1. Chapter 38 Angiosperm Reproduction and Biotechnology

2. Review In angiosperms, the dominant sporophyte (remember that alternation of generations as a key plant trait) – Produces male gametophytes (pollen grains) within anthers – Produces female gametophytes (embryo sacs) within the ovule – With fertilization (union of sperm and egg) the ovules develop into seeds, while the ovary becomes the fruit.

3. An overview of angiosperm reproduction Anther at tip of stamen Filament Anther Stamen Pollen tube Germinated pollen grain (n) (male gametophyte) on stigma of carpel Ovary (base of carpel) Ovule Embryo sac (n) (female gametophyte) FERTILIZATION Egg (n) Sperm (n) Petal Receptacle Sepal Style Ovary Key Haploid (n) Diploid (2n) An idealized flower. angiosperm life cycle. Mature sporophyte plant (2n) with flowers Seed (develops from ovule) Zygote (2n) Embryo (2n) (sporophyte) Simple fruit (develops from ovary) Germinating seed Seed Carpel Stigma

4. Flower Structure Flowers – Are the reproductive shoots of the angiosperm sporophyte – Are composed of four floral organs: sepals, petals, stamens, and carpels – Many variations in floral structure have evolved Bilateral symmetry (orchid) Sepal Radial symmetry (daffodil) Fused petals Semi-inferior ovaryInferior ovary Superior ovary Lupine inflorescence Sunflower inflorescence Maize, a monoecious species Dioecious Sagittaria latifolia (common arrowhead) REPRODUCTIVE VARIATIONS SYMMETRY OVARY LOCATION FLORAL DISTRIBUTION Flower variations (Inflorescences are clusters of small flowers) (Stamate and carpellate flowers on the same plant) (Stamate and carpellate flowers on separate plants. Reduces inbreeding) (Ovary relation to stamen, petal, and sepal attachment site)

5. Flower Parts Sepals - enclose and protect flower bud before it opens Petals – may be colored to advertise the flower to pollinators Carpels – ovary base, slender neck (style), and stigma (a landing platform for pollen) Stamen – filament stalk and terminal anther (which contains the pollen sacs) Complete flowers have all four basic flower organs Incomplete flowers lack something (grass flower may lack petals)

6. Pollination Pollination is the transfer of pollen from an anther to a stigma If pollination is successful, a pollen grain produces a pollen tube, which grows down into the ovary and discharges sperm near the embryo sac

7. Pollen grain development Pollen d evelops from microspores within the sporangia of anthers 3 A pollen grain becomes a mature male gametophyte when its nucleus divides and forms two sperm. This usually occurs after a pollen grain lands on the stigma of a carpel and the pollen tube begins to grow. (See Figure 38.2b.) 2 Each microsporo- cyte divides by meiosis to produce four haploid microspores, each of which develops into a pollen grain. Pollen sac (microsporangium) Micro- sporocyte Micro- spores (4) Each of 4 microspores Generative cell (will form 2 sperm) Male Gametophyte (pollen grain) Nucleus of tube cell Each one of the microsporangia contains diploid microsporocytes (microspore mother cells). 1 75  m 20  m Ragweed pollen grain MEIOSIS MITOSIS KEY to labels Haploid (2n) Diploid (2n) Microsporangium Microsporocyte Microspore Pollen grain

8. Key to labels MITOSIS MEIOSIS Ovule Integuments Embryo sac Mega- sporangium Mega- sporocyte Integuments Micropyle Surviving megaspore Antipodel Cells (3) Polar Nuclei (2) Egg (1) Synergids (2) Within the ovule’s megasporangium is a large diploid cell called the megasporocyte (megaspore mother cell). 1 Three mitotic divisions of the megaspore form the embryo sac, a multicellular female gametophyte. The ovule now consists of the embryo sac along with the surrounding integuments (protective tissue). 3 Female gametophyte (embryo sac) Diploid (2n) Haploid (2n) 100  m The megasporocyte divides by meiosis and gives rise to four haploid cells, but in most species only one of these survives as the megaspore. 2 Embryo sac development Embryo sacs develop from megaspores within ovules Megasporangium Megasporocyte Megaspore Embryo sac

9. Mechanisms That Prevent Self-Fertilization The most common anti-selfing mechanism in flowering plants is known as self-incompatibility, the ability of a plant to reject its own pollen Some angiosperms have structural adaptations that make it difficult for a flower to fertilize itself Stigma Anther with pollen Stigma Pin flowerThrum flower Some species produce two types of flowers: Pin flowers-long styles/short stamens Thrum flowers-short styles/long stamens Pollinating insects would collect pollen on different body areas and deposit the pollen on the opposite flower type!

10. Detaselling corn In corn, hybrid seed corn is far superior to inbred (self-fertilized corn) Detaselling involves removing the pollen-producing top part of the plant, the tassel, so the corn can't pollinate itself. Instead, pollen from another variety of corn grown in the same field is carried by the wind, pollinating the detasseled corn. The result is corn that bears the genetic characteristics of both varieties and can produce healthier crops with higher yields.

11. Detaselling corn…a Midwest tradition for teens? Despite technological advances in agriculture, detasseling is still a task that for the most part is done by hand. The detasseling season lasts only about 20 days beginning in mid-July. Pioneer Hi-Bred International Inc., the world's largest seed company, employed about 35,000 detasselers in the U.S. last summer. The tradition of detasseling could be coming to an end. Seed companies are developing ways to make wider use of "male-sterile corn" - corn whose tassel doesn't produce pollen, thereby eliminating the need for detasselers. It's planted next to a corn variety that is able to pollinate, so cross-pollination can be achieved more efficiently Steps involved include finding the tassel, grabbing it, pulling it off, and throwing it to the ground. That is all there is to it!

12. Double Fertilization After landing on a receptive stigma a pollen grain germinates and produces a pollen tube that extends down between the cells of the style toward the ovary The pollen tube then discharges two sperm into the embryo sac In double fertilization – One sperm fertilizes the egg – The other sperm combines with the polar nuclei, giving rise to the food-storing endosperm

13. Stigma Polar nuclei Egg Pollen grain Pollen tube 2 sperm Style Ovary Ovule (containing female gametophyte, or embryo sac) Micropyle Ovule Polar nuclei Egg Two sperm about to be discharged Endosperm nucleus (3n) (2 polar nuclei plus sperm) Zygote (2n) (egg plus sperm) Growth of the pollen tube and double fertilization If a pollen grain germinates, a pollen tube grows down the style toward the ovary. 1 The pollen tube discharges two sperm into the female gametophyte (embryo sac) within an ovule. 2 One sperm fertilizes the egg, forming the zygote. The other sperm combines with the two polar nuclei of the embryo sac’s large central cell, forming a triploid cell that develops into the nutritive tissue called endosperm. 3

14. From Ovule to Seed After double fertilization – Each ovule develops into a seed – The ovary develops into a fruit enclosing the seed(s)

15. Endosperm Development Endosperm development – Usually precedes embryo development In most monocots and some eudicots – The endosperm stores nutrients that can be used by the seedling after germination In other eudicots – The food reserves of the endosperm are completely exported to the cotyledons (see bean seed  )

16. Seed Structure The embryo and its food supply are enclosed by a hard, protective seed coat In a common garden bean, a eudicot, the embryo consists of the hypocotyl, radicle, and thick cotyledons (seed leaves) Common garden bean, a eudicot with thick cotyledons. The fleshy cotyledons store food absorbed from the endosperm before the seed germinates. Seed coat Radicle Epicotyl Hypocotyl Cotyledons Hypocotyl : The embryonic axis below cotyledon attachment point and above radicle Epicotyl: The embryonic axis above point of cotyledon attachment Radicle: The embryonic root Note lack of obvious endosperm

17. The seeds of other eudicots, such as castor beans have similar structures, but thin cotyledons Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons. The narrow, membranous cotyledons (shown in edge and flat views) absorb food from the endosperm when the seed germinates. Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons. The narrow, membranous cotyledons (shown in edge and flat views) absorb food from the endosperm when the seed germinates.

18. Monocot seed The embryo of a monocot as a single cotyledon, a coleoptile, and a coleorhiza (c) Maize, a monocot. Like all monocots, maize has only one cotyledon. Maize and other grasses have a large cotyledon called a scutellum. The rudimentary shoot is sheathed in a structure called the coleoptile, and the coleorhiza covers the young root. Scutellum (cotyledon) Coleoptile Coleorhiza Pericarp fused with seed coat Endosperm Epicotyl Hypocotyl Radicle Coleoptile : protective sheath enclosing the shoot tip and embryonic leaves of grasses. Coleorhiza : protective sheath enclosing the embryonic root of grasses

19. Fruit A fruit – Develops from the ovary – Protects the enclosed seeds – Aids in the dispersal of seeds by wind or animals – Fruits are classified into several types (Review Lab)

20. Seed Germination and Seed Dormancy Seed dormancy – As a seed matures it dehydrates and enters a phase referred to as dormancy – increases the chances that germination will occur at a time and place most advantageous to the seedling – The breaking of seed dormancy often requires environmental cues, such as temperature or lighting cues Germination of seeds depends on the physical process called imbibition (the uptake of water) – this triggers metabolic changes in the embryo that promote growth

21. Dicot germination Foliage leaves Cotyledon Hypocotyl Radicle Epicotyl Seed coat Cotyledon Hypocotyl Cotyledon Hypocotyl Common garden bean. In common garden beans, straightening of a hook in the hypocotyl pulls the cotyledons from the soil. (a) The radicle is the first organ to emerge from the germinating seed In many eudicots a hook forms in the hypocotyl, and growth pushes the hook above ground

22. Monocot germination Monocots – Use a different method for breaking ground when they germinate – The coleoptile pushes upward through the soil and into the air Foliage leaves Coleoptile Radicle Maize. In maize and other grasses, the shoot grows straight up through the tube of the coleoptile. (b)

23. Asexual Reproduction Many angiosperm species reproduce both asexually and sexually Sexual reproduction generates the genetic variation that makes evolutionary adaptation possible Asexual reproduction in plants – Is also called vegetative reproduction – Results in a clone (a genetic duplicate to the parent plant)

24. Mechanisms of Asexual Reproduction Fragmentation (the separation of a parent plant into parts that develop into whole plants) is one of the most common modes of asexual reproduction In some species the root system of a single parent gives rise to many adventitious shoots that become separate shoot systems Photo shows groups of aspen trees that have descended by asexual reproduction from root system of parent trees. Separate groves derived from the root systems of different parents show a genetic variation in timing of fall color and leaf drop

25. Vegetative Propagation and Agriculture Humans have devised various methods for asexual propagation of angiosperms Many kinds of plants are asexually reproduced from plant fragments called cuttings Grafting: Cuttings a twig or bud from one plant can be grafted onto a plant of a closely related species or a different variety of the same species

26. Test-Tube Cloning (Plant tissue culture) Plant biologists have adopted in vitro methods – To create and clone novel plant varieties Just a few parenchyma cells from a carrot gave rise to this callus, a mass of undifferentiated cells. (a) The callus differentiates into an entire plant, with leaves, stems, and roots. (b)

27. Protoplast Fusion Fusion of protoplasts, plant cells with their cell walls removed, to create hybrid plants. Hybrids can be created from two different plant species that would otherwise be reproductively incompatible

28. Plant Breeding…Artificial Selection Humans have intervened in the reproduction and genetic makeup of plants for thousands of years Maize is a product of artificial selection by humans. It is a staple in many developing countries, but is a poor source of protein for human and livestock Teosinte Modern Maize

29. Interspecific hybridization of plants – Is common in nature and has been used by breeders, ancient and modern, to introduce new genes into important crops – Modern wheat was developed in this fashion

30. Plant Biotechnology Plant biotechnology has two meanings – It refers to innovations in the use of plants to make products of use to humans – It refers to the use of genetically modified (GM) organisms in agriculture and industry It will dramatically change agriculture

31. Reducing World Hunger and Malnutrition Genetically modified plants – Have the potential of increasing the quality and quantity of food worldwide Ordinary rice Genetically modified Golden Rice TransgenicNon-transgenic Daffodil genes allowing for the production of Beta- carotene were introduced into rice Papaya has been engineered to resist Ring spot virus

33. BT Corn

34. BT Corn basics BT protein is produced by the bacterium Bacillus thuringiensis. Toxic to some insects, nontoxic to all other life forms BT corn has the gene inserted so that the corn plant makes the BT protein. Ingestion of BT protein by the larvae of the European Corn Borer kills the larvae The corn plant now has it’s own defense

35. How widespread? 2006 - 250 million acres grown by 10 million farmers in 22 countries were planted with transgenic crops. United States > Argentina > Brazil > India> Canada > China Soybeans 57% of biotech acreage, corn 25%, cotton 13%, canola 5% What’s next – Bananas that produce human vaccines – Fish that mature more quickly – Plants that produce plastics – Fruit/nut trees that yield years earlier – Crops that grow where they could not before

36. The Biotech Floodgate

37. Transgenic plants and vaccines

39. The Debate over Plant Biotechnology Some biologists are concerned about the unknown risks associated with the release of GM organisms (GMOs) into the environment GM crops – Might have unforeseen effects on nontarget organisms – There is also the possibility of the introduced genes escaping from a transgenic crop into related weeds through crop-to-weed hybridization

40. Quotes from your textbook “Technological advances almost always involve the risk of unintended outcomes. In plant biotechnology, zero risk is probably unattainable” “The best case scenario is for these discussions and decisions to be based on sound scientific information and testing rather than on reflexive fear or blind optimism”

41. http://www.learner.org/channel/courses/biology /units/gmo/index.html#http://www.learner.org/channel/courses/biology /units/gmo/index.html# VIDEO CLIP