The unique reproductive biology of angiosperms Flashcards
Describe the life cycle of a fern
- sorus on pinna protected by indusium
- sporangium contains spore mother cells (undergo meiosis)
- produces spores which germinate into gametophyte prothallus (has rhizoids)
- antheridium produces sperm which disperse to the egg-containing archegonium
- fertilisation
- rhizome arms adventitious roots
- young sporophyte produces fiddleheads
- frond formation
Fiddleheads
furled fronds of a young fern
Give a heterosporous spermatophyte
Pinus sylvestris
What is the ovule
Megagametophyte enclosed by integument and nucellus
Describe gymnosperms
- mostly monoecious
- some dioecious
- unisexual cones
- most anemophilous
Describe angiosperms
- mostly hermaphroditic (co-sexual flowers)
- few monoecious or dioecious
- mostly entomophilous
Describe the Androecium
- stamens
- contain anther and filament
anther
- 4 loculi
- contains microsporangium
Describe the pollen grain
- bicellular or tricellular
- generative cell and vegetative cell nucleus
- sperm cells and vegetative cel nucleus
- pollen wall
- colpus
Describe the pollen wall
- intine
- foot layer
- columella
- tectum
colpus
- groove
- pl. colpi
Describe the Gynoecium
- carpel and pistil
Apocarpous
carpels free
Syncarpous
carpels ‘fused’
Connate
carpels ‘united’
embryo sac
- megagametophyte
- 2 integuments
- micropyle
- 2 synergids
- egg cell
- 2 central cell nuclei
- 3 antipodal cells
antipodal cells
embryo nutrition
synergids
cessation of pollen tube growth and release of the sperm cells
Describe pollination and double fertilisation - the basics
- pollen tube delivers the two sperm cells to the embryo sac
- haploid microgametophyte and diploid megasporophyte
Describe pollination and double fertilisation - the specifics
- pollen shed from anther and transferred to stigma
- pollen hydrated on stigma
- pollen germination and tube growth down style
- pollen tube grows down transmitting tract to ovary
- enters micropyle
- double fertilisation occurs
Describe the pre-zygotic events
- Pollen capture
- Pollen adhesion
- Pollen hydration
- Pollen germination
- Pollen tube penetration
of the stigma - Growth of pollen tube
towards the ovule - Entry of pollen tube
into the ovule leading to fertilization
What are the implications of the pollen-pistil interaction?
- evolution of pollen discrimination systems
- pollen competition
Describe pollen discrimination systems
incompatibility systems
SI
self-incompatibility
List some incompatibility systems
- intra-specific SI systems
- interspecific incompatibility
List some incompatibility systems
- intra-specific SI systems
- interspecific incompatibility
Describe pollen competition
- gametophytic selection
- vigorous microgametophytes produce fitter offspring.
- 60-80% of genes expressed in microgametophyte are also expressed in sporophyte: subject to selection during pollen-pistil interaction.
Chemical signalling in the pollen tube
- gradient of water potential created by surface lipids of stigma (or pollen coat)
- various chemical pollen tube attractants in stigma and style
3. Synergid peptide signal (LURE) attracts pollen tube to ovule as prelude to fertilization (Higashiyama et al 2001 Science 293: 1480- 1483)
List some chemical pollen tube attractants
- TTS Arabinogalactan Glycoprotein
- GABA
- Chemocyanin
- Le-STIG1
TTS
Transmitting Tissue Specific
Le-STIG1
cysteine-rich stigma-specific protein 1
Describe double fertilisation
- triploid endosperm is 2 maternal and 1 paternal
- diploid embrue is 1 maternal and 1 paternal
- both vegetative nucleus and endosperm get fertilised
Why is the endosperm ratio 2m:1p
critical for seed size
Describe nuclear endosperm development
- most common form
- fertilisation followed by repeated free-nuclear divisions =
- ‘liquid endosperm’
- if a cell wall is formed it will form after free-nuclear divisions
Describe cellular endosperm development
- fertilisation followed by normal cell divisions with cell- wall formation
Describe Helobial endosperm development
- rarest form
- cell wall is laid down between the first two nuclei, after which one half develops cellular endosperm and half nuclear
Give examples of nuclear endosperm development
coconuts, cereals and beans
Give examples of cellular endosperm development
Impatiens, Petunia, Datura
Give examples of Helobial endosperm development
e.g. Asphodelus, Muscari, Saxifraga, Echium.
Describe Gymnosperm seeds
- 30mm
- food reserves laid down in female gametophyte before fertilisation
Describe Angiosperm seeds
- 2mm
- food reserves laid down in endosperm after fertilisation
- more efficient
Describe fruit derivation
- from various parts of the flower
- ripening swollen ovary
Fleshy fruits are
an adaptation to entomophilous seed dispersal
