Transcript Slide 1

PLANT FORM AND FUNCTION
UNIT SIX
Chapters
35,36,37,38,39
Angiosperm Structure
• Angiosperms are further divided into 4
major categories:
– Basal Angiosperms (older angiosperms
like Water lilies)
– Magnoliids (newer like the Magnolia)
– Monocotyledons a.k.a. monocots
(newer still)
Have a single seed leaf
- Dicotyledons and/or
Eudicotyledons a.k.a. eudicots
(newest)
Have double seed leaves
Palms and Bananas are Monocots
Rice, wheat, corn – all monocots
Monocots vs. Dicots
Basic Angiosperm Morphology
• Shoot system= stems and leaves
• Root system= tap root and lateral
roots
Plant Morphology
•Stems consist of alternating “nodes”, the
site of leaf attachment
•The angle created where the leaf
attaches to the stem is called the axil
•The axil contains an axillary bud, which
can give rise to a lateral shoot or a branch
•The tip of the shoot is called the apex
and holds the terminal bud
•The terminal bud and the apex is where
the elongation of the shoot occurs
•The apical bud inhibits the growth of the
axillary buds - therefore the advent of the
practice of pruning
Modified Stems
1.
2.
3.
4.
5.
6.
7.
Bulb (e.g. onions)when sliced in half, will show
concentric rings.
Clove bulblike structures (e.g. garlic) will separate into
small pieces when broken apart.
Tuber (e.g. potatoes and daylilies) these structures are
either on strings or in clusters underneath the parent
plants.
Rhizome are large creeping rootstock or underground
stems and many plants arise from the "eyes" of these
roots (e.g. ginger)
Stolons – Horizontal, aboveground stems (e.g.
Strawberries)
Corm are similar to bulbs but are solid when cut rather
than possessing rings.
Crown (e.g. the type of root structure found on plants
such as asparagus) looks much like a mop head under
the soil's surface.
Bulb
TUBERS
•
A tuber is a solid, enlarged,
horizontal, shortened stem; it's a
storage area for reserve food. Note
in the center of the picture the
production of young tubers arising
from the rhizome. On the tubers, the
so-called "eyes" are the nodes,
where new shoots arise at the axil
of a scale (modified leaf); these new
shoots can give rise to new plants.
Rhizomes
Ginger, bamboo, many self-naturalizing perennials like lily of the valley
Clove
Bulblike structures
(e.g. garlic) will
separate into small
segments when
broken apart.
Corms
Solid bulb, without concentric segments
Stolons
Purpose of roots
• The entire root structure
serves to anchor the
plant/tree in the soil
• Absorption of water and
nutrients from the soil
actually occurs only at the
tips of each root fiber
• Millions of tiny roots hairs
in these tip areas help
absorption by increasing
surface area
Fibrous vs. Tap Roots
• Seedless vascular
plants (ferns) and
Moncot angiosperms
such as grasses
have fibrous roots
• Dicot angiosperm
have tap roots
Adventitious Roots
Roots that grow out of the stem or trunk - sometimes for
extra support, sometimes for vegetative reproduction
Other modified roots
• Aerating roots (or
pneumatophores): roots
rising above the ground,
have a large number
pores for exchange of
gases.
• Buttress roots are large
roots on all sides of a tall
or shallowly rooted tree.
Typically they are found in
rainforests where soils are
poor so roots don't go
deep. They prevent the
tree from falling over and
help gather more
nutrients.
More modified roots
• Storage Roots:
Beets, radish, turnip,
horseradish, sweet
potato, and cassava
(tapioca).
Types of leaves
Single and double compound leaves
Compound Leaves
Simple Leaves
Modified leaves
• Spines on cacti
are actually
leaves. The
photosynthesis is
carried out by the
green stems
• Bracts on
poinsettias are
actually not
petals, but leaves
around the tiny
yellow flowers
Tendrils for grasping
LEAF STRUCTURE
When guard cells take up water, they become turgid
and this closes the stomata. Loss of water from the
cells makes them flaccid and this opens the stomata.
In a C3 leaf the palisade mesophyll cells typically form a layer in the
upper part of the leaf; the corresponding mesophyll cells in a C4 leaf are
usually arranged in a ring around the bundle sheath cells.
The bundle-sheath cells of C4 plants have chloroplasts (dark green),
those of C3 leaves usually lack them.
C3 Leaf
C4 Leaf
Bundle sheath cells surround vascular bundles – thus the name.
Review of the typical Plant Cell
The Protoplast – the functional,
living part of a cell
• All areas of a plant cell except the cell wall
are considered the protoplast
– Cell membrane
– Cytosol,
– All organelles
Major Plant Cells
• Parenchyma cells
• Collenchyma cells
• Sclerenchyma cells
– Fibers
– Schlereids
• Water-conducting cells of the Xylem
– Tracheids
– Vessel elements
• Food-conducting cells of the Phloem
– Sieve-tube members
– Companion cells
Parenchyma cells
• Typical plant cell – most abundant in plants
• Thin walled (Walls contain cellulose, not lignin)
• Unspecialized – can either photosynthesize, or store starch
– Can be found in leaves – contain chloroplasts and carry out
photosynthesis (mesophyll cells are an example)
– Can also be found in roots and other non-photosynthesizing parts and
store starch in amyloplasts (related to chloroplasts) – in stems they are
called the pith
amyloplasts
chloroplasts
Collenchyma cells
•
•
•
•
•
These cells are usually just under the epidermis of leaves, stems and roots
Collenchyma cells are collectively also called the cortex
Cells are columnar in shape
Also lack lignin in their cell walls, but have thicker walls than parenchyma
cells
Give younger plants or plant parts support
Because they have thick walls but lack lignin, they are able to provide support
without restricting growth – hence found in young, growing parts
Parenchyma
Columnar
Collenchyma
Collenchyma
Epidermis
Parenchyma vs. Collenchyma cells
Sclerenchyma cells
• Thick walls that are fortified with lignin
(secondary wall) making them much more
rigid than collenchyma walls
• Mature sclerenchyma cells usually do not
contain protoplasts and cannot
grow/elongate, so these cells are located
in regions of the plant that have stopped
growing
Sclerenchyma cont’d.
•
Two types of sclerenchyma cells:
–
–
Fibers - long and thin, exist in bundles in stems,
right above above vascular tissue
Sclereids – shorter than fibers and give nutshells
and seed coats their hardness. The gritty texture of
certain fruit like pears is basically due to sclereids
scattered among the parenchyma tissue
Xylem Cells
• Water conducting
• Elongated
• Produce lignin-containing secondary
walls
• Lack protoplasts after maturity
• Two types:
– Tracheids – spindle-shape, with
hole (pits) in them through which
water passes
– Vessel element cells are broader
and lie end to end and form
continuous hollow tubes for water to
flow through
Phloem Cells
• Food conducting – sugar, minerals and other
organic compounds
• Unlike xylem cells, phloem cells can contain
protoplasts* (either complete or incomplete)
• Two types:
– Sieve-tube members – chains of cells that conduct
food (partial protoplasts -lack nuclei and ribosomes)
– Companion cells – connected to sieve-tube cells,
contain nuclei and ribosomes, so help maintain sievetube cells
*see slide #31 for non-protoplast-containing phloem
Sieve-tube elements and companion
cells of the Phloem
Three Tissue System
• The cells we have learned about in the
past slides such as parenchyma, sieve
tube cells, etc. can be placed into 3 main
tissue categories or systems:
– Dermal tissue system
– Vascular tissue system
– Ground tissue system
Three Tissue System, cont’d.
Tissue System
and Its Functions
Dermal Tissue System
• protection
• prevention of water loss
Ground Tissue System
• photosynthesis
• food storage
• regeneration
• support
• protection
Vascular Tissue System
• transport of water and
minerals
• transport of food
Component Tissues
Epidermis
Periderm (in older
stems and roots)
Parenchyma tissue
Collenchyma tissue
Sclerenchyma tissue
Xylem tissue (Tracheids
and vessel elements)
Phloem tissue (Sievetube members and
companion cells)
Location of Tissue
Systems
Cross Section of a Monocot Stem
CROSS SECTION OF AN HERBACEOUS DICOT STEM
 Epidermis
Sclerenchyma
Phloem
 Collenchyma (also called
the cortex – which is ground
tissue between the epidermis
and the vascular bundles)
Vascular bundle
Xylem
A thin layer of cells called the
vascular cambium separates the
xylem and phloem
 Parenchyma or pith
Also known as the Pith in stems – stores food (amyloplasts) and water (central vacuoles)
Summary of dicot & monocot stems
(Parenchyma)
(Collenchyma)
Vascular bundles in celery
Summary of Monocot vs. Dicot Stems
Root Anatomy
Pith – a central core of
parenchyma cells that store
food – mostly in monocots
Stele – a vascular bundle
that gives rise to both xylem
and phloem
Pericycle – the outermost
layer of the stele that sprouts
the lateral roots
Casparian strip – a thin strip
or coating that prevents
water from seeping between
cells
CROSS SECTION OF A MONOCOT ROOT
Epidermis
(Dermal tissue)
Xylem
(Vascular)
Cortex or
schlerenchyma
(ground tissue)
Phloem
(Vascular)
Endodermis
(dermal)
Pith
(Parenchyma or Ground)
Stele (Entire central Vascular region)
Pericycle
(Parenchyma or
ground)
Pericycle
(Parenchyma or
Ground tissue)
CROSS SECTION OF A DICOT ROOT
Endodermis
No pith or parenchyma in dicot roots
Summary of monocot & dicot roots
Growth in Plants
• Animals undergo determinate growth –
they stop growing after they reach a
certain size.
• Plants on the other hand have
indeterminate growth – they continue to
grow throughout their life.
Annual, Biennials, Perennials
• Botanically, an annual plant is a plant that usually
germinates, flowers and dies in one year. (Impatiens,
sunflower, gerbera daisies)
• A perennial plant is a plant that lives for more than two
years. Perennial plants are divided into two large groups,
those that are woody and those that are Herbaceous.
(Roses, sage, peonies)
• A biennial plant is a flowering plant that takes between
twelve and twenty-four months to complete its lifecycle.
(Parsley, foxglove, sweet William)
How can plants have constant growth?
• They can have indeterminate growth
because they have perpetual embryonic
tissues (like stem cells in animals)
• These embryonic tissues are called
Meristems or cambiums.
Meristems
•
There are 2 main types of meristems (embryonic
tissues):
1. Apical meristems – they are located in the
terminal and axillary buds of shoots and root tips
– Apical meristems give rise to primary growth which
means that they make the plant grow in length – in the
roots throughout the soil and in the shoots to increase
surface area for photosynthesis.
– Parenchyma cells, collenchyma cells and sclerenchyma
cells all come from apical meristems
– Herbaceous plants (non-woody) the entire plant
develops due to primary growth from apical meristems
Meristems, cont’d.
2.
Lateral meristems (also called Cambiums) – are also located
in shoots and roots, but are responsible for secondary growth
or lateral growth – they make the stems and roots thicker by
growing sideways Woody plants and trees grow in thickness in
areas where primary growth has stopped.
There are 2 types of lateral meristems:
a. Vascular cambiums: this produces secondary xylem and
phloems which are actually wood. The vascular cambium
is the source of both the secondary xylem (grows inwards,
towards the pith) and the secondary phloem (grows
outwards), and is located between these tissues in the
stem and root.
b. Cork cambiums – replace the epidermis with peridermis
which is bark or cork in some trees
Lateral Growth
• The phloem is constantly being pushed outward
and crushed, only the innermost layers adjacent
to the vascular bundle are functional phloem
(Protoplast-containing and food-conducting). Also
called the inner bark
• The dead, protoplast-lacking phloem cells are
called non-functional phloem, which becomes
part of the outer bark (The bark of trees consists
of cork, cork cambium, cortex, and phloem)
Meristems, cont’d.
Vertical growth
Vertical growth
Lateral growth 
Transpiration vs. Translocation
• Xylem sap (water from the roots) is helped
along by transpiration
• Phloem sap (fluid rich in sugar and
minerals) is moved by translocation
– The predominant sugar in phloem sap is
sucrose
– Phloem sap always moves from a sugar
source (such as leaves) to a sugar sink (cells
that consume sugar – growing plant parts)
Transpiration vs. Guttation
• Transpiration is the loss of water through the xylem
cells, when stomata in leaves open for gas exchange
• Transpiration is essential, because it provides the
“sucking” effect for water to travel up the xylem tissues
(although too much is bad)
• Guttation is the water exuded from leaves as a result
of root pressure (removing excess water due to low
transpiration rates)
Guttation vs. Condensation
Dew appears as many droplets and
is caused by the condensation of
atmospheric water vapor
Guttation appears as single droplets of water
and is the plant’s way of removing water
Opening and Closing of Stomata
• Located throughout the epidermis are paired, guard
cells, and between each pair is a small opening, called a
stoma (plural: stomata). Guard cells contain chloroplasts,
but other epidermal cells do not.
• When the two guard cells are turgid (swollen with water),
the stoma is open
• The increase in osmotic pressure in the guard cells is
caused by an uptake of potassium ions (K+).
• Abscisic acid (ABA) is the hormone that triggers closing
of the stomata when there is a danger of excessive
water loss (hot midday)
Plant Control Systems
• Many hormones are involved in controlling
plant systems:
– Auxins
– Cytokinins
– Gibberellins
– Abscisic acid
– Ethylene
Auxin and elongation
• Auxins promote primary and
secondary growth
• They promote growth of
adventitious roots from cuttings
• They control phototropism,
gravitropism
• They control the release of
ethylene – another plant hormone
• Auxin is made in apical
meristems, young leaves and
seed embryos
• Ehtylene promotes
–
–
–
–
fruit ripening
Promotes apoptosis
leaf and flower aging
leaf abscission or the intentional
shedding of leaves, flowers and
fruit
– Made in aging flowers and
leaves, ripening fruits and stems
Abscisic Acid
•
•
•
•
Causes stomata to close
Inhibits growth in plant parts
Maintains dormancy in plants
Made in leaves, stems and
unripe (green) fruit
Cytokinins
• Promote cytokinesis during plant mitosis
• Delay senescence in leaves and other
parts of a plant
• Made in roots and delivered to other parts
of the plant
Gibberellins
• Fruit growth
• Germination of seeds
• Stem elongation or - the growth of an elongated stalk with
flowers grown from within the main stem of a plant. This
condition occurs in plants that are grown for their leaves, such
as cabbage, lettuce, spinach, and other leafy greens.
Plant Movement
• Phototropism – movement toward light – caused
by photoreceptors on shoot tips and auxins
• Gravitropism – response to gravity (seeds
always germinate in the right direction) – caused
by plastids called statoliths that contain dense
grains of starch, in root tips and auxins
• Thigmotropism – response to touch (ivy
grasping supports), caused by ethylene
Photoperiodism
• When a plant responds to amount to light available e.g. by flowering
• Controlled by proteins called phytochromes
• Phytochrome is a photoreceptor, a pigment that plants
use to detect light. It is sensitive to light in the red and
far-red region of the visible spectrum. Many flowering
plants use it to regulate the time of flowering based on
the length of day and night (photoperiodism) and to set
circadian rhythms. It also regulates other responses
including the
–
–
–
–
germination of seeds,
elongation of seedlings,
the size, shape and number of leaves, and
the synthesis of chlorophyll.
• Plants make several different phytochromes
Red Light Blue Light
• Blue light inhibits seed germination and
shoot elongation and red light promotes it
• This is due to phytochromes – nonphotosynthetic plant pigments and
photoreceptors
Sustainable Agriculture &
Soil Conservation
• Irrigation – primary source is underground water sources
called aquifers. Overuse can cause ground to sink.
• Fertilization – crops deplete soil nutrients, so nutrients
must be added to soil – chemicals or organic materials
such as compost, manure, etc.
• Crop Rotation – alternating types of plants grown, to
prevent depletion of nitrogenous nutrients (alternating
grains and legumes).
– Crop rotation also prevents the accumulation of pathogens
specific to a crop
Sustainable Agriculture &
Soil Conservation
• Phytoremediation – using certain plants to
absorb soil toxins such as zinc, lead, etc.
Alpine Pennycress is used to absorb
Zinc from agricultural soil
Soil-free agriculture
• Hydroponics – plants are grown without
soil, in a solution of water and nutrients.
Advantages:
- Nutrients readily available
- Plants grow better, mature faster
- Less space needed since roots do not need to grow far
in search of nutrients.
- No weeds – no competition and no need for weed killers,
healthier harvest.
- No soil-based insects or pests, so no pesticides needed
Epiphytes
• Plants that attach to other plants
• Epiphytes usually derive only physical
support and not nutrition from their host,
though they may sometimes damage
the host. Hence, they are NOT parasitic
• They do this to get more light and rain
water in a rainforest canopy
Bromeliad
Orchid
Parasitic Plants
• Derive all or some nutrients from host
plant
• Parasitic plants have a modified root, the
haustorium, that penetrates the host plant
and connects to the xylem, phloem, or
both, in stems or roots of the host plant.
• Examples: Mistletoe, Dodder, Rafflesia
Parasitic Plants
Mistletoe
Japanese Dodder
Rafflesia
Carnivorous Plants
• Grow in nutrient poor soil such as bogs.
• High acidity in bogs prevents growth of muchneeded nitrogen cycle bacteria
• Most plants cannot grow in such soil
• Carnivorous plants evolved a mechanism to trap
and digest insects
• This adaptation helped them overcome the
nitrate dilemma
• Examples: Pitcher plants, sundews, Venus flytrap
Carnivorous Plants
Venus Flytrap
Sundews
Pitcher Plant
Plant and Fungal Symbiosis
• Fungal mycorrhizae penetrate plant
tissues
• The fungus derives nutrients from the
plant
• The plant gets: More water-absorbing
surface area, minerals that fungus
absorbs, antibiotics to prevent infections
(many fungi produce antibiotics)
• Ectomycorrhizae
– Hyphae form a mantle around roots
• Endomycorrhizae (arbuscular mycorrhizae)
– Hyphae are not visible
– Tiny vesicles called arbuscules are formed between root
cells
THE END