
(food source for the seed)
- 1 egg  combines with a sperm cell to form the 2n zygote
- 2 synergids  helps attract the pollen tube
48
Development of
Gametophytes
49
50
Brings male and female gametes
together to that fertilization can occur.
Fertilization = fusion
of gametes
51
Double fertilization synchronizes embryo
development with food supply. Remember
each pollen grain contains 2 sperm:
- 1 sperm + egg = 2n zygote
- 1 sperm + 2 polar nuclei =
3n endosperm (food)
BOTH sperm fertilize
nuclei of the female
gametophyte
52
-After double fertilization, ovule develops
into a seed and the ovary develops into a fruit
-Enclosed in a protective seed coat
- Mature seed = dehydrated (dormant!); when
it gets rehydrated, it forms an embryonic root
(radicle)
53
Germination of seeds depends on
imbibition (the uptake of water due to the
low water potential of the seed). Imbibition
causes metabolic changes that resume
growth in the seed.
The radicle (root) emerges first (so it can
supply water to the rest of the plant).
54
Definition of Fruit:
- Angiosperm structure
that protects dormant
seeds and aids in
dispersal
Mature Ovary = FRUIT
-Pollination →
hormonal changes →
Ovarian growth into the
fruit
- The ovary wall
becomes a pericarp
(thickened wall of the
fruit)
-Helps in dispersal by
wind and animals
55
Simple Fruit
-Develop from a single
ovary (Ex. cherry, soybean)
Aggregate Fruit
- Single flower, several
carpals (Ex. blackberry)
Multiple Fruit
- Tightly clustered group of
flowers (Ex. pineapple)
56
-Asexual reproduction is also called Vegetative Reproduction
- Results in CLONES (also called CLONAL reproduction)  no genetic variation!
- Can grow from one parenchyma cell!
-Fragmentation → separation of parent plant into pieces that reform the whole
plant; done to make cuttings; this can also occur naturally
- Apomixis → flowers (ex. dandelions) that can produce seeds without flowers
being fertilized
-Test-tube cloning; can cross genes
57

Asexual Reproduction 



Sexual Reproduction 



Advantages = can clone itself rapidly; seedlings
are sturdy
Disadvantage = no genetic variation
Advantages = genetic diversity
Disadvantages = sometimes seedlings can be
more frail
Seed dormancy suspends growth until
hostile environmental conditions are
reversed.
58
-Prevention of self- fertilization ensures that the egg and sperm are from
different parents
- There are several possibilities to prevent this:
- Stamens/ carpals mature at different times
- Structural arrangement (see below)
- Self-incompatibility → plant rejects its own pollen and that of closely
related individuals (biochemical blocker)
59
Humans do selective breeding for our own
benefit.
Plants are totipotent and have the ability to
go from one cell to a clone of the original
organism.
Transgenic Plants → plants that have genes
from 2 or more species; they have been
genetically modified (GM) OR they can
occur in nature naturally
Much debate surrounds plant biotechnology
with respect to politics, the economy, and
ethical concerns.
60
61
3 Stages in the Cell Signaling Process
*Reception (signal detected by
receptors)
* Transduction (signal amplified by
second messengers and carried)
* Response (enzymes activated)
Greening (De-Etiolation) 
* involves changes in levels of growth
hormones and activation of
enzymes related to photosynthesis:
* shoot reaches sunlight
* stem elongation slows
* leaves expand
* root system elongates
* chlorophyll production begins
62






Plants do not have a circulatory
system like animals do; some
hormones can only act locally
Plant hormones are produced at
very low concentrations, so
signal transduction pathways
amplify the signals
Plant hormones control plant
growth and development by
affecting the division, elongation,
and differentiation of cells
Each hormone has multiple
effects, depending on its site of
action, its concentration, and the
developmental stage of the plant.
Response to a hormone usually
depends not so much on its
absolute concentration as on its
relative concentration compared
to other hormones.
It is hormonal balance, rather
than hormones acting in
isolation, that controls growth
and development of plants.
63

Tropism  growth response
toward OR away from a
stimulus
 Example: phototropism
 (bending toward light is a
positive tropism)
 Bending away from light
is a negative tropism)
 Research
 Darwin & son: plant does
NOT grow toward light if
tip covered or removed
 Went : extracted the
chemical messenger for
phototropism – auxin!
 He realized that there
was more produced on
the DARKER side of
the plant, so those cells
elongated more …and
grew TOWARDS the
light
64
Went’s experiment
represents the first time
anyone had isolated a
hormone from plants.
65
MAKE SURE YOU
KNOW THESE!!






Auxin  made mostly in apical meristem of the shoot; stimulates
cell elongation in different target tissues, enhances apical
dominance, promotes fruit growth (this is what was discovered in
the Went experiment!); role in pattern formation
Cytokinins  produced in actively growing tissues (ex. Roots,
embryos, fruits); stimulate cytokinesis, can stimulate germination
and delay senesence (aging)
Gibberellins  made in roots and young leaves; stimulates
growth in leaves and stems, causes flower and fruit development,
bolting (elongation of stalk)
Abscisic acid  maintains dormancy in seeds by inhibiting
germination and therefore SLOWS GROWTH, reduces drought
stress by closing stomata
Ethylene (gas) controls fruit ripening by positive feedback
(more gas, more ripening), promotes leaf abscission (leaf loss by
deciduous in winter); a chain reaction occurs during ripening:
Ethylene triggers ripening, and ripening triggers more ethylene
production – hence the expression – “one bad apple spoils the
whole bunch”
Brassionsteroids  similar to animal sex hormones; induces cell
elongation and cell division, slows abscission (dropping leaves)
66
67
Photomorphogenesis  effect of light on
plant growth/development; red and blue
light most important
BLUE light – initiates several responses:
bending toward/away from light,
hypocotyl elongation and opening of
stomata
PHYTOCHROMES (reds)
- red light (660nm) – increases
germination
- far red light (730 nm) – inhibits
germination
- the response depends on the LAST flash
of light
- effects of red and far red light are
reversible
68
Circadian rhythm 
 Many plant processes, such as
transpiration and synthesis of certain
enzymes, undergo a daily oscillation.
 Physiological cycles with a
frequency of about 24 hours that are
not directly paced by any known
environmental variable are called
circadian rhythms.
 If an organism is kept in a constant
environment, its circadian rhythms
deviate from a 24-hour period to
free-running periods ranging from
21 to 27 hours.
 Photoperiodism 
 Relative length of night and day and
the resulting physiological response
 Critical Night Length – length of
NIGHT (not day) controls flowering
and other photoperiod responses

69
70

Gravity –


Roots show POSITIVE gravitropism and shoots show
NEGATIVE gravitropism; this ensure that the roots reach
soil and the shoots reach the sunlight regardless of how
the seed lands
Stress -
Drought – mechanisms to reduce transpiration include
guard cells closing stomata and slowing shallow root
growth help plants deal with drought
 Heat – heat shock proteins aid to scaffold protein folding
(can function as chaperonin proteins)
 Cold – increase unsaturated fatty acids for fluidity, when
freezing – ability to resist dehydration from water loss
affects survival

71
 Physical
– first line of defense
is the epidermis and
periderm; also plants have
thorns to deter predators
 Chemical – chemical attacks
are the second line of defense;
this helps to destroy
pathogens to prevent spread
of infection; production of
distasteful/toxic compounds;
 Recruitment of predators of
herbivores
 Wasp (predator)
caterpillars (herbivore) 
plants
72

Hypersensitive Response


Complex early defense
response that causes cell and
tissue death near the infection
site and restricts the spread of
a pathogen.
Systematic Acquired
Resistance (SAR)
 Provoked by chemicals
that “sound the alarm”
 Non-specific, and
provides protection
against diverse
pathogens
 SAR = alarm hormones!
 One hormone example
is salicylic acid
(ingredient in aspirin)
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