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reproduction in plants
Essential idea: Reproduction in flowering plants is influenced by the biotic and abiotic environment.
Nature of science:
Paradigm shift—more than 85% of the world’s 250,000 species of flowering plant depend on pollinators for reproduction. This knowledge has led to protecting entire ecosystems rather than individual species
Understandings:
Nature of science:
Paradigm shift—more than 85% of the world’s 250,000 species of flowering plant depend on pollinators for reproduction. This knowledge has led to protecting entire ecosystems rather than individual species
Understandings:
- Flowering involves a change in gene expression in the shoot apex.
- The switch to flowering is a response to the length of light and dark periods in many plants.
- Success in plant reproduction depends on pollination, fertilization and seed dispersal.
- Most flowering plants use mutualistic relationships with pollinators in sexual reproduction.
- Application: Methods used to induce short-day plants to flower out of season.
- Skill: Drawing internal structure of seeds.
- Skill: Drawing of half-views of animal-pollinated flowers.
- Skill: Design of experiments to test hypotheses about factors affecting germination.
- Students should understand the differences between pollination, fertilization and seed dispersal but are not required to know the details of each process.
- Flowering in so-called short-day plants such as chrysanthemums, is stimulated by long nights rather than short days.
flowering and gene expression
Flowering involves a change in gene expression in the shoot apex.
When a seed germinates a young plant is formed that grow roots, stems and leaves. These are called vegetative structures and the plant is in the vegetative phase which can last for weeks to years until a trigger causes the plant to change int the reproductive phase and produces flowers. That change happens when the meristems in the shoot start to produce parts of flowers instead of leaves.
Temperature can play a role in transforming a leaf-producing shoot into a flower-producing shoot, but day length is the main triggers or more precisely the length of the dark period. Some plants are categorized as short day plants because they flower when the dark period becomes longer than a critical length for example in the autumn. Other plants are long dat plants because they flower during the long day of early summer when nights are short.
Light plays a role in the production of either inhibitors or activators of genes that control flowering. The long day plants, active form of the pigment phytochrome leads to the transcription of a flowering time (FT gene). The FT mRNA is then transported in the phloem to the shoot apical meristem where it is translate into FT protein. The FT protein binds to a transcription factor. This interaction leads to the activation of many flowering genes which transform the leaf-producing apical meristem into a reproductive meristem.
When a seed germinates a young plant is formed that grow roots, stems and leaves. These are called vegetative structures and the plant is in the vegetative phase which can last for weeks to years until a trigger causes the plant to change int the reproductive phase and produces flowers. That change happens when the meristems in the shoot start to produce parts of flowers instead of leaves.
Temperature can play a role in transforming a leaf-producing shoot into a flower-producing shoot, but day length is the main triggers or more precisely the length of the dark period. Some plants are categorized as short day plants because they flower when the dark period becomes longer than a critical length for example in the autumn. Other plants are long dat plants because they flower during the long day of early summer when nights are short.
Light plays a role in the production of either inhibitors or activators of genes that control flowering. The long day plants, active form of the pigment phytochrome leads to the transcription of a flowering time (FT gene). The FT mRNA is then transported in the phloem to the shoot apical meristem where it is translate into FT protein. The FT protein binds to a transcription factor. This interaction leads to the activation of many flowering genes which transform the leaf-producing apical meristem into a reproductive meristem.
photoperiods and flowering
The switch to flowering is a response to the length of light and dark periods in many plants
Long-day plants flower in summer. Short day plants flower in autumn.
Observations of flowering suggested that the trigger for this in some plants might be a particular day length, but experiments have shown that it is the length of darkness that matters not the daylight.
A pigment was discovered in leaves that plants use to measure the length of dark periods. It is called phytochrome and is unusual as it can switch between two forms Pr and Pfr.
Long-day plants flower in summer. Short day plants flower in autumn.
Observations of flowering suggested that the trigger for this in some plants might be a particular day length, but experiments have shown that it is the length of darkness that matters not the daylight.
A pigment was discovered in leaves that plants use to measure the length of dark periods. It is called phytochrome and is unusual as it can switch between two forms Pr and Pfr.
- When Pr absorbs red light of wavelength 660 nm it is converted into Pfr
- When Pfr absorbs far-red light, of wavelength 730 nm, it is converted into Pr. But it is mostly converted rapidly again into Pfr because of the sunlight.
- However Pr is more stable than Pfr, so in darkness Pfr very gradually changes to Pr.
- In long day plants, large enough amounts of Pfr remain at the end of short nights to bind to the receptor, which then promotes transcription of genes needed for flowering
- In short day plants the receptor inhibits the transcription of the genes needed for flowering when Pfr binds to it. However at the end of long nights very little Pfr remains so the inhibition fials and the plant flowers.
mutualism between flowers and pollinators
Most flowering plants use mutualistic relationships with pollinators in sexual reproduction.
Sexual reproduction in flowering plants depends on the transfer of pollen form the stamen to a stigma of another plant. Pollen is transferred between plants via a number of strategies including wind and less commonly water but most commonly by animals known as pollinators. (bees, butterflies)
Mutualism is a close association between two organisms where both organisms benefit from the relationship. Pollinators gain food in the form of nectar and the plant gains a means to transfer pollen to another plant.
Sexual reproduction in flowering plants depends on the transfer of pollen form the stamen to a stigma of another plant. Pollen is transferred between plants via a number of strategies including wind and less commonly water but most commonly by animals known as pollinators. (bees, butterflies)
Mutualism is a close association between two organisms where both organisms benefit from the relationship. Pollinators gain food in the form of nectar and the plant gains a means to transfer pollen to another plant.
pollination, fertilization and seed dispersal
Success in the plant reproduction depends on pollination, fertilization and seed dispersal.
The next process after pollination is fertilization. From each pollen grain on the stigma a tube grows down the style to the ovary. The pollen tube carries male gametes to fertilize the ovary. The ovary is located inside a small rounded structure called an ovule.
The fertilized ovule develops into a seed and the ovary develops into a fruit.
Seeds cannot move themselves but nonetheless they often travel long distances form the parent plant. This is called seed dispersal and it reduces competition between offspring and parent and helps to spread the species. The type of seed dispersal depends on the structure of the fruit.
The next process after pollination is fertilization. From each pollen grain on the stigma a tube grows down the style to the ovary. The pollen tube carries male gametes to fertilize the ovary. The ovary is located inside a small rounded structure called an ovule.
The fertilized ovule develops into a seed and the ovary develops into a fruit.
Seeds cannot move themselves but nonetheless they often travel long distances form the parent plant. This is called seed dispersal and it reduces competition between offspring and parent and helps to spread the species. The type of seed dispersal depends on the structure of the fruit.