Essential Idea v Reproduction in flowering plants is

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

Chapter 38 Angiosperm Reproduction travismulthaupt. com

Flowers are the reproductive shoots of the angiosperm sporophyte. v Floral organs are the sepals, petals, stamens and carpels. v

Flowering involves a change in gene expression at the shoot apex. v This change in gene expression happens when meristems in the shoot apex produce flowers instead of leaves. v

Flowers v Flowers are the sexual structures of plants.

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

Flowering v It is the dark period, specifically, that is the main trigger for the production of a flower.

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

Classic Experiments v 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.

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

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

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

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

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

USDA Flowering Experiments v One form caused seed germination, the other inhibited the germination response.

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

USDA Flowering Experiments v The question: How do plants in nature illicit a response to light and begin germination?

USDA Flowering Experiments If seeds are kept in the dark, they synthesize Pr. v When seeds are illuminated with sunlight, the Pr begins to be converted to Pfr. v The appearance of Pfr is one of the ways plants detect sunlight. v Adequate sunlight converts Pr to Pfr and triggers germination. v

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. v Again, the 2 forms of light canceled each other. v

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

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

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

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

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

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

Mechanisms Preventing Self. Fertilization v Monoecious plants often have floral organs that develop at different times.

Mechanisms Preventing Self. Fertilization v Some flowers arrange floral parts so plants can’t self-fertilize.

Mechanisms Preventing Self. Fertilization The most common mechanism is selfincompatibility. v An individual rejects its own pollen and that of its close relatives. v Biochemical blocks prevent pollen development. v

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

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

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

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

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

Fruit Development While the seeds are developing, the walls of the ovary are developing into a fruit. v The pericarp is the thickened walls of the ovary. v

Fruits v Simple fruits-derived from a single carpel or several fused carpels. – Examples: peas, peach, nut.

Fruits v Aggregate fruits result from a single flower that has more than one separate carpel. Each one grows a small fruit. – Example: raspberry.

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

Fruits v Fruit usually ripens around the time seeds complete their development. – Example: Peaches v 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 l 7 q. Tq. Gp. Kq. Xr 0 g. G 72 v 21 CQ&sa=X&oi=mode_link&ct=mode&cd=2&sqi=2&ved=0 CCo. Q_AUo. AQ &biw=1238&bih=819

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

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

Plant Reproduction v 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.

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