Lecture 14: Flowers & Fertilisation Flashcards
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
plant gametes are formed by ___ of ___ nuclei produced by __ of diploid cell
Plant gametes are formed by mitosis of haploid nuclei produced by meiosis of diploid cell
the structures in which the gametes are produced are called
gametophytes
- female = embryosac
- male = pollen
plant reproduction involved a _____ event
plant reproduction involves a DOUBLE-FERTILISATION event
explanation of double-fertilisation
- the pollen generates 2 sperm nuclei
- 1 sperm nucleus fuses with the 2 polar nuclei (triploid endosperm formation)
- 1 sperm nucleus fuses with the egg (diploid zygote formation )
Endosperm feeds the world!
starchy endosperm in brown rice etc
how does the double fertilisation complete the life cycle
- the zygote develops into the embryo
- the endosperm helps nourish the embryo
The seed as dormant stage of development =
•(internal)endogenously-imposed dormancy
•(external) exogenously-imposed dormancy
Germination is dependent on environmental factors.
Germination involves uptake of water and activation of metabolism.
Prevention of self-fertilisation is achieved by
genetic self-incompatibility factors
explanation of genetic self-incompatibility factors
If both pollen (male genotype dependent) and stigma (diploid tissue of mother plant) possess same allele, pollen germination is Inhibited.
Whereas animals can use behaviour to control fertilisation plants focus on genetic mechanisms and timing of gamete formation
the male gametophyte consists of the pollen grain in which _ sperm nuclei are formed
2
the female gametophyte costs of the embryonic in which the ___
egg cell is formed & the polar nuclei
a double fertilisation event occurs =
- a sperm nucleus fuses with the egg cell to form a zygote.
- -a sperm nucleus fuses with the polar nuclei to form the endosperm
the zygote developed into
an embryo contained within a seed
how doe the dormant stage of development aid the pant
aids in dispersal and stress resistance
