Transcript HYBRIDIZATION - Gadjah Mada University

Reproduction system
Reproduction systems in
plants
• Seed propagated species
– self-pollinated
– cross pollinated
– self- and cross pollinated
• Vegetatively propagated species
Sexual reproduction
In animals: It’s easy because you have
separate male and female individuals.
In flowering plants: Not so easy, because
most flowers have both male and female
parts in them, called perfect flowers.
So flowering plants have evolved special
ways to insure out-breeding/out-crossing –
and to prevent inbreeding.
Plant Reproduction
Plant Reproduction: male
gametophyte
•Cells within anther
undergo meiosis
•Produce 4 spores
•Each spore undergoes
mitosis
•Results in pollen grain
containing 2 sperm
Plant Reproduction: female
gametophyte
• Within ovule, a cell
undergoes meiosis
• Produces 4 spores
• 1 spore undergoes mitosis
• Produces embryo sac
• Egg is contained within
embryo sac
Plant
Reproduction
•During pollination, pollen
lands on stigma
•Sperm travels down
pollen tube
•1 sperm fertilizes egg
•The other contributes to
formation of tissue that
will provide nourishment
to embryo
Ovule develops into seed
Basic Terms
• Outbreeding
Sexual reproduction between individuals (crosspollination). (It involves two individual plants)
• Inbreeding
Sexual reproduction within an individual
(self-pollination). (It involves one individual plant)
• Sexual Reproduction
The sexual process is a mechanism to bring about gene
recombination.
Recombination is the chief source of hereditary variation
and provides the raw materials for species to adapt to
changing environmental conditions.
Function of flower
attract pollinators with colorful petals, scent,
nectar and pollen
Carpel/
Overview of floral organs
Reproductive floral organs: female
 Carpel or pistil – female
reproductive organs; contains:
• Stigma – is where pollen sticks to
• Style – is the long tube that connects
stigma to ovary
• Ovary – enlarged structure at the
base of carpel/pistil where the
ovules are located; it will become
the fruit.
• Ovules – contains female
gametophyte, becomes
the seed
• Plants have style!
ovary
carpel
or
pistil
Reproductive floral organs: male
 Stamen – male floral organ,
consists of:
 Anther – part of the stamen
that produces pollen
 Filament – stalk-like
structure that holds anther
 Pollen – immature male
gametophyte
Non-reproductive floral organs
 Petals – whorl of flower organs that
are often brightly colored to attract
pollinators
 Corolla – whorl of petals
in a flower
 Sepals – whorl of leaf-like organs
outside the corolla; help protect the
unopened flower bud.
 Calyx – whorl of sepals in a flower
 Tepals – when sepals and petals look
the same
Pollination and Fertilization
• Pollen contains TWO nuclei: a sperm nucleus and tube
nucleus
• Sperm nucleus is protected in gametophyte tissue (pollen
can travel in the air)
Pollination and Fertilization
 For pollen sperm to successfully fertilize the egg, there must be
pollination: a method to get the pollen from the male anther to the
stigma.
 Pollen sticks to the stigma, starts growing a pollen tube
 Fertilization begins when
tube begins to grow
toward the egg
Double Fertilization
• Double fertilization occurs: One sperm nucleus (1n)
•
•
fertilizes the egg, producing a zygote (2n)  which
becomes the plant embryo inside the seed
Another sperm nucleus fuses with the polar nuclei, resulting
in a triploid endosperm (3n)
Endosperm is a source of food for the young embryo.
Endosperm
The seed
Parts of the seed:
• Seed Coat offers
protection
• Endosperm supplies
food for the seed
• Embryo is the young
plant
Hermaphroditic Flowers
• Self-compatible (SC)
– Capable of selffertilization or crossfertilization
• Self-incompatible (SI)
– Only capable of crossfertilization
– Inability of
hermaphroditic plant
to produce zygotes w/
self pollen
Autogamy
• Self-fertilization
• Pollen transfer within
or among flowers of
same individual
• ~25% of plant taxa
Advantages of Autogamy
• Insures seed set in absence of pollinators.
• Overcomes sterility.
• Selectively advantageous by transmitting
both sets of genes to offspring.
– Well-adapted genotypes preserved.
• Only single colonizing individual needed.
Disadvantages of Autogamy
• Decreases genetic variability.
• Inability to adapt to changing conditions.
• Increases inbreeding depression.
– Reduces heterozygosity and increases
homozygosity of deleterious alleles.
– More uniform populations.
Cleistogamy
• Flowers never open and
only capable of selffertilization in bud.
• Inconspicuous, bud-like
apetalous flowers that
form directly into seed
capsules.
• Has evolved independently
multiple times
– throughout the angiosperms,
including some basal
lineages.
• 488 species, across 212
genera and 49 families.
– Violaceae, Fabaceae,
Poaceae
Outbreeding (Cross-pollination)
• Advantages:
Increases genetic variability
Strong evolutionary potential
Adaptation to changing conditions
Successful long-term
• Disadvantages:
Can destroy well-adapted genotypes
Relies on effective cross-pollination, seed
dispersal and establishment
How do plants get pollen from one
plant to another?
• Because plants are rooted in
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the ground, they must use
different strategies:
WIND POLLINATION:
Gymnosperms and some
flowering plants (grasses, trees)
use wind pollination.
Flowers are small, grouped
together
Not a very efficient method
(too chancy and wasteful)
ANIMALS
Many flowering plants rely on animals for crosspollination:
 Insects – bees, wasps, flies, butterflies, moths
 Birds – hummingbirds, honey creepers
 Mammals – bats, mice, monkeys
 Even some reptiles and amphibians!
Coevolution
• Coevolution
•
interactions between two different species as
selective forces on each other, resulting in
adaptations that increase their interdependency.
Animal-flowering plant interaction is a classic
example of coevolution:
1. Plants evolve elaborate methods to attract animal
pollinators
2. Animals evolved specialized body parts and behaviors
that aid plant pollination
A word about pollen…
• The shape and form of
pollen is related to its
method of pollination…
 Insect-pollinated species
have sticky of barbed
pollen grains
 Wind-pollinated species
is lightweight, small and
smooth (corn pollen)
Palynology: the study of pollen
• Palynology is useful in many fields:
 Petroleum geology – fossil pollen can determine if
a field will have oil-rich deposits
 Archeology – studying ancient pollen samples,
archeologists can determine agricultural practices,
diet, etc.
 Anthropology – uses of pollen in rituals
 Criminology – to determine the whereabouts of an
individual, examine pollen clinging to clothes
 Aerobiology – to determine what plants cause hay
fever and allergic reactions – in landscaping
Animal pollinators: Bees
• Bees – the most important
group of flower pollinators
 They live on the nectar and
feed
larvae, also eat the pollen.
 Bees are guided by sight and
smell
 See yellow and blue colors,
also ultraviolet light (not red)
 Flowers have
“honey guides”
and bee landing
platforms..
Butterflies and moths
• Also guided by sight and smell
• Butterflies can see red and
•
•
orange
flowers
Usually shaped as a long tube
because of insect’s
proboscis – to get nectar
Moth-pollinated flowers
are usually white or pale,
with sweet, strong odor –
for night pollination.
Flies and beetles
• Flies like flowers that smell
like dung or rotten meat.
• Lay their eggs there, but larvae
die due to lack of food
• Beetles pollinate flowers
that are dull in color, but
have very strong odor
Birds
• Birds have a good sense
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•
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of color, they like yellow or
red flowers…
But birds do not have a good
sense of smell, so bird-pollinated
flowers usually have little odor.
Flowers provide fluid nectar in
greater quantities than insects
Hummingbird-pollinated flowers
usually have long, tubular corolla
Pollen is large and sticky
Mammals: bats and mice
• Bats pollinate at night,
so flowers are white
• Mouse-pollinated flowers
are usually inconspicuous,
they open at night
Why do animals pollinate plants?
• They get a REWARD: food! In
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exchange for moving their pollen
to another flower
Nectar – a sugary solution produced
in special flower glands called nectaries
Nectar concentration matches energy
requirements of the pollinator: bird- and
bee-pollinated flowers have different
sugar conc.
Pollen – is high in protein, some bees and
beetles eat it.
Flowers can produce two kinds of pollen:
a normal and a sterile, but tasty, kind, for
the insect.
Getting the pollinator’s attention
• Plants advertise their pollen and
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nectar rewards with
Colors – bees see blue, yellow, UV;
while birds see red. Bats don’t see
well, so flowers are white.
Nectar or honey guides –
a visual guide for pollinator
to locate the reward (pansy flower)
Aromas – for insects, nectar.
Can also be carrion or dung smell
Plant Mimicry
• Some plants take advantage of
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the sex drive of certain insects…
Certain orchids look like female
wasps, and even smell like
them!
Males try to mate with them,
and in the process they
pollinate the plant
The orchid gets pollinated,
but the male wasp only gets
frustrated!
Selfers vs. Outcrossers
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SC
Small flowers (few)
Unscented flowers
Nectaries & nectar
guides absent
• Maturation of
reproductive parts
– Anthers near stigma
– Style included
• All fruits mature
• Low pollen/ovule ratio
• SI or SC
• Large showy flowers
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(many)
Scented flowers
Nectaries & nectar guides
present
Differential maturation of
reproductive parts
– Anthers far from stigma
– Stigma well-exserted
• Only some fruits mature
• High pollen/ovule ratio
Strategies to Prevent Selffertilization
Strategies to avoid self-pollination
Perfect flowers have both male and female
organs, so plants have strategies to
avoid self-pollination:
1. Timing – male and female structures
mature at different times
2. Morphological – structure of
male and female organs prevents
self-pollination (imperfect flower)
3. Biochemical – chemical on
surface of pollen and stigma/style
that prevent pollen tube germination
on the same flower (incompatible)
Physical Separation of
Reproductive Parts
Herkogamy:
Pollination by the neighbor individual, population or
species
• Within flowers
• Among flowers
Heterostyly
A polymorphism among flowers that ensures crossfertilization through pollination by visiting insects
Flowers have anthers and styles of different length
Flowers in different individuals of the same species
having 2 or 3 different style lengths
–With stamen lengths varying inversely
• Distyly
• Tristyly
Distyly
• 2 floral morphs.
• “Thrum” flower
– long filaments with short
styles
• “Pin” flower
– short filaments with long
styles
• Only pollinations
between different floral
morphs are successful.
• E.g.: Primula
Tristyly
• 3 floral morphs
• Style long, stamens
•
•
short and medium
Style medium,
stamens short and
long
Style short, stamens
medium and long
Physical Separation of Reproductive
Parts
• Unisexual flowers
– Staminate and
carpellate flowers
• Monoecy
• Dioecy
Monoecy
• Common in windpollinated plants.
• Common in
temperate regions.
• Self-pollination
possible but less
likely.
Dioecy
• 4% of angiosperms
– Scattered throughout
• Common in tropical
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regions and oceanic
islands
Gen small fl size
100% out-crossing, but
inefficient
Often controlled by sex
chromosomes
– Silene
Polygamous Flowers
• Both bisexual and unisexual flowers on the same
plant.
– Androdioecy = bisexual and staminate individuals in a population.
– Andromonoecy = bisexual and staminate flowers on same individual.
• Euphorbia, Solanum
– Gynodioecy = bisexual and carpellate individuals in a population.
• Sidalcea hendersonii, Silene
– Gynomonoecy = bisexual and carpellate flowers on same individual.
• Silene, Solidago
– Polygamodioecy = some plants with bisexual and staminate flowers
& some plants with bisexual and carpellate flowers in a population.
– Polygamomonoecy = bisexual, staminate, and carpellate flowers on
same individual.
Evolution of Dioecy
• From hermaphroditism
– Vestigial sex organs
– Few families entirely dioecious
• From monoecy
• From SC
– Within groups that have lost
original GSI system
• From distyly
– Unequal pollen flow & gender
function
– Change in pollinator frequency
– Non-functional anthers at low
level in female flowers
– Non-functional pistil in male
flowers
Temporal Separation of Reproductive
Parts (Dichogamy)
• Protandry
– Anthers release pollen
before stigma
receptive
– Common in insectpollinated plants
• Geranium maculatum
– 1st day flower
– 2nd day flower
Temporal Separation of Reproductive
Parts (Dichogamy)
• Protogyny
– Stigma receptive
before pollen release
– Less common than
protandry
• Magnolia grandiflora
– 1st day flower
– 2nd day flower
Geitonogamy
• Self pollination between different flowers on
same plant.
Asexual
propagation...
“vegetative reproduction, i.e.,
multiplication that does not involve
the seed cycle - clonal propagation.”
Clone...
A genetically identical assemblage of
individuals produced from a plant
entirely by vegetative means.
Hartmann and Kester
Benefits of clonal
propagation...
•Some plants produce few (if any) viable seeds.
•Clonal progeny are highly uniform in all
characters.
•Outcrossing plants produce highly variable
progeny.
•Plants may have extended juvenile period.
•Cloning allows for combining genotypes in one
plant.
•Seeds may have lengthy and complex dormancies.
Cutting Propagation
– Produce adventitious roots.
Cells near the wound must dedifferentiate and create a
new meristematic region.
Cutting
•
Cutting propagation...
•Cutting capable of regenerating roots (or shoots)
from adventitious meristem.
•Cuttings defined by size and location on parent
plant:
– stem tip
– nodal
– root
– leaf
•Cuttings also defined by condition of growth:
–softwood, semihardwood, hardwood
Conditions required for rooting
cuttings...
•Hardwood and root cuttings require well drained
medium, but little moisture control.
•Leafy cuttings require high humidity to prevent
excessive dehydration:
– intermittent mist systems.
– poly tents or cold frames.
– fog.
•Medium into which cuttings are stuck must be
disease free, well drained, and light.
•Auxin application now standard treatment.
Examples of cutting
propagation...
Species
Cutting Type
African violet, begonia
leaf cuttings
Many woody shrubs
stem tip cuttings (softwood)
brambles
root cuttings
Willow, poplars
dormant hardwood cuttings
Grafting and budding...
“The vascular cambium can regenerate the
vascular connections between the scion and
rootstock resulting in a complete plant composed
of more than one genotype.”
•Can graft scion cultivar onto size controlling
rootstock.
•Many difficult to root plants are graft compatible.
•Grafting defined by season and type of tissue.
– budding (T-budding, inverted T, patch)
– wedge, veneer, whip and tongue, cleft, etc.
•Scion cultivar may be changed on mature trees (top
working)
Grafting
–Segments of different plants
are connected and induced to
grow together as one plant.
• Scion - Top section of a graft.
• Rootstock - Bottom section of a
graft.
–Successful grafting depends
on good contact between the
vascular cambium of the
scion and that of the
rootstock.
Grafted and budded
plants...
Species
Graft/bud Type
apples
chip, T-bud, cleft
conifers
side veneer
pecans
patch
roses
T-bud (shield)
grapes
modified wedge
Layering...
“Layering involves inducing roots on an
intact (or nearly so) plant .”
• Air layering - interrupt cambium and cover wound with
moistened medium.
Ficus elastica, Magnolia
• Simple layering - low hanging branch covered with soil (with
or without wounding) - many shrubs
• Tip layering - tips of plants (brambles) at certain times of
year (rat-tail condition) develop roots where they touch the
soil Blackberries, raspberries
• Mound layering - soil mounded to cover base of specially
pruned young tree (also referred to as stool layering)
Apple rootstocks
Air Layering
Layering
•
Specialized Structures
Modified Stems
bulb, corm, tuber, rhizome
pseudobulb, runner
Modified Roots
tuberous root
Propagation by specialized
structures...
Species
Structure
tulip, onion, Easter lily
bulb
potato, Jerusalem artichoke
tuber
Iris, lily-of-the valley
rhizome
Gladiolus, Crocus
corm
strawberry, Ajuga
runner
Dahlia, sweet potato
tuberous root
Apomixis...
“an exception to the rule of nonclonal embryony.”
“the development of an embryo within a seed or
flowering structure from a source other than the egg,
resulting in the formation of an embryo (sometimes in
addition to the sexual embryo) that is a clone of the
maternal parent.
Examples include polyembryony in citrus and
crabapples, and the formation of bulbils in garlic.”
Micropropagation...
“Micropropagation has many synonyms tissue culture, mass propagation, in vitro
culture, cloning.”
• Micropropagation is rapid, continuous, and efficient.
• Specialized equipment, facilities, and technically trained
personnel are required.
• Steps can be taken to obtain and maintain certified pest-free
plants.
• Cost effective if large numbers of a given clone are produced.
• Widely used for orchids, ferns, many interior foliage plants,
rootstocks, etc.
Plants amenable to
micropropagation...
Flowering pot plants - Begonia, African violets, orchids
Interior foliage plants - ferns, Syngonium, Ficus,
Diffenbachia
Woody ornamentals - red maples, Rhododendrons,
Nandina
Forest trees - Poplar, birch, loblolly pine
Fruit trees - apple, cherry, pear (many rootstocks)
Vegetable crops - potato, celery, tomato, onion (male
sterile)
Plantation crops - banana, date palm, coffee
Types of development in
vitro...
Proliferation of axillary buds from shoot tip cultures.
Differentiation of adventitious shoots from leaves, stems,
or roots.
Formation and proliferation of somatic embryos.
Seed germination - orchids.
Development of haploid plants from anthers or ovules.
Protoplast fusion and somatic hybrid development.