lecture 10 - precision and control in pollination

Question 1

Explain the importance of seeds

Answer 1

Evolution of seeds marks a major turning point in the history of the planet
Seeds are a storable food supply for many organisms and vital to the terrestrial ecosystem
Seeds, or the lack of them, have been responsible for civilisations, famines and hunger
Seeds allowed flowering plants to survive mass extinction events
Seeds allow flowering plants to germinate more quickly and better able to exploit ideal conditions than any other plant

Question 2

Explain the issues and importance with pollination

Answer 2

Evolution of seed required pollination mechanisms
New vectors for pollen
The diversity of flower shape and form reflects all of the possible pollinations mechanisms
Pollination success generates a new problem
A conflict between certainty of fertilisation (selfing) and outbreeding:
Plants evolved new strategies to avoid inbreeding: dichogamy, heterostyly, self-incompatibility and dioecy

Question 3

Give some examples of pollination strategies

Answer 3

1 - exploitation of echolocation - pollinated by bats
dish-shaped leaf halves foraging time for flower-visiting bats
can measure amount of echolocation from leaf
2 - multiple rewards strategy - scarab beetles spend most of their lives in the flower, receiving energy and food rewards and leave to pollinate other flowers
3 - deceit by resource mimicry - floral and rotting carcass volatiles are similar and flies respond in same way to both sets of chemicals
flies enter expecting to find rotting meat, fly in and pollinate, are trapped in overnight and covered in pollen then fly out in the morning and can cross-pollinate
4 - wind pollination: trees - flowers in catkins, early in the year before buds and flowers expand no attractants required
5 - wind pollination: grasses - specialisation of flower structure - hanging antlers, feathery stigmas, petals and sepals reduced to scales (lemma, palea)

Question 4

How can inbreeding be avoided?

Answer 4

1. dichogamy - anthers and stigma mature sequentially
   phase 1 - stigmas open: cross-pollination favoured
   phase 2 - first 5 anthers: cross and selfing possible
   phase 3 - stigmas wither; next 5 anthers mature: can act as male parent to another flower
2. dichogamy - fail-safe mechanisms
   Ensuring pollination by selfing in protandrous flowers (male/pollen first)
   stigma lobes initially receptive to cross pollen, then curl round and collect pollen
   Secondary pollen presentation
3. dioecy and monoecy
   Male and female flowers on separate male and female plants (dioecious)
   In some plants dioecy is due to sex chromosomes
   Male and female flowers on a single plant (monoecious)
4. self incompatibility - inability of pollen to fertilise ovules of the same flower

Question 5

What is sporophytic incompatibility?

Answer 5

SI proteins are produced by the diploid sporophyte and deposited on the developing pollen grains
The pollen is marked by 2 SI alleles
if any SI proteins match the pollen tubes are inhibited

Question 6

What is gametophytic incompatibility?

Answer 6

SI proteins are produced by haploid pollen cells
Each pollen grain is marked by only one of the two SI alleles from the male sporophyte
if any SI proteins match the pollen tubes are inhibited