1. Angiosperm Reproduction and Plant Responses

2. Angiosperm Life Cycle Three unique features Flowers Fruits Double Fertilization

3. Gamete production Male – takes place in pollen sacs in the anther Produces pollen grains with 2 nuclei (1n) Tube nucleus – produces pollen tube Generative nucleus – yields two sperm Female – takes place in ovules in the ovary 3 important nuclei Egg – later fertilized to form zygote Two polar nuclei – later fuse with sperm to form endosperm (3n)

4. Pollination Transfer of pollen from anther to stigma If successful, a pollen tube is produced, which grows down to ovary Once it reaches the ovule two fertilization events occur….

5. Double Fertilization 1. One sperm fertilizes the egg  zygote Will develop into embryo and eventually new sporophyte 2. Other sperm combines with two polar nuclei  (3n) nucleus Gives rise to endosperm – food storing tissue within the seed

7. Seeds As the seed matures it enters dormancy Low metabolic rate and suspended growth Resumes growth when conditions are suitable for germination Germination may by triggered by: Water Temperature Light Chemicals

8. Self-fertilization Since some plants contain both male and female gametophytes, they are able to self- fertilize Some flowers prevent this to maximize variation Self-incompatibility genes plants reject their own pollen usually through biochemicals Physical barriers Often the stigma is higher than the anther Variation of gamete production times

9. Plant Response - Tropisms Plant response that results in growth toward or away from a stimulus Triggered by hormones – chemical messengers that are produced in one part and transported to another Phototropism – growth of shoot in response to light Positive – toward light Negative – away from light

10. Gravitropism – response to gravity Roots grow down (positive), shoots grow up (negative) Tell up from down by settling of statoliths (specialized plastids) Thigmotropism – directional growth of plant as a response to touch Tendrils are modified leaves that wrap around structures to support climbing plants Closing of mimosa leaves when touched

12. Hormones Auxins Stimulate elongation of cells within developing shoots Weakens cell wall by acidification and allows for expansion by turgor pressure Major role in tropisms Cause cells on the shady side to elongate (bending) Regulates fruit development

13. Cytokinins Essential role in cell division and differentiation Stimulate cytokinesis Stimulate germination Gibberellins Work with auxins to stimulate stem elongation Often non-functional in dwarf plants Help loosen cell walls Signal to end dormancy and germinate Stimulate flowering and fruit development

14. Abscisic acid Slows growth Promotes dormancy May signal closing of stomata Ethylene Is a gas Critical role in apoptosis Loss of leaves Triggers ripening of fruits

15. Response to Light Plants can detect direction, intensity and wavelength of light Red and blue are the most important colors in plant responses Phytochromes – absorb mostly red light Two forms: P r (red) and P fr (far red) Switch back and forth depending on which wavelength is in greatest supply Plant produces P r form which converted to the P fr form upon illumination P fr triggers many developmental responsesdevelopmental responses

16. Circadian Rhythms Physiological cycle that have a frequency of about 24 hours Not triggered by environmental variables Like an internal biological clock Reset by a surge of P fr Allows plant to asses the amount of daylight and darkness and time of year

17. Flowering Flowering may be triggered by environmental cues or as part of a predetermined developmental program. Genes often determine the transition from vegetative to reproductive growth Indeterminate, apical meristems on the shoots develop into a floral meristem with determinate growth Some flowering is a response to temperature Vernalization – plants flower after a period of cold

18. Photoperiodism Flowering response to photoperiod or relative lengths of night and day Short-day plants – require long period of continuous darkness Flower in winter, early spring, or fall Will not flower if exposed to flashes of light Long-day plants – flower only during short periods of continuous darkness Flower in late spring or early summer Day-neutral plants – can flower in days of any length

20. Response to Stress Drought – guard cells lose turgor to close stomata, young leaves stop growing, and deep roots continue to grow Flooding – ethylene production to cause apoptosis, creating air tubes Heat – close stomata and produce heat-shock proteins Cold – alter lipid composition of membranes

21. Response to herbivores and pathogens Thorns Poisonous or distasteful compounds Airborn attractants to herbivore predators Epidermal layer protects from viruses Biochemical methods for recognizing and dealing with pathogens