Transcript plants 2014 in class

• Introduction
• More than 280,000 species of plants
inhabit Earth today.
• Most plants live in terrestrial environments,
including deserts, grasslands, and forests.
– Some species, such as sea grasses, have
returned to aquatic habitats.
• Land plants (including the sea grasses) are
believed to have evolved from a certain
green algae, called charophyceans.
Remember the Big 4 events in Plant evolution
• Bryophytes, pteridiophytes, gymnosperms,
ands angiosperms demonstrate four great
episodes in the evolution of land plants:
– the origin of bryophytes from algal ancestors
– the origin and diversification of vascular plants
– the origin of seeds
– the evolution of flowers
Plant Structure & Organization
• Cells make tissues, tissues make organs,
organs make systems, systems make organisms
• 5 Basic plant cell types
– Parenchymal cells
– Collenchymal cells
– Sclerenchymal cells
– Xylem cells
– Phloem cells
3 Cell types that make up all plant tissue
• Parenchyma – perform most of metabolism (including
photosynthesis)
– Present throughout the plant
• Collenchyma – help support growing parts of plants
– Grouped in cylinders
• Schlerenchyma – support in parts that are no longer
growing
– Have tough cell walls
– 2 types just for support
• Fibers
• Scleroids
Plants have tissues:
A.) Dermal tissue
B.) Ground Tissue
C.) Vascular tissue
D.) Meristem =
embryonic tissue
3 tissue types that make up all plant organs
• Dermal – single layer, closely packed, cover and
protect the entire plant (epidermis and periderm)
• Vascular – continuous throughout the plant
– Transport tissue
– 2 types
• Xylem – moves water and minerals up (from roots)
– Made of tracheids and vessel elements (dead cells)
• Phloem - moves “food” down (from leaves)
– Made of sieve tube members
• Ground – anything that isn’t dermal or vascular (fills
and stores)
– Pith – inside the ring of the ground tissue
– Cortex – Outside the ring of the ground tissue
Parts of a Plant - Shoots and Roots
• Shoots (above ground: stems & leaves)
– Produce food by photosynthesis
– Carry out reproductive functions
• Roots (below ground)
– Anchor the plant
– Penetrate the soil and absorb water and dissolved minerals
– Store food
• Roots, stems & leaves are all considered plant organs
– We are going to look at these organs next
Angiosperm
Body Plan
• Ground tissue
system
• Vascular tissue
system
• Dermal tissue
system
Figure 29.2
Page 506
EPIDERMIS
VASCULAR TISSUES
GROUND TISSUES
SHOOT SYSTEM
ROOT SYSTEM
Internal Anatomy : Stems
• Vascular bundles (xylem and phloem)
• Surrounded by ground tissue (xylem faces pith and phloem
faces cortex)
• Mostly parenchyma; some collenchyma and sclerenchyma for
support
•
Leaf Structure:
Internal Anatomy :
Leaf Structure
UPPER
EPIDERMIS
cuticle
PALISADE
MESOPHYLL
xylem
SPONGY
MESOPHYLL
phloem
LOWER
EPIDERMIS
O2
&
H20
Guard cell
CO2
one stoma
Figure 29.16
Page 513
Adapted for Photosynthesis
• Leaves are usually thin
– High surface area-to-volume ratio
– Promotes diffusion of carbon dioxide in, oxygen
out
• Leaves are arranged to capture sunlight
– Are held perpendicular to rays of sun
– Arranged so they don’t shade one another
Mesophyll:
Photosynthetic Tissue
• A type of parenchyma tissue
• Cells have chloroplasts
• Two layers in dicots
– Palisade mesophyll - most photosynthesis
takes place here
– Spongy mesophyll - gas circulation
• One layer in monocots
Leaf Veins: Vascular Bundles
• Xylem and phloem; often
strengthened with fibers
• In dicots, veins are netlike
• In monocots, they are parallel
•
Root Systems
2 types of root systems
1. fibrous – mat of thin roots just below soil surface
2. taproot – 1 thick vertical root with many lateral
roots extending from it
Figure 29.17
Page 514
Taproot system
Fibrous root system
Internal Anatomy:
Roots
-Outermost layer is epidermis
-Root cortex is beneath the epidermis
-Endodermis, then pericycle surround the
vascular cylinder (this is called the Casparian
Strip)
-the inner part called the stele contains the
vascular tissue (xylem & phloem)
•
Root Hairs and Lateral Roots
• Both increase the surface area of a
root system and help in absorption
new
lateral
root
• Root hairs are tiny extensions of
epidermal cells
• Lateral roots arise from the
pericycle and must push through
the cortex and epidermis to reach
the soil
Figure 29.19
Page 515
•
Root Hairs
Increase surface area for absorption
Flower
Structure
STAMEN
(male reproductive part)
filament
anther
CARPEL or pistil
(female reproductive part)
stigma
style
ovary
• Nonfertile parts
– Sepals
– Receptacle
• Fertile parts
OVULE
(forms
within
ovary)
petal (all petals
combined are the
flower’s corolla)
– Male stamens
– Female carpel
(ovary)
sepal (all sepals
combined are the
flower’s calyx)
receptacle
Figure 31.3
Page 538
•
•
Two major groups (classes) of angiosperms
Kinds of Flowers
• Perfect flowers
– Have both male and female parts
• Imperfect flowers
– Are either male or female
– Same plant may have both male and female flowers
– Sexes may be on separate plants
Kinds ofPlants
– dioecious
– Have both male and female parts
– monoecious
– Sexes on separate plants
Plant Growth: Meristems
• Regions where cell divisions produce plant growth
• Apical meristems – located at ends (roots and shoots)
– Lengthen stems and roots
– Responsible for primary growth
• Lateral meristems
– Increase width of stems
– Responsible for secondary growth (thickening of roots and
shoots)
– 2 types
• Vascular cambium
• Cork cambium
Plant growth: perpetual meristems
• Primary growth
–
–
–
–
From tips of root
From tips of shoots
Growth in length
Growth in to the
environment
– Pattern can reflect
environmental pressures
– Pericycle and auxiallary
• Provide branching
• Secondary growth
–
–
–
–
Growth in width
Not all plants have
Monocots lack
Comes from division of:
• Cork cambium
• Vascular cambium
– Produces structural
strength
• Two lateral meristems
• vascular cambium ~
produces secondary xylem
(wood) and secondary
phloem (diameter increase;
annual growth rings)
• cork cambium ~
produces thick covering
that replaces the epidermis;
produces cork cells; cork plus
cork cambium make up the
periderm; lenticels (split
regions of periderm) allow for
gas exchange; bark~ all
tissues external to vascular
cambium (phloem plus
periderm)
Secondary Growth
Major Meristems
•
3 growth zones
• Zone of:
– Cell division –
includes the
meristems, rapid cell
division, new growth
– Elongation – cells
elongate
– Maturation – cell
differentiation
occurs and cells
become fuctionally
mature
Tissue Differentiation – three primary
meristematic tissues
•Cells descended from apical meristem divide, grow
and differentiate to form shoot’s primary tissue system
Protoderm
Epidermis
Ground meristem
Ground tissue
Procambium
Primary vascular tissue
•From lateral meristems
Vascular cambium
Secondary vascular tissue
Cork cambium
Periderm & cork
•
Stem growth summary
•
Plant Transport
3 types
1. Uptake and loss of water and minerals from individual cells
• Occurs through:
– Osmosis – diffusion of water through the membrane
– Water potential – the combined effect of solute
concentration and cell wall pressure (remember,
turgor pressure is the pressure against the cell wall
from water)
– Aquaporins – channels in plant cell walls designed for
passage of water
– Tonoplasts – surround the vacuoles to regulate
molecules going in and out of the vacuoles
2. Transport of substances short distances
(from cell to cell)
•
Is accomplished by:
•
•
•
Symplasts – cytoplasm connections between cells
through plasmodesmata
Apoplasts – nonliving continuum that is formed by
extracellular pathways through the continuous matrix
of cell walls
Water flows through both symplasts and
apoplasts
•
3 major compartments
and lateral transport!
Apoplast- between cell walls
between cells of the cortex
Symplast- inside cells and
thru plasmodesmata
•
3.
Transport of sap within xylem and phloem (throughout the
entire plant)
A. Absorption of water and minerals by roots
• Usually near root tips in root hairs
• Mycorrhizae – symbiosis between roots and fungi
• Helps roots absorb water and minerals
• Water and minerals in root cortex must pass through
endodermis to enter the stele and get to the xylem to be
transported to the rest of the plant
• Endodermis contains the “Casparian strip” which
prevents subtances from going around or between the
cells, therefore the water and minerals must pass
through the endodermal cell to get into the vascular
tissue
Casparian Strip
• Prevents water and solutes
from passing between
cells into vascular cylinder
exodermis
root hair
epidermis
forming
vascular
cylinder
• Water and solutes must
flow through cells
cortex
• Transport proteins control
the flow
Casparian
strip
• Allows plants to adjust the
quantity and types of
solutes absorbed from soil
water
Figure 30.4
Page 526
3.
Transport of sap within xylem and phloem (throughout the
entire plant), continued
B. Transport within the Xylem
-Water is “pulled” through the plant in two ways
• Root pressure – water flows into the roots cause
positive pressure that forces the liquid up through the
xylem
• Cohesion-Tension mechanism – water lost through the
leaves creates a negative pressure which draws water
up through the xylem with the help of
adhesion/cohesion
- Transpiration – loss of water from leaves and other
parts of plants in contact with air
-especially through open stomata
-plants have guard cells around stomata that
open and close them to help control water loss
Transpiration-Cohesion-Tension
Theory of how water moves UP
xylem
•
Factors in water movement up the stem by
bulk transport
1.Transpiration evaporation of water from the leaf.
2.Cohesion water molecules stick together by
hydrogen bonding because they are polar.
3. Tension is the pull as water molecule go to vapor
because there is less water in the air.
(Note: structure of xylem and how its function is related, how
important xylem is to life on land both for support and transport,
don’t forget lignin.)
Xylem
• Conducts water and
dissolved minerals
• Conducting cells are
dead at maturity
• hollow at maturity
tracheids
Figure 29.8
Page 509
vessel
member
•
•
Xylem! Cells Stacked!!
Vascular Tissue
Root pressure is a PUSH!
As solutes accumulate in xylem
and water transpiration has stopped
water continues to move in to dilute.
Guttation is evidence
•
Guttation pushes water out of the tips of xylem-root pressure
Control of Stomata
• When stomata are opened; the cells have a high solute content
causing water to move in building up turgor pressure (the cells
swell opened)
• Close in response to water loss; ABA (abscisic acid - hormone)
binds to receptors on guard cell membranes
– calcium ions flow in and open gates for other solutes
(chloride, potassium and malate) to flow out from cytoplasm
to extracellular matrix
• This causes a change in gradients and water moves out of guard
cells, they collapse and close
•
•
How are things transported in the
phloem?
Mass flow theory.
From source to sink.
Sucrose is the sugar transported.
3.
Transport of sap within xylem and phloem (throughout the
entire plant), continued
C. Translocation of Phloem sap
-Phloem transports “food” from photosynthesis
(usually in leaves) to the rest of the plant
-sieve tubes carry food from the source (where it is
made) to the sink (the place that needs the food or
where food is stored)
-mainly a result of bulk flow
•
Phloem: cells stacked!!
Phloem:
A Complex Vascular Tissue
sieve plate
• Transports sugars
• Main conducting
cells are sieve-tube
members
• Companion cells
assist in the loading
of sugars
sieve-tube
member
companion
cell
Figure 29.8
Page 509
Transport through Phloem
• Driven by pressure gradients
• Fluid pressure is greatest at a source
• Solute-rich fluid flows away from the high-pressure
region toward regions of lower pressure
• Sink - Region where compounds are being stored or
used (ex. roots)
• Solutes are unloaded into sink cells and water follows
• Called pressure flow theory or mass flow theory
•
Sucrose Loading in Phloem
•
Plant Nutrition
• Require carbon dioxide, water, nitrogen,
minerals
– Macronutrients – needed in large amounts
• 9 of them: C, H, O, N, S, P, K, Ca & Mg
– Micronutrients – needed in small amounts
• @ least 8: Cl, Fe, B, Mn, Zn, Cu, Md, Ni
– Essential nutrients – needed for completion of
life-cycle
Nitrogen
• Nitrogen must be in certain forms for the plants to
be able to absorb and use it.
• Nitrogen fixing bacteria convert nitrogen to its
useable form. It can do this in the soil.
– nitrogen gas (N2) to forms that plants can use (ammonium
and nitrate)
• Sometimes, nodules on roots – swelling where there
is a symbiosis (mutualism) between the plant cells
and the nitrogen fixing bacteria
•
Mycorrhizae
• Symbiosis between a young plant root
and a fungus
• Fungal filaments may cover root or
penetrate it
• Fungus absorbs sugars and nitrogen
from the plant
• Roots obtain minerals absorbed from
soil by fungus
Nutritional Adaptations
• Parasitic plants – rely on other plants for
nutrients
• Epiphytes – not parasitic, just grow on the
surface of other plants
• Carnivorous plants – can “trap” and “digest”
small animals for supplemental nutrition
Moss Reproduction
• At the tip of a male gametophyte are antheridia, in which
swimming sperm are produced. After rain or heavy dew, the
sperm swim to the tip of a female gametophyte, where eggs have
been produced within the archegonia. After an egg is fertilized,
the developing sporophyte is retained within the archegonium as
an embryo. The sporophyte is dependent on the gametophyte and
it consists of a foot, a stalk, and an upper capsule (or sporangium)
where meiosis occurs and where haploid spores are produced.
When a spore is released and lands on an appropriate site, it
germinates into the upright shoots of a moss gametophyte. The
gametophytes produce gametes, and the moss life cycle begins
again.
• See diagram on next slide
Conifer Reproduction
• Typically, male pine cones are quite small and develop near the tips
of lower branches. Inside each scale of the male cone pollen is
produced, which is a sperm-bearing male gametophyte. The
female pine cones are larger and located near the top of the tree.
In each scale of the female cone ovules contain the female
gametophytes (archegonia) which contain the eggs. Pollen grains
are transferred from the male cone to the female cone. Once
enclosed within the female cone, the pollen grain develops a
pollen tube that slowly grows toward the ovule. The pollen tube
discharges two nonflagellated sperms. Only one of the sperms
fertilizes an egg in the ovule 15 months after pollination. After
fertilization, the ovule matures and becomes the seed composed
of the embryo, its stored food, and a seed coat. Finally, in the third
season, the female cone, by now woody and hard, opens to release
its seeds. When a seed germinates, the sporophyte embryo
develops into a new pine tree, and the cycle is complete.
Steps of Angiosperm Reproduction:
• Meiosis produces heterospores which produce
gametophyte stages:pollen/embryo sac
• Pollination: cross/self and wind water and animal
• Formation of mature Gametophytes:
– Male = pollen tube + 2sperm (no flagella)
– Female = embryo sac 8 nuclei
• Fertilization: double
• Production of embryo/seed and fruit together
– Embryonic development of plant (young sporophyte)
• Dispersal and dormancy
• Germination of seed:
Angiosperm Reproduction :
Pollination
• In angiosperms, the reproductive structures
are located in the flower. The flower attracts
insects and birds that aid in pollination, and it
produces seeds enclosed by fruit. There are
many different types of fruits, some of which
are fleshy (e.g., apple, tomato, peach, ...) and
some of which are dry (e.g., pea enclosed by
pod, nut, grain, ...).
Pollen Formation
pollen sac
• Sperm packed inside a
nutritious package
• Each anther has four
pollen sacs
• Inside pollen sacs, cells
undergo meiosis and
cytoplasmic division to
form microspores
• Microspores undergo
mitosis to form pollen
grains
anther
filament
microspore
mother cell
Meiosis
Diploid Stage
Haploid Stage
microspores
Figure 31.6
pollen grain
pollen tube
sperm nuclei
mature male
gametophyte
Page 540
stigma
style of carpel
Egg Formation
• The mother cell divides by meiosis to produce 4
haploid megaspores.
• Three of these 4 megaspores disintegrate.
• The fourth megaspore undergoes 3 cycles of mitosis
to produce the female gametophyte, consisting of 7
cells with a total of 8 haploid nuclei. The central cell
contains 2 polar nuclei.
• Three cells are found at each end of the large central
cell of the ovule. The middle cell located near the
micropyle, a small opening in the ovule, is the egg
cell.
•
• When pollen lands on a stigma it germinates producing a pollen tube
which delivers 2 sperm nuclei to the ovule.
• Double fertilization takes place to produce seeds and fruits. One sperm
nucleus from the pollen tube unites with the egg nucleus, forming a
diploid (2n) zygote, and the other sperm nucleus unites with the 2 polar
nuclei, forming a triploid (3N) endosperm nucleus.
• The endosperm nucleus divides, forming the endosperm, which is a
nutrient material for the developing embryo and sometimes for the young
seedling as well.
• The zygote develops into an embryo.
• The outer layers (integuments) of the ovule harden and become the seed
coat.
• A seed is a structure formed by the maturation of the ovule; it contains a
sporophyte embryo plus stored food (the endopserm).
• The ovary and sometimes other floral parts develop into the fruit. A fruit
is a mature ovary that usually contains seeds. Therefore, angiosperms are
said to have covered seeds.
• The result is a seed - composed of the seed coat, nutritive endosperm
(cotyledon), and embryo.
•
Seeds and Fruits
• The seed is the mature ovule
• The fruit is the mature ovary
•
Structure of a Seed
• Protective seed coat is derived from integuments
that enclosed the ovule
• Nutritious endosperm is food reserve
• Embryo has one or two cotyledons
– Monocot has one
– Dicot has two
• When the seed matures it goes dormant (slows
metabolism) until conditions are right and then it
will resume growth (germination)
Seed Germination
• Process by which the plant embryo resumes growth after seed
dispersal
• Depends upon environmental factors
– Temperature
– Soil moisture
– Oxygen levels
Splitting the Seed Coat
• Imbibition
– Water molecules move into a seed
• As water moves in, the seed swells and the coat ruptures
Stages of germination of dormant seed
•
Imbibition-hormone signaling-response enzyme to release
sugar- energy for metabolism and growth of embryo
Two Types of Angiosperms:
Monocots and Dicots
The term cotyledon actually means
seed leaf. So…
•In monocot seeds there is 1 leaf.
•In dicot seeds there are 2 leaves.
•See following slides.
Nourishing the Embryo
• Dicot embryo
– Absorbs nutrients from endosperm
– Stores them in its two cotyledons
• Monocot embryo
– Digestive enzymes are stockpiled in the single
cotyledon
– Enzymes do not tap into the endosperm until the
seed germinates
Key things about seeds!
•
•
•
•
Dormancy
Dispersal
It’s the young sporophyte!
What does it contain?
– Protective coat
– Food
– Young embryo sporophyte plant
Asexual Reproduction - apomixis
• New roots or shoots grow from extensions or
fragments of existing plants
• Proceeds by way of mitosis
• All offspring are genetically identical (unless
mutation occurs)
• Sometimes called vegetative reproduction by
fragmentation
Comparison of Monocot, Dicot and
Gymnosperms
Characteristic
Embryo
Dicots
Monocots
Two cotyledons (seed One cotyledon (seed
leaves)
leaf)
Gymnosperms
One to many
Flowers
Parts in 4 / 5
Parts in 3x
No true flower
Vascular Bundles
Ring
Scattered
Ring
Roots
Herbaceous or
Woody
Taproot
Fibrous
Herbaceous or
Woody
Taproot
Leaf Venation
Net
Parallel
Needle-like
Pollen
Tricoplate (3 furrows
or pores)
Monocoplate (1
furrow or pore)
Tow lobular wings
Growth
Primary and
Secondary
Primary
Primary and
Secondary
Habit
Herbaceous
Control of Development
• Inheritable, internal mechanisms govern plant
development
• Environmental cues turn such mechanisms on
or off at different times, in different seasons
• Hormones are chemical signals that
coordinate parts of an organism
Plant Hormones:
(chemical messengers)
• Not like Animal hormones:
– Do not control homeostasis
– Not produced in glands
– Not transported by blood
• Like Animal hormones:
– Do have specific receptors in target cells
– Only minute amount needed
Plant Hormones
•
•
•
•
•
Gibberellins
Auxins
Cytokinins
Abscisic Acid
Ethylene
Gibberellin
• Found in meristems of apical buds and roots, young
leaves and embryos
• In nature, gibberellin functions to:
– Helps seeds and buds break dormancy (germination)
– Makes stems lengthen
– Influences leaf growth, flowering and fruit development
– Influence root growth and differentiation
– growth
• Applied by growers to enhance stem length, control
ripening
Auxins
• Found in seed embryo, meristems of apical buds and
young leaves
• Promote stem lengthening, root
growth/differentiation/branching, fruit development
• Play a role in responses to gravity and light (tropisms)
• Indoleacetic acid (IAA) is the most common auxin in
nature
• Certain synthetic auxins are used as herbicides
Cytokinins
• Found in roots (and actively growing tissue)
• Promote cell division, root growth/differentiation,
germination, delay senescence (aging)
• Most abundant in root and shoot meristems and in maturing
fruits
• In mature plants, produced in roots and transported to shoots
• Used to artificially extend the shelf life of cut flowers; delays
leaf death
Abscisic Acid (ABA)
• Found in leaves, stems, roots and green fruit
• Causes the suspension of growth; promotes dormancy of
buds and seeds
• Used to induce dormancy in plants to be shipped
• Inhibits growth, closes stomata during stress, counteracts the
breaking of dormancy
• Also plays a role in drought response
Ethylene
• Found in ripening fruit, stems nodes and aging leaves
and flowers
• Induces aging responses (ex. ripens fruit )
• Unlike other plant hormones, ethylene is a gas
• Used to ripen fruits for market
Control of Abscission
• Abscission
– Dropping of flowers, fruits, or leaves
• What brings it about?
– Auxin production declines
– Cells in abscission zone produce ethylene
– Enzymes digest cell walls that attach leaf or fruit
to plant
Biological Clocks
• Internal timing mechanisms
– Trigger shifts in daily activity
– Help induce seasonal adjustments
• Phytochrome is part of the switching mechanism
– Blue-green plant pigment, measure length of darkness in
a photoperiod (red light)
Photoperiodism
•Plants biological response to change in relative lengths
of daylight and darkness
•Types of plants in terms of flowering
•Long day – flower when days are long
•Short day – flower when days are short,
•Day neutral – flower when mature, independent of
light amount
Circadian Rhythm
•24 hour periodicity
What is vernalization?
Period of cold required before a seed will germinate.
Why would this be a selective advantage?
Senescence
• Sum total of processes that lead to death of
a plant or some of its parts
• Factors that influence senescence:
– Decrease in daylight is recurring factor
– Wounds, drought, or nutritional deficiencies can
also bring it about
Dormancy
• A predictable period of metabolic inactivity
• Short days; long, cool nights trigger dormancy
– Experiments have shown that exposure to light
blocks dormancy
– Demonstrates involvement of phytochrome
Plant Tropisms
• Adjustment of plant growth toward or away
from an environmental stimulus
• Phototropism - stimulus is light
• Gravitropism - stimulus is gravity
• Thigmotropism - stimulus is contact with an
object
Phototropism
• Change in growth in response to light
• Controlled by the flow of auxin produced in
the plant tip
Figure 32.10
Page 557
Gravitropism
• Roots tend to grow toward pull of gravity; shoots
grow against it
• Gravitational field is sensed via position of statoliths
(a type of amyloplast – a type of plastid)
• Auxin is involved in response; causes asymmetric cell
elongation
Thigmotropism
• Growth in response to contact with a solid
object
• Allows vines and tendrils to wrap around
supports
• Cells on contact side elongate, causing stem to
curl
• Auxin and ethylene may be involved
Thigmotropism
Mimosa
Closed
•
Ways plants protect
against pathogens:
• Thick epidermis and cork layer with wax,
suberin and cutin.
• Seal off the infected area: make a gall
• Deposit more polysaccharides in the cell wall
to seal off the plasmodesmata
• Produce defensive chemicals:
– Phytoalexin
– Pathogen related proteins (PR)