Reproduction in plants Topic 9.4

U: Flowering involves a change in gene expression in the shoot apex Stages of a Flowering Plant: Germination = sprouting of a plant from a seed Vegetative phase = period of growth between germination & flowering (weeks, months, yrs) Vegetative structures = roots, stems, leaves Reproductive phase = shoot apical meristems start producing parts of flowers instead of leaves Flowers “reproductive shoot” allow for sexual reproduction increase variety

Flowering & gene expression Triggers that cause flowering: Temp Day length (main trigger)  it’s really the length of darkness that matters Short-day plants (flower in autumn) Long-day plants (flower in summer) Light plays role in production of inhibitors or activators of genes that control flowering: LD plants  phytochrome pigment activates flower-time (FT) gene SD plants  phytochrome pigment inhibits FT gene

U: The switch to flowering is a response to the length of light & dark periods in many plants Phytochrome = pigment in leaves that plants use to measure the length of dark period Switches between 2 forms: PR  absorbs red light (660 nm); more stable form PFR  absorbs far-red light (730 nm); active form Long-day plants (short nights) = large amount of PFR (promoter), causing transcription of flowering gene Short-day plants (long nights) = little amount of PFR (inhibitor), so since there’s very little inhibitor, plant will flower

App: Methods used to induce short-day plants to flower out of season Flower-forcing = getting flowers to bloom out of season or at a specific time such as during holidays Growers manipulate length of days and nights http://bcs.whfreeman.com/WebPub/Biology/hillis1e/Animated%20Tutorials/at2702/at_2702_days_ni ghts.html

Skill: Drawing of half-views of animal-pollinated flowers

U: Most flowering plants use mutualistic relationships w/ pollinators in sexual reproduction Pollination = transfer of pollen from stamen to stigma Methods of transfer: Wind Water Animal pollinators (birds like hummingbird, insects like butterflies & bees, bats) Mutualism = relationship where both organisms benefit Pollinator gains food (nectar), plant gains mean to transfer pollen

U: Success in plant reproduction depends on pollination, fertilization & seed dispersal Order of events in a flowering plant: Pollination = transfer of pollen from stamen to stigma Fertilization Pollen grain lands on sticky stigma Pollen tube grows down style; male gametes travel down tube Male gamete fuses with female gamete (ovule = small egg) Ovules develop into seeds; ovary develops into fruit Seed dispersal Reduces competition between offspring & parent Spreads the species Different types of seeds for different methods of dispersal (e.g. feathery to catch wind; hooks to catch animal fur; fleshy to attract animals to eat) Fertilization:

NOS: Paradigm shifts: more than 85% of world’s 250,000 species of flowering plants depends on pollinators for reproduction. This knowledge has led to protecting entire ecosystems rather than individual species Traditionally, focus of conservation efforts was on single populations & single species Now, we know the whole ecosystem must be protected! Why? Mutualistic relationships between pollinators and flowering plants Example: Saguaro cactus in Sonoran desert Cactus provides perching & nesting sites for several species of birds Bats & several species of birds eat cactus fruit & disperse seeds Flowers attract different species of bats to their nectar, transferring pollen One bat (lesser long-nosed bat) is endangered Invasive grasses, development of desert, and changes in natural fire cycles threaten cactus Must protect the bats, cactus and seed-dispersing animals  the whole ecosystem!

Skill: Drawing internal structure of seeds

Cotyledon = seed leaf

Skill: Design of experiments to test hypotheses about factors affecting germination Germination is the process by which a seed emerges from a period of dormancy and starts to sprout For germination to occur, a seed requires a combination of: Oxygen:  For aerobic respiration (need ATP in order to grow) Water:  To metabolically activate the cells Temperature:  For the optimal function of enzymes In addition, particular seed species may require other specialised conditions, such as: • Fire            • Light or darkness            • Freezing            • Prior animal digestion            • Erosion of the seed coat            • Washing (to remove inhibitors)

Metabolic process during germination: Absorption of water, which causes gibberellin (gibberellic acid (GA)) to be produced Gibberellin causes the synthesis of amylase, which breaks down starch into maltose Maltose transported to embryo, where it’s either hydrolyzed to glucose (for energy) or condensed to cellulose (for cell wall) Stored proteins & lipids will also be hydrolyzed to form enzymes, triglycerides and phospholipids Germination uses food stored in cotyledons as energy source until developing shoot reaches light & begin photosynthesis