BIOL10004 Lecture Notes - Lecture 5: Cell Potency, Mate Choice, Genetically Modified Crops
Plant Reproduction
● Plant reproduction is multidisciplinary: cell and molecular biology, growth and
development, genetics, and ecology
● Reproductive organs in angiosperms are aggregated into flowers
● Angiosperms have double fertilization
● Pollination is achieved by a diverse array of mechanisms
● Breeding systems determine the pattern of mating within a population
● Fruits are variously adapted for seed protection and dispersal
● Vegetative (non-sexual) reproduction is important in some instances
● Important knowledge for biodiversity
conservation and plant breeding
● Diplontic life cycle- animals, only
gametes are in haploid state, diploid
undergo mitosis
● Haplodiplontic- gametes are not the
direct result of meiotic division
● Gametophyte- Meiosis produces
haploid spores that undergo further
rounds of cell division by mitosis to
produce a multicellular haploid stage
○ Plant produce haploid by
mitotic division
● Sporophyte- Two gametes fuse to
form a diploid zygote, which then
undergoes mitotic divisions to produce the diploid life stage, produces spores
○ Heterospory- flowering plant gametophytes, produce 2 spores different in size
○ Microspores- smaller spores, develop into male gametophytes containing sperm
cells- microgametophyte/ pollen grain also
○ Megaspores- larger spores- develop into female gametophytes, each containing
egg cell, megagametophyte/ embyro sac
Asexual (vegetative) reproduction
- No sex. No seed. Results in clones
- Tubers (potato), Suckers, Runners
- Budding
- Fragmentation/Shedding
Meristem
- Important for taking over new environments, colonisation in plants
- Clonal reproduction in strawberries
- new plants arise from a single parent by mitotic division and are genetically identical to
their parents
Anatomy of a flower
● Stamens (male) consist of a filament and anther- full of pollen, Andritian ??
● Carpels (female) consist of ovary, ovules, style and stigma
● Pollen lands on stigma surface; pollen tube grows to the ovule
● Angiosperms - “seed in a vessel” (refers to the carpel)
● ~90% pollinated by animals
● Sepal- protective function for buds
● Petal- modified to be large, light reflecting structures, for signalling
● Stiga- pollen lands here and it germinates, sticky to catch and retain
Angiosperm Life Cycle ** need to know
- alternation
- Independent Sporophyte- produce sex cells through first round of meiosis then mitosis
Fertilization between diminutive gametophytes
- Female gametophyte is inside the ovule (8 cells)
- Male gametophyte develops from the pollen grain (3 cells)
- Polar nuclei
- Egg cell
- 2 sperm, 1 tube nucleus, tube will reach micropyle, interacts with synergence, can
fertilise polar nuclei
● Sexual reproduction begins when pollen alights on the stigma.
● Pollen tubes emerge from the pollen grains and grow through the stigma and style to the
ovary, where they penetrate the ovules.
● Flowering plants are unique in having double fertilisation.
● In double fertilisation one of the pair of sperm cells in the pollen tube fuses with the egg
to produce the diploid zygote. The other sperm cell fuses with the central cell to produce
the triploid nutritive endosperm.
● Wet-type stigmas are covered by a drop of liquid in which pollen grains germinate.
● Dry-type stigmas have no liquid covering and pollen grains stick to the surface of
papillae cells.
A Unique double fertilization
- Iron, protein and/or carbohydrates
- Triple zygote
- Coconut- triploid endosperm
Ovules develop into seeds
Carpel wall develops into fruit- for dispersal or protection of the seeds, can develop into tough
woody coating
- Mature seeds contain a dormant embryo- dehydration state and low metabolic rate
- Seed germination can’t occur until water and O2 reach the embryo- requires fracture of
seed coat
Seed Dispersal-
Abiotic:
- wind, water, gravity
Biotic:
- Fresh fruits to attract frugivores
- Sticky seeds to catch on animals
- Specialised reward for ant dispersal in Acacia
Document Summary
Plant reproduction is multidisciplinary: cell and molecular biology, growth and development, genetics, and ecology. Reproductive organs in angiosperms are aggregated into flowers. Pollination is achieved by a diverse array of mechanisms. Breeding systems determine the pattern of mating within a population. Fruits are variously adapted for seed protection and dispersal. Vegetative (non-sexual) reproduction is important in some instances. Important knowledge for biodiversity conservation and plant breeding. Diplontic life cycle- animals, only gametes are in haploid state, diploid undergo mitosis. Haplodiplontic- gametes are not the direct result of meiotic division. Gametophyte- meiosis produces haploid spores that undergo further rounds of cell division by mitosis to produce a multicellular haploid stage. Sporophyte- two gametes fuse to form a diploid zygote, which then undergoes mitotic divisions to produce the diploid life stage, produces spores. Heterospory- flowering plant gametophytes, produce 2 spores different in size. Microspores- smaller spores, develop into male gametophytes containing sperm cells- microgametophyte/ pollen grain also.
