Lecture 14: Flowers & Fertilisation Flashcards
(38 cards)
the main reproductive structure of the plant is known as the
flower
The main reproductive structure, the flower, is derived from
the shoot apical meristem
the function of the flower is to
generate gametes
2 systems of a plant
shoot & root
root system of a plant includes
- Taproot
- Lateral roots
Shoot system of a plant includes
- Flower
- Terminal bud (shoot apex)
- Node
- internode
- Axillary bud
- Terminal bud of branch
- Vegetative branch
- Leaf: Petiole & blade
- stem
standard floral structure =
- Receptacle
- Sepal
- Ovule
- Petal
- Stamen: Anther & Filament
- Carpel: Stigma, Style, Ovary.
Female gametes in flowers form
within the carpels
-The cells that form the gametes are not laid down early in development
(contrast with animals)
Male gametes in flowers form
within the stamens
-The cells that form the gametes are not laid down early in development
(contrast with animals)
Arabidopsis thaliana
- A model for studying plant development
- sequenced genome encoding c. 25000 genes
- short life cycle (seed-seed/3months)
- small (limited growth space)
- tools for identifying & characterising gene function
how to identify developmental genes using molecular genetics
•Create mutants with altered phenotype.
•Clone mutated gene responsible for phenotype.
•Examine where and when gene is expressed and what type of protein the gene encodes.
-Mutation leads to only a few combinations of flower parts
ABC model of flow formation
order= Sepal, petal, stamen, carpels, carpels, stamen, petal, sepal (SPSC)
-ABC forms triangle (aBc)
what determines organ fate
specific spatial/temporal combinations of transcription factors
ABC model: A domain gene =
A function alone = Sepal
ABC model: B domain gene =
A+B function = Petal
ABC model: C domain gene
C function = carpel
B + C function = stamen
ABC model: what happens when all A,B,C factors are mutated?
FLOWER MADEOF LEAVES
what causes a flower to form?
- The activation of transcription factor LEAFY is required to switch the meristem from making leaves to making a flower
- the activation of LEAFY depends on environment signals perceived in the leaves
understanding the molecular basis of flower formation has allowed the
manipulation of flower structure
-Transgenic Aspen expression the Arabidopsis LFY transcription factor flowers after 3-6 months (rather than 10 yrs)
how to make gametes in plants
- meiosis is KEY
- in plants meiosis is followed by MITOTIC divisions to create a haploid has of the life cycle which generates gametes
cells which generate gametes differences in animals and plants
- Cells which generate gametes in animals are set apart as a germline
- In plants the germline cells are determined late in development
Development of a male gametophyte (within pollen grain)
MEIOSIS -micro-sporocyte divides -microspores (4) -all 4 microspores used MITOSIS -Generative cell (wi form 2 sperm) = Male gametophyte (within pollen grain )
Development of a female gametophyte (embryo sac)
MEIOSIS
-Ovule (Sporangium, mega-sporocyte & integuments)
-4 megaspores produced, only 1 survives (surviving megaspore)
MITOSIS
-Female gametophyte (embryo sac) contains =
-integuments
-ovule
-Antipodal cells (3) (dead megaspores)
-Polar nuclei (2)
-Egg (1)
-Syngerids (2)
syngerids =
part of the egg apparatus and are thought to help the pollen nucleus reach the egg cell for fertilization
