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Plant Reproductive Biology

Plant animal interaction

What is pollination?

The transfer of pollen from the male anther tothe female stigma

Why is pollination important? Sexual reproduction

important for evolution

produces variable offspring, creating diversity and variationamong populations (shuffling of genes) for NaturalSelection to occur

advantageous to an organism only if it happens withsomeone other than itself!

Outbreeding good

inbreeding >>>>> homozygous plants

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Path in

pollination

process

Inbreeding

1. autogamy (in the same flower) &

2. geitonogamy (between flowers in one individu)

Selective advantage: ensures propagule production

Disadvantage: reduced to absent genetic variability

allautogamy: both outcrossing & inbreeding

e.g., Viola, Clarkia: two flower types:

chasmogamous flowers - normal, open

cleistogamous flowers - remain closed

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Strategies to avoid self-pollination

Perfect flowers have both male and femaleorgans, so plants have strategies to avoid self-pollination Outbreeding = outcrossing /allogamy / xenogamy1. Timing male and female structures mature at

different times

2. Morphological structure of male and femaleorgans prevents self-pollination (imperfect flower,heterostily)

3. Biochemical chemical on surface of pollen andstigma/style that prevent pollen tube germinationon the same flower (incompatible)

Difference in timing of floral parts = dichogamy

1. protandry - male first

2. protogyny - female first

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Morphology

Spatial separation of anthers and stigmas =hercogamy, heterostyly

Tristyly

Other mechanisms used by bisexual flowersto avoid self-fertilization:

Genetic self-incompatibility S-genes

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self-incompatibility SSI sporophytic self

incompatibility outcome of pollen tube and style

interactions determined by thegenotype of diploid sporophyte thatproduced the pollen

pollen tube growth arrested onsurface of stigma

S-allele produced before completionof meiosis

GSI - Gametophytic SI outcome of pollen tube and style

interaction determined by thegenotype of the pollen itself

pollen tube growth arrested in thestyle

S-allel produced after meiosis

How do plants get pollen from one plant to another?

Plants are rooted in the groundmust use different strategies:

WIND POLLINATION:

Gymnosperms andsome flowering plants (grasses,trees) use wind pollination.

Flowers are small, groupedtogether not efficient (too chancyand wasteful)

flowers small, numerous, oftenunisexual

perianth absent or non-showy

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Gymnosperms rely on wind to move pollenfrom male to female cones

The ovule exudes sap to trap pollen

Angiosperms have formed many partnerships

with animals to move their pollen

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Co-evolution

Animal plant partnerships are the best known casesof co-evolution: mutual evolutionary influence

Co-evolution interactions between two differentspecies as selective forces on each other, resulting inadaptations 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 thataid plant pollination

Figs and fig wasps

Some flowers provide nurseries for their pollinatorsoffspring

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Why do animals pollinate plants?

Pollinator will get a REWARD: food! In exchange for

moving their pollen to another flower

Nectar a sugary solution produced in specialflower glands called nectariesNectar 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.

Nectary gland

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Definition Nectaries are structure thatusually located within the

base of the flower (floral

nectaries) or on other

portions of the plant

(extrafloral nectaries)

A multicellular glandularstructure secreting nectar.

Found in flowers and onvegetative parts in some

species ofplants, often

forming projections, lobes, or

disk-like structures.

Floral Nectar

The sweet fluid used to attract insect pollinators. Thecomposition of nectar varies among plant species.

Floral glands produce nectar which is energy-rich foodfor animal pollinators. Pollinator visits flower due toattracted showy petals (visual attractant) or scent

(olfactory attractant) The secretion of nectar is usually under developmental

control beginning when the flowers open.

After pollination, the nectar is frequently resorbed

Nectar secretion increases as the flower is visited bypollinators

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Floral nectar in Petunia and Nicotiana

Some flowers provide food (e.g., nectar or pollen) to

their pollinators

Honey beecollecting pollen

and nectar

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Some flowers provide food (e.g., nectar or pollen) totheir pollinators

Kigelia africana

sausage tree

Night Blooming Cirrus

Nectar is usually presented together with

attractive structures, e.g., showy petals and

fragrances

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Getting the pollinators attention

Plants advertise their pollen and nectarrewards with

Colors bees see blue, yellow, UV; while birds seered. Bats dont 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 flys

pollination

Ultraviolet patterns

Petals sometimes exploit the sensory

capabilities of pollinators nectary guide

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Wax or resinreward Collected and used by

female bees for nest

construction

Found in Maxillaria andCymbidium; poorly

studied

Maxillaria notylioglossa

Waxy resin

crystals

Oil reward flowers

Oils (triacyl glycerides) produced on surface offlowers, often in specialized glands--

elaiophores.

Oils are collected by female anthophorid bees;

used to provision nest (food for larvae)

Many orchids mimic Malpighiaceae

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CyrtochilumWith oil gland (elaiophore)

Scents

Insects have great sense of smell may bepleasant or foul to humans but not to insect

Carrion flower smells like rotten flesh andattract flies (ex. Rafflesia)

flies lay eggs, pick up pollen and move on to nextflower looking to lay more eggs and spreadingpollen

eggs never survive as it isnt really poop

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carrion

maroon / brown in color, foul smelling (like rotting flesh)

Plant Mimicry

Some plants take advantage of the sex drive of certaininsects

floral fragrance mimicry of sexual pheromones ofpollinators

Usually visual, tactile mimicry, too Has evolved repeatedly in several different orchid groups

Certain orchids look like female wasps, and even smell likethem!

Males try to mate with them, and in the process they pollinatethe plant

The orchid gets pollinated, but the male wasp onlygets frustrated!

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Some flowers trick their

pollinators

Bucket Orchid

Some flowers trick their pollinators

Bee Orchid

Calochilus paludosa