Transcript Plant Form and Function Introx

Simple Tissues – consisting of one cell type
• Parenchyma – thin walled & alive at maturity;
often multifaceted.
• Collenchyma – thick walled & alive at maturity
• Sclerenchyma – thick walled and dead at maturity
– Sclerids or stone cells – cells as long as they are wide
– Fibers – cells longer than they are wide
• Epidermis – alive at maturity
– Trichomes – “pubescence” or hairs on epidermis
– Root Hairs – tubular extensions of epidermal cells
Parenchyma
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All other plant cells are evolved from these.
Alive when functional.
Thin walls.
Caused to divide, usually as a result of injury.
Cells that are often the site of storage, starch.
Sites of photosynthesis.
Involved in short distance movement of water
and nutrients.
• Originate from root apical meristem.
Collenchyma
• Alive when functional.
• Derived from parenchyma.
• Walls are variously thickened compared to
parachyma.
• Function is to support. Strands in petiole.
• Elongate stems and leaves in the petiole.
• Celery: strands are collenchyma.
Schlerenchyma
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Scheloros: greek for hard.
Derived from parenchyma.
Alive or dead when functional.
Cells compromising schlerenchyma have hard
walls.
• Walls made hard by deposition of lignin.
• Function in support and protection.
• Lignin: broken into two types.
– Fiber
– Schlerids
Fiber
• Elongated fibers which
overlap each other to
form bundles.
• Linum
• Luffa
• Rope
Schlerids
• Also known as stone
cells.
• Small, often round.
• Function in protection.
• Peach pit, walnut.
• Pear, gritty due to
schlerids.
• Fig Newtons.
• Reduce insect ingestion.
Vascular Tissue
• Consists of several cell types.
• Transport
• Two main types
– Xylem: water movement.
– Phloem: Nutrient movement.
Xylem
• Dead when functional.
• Consists of two types of transport cells.
– Traceids
– Vessels.
Tracheids
• Found in gymnosperms and angiosperms.
• Elongated like a fiber, tapering with
overlapping end walls.
• Closed where they overlap, with
communication through pits (Small holes)
Vessels
• Found only in angiosperms.
• Short, wide cells with open end walls.
• Stacked on top of one another.
Phloem
• Principal cell type is the sieve element.
Sieve Element
• Alive when functional.
• Sieve elements stack on top of one another to
form a sieve tube.
Formation of a Sieve Element
Root Structure and Development
• Root functions:
– Support/Anchorage
– Storage of nutrients (most often starch)
– Site of absorption of water and nutrients
– Establish symbiotic relationships between root
and soil microorganisms.
Types of Roots
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Prop Roots
Storage Roots
Pneumatophores
Strangling/Aerial Roots
Buttress Roots
Prop Roots
Storage Roots
Pneumatophores
Strangling/Aerial Roots
Buttress Roots
Development of a root
• When a seedling germinates, 1st root that is
formed is called primary root (Taproot)
• In eudicots, taproot goes straight down and
becomes elongated.
• In monocots, taproot is short lived, it is replaced
by roots forming on the stem.
• Monocots, root system is a shallow fibrous
network of fibers.
• Allows roots to hold top of soil together. (Very
Important Function)
Root system vs Shoot system
• In seedlings, the root system is much larger
that the shoot system. As it grows it comes to
a ratio close to 1:1 of vegetative mass of root
and shoot.
Root Cap
• Functions to protect meristem as it grows
through soil.
– Secretes a lubricant (slime) which allows it to
move through the soil easier
– Site of perception of gravity.
Dicot vs Monocot
• Dicot (like trees, etc) - broad leaves, has a tap
root (like the root of a carrot), conspicuous
(obvious) flowers and a network of leaf veins.
• Monocot (Grasses) – narrow leaves, a network
of very fine roots, not obvious flowers, parallel
veins.
Dicot Root vs Monocot Root
Statocytes
• Amyloplasts
• Aid in perception for
change in direction.
• Similar to a statocyst.
• As it moves the
statocytes shift due to
gravity.
Shoot System/Primary Structure
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Comprised of the stem, leaf, flower, and fruit.
Stem: Comprised of nodes and internodes.
Leaf: Comprised of blade and petiole.
Flower: Reproductive Structure.
Fruit: Part of the flowering plant that derived
from specific tissues of the flower, mainly one of
more of the ovaries.
• *All primary tissues are derived from apical
meristem. Can be traced back to mitotic events
in apical meristem.
Stem
Leaf
Shoot Apical Meristem (SAM)
• Zone at top of plant where all activities go on
to activate all primary tissues.
• Always elongating/growth.
• (A) Apical Dome, apical meristem
• (B) Leaf Primordia, beginning of new leaf.
• (C) Axillary Buds, become branches.
• (D) Older leaf primordia
• (E) Zone of high cell division activity.
Shoot Apical Meristem
Longitudinal Section
SAM
Transverse Section
Dicot
• Bundles consist of xylem and
phloem.
• Phloem to the outside of
bundle, xylem to the inside,
always.
• Bundles are arranged in an
ordered pattern.
• Center is called pith. Pith is
parenchyma cells.
• Cortex: region between
epidermis and bundles.
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Monocot
Bundles consist of xylem
and phloem.
Phloem and xylem and
randomly distributed in
bundles.
Bundles are randomly
distributed.
No obvious pith.
Axillary Buds
• Grow into branches.
• *Every branch that is growing/elongating has
an axillary bud.
Leaf
• Come in various sizes from several yards to mm.
• Function is primarily for photosynthesis, shape to
capture light.
• Leaf shape and size is modified by environment it
grows in.
• Form and function can change based on
environment.
• Originate from apical dome, leaf primordia.
• Consists of blade and petiole.
• Blade can be giant, petiole small, or vice versa.
Leaf
Cross Section of Leaf
Leaf Vascular Tissue
• Vascular tissue is made
up of xylem and
phloem.
• Made up of midvein
and mesh like veins.
• Cross section of leaf.
Special adaptations of Leaves
• Tendrils: used for
climbing, allows for
growth where they
typically can’t grow.
• Spines: protection.
• Storage of nutrients.
Adaptations of plants
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Venus Fly Trap
Pitcher Plant
Black Horn Acacia
Lily Pads
Stove Plants
Primary Growth
Shoots/Secondary Structure
• Primary growth helps to give
height/elongation.
• Secondary growth gives rise to increase in
circumference.
• Going from twig to tree allows trees to
achieve great size, mass, age.
Vascular Cambrium
• Because new cells are formed not only by
apical meristems, which promotes elongation,
but also by a lateral meristem, we call these
tissues secondary tissues.
Consequences of Secondary Tissue
• Xylem and pith are pushed towards center.
• Primary phloem/cortex/epidermis are pushed
to the outside.
• New secondary cells produced inside the
vascular cambium, called secondary xylem
(Commonly known as wood)
• To the outside of vascular cambium, new cells
produced are secondary phloem, known as
bark.
Annual Growth Rings
Annual Growth Rings
Monocot Adaptations to growth
Fibonacci Sequence
Cork Cambium
Charles and Frances Darwin
• Interested in tropisms. (Plant Movement)
– Specifically phototropism.
– Studied grass seed (monocot) seedlings. Focused
primarily of coleoptile.
Coleoptile
• Question that arose: Is there a region in the
coleoptile that perceives light?
– The tip of the coleoptile perceives light, also there
was some material moved from the tip to the
differentially elongated cells.
Discovery of Auxin
Addition of Auxin to plants
Discovery of Auxin and Functions
• From coleoptile agar plates, the substance was
analyzed and found to be Indole 3 Acetic Acid,
IAA, or Auxin.
• Auxin is responsible to apical dominance.
• Control of vascular cambium.
• Fruit development.
• Root formation
• Abscission of leaves.
• Plant Orientation.
Apical Dominance
• Auxin is found in apical meristem.
• Shoot system unbranched, axillary bud growth
inhibited by auxin.
• If apex is destroyed, removing auxin, brances
grow out.
Control of Vascular Cambium
• Determines the derivatives and the quantity
of each.
Root Formation
• Stimulates the pericycle to form roots.
• Ex. Rootone, synthetic auxin to put on broken
plants to stimulate the roots to form.
Abscission of Leaves
• Auxin is able to measure the amount of
daylight.
• Uses the photoperiod to tell the leaves to
reduce the amount of auxin when daylight
lengths reduce.
Plant Orientation
• Allows a plant that has been knocked over, or a
seed establish roots and shoot system.
• Auxin has opposite effects due to the sensitivity,
or threshold, of auxin in those types of cells.
• Shoot: Auxin promotes elongation.
• Root: Auxin inhibits elongation.
• This is the premise for herbicides to kill specific
plants while others live. Due to the sensitivity of
auxin.
Gibberellin
• Second PGR found by accident.
• Found during the studying of a fungus,
gibberella.
• Fungus caused rice to elongate to high and fall
from winds into water, making rice inedible.
• Rice produced a substance called gibberellin,
GA, gibberellic acid.
• Discovered in Japan, but results were not
available due to language barrier and WWII.
Gibberelin continued
• Gibberelin is also produced in plants.
• Over a 100 types of gibberelins.
• Have very distinctive effects on plants.
– 1. Promote cell elongation.
– 2. Affects flowering.
– 3. Used commercially, can be applied to plant.
• Grapes: Round vs elongated.
Gibberelin continued
– 4. They control the maturity of plants, juvenile vs
adult.
• Juvenile has high levels of gibberelin, adult has low
level. Gibberelin can cause plants to alternate from
juvenile to adult.
Gibberelin
– 5. Most important function is seed germination.
• A. signal to germinate is received.
• GA is produced and/or released by embryo and moves
to aleurone layer.
• Aleurone then stimulates an enzyme formation, alpha
amylase, which converts starch to sugar.
• Leads to germination.
Growth Regulator Research
• Scientists knew of auxin and gibberelin so they
hypothesized that there may be more.
• Took pith cells (Parenchyma, undifferentiated).
• They were in the center of tree, away from
any microbial contamination.
• They are sterile or aseptic.
Procedure
• Ground up plant cells.
• After 100’s of samples, they would add it to
the culture/medium.
• The result was from one of the mediums they
found pith cells dividing.
• When they divided, the pith cells formed a
mass of undifferentiated cells called a callus.
• Analyzed the callus, found substance
responsible was cytokinins.
Cytokinins Functions
• Stimulate cell division.
• Delay sonescense, slowing the death process of a
cell.
• In combination with other GR, (mainly auxin)
they can cause the callus to yield organs.
• Auxins and cytokinins were added in different
ratios to callus and yielded different results.
• Overcome apical dominace.
– Axillary bud is inhibited by auxin, if we add cytokinins
to the bud, it is released from apical dominace and
branches out.
Result of cytokinin
• Witches broom
• Tumors
Growth Regulators
• 1st three groups, auxin, gibberelins, cytokinins,
are distributed via the vascular tissue.
• 4th GR is a gas, external to plant/tree.
• Discovered by gas heat, gas lamps.
– When plants were in rooms with gas, pedals
started to discolor and eventually fell off.
– Leaves showed epinasty.
– Gas caused weakening of abscission zone.
PGR
• This gas was analyzed in detail and found to
be ethylene.
• Ethylene affects and promotes fruit ripening.
– It is autocatalytic, stimulates its own production.
• Apples, oranges, banana ripen as a result of ethylene.
Ethylene
• Ethylene catalyzes more of itself in fruits.
• Also formed in damaged fruits.
– Green bananas are still starch, no sugar yet. Prior
to being set out, they are sprayed with ethylene to
stimulated ripening. Converting the starches to
sugars.
• One rotten apple spoils the whole barrel.
Agricultural uses of ethylene
• Pineapple and mangos are sprayed with ethylene
to stimulate flowering.
• Synchronizes harvest all at once.
• Ethylene is used to harvest energy intensive
crops. Walnuts and cherries.
– Treat orchards with ethylene. Walnut fruits have
abscission zone that is weakened by ethylene.
– Tarps placed underneath.
– Trees shaken with machinery.
Last Group of PGR
• Auxin, cytokinins, gibberlins, and ethylene.
• Last group was discovered in unison from Wales and
UC Davis
• Wales group from UK was looking at a dormant tree, its
buds were covered with scales.
• The scales protected the shoot apex during winter.
• If you removed scales prematurely, the bud would start
to grow.
• Some substance in scales inhibited growth.
• Extracted and analyzed bud scales, identified Dormin,
promoted dormancy.
UC Davis Discovery
• Problem was presented by cotton farmers.
• Every June, cotton fruit, a large percentage of
fruit was falling in June. (June drop)
• Decreased yield and therefore profit.
• Question presented to Davis was why are they
falling early.
• There was a compound that increased in amount
just before cotton fruit dropped.
• Compound identified was abscisic acid.
• Important group with regard to abscission.
Abscisic Acid
• 1. Generally associated with stress responses
to plant.
– If plant is put under water stress (drought
conditions), plant is going to continue to open
stomata and lose water through leaves, killing
shoot.
– In drought conditions, the root makes abscisic acid
and moves to stomata and in stomata ABA causes
closure.
2nd Function of ABA
• Plants that grow in high saline concentrations.
– Salty environments in some plants, ABA increases
and causes production of proteins that lessen the
detrimental effects of salt.
3rd Function of ABA
• Seed has the ability to go dormant in less than
favorable conditions, winter or drought.
• Question is how does it know when conditions are
favorable.
– One mechanism is ABA in seed coat.
– In seed coat, they have ABA plus other inhibitors that
prevent germination.
– The ABA and other inhibitors are cold-labile, cold causes
their break down.
– Cold equals low levels of ABA, as temperature rises the
ABA levels rise telling the plant to germinate.
Flowering
• When a plant undergoes its transition to
flowering, it makes a significant change.
• SAM which is comprised of undifferentiated
cells which could divide forever.
• When it flowers it loses these changes.
What Causes the transition to
flowering?
• Signs that flowering transition has occurred.
• SAM (transition to flowering)
– 1. Apex stops producing new leaves.
– 2. Apex enlarges.
– 3. SAM starts to produce the organs of the flower.
– 4. All of SAM becomes commited to yielding
flowers. No longer undifferentiated.
Works that discovered flowering
• 1920’s Garner and Allard worked with tobacco.
• Controls of flowering:
– The length of photoperiod controls flowering.
– Some plants have to have less than some specific
number of hours of light to flower.
– These plants are called Short Day Plants. SDP.
– Others have to be more than some minimum numbers
of hours.
– These plants are referred to as Long Day Plants. LDP.
3rd Group
• Last group has flowers irrespective of the
length of the photoperiod.
• These are called day neutral plants. DNP.
• Examples; Easter lily, poinsettia.
• We manipulate the photoperiod.
An accident in the lab
• Lab accident in the lab determined what we
knew about photoperiod and flowering turned
out to be wrong.
• In a controlled experiment dealing with light
dependency, someone inadvertently turned
on the light switch. SDP did not flower. Too
much sunlight, has to be the length of
darkness that triggers flowering.
• For both SDP and LDP, light is important for
photosynthesis, but the length of the dark
period controls flowering.
• For a SDP, the length of the dark period must
equal or be greater to some number of hours.
• For a LDP, the length of the dark period must
be shorter than some number of hours.
Environmental Factors for Flowering
• Temperature – some plants require both a correct
photoperiod and a correct temperature.
Including celery, beets, both SDP with cold temp.
• Effects of cold on promoting flowers is called
vernalization.
• Flowers are extremely important because they
are the basis for us getting our fruits, grains, and
our seed crops.
Where is photoperiod detected?
• Photoperiod is important.
• It is measured in the leaf.
Experiment that determined leaf as
photoperiod signal.
How is flower formed
• Signal to flower is formed in leaf.
• Signal moves via vascular tissue to SAM.
• At SAM, the signal induces transition to
flowering.
Research
• A lot of research has been done to identify the
signal, but done unsuccessfully. This ability
would allow us to get plants to flower outside
of their normal photoperiod.
• Some observations were found during this
research.
Observations
• GA caused flowering in LDP, but not in SDP, so
GA could not be a universal signal. (Florigen)
What happens when florigen arrives at
apex
• When signal arrives, there are groups of genes
turned on.
• Grouped genes into three groups, A B C.
• Grouped according to when they were turned
on.
• If you turned on A genes = Sepals
– A+B = Petals formed
– B+C = Stamens
– C = Carpels
ABC Model