Angiosperm Reproduction.pptx

Angiosperm Reproduction  Angiosperm Reproduction I. Flower Structure and Function II. Seed Development, Form, and Function III. Fruit Form and Function IV. Asexual Reproduction V. Plant Biotechnology  Learning Objectives 1. Describe the structures and functions of a flower’s parts 2....

Angiosperm Reproduction  Angiosperm Reproduction I. Flower Structure and Function II. Seed Development, Form, and Function III. Fruit Form and Function IV. Asexual Reproduction V. Plant Biotechnology  Learning Objectives 1. Describe the structures and functions of a flower’s parts 2. Distinguish between complete and incomplete flowers 3. Compare and contrast the male and female gametophyte of an angiosperm 4. Explain the importance of pollinators and their modes of delivering pollen 5. Evaluate the purpose of double fertilization 6. Describe the development of embryos and seeds Learning Objectives (contd.) 7. Compare and contrast the structures of dicot and monocot seeds 8. Explain how germination in dicots differs from germination in monocots. 9. Explain the difference between simple, aggregate, and multiple fruits. 10. Evaluate the benefits and concerns of biotechnology on the development of new crops  I. Flower Structure and Function A. Flowers are the reproductive shoots of the angiosperm sporophyte; they attach to a part of the stem called the receptacle 1. Flowers consist of four floral organs: sepals, petals, stamens, and carpels 2. Sepals and petals are sterile 3. A stamen consists of a filament topped by an anther with pollen sacs that produce pollen 4. A carpel has a long style with a stigma on which pollen may land 6. At the base of the style is an ovary containing one or more ovules 7. A single carpel or group of fused carpels is called a pistil 8. Complete flowers contain all four floral organs 9. Incomplete flowers lack one or more floral organs, for example stamens or carpels 10. Clusters of flowers are called inflorescences B. Development of Male Gametophytes 1. Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers 2. A microspore undergoes mitosis to produce two cells: the generative cell and the tube cell 3. A pollen grain consists of the two-celled male gametophyte and the spore wall 4. If pollination succeeds, a pollen grain produces a pollen tube that grows down into the ovary and discharges two sperm cells near the embryo sac C. Development of the Female Gametophyte 1. The embryo sac, or female gametophyte, develops within the ovule 2. Within an ovule, two integuments surround a megasporangium 3. One cell in the megasporangium undergoes meiosis, producing four megaspores, only one of which survives 4. The megaspore divides, producing a large cell with eight nuclei D. Pollination 1. In angiosperms, pollination is the transfer of pollen from an anther to a stigma 2. Pollination can be by wind, water, or animals 3. Wind-pollinated species (e.g., grasses and many trees) release large amounts of pollen E. Flower-Pollinator Coevolution 1. Coevolution is the evolution of interacting species in response to changes in each other 2. Many flowering plants have coevolved with specific pollinators 3. The shapes and sizes of flowers often correspond to the pollen transporting parts of their animal pollinators For example, Darwin correctly predicted a moth with a 28 cm long tongue based on the morphology of a particular flower F. Double Fertilization 1. Double fertilization results from the discharge of two sperm from the pollen tube into the embryo sac 2. One sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid food-storing endosperm (3n)  II. Seed Development, Form, and Function A. Endosperm Development 1. Endosperm development usually precedes embryo development 2. In most monocots and some eudicots, endosperm stores nutrients that can be used by the seedling 3. In other eudicots, the food reserves of the endosperm are exported to the cotyledons B. Embryo Development 1. The first mitotic division of the zygote splits the fertilized egg into a basal cell and a terminal cell 2. The basal cell produces a multicellular suspensor, which anchors the embryo to the parent plant 3. The terminal cell gives rise to most of the embryo 4. The cotyledons form and the embryo elongates C. Seed Development 1. The embryo and its food supply are enclosed by a hard, protective seed coat 2. The seed enters a state of dormancy 3. A mature seed is only about 5–15% water 4. In some eudicots, such as the common garden bean, the embryo consists of the embryonic axis attached to two thick cotyledons (seed leaves) 5. Below the cotyledons the embryonic axis is called the hypocotyl and terminates in the radicle (embryonic root); above the cotyledons it is called the epicotyl 6. The plumule comprises the epicotyl, young leaves, and shoot apical meristem 7. The seeds of some eudicots, such as castor beans, have thin cotyledons 8. A monocot embryo has one cotyledon 9. Grasses, such as maize and wheat, have a special cotyledon called a scutellum 10. Two sheathes enclose the embryo of a grass seed: a coleoptile covering the young shoot and a coleorhiza covering the young root D. Seed Germination 1. Germination depends on imbibition, the uptake of water due to low water potential of the dry seed 2. The radicle (embryonic root) emerges first 3. Next, the shoot tip breaks through the soil surface 4. In many eudicots, a hook forms in the hypocotyl, and growth pushes the hook above ground 5. Light causes the hook to straighten and pull the cotyledons and shoot tip up 6. In maize and other grasses, which are monocots, the coleoptile pushes up through the soil  III. Fruit Structure and Function A. A fruit develops from the ovary 1. It protects the enclosed seeds and aids in seed dispersal by wind or animals 2. A fruit may be classified as dry, if the ovary dries out at maturity, or fleshy, if the ovary becomes thick, soft, and sweet at maturity B. Fruits are also classified by their development 1. Simple, a single or several fused carpels 2. Aggregate, a single flower with multiple separate carpels 3. Multiple, a group of flowers called an inflorescence 4. An accessory fruit contains other floral parts in addition to ovaries C. Fruit dispersal mechanisms include – Water – Wind – Animals  IV. Asexual Reproduction A. Fragmentation, separation of a parent plant into parts that develop into whole plants, is a very common type of asexual reproduction B. In some species, a parent plant’s root system gives rise to adventitious shoots that become separate shoot systems C. Apomixis is the asexual production of seeds from a diploid cell D. Asexual Plant Reproduction and Agriculture 1. Many kinds of plants are asexually reproduced from plant fragments called cuttings 2. A callus is a mass of dividing undifferentiated cells that forms where a stem is cut and produces adventitious roots 3. Grafting a) A twig or bud can be grafted onto a plant of a closely related species or variety b) The stock provides the root system c) The scion is grafted onto the 4. Transgenic plants are genetically modified (GM) to express a gene from another organism 5. Protoplast fusion is used to create hybrid plants by fusing protoplasts, plant  V. Plant Biotechnology A. Humans have intervened in the reproduction and genetic makeup of plants for thousands of years 1. Hybridization is common in nature and has been used by breeders to introduce new genes 2. Maize, a product of artificial selection, is a staple in many developing countries B. Plant biotechnology has two meanings – In a general sense, it refers to innovations in the use of plants to make useful products – In a specific sense, it refers to use of GM organisms in agriculture and industry Modern plant biotechnology is not limited to transfer of genes between closely related species or varieties of the same species C. Genetically modified plants may increase the quality and quantity of food worldwide Transgenic crops have been developed that – Produce proteins to defend them against insect pests – Tolerate herbicides – Resist specific diseases Nutritional quality of plants is being improved – For example, “Golden Rice” is a transgenic variety being developed to address vitamin A deficiencies among the world’s poor D. Human Health Concerns One concern is that genetic engineering may transfer allergens from a gene source to a plant used for food Some GMOs have health benefits – For example, maize that produces the Bt toxin has 90% less of a cancer- causing toxin than non-Bt corn – Bt maize has less insect damage and lower infection by Fusarium fungus that produces the cancer-causing toxin