Lecture AP Biology Chapter 38, 39 Angiosperm reproduction Plant responses to internal and external signals

Chapter 38 and 39 provides knowledge of angiosperm reproduction Plant responses to internal and external signals. In this chapter, the following content will be discussed: Types of fruit, plant peproduction, experiments with light and the coleoptile, ethylene gas: fruit ripening, plant movement, plant responses to light, plant responses to stress.

Chapter 38 Angiosperm Reproduction Angiosperms have unique F eatures: F lowers F ruits Double F ertilization (by sperm) REPRODUCTIVE VARIATIONS  Pollination : transfer pollen from anther to stigma   Some plants are self-pollinated Cross-pollinated plants: ◦ Self-incompatibility: plant rejects own pollen or closely related plant ◦ Maximize genetic variation Stigma Stigma Anther with pollen Pin flower Thrum flower “Pin” and “thrum” flower types reduce self-fertilization The development of a plant embryo Fruit      Egg cell  plant embryo Ovules inside ovary  seeds Ripe ovary  fruit Fruit protects enclosed seed(s) Aids in dispersal by water, wind, or animals Seeds Mature seed  dormancy (resting) ◦ Low metabolic rate ◦ Growth & development suspended ◦ Resumes growth when environmental conditions suitable for germination Important plant hormones : Auxin – stimulate cell elongation  phototropism & gravitropism (high concentrations = herbicide) Cytokinins – cell division (cytokinesis) & differentiation Gibberellins – stem elongation, leaf growth, germination, flowering, fruit development Abscisic Acid – slows growth; closes stomata during H2O stress; promote dormancy Ethylene – promote fruit ripening (positive feedback!); involved in apoptosis (shed leaves, death of annuals) The effects of gibberellin on stem elongation and fruit growth Ethylene Gas: Fruit Ripening Canister of ethylene gas to ripen bananas in shipping container Untreated tomatoes vs Ethylene treatment Plant Movement Tropisms: growth responses  SLOW  Phototropism – light (auxin)  Gravitropism – gravity (auxin)  Thigmotropism – touch Turgor movement: allow plant to make relatively rapid & reversible responses  Venus fly trap, mimosa leaves, “sleep” movement Positive gravitropism in roots: the statolith hypothesis Thigmotropism: rapid turgor movements by Mimosa plant  action potentials Plant Responses to Light Plants can detect direction, intensity, & wavelenth of light  Phytochromes: light receptors, absorbs mostly red light  ◦ Regulate seed germination, shade avoidance Biological Clocks Circadian rhythm: biological clocks  Persist w/o environmental cues  Frequency = 24 hours Phytochrome system + Biological clock = plant can determine time of year based on amount of light/darkness Photoperiodism : physiological response to the relative length of night & day (i.e flowering)  Short-day plants: flower when nights are long (mums, poinsettia)  Long-day plant: flower when nights are short (spinach, iris, veggies)  Day-neutral plant: unaffected by photoperiod (tomatoes, rice, dandelions) How does interrupting the dark period with a brief exposure to light affect flowering? Plant responses to stress Drought (H2O deficit):  close stoma  release abscisic acid to keep stoma closed  Inhibit growth  roll leaves  reduce SA & transpiration  deeper roots Flooding (O2 deprivation):  release ethylene  root cell death  air tubes formed to provide O2 to submerged roots Excess Salt:  cell membrane – impede salt uptake  produce solutes to ↓ψ - retain H2O Heat:  evap cooling via transpiration  heat shock proteins – prevent denaturation Cold:  alter lipid composition of membrane (↑unsat fatty acids, ↑fluidity)  increase cytoplasmic solutes  antifreeze proteins Herbivores:  physical (thorns)  chemicals (garlic, mint)  recruit predatory animals (parasitoid wasps) Pathogens:  1st line of defense = epidermis  2nd line = pathogen recognition, host-specific ... protein toxic to insects ◦ Biofuels – reduce CO2 emissions  Biodiesel: vegetable oils  Bioethanol: convert cellulose into ethanol Chapter 39 Plant Responses to Internal and External Signals. .. changes to begin growth  ◦  Root develops  shoot emerges  leaves expand & turn green (photosynthesis) Very hazardous for plants due to vulnerability  Predators, parasites, wind Plant Reproduction. .. statolith hypothesis Thigmotropism: rapid turgor movements by Mimosa plant  action potentials Plant Responses to Light Plants can detect direction, intensity, & wavelenth of light  Phytochromes: