Transcript Unit XI: Plant Structure and Function

Chapters 35-39
All Plants…
• multicellular, eukaryotic, autotrophic, alternation of generations
Alternation of Generations
Sporophyte (diploid)
• produces haploid
spores via meiosis
Gametophyte (haploid)
• produce haploid
gametes via mitosis
Fertilization
• joins two gametes to
form a zygote
Angiosperms
Monocots vs. Dicots
• named for the number
of cotyledons present on
the embryo of the plant
+ monocots
- orchids, corn,
lilies, grasses
+ dicots
- roses, beans,
sunflowers, oaks
Plant Morphology
Morphology (body form)
• shoot and root systems
+ inhabit two environments
- shoot (aerial)
+ stems, leaves, flowers
- root (subterranean)
+ taproot, lateral roots
• vascular tissues
+ transport materials between
roots and shoots
- xylem/phloem
Plant Anatomy
Anatomy (internal structure)
• division of labor
+ cells differing in structure and function
- parenchyma, collenchyma, sclerenchyma (below)
- water- and food-conducting cells (next slide)
Parenchyma
St: “typical” plant cells
Fu: perform most metabolic functions
Collenchyma
St: unevenly thickened primary walls
Fu: provide support but allow growth
in young parts of plants
Sclerenchyma
St: hardened secondary walls
(LIGNIN)
Fu: specialized for support; dead
Plant cell types
Cell wall
Parenchyma cells
Collenchyma cells
Sclerenchyma cells
• Xylem
• Phloem
Plant cell types
WATER-CONDUCTING CELLS OF THE XYLEM
SUGAR-CONDUCTING CELLS OF THE PHLOEM
Sieve-tube members:
longitudinal view
Vessel Tracheids
Pits
Companion cell
Sieve-tube
member
Sieve
plate
Tracheids and vessels
Nucleus
Vessel
element
Tracheids
Cytoplasm
Companion
cell
Water- and Food-conducting
Cells
Xylem (water)
Phloem (food)
• dead at functional maturity
• tracheids- tapered with pits
• vessel elements- regular tubes
• alive at functional maturity
• sieve-tube members- arranged
end to end with sieve plates &
Companion cells
Plant Tissues
Three Tissue Systems
• dermal tissue
+ epidermis (skin)
- single layer of cells that
covers entire body
- waxy cuticle/root hairs
• vascular tissue
+ xylem and phloem
- transport and support
• ground tissue
+ mostly parenchyma
- occupies the space b/n
dermal/vascular tissue
- photosynthesis, storage,
support
Plant Growth
Meristems
• perpetually embryonic tissues located at regions of growth
+ divide to generate additional cells (initials and derivatives)
- apical meristems (primary growth- length)
+ located at tips of roots and shoots
- lateral meristems (secondary growth- girth)
Roots
• A root
– Is an organ that anchors the vascular plant
– Absorbs minerals and water
– Often stores organic nutrients
– Taproots found in dicots and gymnosperms
– Lateral roots (Branch roots off of the taproot)
– Fibrous root system in monocots (e.g. grass)
Modified Roots
• Many plants have modified roots
(a) Prop roots
(a) Prop roots
(d) Buttress roots
(b) Storage roots
(b) Storage roots
(c) “Strangling” aerial
roots
(e) Pneumatophores
Primary Growth of Roots
Primary Growth of Roots
• apical meristem
+ root cap
+ three overlapping zones
- cell division
- elongation
- maturation
Stems
• A stem is an organ consisting of
– Nodes (could be opposite or alternate)
– Internodes
Modified Stems
(a)
Stolons
Storage leaves
(d)
Rhizomes
Stem
Node
Root
Bulbs
(c)
Tubers
Rhizome
Root
Buds
• An axillary bud
– Is a structure that has the potential to form a lateral shoot, or
branch
• A terminal bud
– Is located near the shoot tip and causes elongation of a young
shoot
Gardening tip:
Removing the terminal bud
stimulates growth of
axillary buds
Primary Growth in Shoots
Primary Growth in Shoots
• apical meristem (1, 7)
+ cell division occurs
+ produces primary meristems
- protoderm (4, 8)
- procambium (3, 10)
- ground meristem (5, 9)
• axillary bud meristems
+ located at base of
leaf primordia
• leaf primordium (2, 6)
+ gives rise to leaves
The leaf
Is the main photosynthetic organ of most vascular plants
Leaves generally consist of
Blade
Stalk
Petiole
Leaf Morphology
• In classifying angiosperms
– Taxonomists may use leaf morphology as a criterion
(a) Simple leaf
Petiole
Axillary bud
(b) Compound leaf.
Leaflet
Petiole
Axillary bud
(c) Doubly
compound leaf.
Leaflet
Petiole
Axillary bud
Modified Leaves
Tendrils
Spines
Storage leaves
Bracts
Reproductive leaves. The leaves
of some succulents produce adventitious
plantlets, which fall off the leaf and
take root in the soil.
Leaf Anatomy
Epidermal Tissue
• upper/lower epidermis
• guard cells (stomata)
Ground Tissue
• mesophyll
+palisade/spongy
parenchyma
Vascular Tissue
• veins
+ xylem and phloem
Leaf Anatomy
Guard
cells
Key
to labels
Dermal
Ground
Stomatal pore
Vascular
Cuticle
Epidermal
cell
Sclerenchyma
fibers
50 µm
(b) Surface view of a spiderwort
(Tradescantia) leaf (LM)
Stoma
Upper
epidermis
Palisade
mesophyll
Bundlesheath
cell
Spongy
mesophyll
Lower
epidermis
Guard
cells
Cuticle
Vein
Xylem
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Vein
Air spaces
(c) Transverse section of a lilac
(Syringa) leaf (LM)
Guard cells
100 µm
The Three Tissue Systems:
Dermal, Vascular, and Ground
Dermal
tissue
Ground
tissue
Vascular
tissue
Dermal Tissue
–
•
•
•
Protects plant from:
Physical damage
Pathogens
H2O loss (Cuticle)
Vascular tissue
– Carries out long-distance transport of materials
between roots and shoots
– Consists of two tissues, xylem and phloem
Ground Tissue
– Includes various cells specialized for functions such as
storage, photosynthesis, and support
– Pith = ground tissue internal to the vascular tissue
– Cortex = ground tissue external to the vascular tissue
Secondary Growth
Lateral Meristems
• vascular cambium
+ produces secondary xylem/phloem (vascular tissue)
• cork cambium
+ produces tough, thick covering (replaces epidermis)
• secondary growth
+ occurs in all gymnosperms; most dicot angiosperms
The Vascular Cambium and Secondary Vascular Tissue
• The vascular cambium
– Is a cylinder of meristematic cells one cell thick
– Develops from parenchyma cells
2° Growth
• As a tree or woody shrub ages
– The older layers of secondary xylem, the
heartwood, no longer transport water and
minerals
• The outer layers, known as sapwood
– Still transport materials through the xylem
Cork Cambium
Periderm
• protective coat of
secondary plant body
+ cork cambium and
dead cork cells
- bark
• cork cambium produces
cork cells
CHAPTER 36
• A variety of physical processes
– Are involved in the different types of transport
4 Through stomata, leaves
take in CO2 and expel O2.
The CO2 provides carbon for
photosynthesis. Some O2
produced by photosynthesis
is used in cellular respiration.
CO2
O2
5 Sugars are produced by
photosynthesis in the leaves.
Light
H2O
Sugar
3
Transpiration, the loss of water
from leaves (mostly through
stomata), creates a force within
leaves that pulls xylem sap upward.
6 Sugars are transported as
phloem sap to roots and other
parts of the plant.
Water and minerals are
transported upward from
roots to shoots as xylem sap.
2
1
Roots absorb water
and dissolved minerals
from the soil.
O2
H2O
Minerals
CO2
7 Roots exchange gases
with the air spaces of soil,
taking in O2 and discharging
CO2. In cellular respiration,
O2 supports the breakdown
of sugars.
The Central Role of Proton Pumps
• Proton pumps in plant cells
– Create a hydrogen ion gradient
– Contribute to membrane potential
CYTOPLASM
ATP
–
–
–
EXTRACELLULAR FLUID
+
H+
+
H+
+ H+
H+
H+
H+
–
–
+
+
H+
H+
Proton pump generates
membrane potential
and H+ gradient.
• Plant cells use energy stored in the proton
gradient and membrane potential
– To drive the transport of many different cations
CYTOPLASM
+
–
EXTRACELLULAR FLUID
–
K+
K+
+
+
–
Cations ( K+, for
example) are driven
into the cell by the
membrane potential.
K+
K+
K+
K+
K+
–
+
–
+
(Membrane potential and cation uptake
Transport protein
Soil particle
–
K+
–
Cu2+
–
–
–
–
–
K+
–
–
K+
Ca2+
Mg2+
H+
H2O + CO2
H2CO3
HCO3– +
H+
Root hair
(b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients available by displacing positively charged minerals
(cations such as Ca2+) that were bound tightly to the surface of negatively charged
soil particles. Plants contribute H+ by secreting it from root hairs
and also by cellular respiration, which releases CO2 into the soil solution, where it reacts with H2O to form carbonic acid
(H2CO3). Dissociation of this acid adds H+ to the soil solution.
Figure 37.6b
• Cotransport
– A transport protein couples the passage of H+ to
anions
H+
–
+
–
+
–
+
H+
H+
H+
H+
H+
H+
H+
Cotransport of anions
–
+
–
+
–
+
H+
H+
H+
H+
Cell accumulates
anions ( NO3,–for
example) by
coupling their
transport to the
inward diffusion
of H+ through a
cotransporter.
• Cotransport
– Is also responsible for the uptake of sucrose by plant
cells
–
H+
H+
+
H+
H+
–
+
–
+
Plant cells can
also accumulate a
neutral solute,
such as sucrose
H+
H+
S
–+
H
H+
H+
–
–
+
+
H+
–
Contransport of a neutral solute
steep proton
gradient.
H+
S
+
( S ), by
cotransporting
H+ down the
H+
• Water potential
– Is a measurement that combines the effects of solute
concentration and pressure
– Determines the direction of movement of water
• Water
– Flows from regions of high water potential to regions
of low water potential
Quantitative Analysis of Water Potential
• The addition of solutes
– Reduces water potential
(a)
0.1 M
solution
Pure
water
H2O
• Negative pressure
– Decreases water potential
(d)
H2O
• Application of physical pressure
– Increases water potential
(b)
(c)
H2O
H2O
Aquaporin Proteins and Water
Transport
• Aquaporins
– Are transport proteins in the cell membrane that
allow the passage of water
– Do not affect water potential
Fluid Movement
Movement of fluid in the xylem &
phloem is driven by pressure
differences at opposite ends of the
xylem vessels and sieve tubes
• Water and minerals ascend from roots to shoots
through the xylem
• Plants lose an enormous amount of water
through transpiration, the loss of water vapor
from leaves and other aerial parts of the plant
• The transpired water must be replaced by water
transported up from the roots
Pushing Xylem Sap: Root Pressure
• At night, when transpiration is very low
– Root cells continue pumping mineral ions into the
xylem of the vascular cylinder, lowering the water
potential
• Water flows in from the root cortex
– Generating root pressure
• Root pressure sometimes results in guttation
Transpiration produces negative pressure
(tension) in the leaf
Which exerts a pulling force on water in the
xylem, pulling water into the leaf
The transpirational pull on xylem sap
Is transmitted all the way from the leaves to the
root tips and even into the soil solution
Is facilitated by cohesion and adhesion
• The stomata of xerophytes
– Are concentrated on the lower leaf surface
– Are often located in depressions that shelter the
pores from the dry wind
Cuticle
Upper epidermal tissue
Lower epidermal
tissue
Trichomes
(“hairs”)
Stomata
100 m
Translocation through Phloem
Translocation
Is the transport of organic nutrients in the plant
Phloem sap
Is an aqueous solution that is mostly sucrose
Travels from a sugar source to a sugar sink
Sugar Source & Sink
A sugar source
Is a plant organ that is a net producer of sugar,
such as mature leaves
A sugar sink
Is an organ that is a net consumer or storer of
sugar, such as a tuber or bulb
Transpiration
Lab
Control of Transpiration
Photosynthesis-Transpiration
Compromise
• guard cells help balance plant’s
need to conserve water with its
requirement for photosynthesis
Stomatal closing
• 1. Potassium ions move out of the vacuole and out of the cells.
• 2. Water moves out of the vacuoles, following potassium ions.
• 3. The guard cells shrink in size.
• 4. The stoma closes.
Stomatal opening
1. Potassium ions move into the vacuoles.
2. Water moves into the vacuoles, following potassium ions.
3. The guard cells expand.
4. The stoma opens.
• Chapter 37
Plant nutrition
Plant Nutrition
What does a plant need to
survive?
• 9 macronutrients, 8 micronutrients
+ macro- required in large quantities
- C, H, N, O, P, S, K, Ca, Mg
+ micro- required in small quantities
- Fe, Cl, Cu, Mn, Zn, Mo, B, Ni
+ usually serve as cofactors
of enzymatic reactions
• The most common deficiencies
– Are those of nitrogen, potassium, and phosphorus
Healthy
Phosphate-deficient
Potassium-deficient
Nitrogen-deficient
• Remove only one
macronutrient to
see effects on
plant
Soil
Texture and Composition
• texture depends on size of particles
+ sand-silt-clay
- loams: equal amounts of sand,
silt, clay
• composition
+ horizons
- living organic matter
- A horizon: topsoil, living
organisms, humus
- B horizon: less organic, less
weathering than A horizon
- C Horizon: “parent” material
for upper layers
• soil conservation issues
+ fertilizers, irrigation, erosion
• A mixture of mineral particles, decaying
organic material, living organisms, air, and
water, which together support the growth of
plants
Soil Bacteria and Nitrogen Availability
• Nitrogen-fixing bacteria convert atmospheric N2
– plants absorb ammonium (NH4+), nitrate (NO3-)
Atmosphere
N2
N2
Atmosphere
Soil
N2
Nitrogen-fixing
bacteria
Denitrifying
bacteria
H+
(From soil)
Soil
NH4
NH3
(ammonia)
+
–
+
NH4
(ammonium)
Organic
material (humus)
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
Nitrifying
bacteria
NO3
(nitrate)
Ammonifying
bacteria
Root
Nutritional Adaptations
Symbiotic Relationships
• symbiotic nitrogen fixation
+ Legume root nodules contain bacteroids (Rhizobium bacteria)
- mutualistic relationship
- Crop rotation (Legumes
• mycorrhizae
+ symbiotic associations of fungi and roots
- mutualistic relationship
• parasitic plants
+ plants that supplement their nutrition from host
- mistletoe, dodder plant, Indian pipe
• carnivorous plants
+ supplement nutrition by digesting animals
Mycorrhizae and Plant Nutrition
• Mycorrhizae
– Are modified roots consisting of mutualistic
associations of fungi and roots
• The fungus
– Benefits from a steady supply of sugar donated
by the host plant
• In return, the fungus
– Increases the surface area of water uptake and
mineral absorption and supplies water and
minerals to the host plant
• Unusual nutritional adaptations in plants
EPIPHYTES
Staghorn fern, an epiphyte
PARASITIC PLANTS
Host’s phloem
Dodder
Haustoria
Mistletoe, a photosynthetic parasite
Dodder, a nonphotosynthetic
parasite
Indian pipe, a nonphotosynthetic parasite
CARNIVOROUS PLANTS
Venus’ flytrap
Pitcher plants
Sundews
Phytoremediation
• Poplars remove nitrates
• Mustard removes uranium
Pesticide Levels (ppb) in
Ground Water Before & After Phytoremediation Activities
Wetlands
Uptake of Soil Solution
Symplastic Route
• continuum of cytosol based
on plasmodesmata
Apoplastic Route
• continuum of cell walls and
extracellular spaces
Lateral transport of soil
solution alternates between
apoplastic and symplastic
routes until it reaches the
Casparian strip
Casparian Strip
A belt of suberin (purple) that blocks the passage of water and
dissolved minerals.
Chapter 38
PLANT REPRODUCTION
Plant Reproduction
Sporophyte (diploid)
• produces haploid
spores via meiosis
Gametophyte (haploid)
• produce haploid
gametes via mitosis
Fertilization
• joins two gametes to
form a zygote
• An overview of angiosperm reproduction
Stigma
Anther
Stamen
Carpel
Germinated pollen grain
(n) (male gametophyte)
on stigma of carpel
Anther at
tip of stamen
Style
Filament
Ovary (base of carpel)
Ovary
Pollen tube
Ovule
Embryo sac (n)
(female gametophyte)
Sepal
Egg (n)
FERTILIZATION
Petal
Receptacle
Sperm (n)
Mature sporophyte
Seed
plant (2n) with
(develops
flowers
from ovule)
(a) An idealized flower.
Key
Zygote
(2n)
Seed
Haploid (n)
Diploid (2n)
(b) Simplified angiosperm life cycle.
See Figure 30.10 for a more detailed
version of the life cycle, including meiosis.
Germinating
seed
Embryo (2n)
(sporophyte)
Simple fruit
(develops from ovary)
Mechanisms That Prevent SelfFertilization
Stigma
Stigma
Pin flower
Thrum flower
Anther
with
pollen
The most common anti-selfing mechanism in flowering plants
Is known as self-incompatibility, the ability of a plant to reject its own pollen
Preventative Selfing
• Some plants
– Reject pollen that has an S-gene matching an
allele in the stigma cells
• Recognition of self pollen
– Triggers a signal transduction pathway leading
to a block in growth of a pollen tube
Double Fertilization
Double Fertilization
• pollen grain lands on stigma
+ pollen tube toward ovule
+ both sperm discharged down the tube
- egg and one of the sperm
produce zygote
- 2 polar nuclei and sperm
cell produce endosperm
+ ovule becomes the seed coat
+ ovary becomes the fruit
Seed Structure and Development
• The radicle
– Is the first organ to emerge from the germinating seed
• In many eudicots
– A hook forms in the hypocotyl, and growth pushes the
hook above ground
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
• Monocots
– Use a different method for breaking ground when they
germinate
• The coleoptile
– Pushes upward through the soil and into the air
Foliage leaves
Coleoptile
Coleoptile
Radicle
Chapter 39
PLANT RESPONSES TO
INTERNAL AND EXTERNAL
SIGNALS
Tropisms
• Growth toward or away from a stimulus
• Gravitropism (Gravity)
• Phototropism (Light)
• Thigmotropism (Touch)
Etiolation
• The stems of plants raised in the dark
elongate much more rapidly than normal, a
phenomenon called etiolation.
Signal Transduction Pathway
CELL
WALL
1 Reception
CYTOPLASM
2 Transduction
Relay molecules
Receptor
Hormone or
environmental
stimulus
Plasma membrane
Figure 39.3
3 Response
Activation
of cellular
responses
Plant hormones help coordinate growth, development,
and responses to stimuli
• Hormones
– Are chemical signals that coordinate the different parts of
an organism
Photoperiod, the relative lengths of night and day
+ Is the environmental stimulus plants use most often to detect the
time of year