1. 1 travismulthaupt.com Essential Idea  Reproduction in flowering plants is influenced by the biotic and abiotic environment. 1

2. travismulthaupt.com Chapter 38 Angiosperm Reproduction

3. travismulthaupt.com Flowers  Flowers are the reproductive shoots of the angiosperm sporophyte.  Floral organs are the sepals, petals, stamens and carpels.

4. 4 travismulthaupt.com Flowering  Flowering involves a change in gene expression at the shoot apex.  This change in gene expression happens when meristems in the shoot apex produce flowers in stead of leaves. 4

5. 5 travismulthaupt.com Flowers  Flowers are the sexual structures of plants. 5

6. 6 travismulthaupt.com Flowering  Temperature and the length of day influence the formation of flowers.  Light plays a role in the production of inhibitors and activators of genes that control flowering. 6

7. 7 travismulthaupt.com Flowering  It is the dark period, specifically, that is the main trigger for the production of a flower. 7

8. travismulthaupt.com Classic Experiments  In the 1940’s scientists began experimenting with photoperiods.  They looked at the length of the night and day.  In these experiments, they found that short- day plants flower when days are 16 hours or shorter (nights are 8 hours or longer).

9. travismulthaupt.com Classic Experiments  They looked at flowering: –They found that if the daytime portion of photoperiod is broken by a brief period of darkness, there is no effect--that is, the plant still flowers. –However, if the nighttime portion of the photoperiod is interrupted by a short period of dim light, the plant doesn’t flower.

10. travismulthaupt.com Classic Experiments  The opposite is true for long-day plants.  When long day plants are grown in a photoperiod of a long night, flowering doesn’t occur.  However, if the long night portion of the experiment is interrupted by a brief period of dim light, flowering will occur.

11. travismulthaupt.com From These Experiments  Red light is most effective at interrupting the nighttime portion of the photoperiod.  Scientists have demonstrated that phytochrome is the pigment that measures the photoperiod.

12. travismulthaupt.com Extending the Experiments  Scientists at the USDA conducted these experiments.  Phytochrome was demonstrated to be the pigment responsible for seed germination.  From this, they were able to elucidate the flowering cycle.

13. travismulthaupt.com USDA Flowering Experiments  Seeds were subjected to a variety of monochromatic light.  Red and far-red light opposed each other in their germinating ability.  One induced germination, the other inhibited it.

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15. USDA Flowering Experiments  It was determined that the two different forms of light switched the phytochrome back and forth between two isomeric forms.

16. travismulthaupt.com USDA Flowering Experiments  One form caused seed germination, the other inhibited the germination response.

17. 17 travismulthaupt.com Flowering  The active form of phytochrome results in the transcription of the FT gene (flowering time).  FT mRNA gets transported in the phloem to the shoot apical meristem where it is translated into FT protein.  FT protein binds to a transcription factor enabling the activation of flowering genes. 17

18. travismulthaupt.com USDA Flowering Experiments  The question: How do plants in nature illicit a response to light and begin germination?

19. travismulthaupt.com USDA Flowering Experiments  If seeds are kept in the dark, they synthesize P r.  When seeds are illuminated with sunlight, they begin to be converted to P fr.  The appearance of P fr is one of the ways plants detect sunlight.  Adequate sunlight converts P r to P fr and triggers germination.

20. travismulthaupt.com USDA Flowering Experiments  In the flowering response, scientists were able to show the effects of the red and far red light on the flowering ability in plants.  Again, the 2 forms of light canceled each other.

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22. Pollination  Pollination is the first step in the chain of events which leads to fertilization.  It occurs when pollen from the stamen of one plant lands on the stigma of another plant.

23. 23 travismulthaupt.com Pollination  Pollination often occurs when pollen is transferred by the wind and/or animals.  Animals such as birds, bats and insects are the main sources of pollination. 23

24. 24 travismulthaupt.com Pollination  Pollinators are attracted to the plants by scents given off by plants.  The nectar in plants serve as a food source for pollinators.  When the pollinators are getting the nectar, they are picking up pollen and transferring it from one plant to another. 24

25. 25 travismulthaupt.com Pollination  Through the course of time, plants and pollinators have developed a mutualistic relationship where both of them benefit. 25 http://www.sciencedaily.com/releases/2015/08/150819103650.htm https://www.emaze.com/@AOZZTWOT/Presentation-Name

26. 26 travismulthaupt.com Pollination  Ideally plants don’t self-fertilize.  This ensures variety and a good mix of genes for future generations of plants. 26

27. travismulthaupt.com Mechanisms Preventing Self- Fertilization  Dioecious species can’t self-fertilize because they are either stamenate or capellate.

28. travismulthaupt.com Mechanisms Preventing Self- Fertilization  Monoecious plants often have floral organs that develop at different times.

29. travismulthaupt.com Mechanisms Preventing Self- Fertilization  Some flowers arrange floral parts so plants can’t self-fertilize.

30. travismulthaupt.com Mechanisms Preventing Self- Fertilization  The most common mechanism is self- incompatibility.  An individual rejects its own pollen and that of its close relatives.  Biochemical blocks prevent pollen development.

31. 31 travismulthaupt.com Fertilization  Fertilization occurs after pollination.  In this process, when a pollen grain lands on the stigma of a plant, a pollen tube grows down the carpel.  The male gametes travel through this pollen tube and eventually make their way to the egg. 31

32. travismulthaupt.com Double Fertilization  Double fertilization is unique to angiosperms.  One sperm fertilizes the egg.  The second sperm fertilizes the polar nuclei forming a triploid (3n) nucleus in the center of the large, central cell of the embryo sac.  This large cell gives rise to the endosperm--the food storing tissue of the seed.

33. travismulthaupt.com Double Fertilization  Double fertilization is an evolutionary mechanism which ensures the development of the endosperm only in ovules where the egg has been fertilized.  This helps prevent wasted resources.

34. travismulthaupt.com Double Fertilization  After double fertilization: –Each ovule develops into a seed. –The ovary develops into the fruit that encloses the seed.  The triploid nucleus divides forming a multi-nucleated supercell.

35. travismulthaupt.com Fruit Development  Once fertilization occurs and a zygote is formed.  The zygote gives rise to an embryo which grows inside the ovule that contains the developing seed.  The entire ovary develops into a fruit containing one or more seeds.

36. travismulthaupt.com Fruit Development  While the seeds are developing, the walls of the ovary are developing into a fruit.  The pericarp is the thickened walls of the ovary.

37. travismulthaupt.com Fruits  Simple fruits-derived from a single carpel or several fused carpels.  Ex: peas, peach, nut.

38. travismulthaupt.com Fruits  Aggregate fruits result from a single flower that has more than one separate carpel. Each one grows a small fruit.  Example: raspberry.

39. travismulthaupt.com Fruits  Multiple fruits develop from inflorescence. A group of flowers tightly clustered together.  When the walls of the ovaries thicken, they fuse together forming the fruit.  Example: pineapple.

40. travismulthaupt.com Fruits  Fruit usually ripens around the time seeds complete their development. –Example: Peaches  Some fruit ripens and then ages and dries out. –Example: Soybeans http://www.google.com/search?q=soybeans&hl=en&prmd=imvnsu&source=lnms&tbm=isch&ei=l l7qTqGpKqXr0gG72v21CQ&sa=X&oi=mode_link&ct=mode&cd=2&sqi=2&ved=0CCoQ_AUoAQ &biw=1238&bih=819

41. travismulthaupt.com Seed Maturation and Development  As a seed matures, it prepares for dormancy.  To break the dormancy, the seed has to find an optimal condition.

42. travismulthaupt.com Seed Production  The chances that a seedling will survive and produce offspring is very low.  This is why many plants produce so many seeds.  This is also why so many plants use asexual reproduction.

43. travismulthaupt.com Plant Reproduction  Some plants use both sexual and asexual reproduction. –Asexual reproduction –Advantages and disadvantages: Offspring more hearty than seedlings. Susceptible to catastrophe. –Sexual reproduction: Genetic variability to deal with changing environments. May not always have a mate.

44. travismulthaupt.com Seed Dispersal  Once seeds have been produced, there are a variety of mechanisms by which they are dispersed.  Wind and animals play a major role in seed dispersal.