Plant Reproduction Flashcards
What are the origins of the flower?
Angiosperms dominate the worlds flora:
-450 families with over 220, 000 species.
Practically every important crop plant is an angiosperm.
Exceptions – pine nuts, sea weed, Ginkgo seeds, Burrawang seeds.
Eudicots are the most highly derived angiosperms.
Monocots are food crops.
What are gymnosperms?
Cone bearing plants.
Cone structures of gymnosperms are related to flowers of angiosperms- reproductive and developmental.
Sporophyte- spore producing version of plant. Dominant in gym and angio.
Captive Gametophyte- ovule.
Alternation of generations.
What is a strobili? Howis it similar and different to flowers?
Strobili is a cone.
Only have distinct male or female cones.
Ovule is open to environment- on surface of leaf bit.
Megasporophyll- carpal.
Microsporophyll- stamen.
Petal and sepal- highly derived structures.
Flower- male and female parts both found.
Cones and flowers have same sort of parts. Difference is distinct male and female cones, but flower has both male and female parts in it.
What are the specific flower structures in an angiosperm?
Sepal. Petal. Microsporophyll (stamen). Microsporangium (anther). Megasporangium (ovary). Megasporophyll (closure to form carpel.
These parts make up the ovary, style, stigma.
What is amborella?
Amborella- most basal angiosperm we’re aware of.
Distinct male and female flowers- this is the derived state (ancestor would have had combined male and female).
Sporophyte dominant.
Enclosed gametophyte. (this is for all angiosperms).
What are the structures of the avocado flower?
Stamen, staminode, tepals (these are tougher than petals, more leaf like).
What is the original ABCE model? What does it code for?
Genetic model that codes for parts of the flower? A – Sepal (AP1/2) AB – Petal (AP1/2, AP3/PI) BC – Stamen (AP3/PI, AG) C – Carpel (AG) E – Flower (SEP1/2/3/4)
E function (across bottom of entire model)- part of switch from vegetative state to flower initiation. Flower is a highly copacted stem. No room in the model fo tepals and staminodes.
What is different about the newer ABCE model?
ABCE model A - Sepal AB - Petal BC - Stamen C - Carpel (E - Flower)
Tepals –
aBC – Sepaloid tepal
aBC– Petaloid tepal
Staminodes - bC
Rather than tightly bound expression, have leaky boundaries- some function found in next whorl.
Confused developmental process.
BC- end up with feminised stamens- sterile.
ABCE model only strictly applies to highly derived eudicots like Arabidopsis.
How does the ABCE model affect gymosperms, basal angiosperms, and eudicots?
Gymnosperm cone and angiosperm flower are both formed by interaction of B and C function genes implying presence in common ancestor.
Angiosperm flowers are therefore tinkering with an existing set up rather than an entirely new structure.
Current best hypothesis: “out of female” – B function genes became expressed to generate stamen like structures from carpel like organs.
Angiosperms show elaboration on this with A and E function.
A and E act as floral meristem identity specifiers – make the reproductive structure more recognisable as a “flower” to us.
Only higher Eudicots show truly differentiated petals and sepals, lower Eudicots, Monocots and basal angiosperms show varying degrees of differentiation of petaloid and sepaloid organs from leaf-like structures.
(Female flower that would become an angio flower- express B genes inappropriately- stamens outside carpal- how combined male and female happened.)
Why develop flowers?
Gymnosperms are largely wind pollinated but fossil record indicates that some, now-extinct, gymnosperms were pollinated by scorpion flies.
Fossil record shows insects with specialised mouth parts with guts containing gymnosperm pollen and nectar.
Most angiosperms are pollinated by animals.
(Basal angiosperms less so than eudicots.)
Wind pollination in monocots, particularly the grasses (Poaceae), is a derived feature.
How do gymnosperms protect pollen from attack?
Phytophagous insects, largely beetles and dipteran flies, eating flowers, pollen, etc. of ancestral seed plants- pollen is attractive as it is very high energy.
Gymnosperms:
Tough “cone” to protect organs.
Remain mostly wind or water pollinated.
Angiosperms: Use (co-opt) phytophagous insects to transfer pollen: -Reduce quantity of pollen produced. -Reduce number of female organs. -Increase distance of transfer. -Prevailing wind independent. -Opens up more ecological niches.
What does co-opting with insects to transport pollen allow for angiosperms, and what does it require?
Co-evolution with pollinators: “arms race” that may lead to mutualism.
Evolution of “rewards”: sacrifical pollen, nectar production.
Elaboration of flower structure: Plasticity of ABCE model and downstream effects allows wide range of structures to form by changing gene regulation rather than requiring new genes.
Shape, size, colour and scent as attractants.
Reduction in number of flowers allows more energy to be spent on making more elaborate flowers.
Pollen can be much more complex with larger reserves.
Size, shape etc. are small changes to make.
Give an example of reward and deception strategies used by angiosperms for insect pollination.
Reward:
Bee balm (Monarda punctata):
General insect attracting scent, pollen transfer occurs during nectar feeding. Rewards insect with nectar.
Deception: Bee orchid (Ophrys apifera): Smells like a female bee, mimics a female bee abdomen, pollen transfer occurs to male back during pseudocopulation, no nectar reward. This costs the plant nothing.
What are the features of flowers designed for differentinsects?
Beetle – usually green or white, heavily scented, flowers usually open/dished.
Bees/Wasps – generalist pollinator flowers, flowers often have UV visible “floral guides”.
Butterflies – Pink or purple, often have landing areas, some really specialist pairings have long tongues and nectaries, flowers often have UV visible “floral guides”.
Moths – Usually white with strong scents for detection in the dark some really specialist pairings have long tongues and nectaries, flowers often have UV visible “floral guides”.
Flies – usually scent attractants, blue, purple or white flowers, pollen and nectar reward.
Birds – bright red or orange, often odourless, nectar reward.
Bats – similar to moths but much larger.
(Flowers have decoration only visible in UV range- directs insects in.
Can tell what the likely pollinator of a flower will be.
Moth has tongue 3x length of body. Can only access Gladiolus cause other plants are not efficient for feeding. Extreme example of co evolution.)
What are flowers in the Poacea?
Major staple crops: Wheat Rice Maize (corn) Sorghum Millet Barley Oats Rye
Spike, raceme or panicle, depending on structure.
All wind pollinated. Secondary trait.
Not bright or colourful, so not going to attract insects.
Appeared about 55mya.
Flowers and flower spikes are plain yet highly derived structures.
Wind pollinated (derived characteristic).
Recent occurrence.
Grass flowers are complex.
Lodicule- equivalent of petal.
Palea and lemma- sepals.
