Pollination and double fertilization (Not finished - take from Lecture 3)

What problem to plants have reproduction wise?

they don’t move - because of this various independent and assisted methods have evolved to move plant male gamete (pollen) and progeny (seeds)

Which species that pollinates is the most dominant

Animals

80% of plants are animal or insect pollinated True or False?

True

Which invertebrates(no spine) are mostly involved in pollination

Wasps, Butterflies, Flies, Beetles, Moths

Different ways flowers attract animal pollinators

Colour, Nectar, Odor, Deception/mimicry - these methods are more metabolically efficient than relying on wind as a transfer system

Why do animals visit pollinators?

• Animals visit plants for a reward (Pollen, nectar) - and only incidentally pollinate other plants in the process

• Pollen is an excellent food source for animals - the cytoplasm contains proteins, sugar, fats, starch, and trace amounts of vitamins and essential elements

• Nectar is a primary source of energy for many insects (ex. its rich sugar conent fuels flight and other activities)

What are some precise ways plants have evolved to attract specifically pollinators?

• Most pollen is orange to yellow (highly noticeable)

• Many pollen grains have a distinctive order

• The timing of when pollen matures can be very precise (ex., lining up with seasonal or daily activities of pollinators - Corn anthers split open in the morning, Apple Anthers split in the afternoon, some bat-pollinated flowers release pollen only at night)

• Nectar also has a limited time of availability like pollen

What is Mimicry (aka. Plant scamming)

• Some flowers mimic insect shapes

• The insect then attempts to copulate (have sex) or tries to fight the plant

• In the end the insect ends up picking up the pollen and transfers the pollen to the next flower

Modes of Pollination

• Pollen may be moved by either biotic (animal) or abiotic (wind and water) vectors

• Plants have evolved unique flower and pollen traits that adapt and facilitate pollination by a particular vector

• Beetles are attracted to the Tulip tree as its flowers emit musty, yeasty, and spicy fermented odours

Birds as Pollinators

• Birds were not recognized as pollinators until recently

• Now its known that thousands of plant species are pollinated by birds in many parts of the world (ex. Hummingbirds, Sunbirds, Honeyeaters)

Co - evolution

• Plants and the animals that pollinate them have co-evolved

• In some cases the flowers have shapes that are only accessible to certain pollinators

• Examples: Moth visited flowers are often closed during the day

• Both butterfly and moth flowers have long narrow tubes with pools of nectar at their bases - this makes it impossible for bees and beetles to enter

• Some flowers specifically adapted for bird pollination

Bats as Pollinators

• Most bats eat insects, but some are vegetarian - they have long snouts and tongues, small teeth, large eyes, and a good sense of smell

  • Bat-pollinated flowers are open at night and positioned below the foliage(leaves) of the plant

  • Colours are drab white, green, or purple because bats are colour blind

  • Exude a strong musty odor at night

  • Large and tough with lots of pollen and nectar (bats don’t land gracefully compared to butterflies or bees)

  • Plants pollintaed by bats include Bananas(Musa), Baobab, and Agave

What was Darwin’s first prediction?

• The star orchid is an orchid endemic (commonly found) to Madagascar that has an extremely long nectar tube

• Darwin predicted that in Madagascar, there must be moths with proboscis capable of extension to a length of between ten and eleven inches

• No animal existed though

Darwins prediction (2)

• in 1904 (41 years later) Xanthopan morganii praedicta was described and discovered by Karl Jordan and Lord Walter Rothschild

Study this

Wind-pollinated flowers produce many more
pollen grains per ovule than animal-pollenated
plants. True or False

True

Characteristics of Wind-pollinated flowers

• Small

• Colorless

• Odorless

• Lacking in nectar

• Lacking petals or having petals reduced to small scales

• Flowers or inflorescences are positioned to dangle or wave in the open

• Grasses and sedges position their flowers well above the leaves so they are exposed to wind currents

• Some trees produce flowers before new leaves emerge in the spring

• Pollen grains are generally smaller, smoother, and drier

• Shape is often frisbee-like to improve aerodynamic form

• stigmatic surfaces are enlarged and elaborate, often extending

• architecture of the flower and the inflorescence
  creates vortices that trap pollen and permit the
  grains to settle onto stigmas at a rate greater than
  predicted by chance

Pollen development

• Surrounded by elaborate cell walls

• Contain Sporopollenin

Sporopollenin

• a highly resistant biopolymer that forms the protective outer layer (exine) of plant spores and pollen grains.

• a very hard material that resists decay and makes pollen grains good fossil

What is the main life cycle phase in the Angiosperm Life Cycle

Adult (sporophyte stage) -

What contributed to the Angiosperms evolutionary success

Miniaturization of the seed plant gametophyte

Angiosperms are heterosporous - what does that mean?

Land plants that produce two different types of spores: smaller male microspores that will generate pollen grains as the male gametophytes, and larger female megaspores, which will form an ovule that contains female gametophytes

What are anthers usually made of?

• four elongated tubes called pollen sacs

• each pollen sac contains a mass of dividing cells called microsporocytes

What do microsporocytes do?

• Each microsporocyte divides by meiosis to form four haploid (n) microspores

• The nucleus of each microspore divides by mitosis to form a two-celled pollen grain, which contains a tube cell and a smaller generative cell

What is the role of the two-celled haploid male gametophyte that was divided by mitosis

Produce sperm cells for fertilization

How much fertilization do flowers go though

2 - double fertilization

What does germination of a pollen grain produce?

A pollen tube which grows down though the stigmas and style and enters the ovary

What is germination?

The process when a dormant seed begins to grow and develop into a young plant or seedling

Many pollen grains may germinate and their pollen tubes may grow through the pistil, but only one usually enters the ovule and its embryo sac - true or false?

true

Where is the growth of the pollen tube directed?

Down the style and to the embryo sac by molecules produced by the style and embryo sac tissues