9.4 Reproduction in Plants

Flowering and Gene Expression Flowering involves a change in gene expression in the shoot apex. Vegetative structures = roots, stems, and leaves When a seed germinates, the young plant is in the VEGETATIVE PHASE. Can last for weeks, months, years

Flowering and Gene Expression Flowering involves a change in gene expression in the shoot apex. The change from vegetative to REPRODUCTIVE PHASE is marked by the production of the parts of flowers instead of leaves by the shoot apical meristems. Flowers allow for sexual reproduction. What is sexual reproduction? Why is it beneficial? What are its challenges?

Flowering and Gene Expression Flowering involves a change in gene expression in the shoot apex. What triggers the change from vegetative to reproductive phase? Temperature can play a role Day length More precisely it is the length of dark period Some plants are short-day (ie long-night) plants: Poinsettia Others are long-day (ie short-night) plants: Red clover Why does the length of night matter?

Flowering and Gene Expression The switch to flowering is in response to the length of light and dark periods in many plants. Light plays a role in the inhibition or activation of genes that control flowering. Experiments have shown that plants measure the length of dark periods. A pigment in leaves of plants is used to measure the dark… Called phytochrome Switches between two forms: PR and PFR PFR is the active form Receptor proteins in the cytoplasm are able to bind PFR not PR

Flowering and Gene Expression How does the plant use phytochrome to measure the length of dark? When PR absorbs red light it is converted to PFR When PFR absorbs far-red light it is converted to PR In normal sunlight, the red light is more plentiful, so PR is rapidly converted to PFR However, PR is more stable, so in the dark the PFR slowly converts back to PR

Flowering and Gene Expression In “long-day” plants, large amounts of the PFR remain after the short night. The binding of PFR to the receptor promotes the transcription of a “flowering time” gene (FT). The FT mRNA is transported in the phloem to the shoot apical meristem In the meristem, it is translated into FT protein. The FT protein then binds to a transcription factor. This binding activates other genes necessary for flowering to occur.

Flowering and Gene Expression In “short-day” plants, the binding of PFR to the receptor inhibits the transcription of the “flowering time” gene. At the end of long nights, very little PFR remains. The inhibition fails. The transcription and translation of genes needed for flowering are signalled. QUESTION: Contrast the control of flowering in short and long day plants.

Mutualism between flowers and pollinators Most flowering plants use mutualistic relationships with pollinators in sexual reproduction. Sexual reproduction requires the transfer of pollen. QUESTION: List methods of pollen transfer. State advantages and disadvantages of each.

Mutualism between flowers and pollinators Animals that transfer pollen are known as “pollinators”. Examples: birds, insects, rodents Mutualism = a close association between 2 organisms where both organisms benefit. Question: Explain how both plants and animals benefit from this relationship.

Parts of a flower Draw your version of the structure of an animal pollinated flower Label and annotate Discuss how this structure aligns with its function. See pg 431

Pollination, fertilization, and seed dispersal Success in plant reproduction depends on pollination, fertilization, and seed dispersal. Pollination = is the process by which pollen is transferred from the anther (male part) to the stigma (female part) of the plant.

Pollination, fertilization, and seed dispersal when pollen has landed on the stigma of a suitable flower of the same species, a chain of events happens that ends in the making of seeds: A pollen grain grows a tiny tube, all the way down the style to the ovary. This pollen tube carries a male gamete to meet the ovary in an ovule.

Pollination, fertilization, and seed dispersal Fertilization = the process during which two gametes join and their chromosomes combine, so that the fertilised cell contains a normal complement of chromosomes.

Pollination, fertilization, and seed dispersal The fertilized ovule goes on to form a seed, contains a food store and an embryo that will later grow into a new plant. The ovary develops into a fruit to protect the seed.

Pollination, fertilization, and seed dispersal Seeds can not move themselves, yet often travel long distances from the parent plant. Why? How?

Pollination, fertilization, and seed dispersal Reduces the competition between offspring and parent. Helps spread the species.

The structure of seeds Draw the internal structure of a seed Label and annotate See page 434