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Biology Sylvia S. Mader Michael Windelspecht Chapter 27 Flowering Plants: Reproduction Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outline • • • • 27.1 Sexual Reproductive Strategies 27.2 Seed Development 27.3 Fruit Types and Dispersal 27.4 Asexual Reproductive Strategies 2 27.1 Sexual Reproductive Strategies • Plants have a two-stage, alternating life cycle – Sporophyte produces haploid spores by meiosis – Spores divide mitotically to become haploid gametophytes – Gametophytes produce gametes – Gametes fuse to produce a diploid zygote – Zygote divides mitotically to become the diploid sporophyte 3 Sexual Reproduction in Flowering Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. anther 2 ovule ovary microspore megaspore 4 Sexual Reproduction in Flowering Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. anther 7 seed 2 zygote ovule ovary 6 MEIOSIS FERTILIZATION 3 egg sperm 5 microspore megaspore 4 Male gametophyte (pollen graIn) Female gametophyte (embryo sac) 5 Sexual Reproduction in Flowering Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8 anther 1 7 sporophyte seed 2 zygote diploid(2n) 6 ovule ovary MEIOSIS FERTILIZATION haploid(n) 3 egg sperm 5 microspore megaspore 4 Male gametophyte (pollen graIn) Female gametophyte (embryo sac) 6 Sexual Reproductive Strategies • A flower produces two types of spores – Microspore - Male gametophyte • Undergoes mitosis • Becomes pollen grain – Megaspore - Female gametophyte • Undergoes mitosis • Becomes the female gametophyte, an embryo sac within an ovule within an ovary • Ovule becomes a seed • Ovary becomes a fruit 7 Sexual Reproductive Strategies • Flowers – Flowering occurs in response to environmental signals such as day length • In monocots, flower parts occur in threes and multiples of three • In eudicots, flower parts occur in fours or fives and multiples of four or five 8 Sexual Reproductive Strategies • A typical flower has four whorls of modified leaves attached to a receptacle at the end of a flower stalk called a peduncle – Sepals protect the bud – Petals attract pollinators – Stamens are male portion of flower • Anther - Saclike container • Filament - Slender stalk – Carpel is the female portion of flower • Stigma - Enlarged sticky knob • Style - Slender stalk • Ovary - Enlarged base enclosing ovules 9 Anatomy of a Flower Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. stamen anther filament petal sepal carpel stigma style ovary ovule receptacle peduncle 10 Monocot vs. Eudicot Flowers Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. p3 p2 carpel stamen p4 petal p1 p5 b. Festive azalea, Rhododendron sp. b: © Pat Pendarvis 11 Life Cycle of Flowering Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. anther ovule ovary Sporophyte 12 Life Cycle of Flowering Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. anther Development of the male gametophyte: Development of the female gametophyte: In pollen sacs of the anther, a microspore mother cell undergoes meiosis to produce 4 microspores each. In an ovule within an ovary, a megaspore mother cell undergoes meiosis to produce 4 megaspores. anther ovule ovary Sporophyte Pollen sac ovary microspore mother cell Ovule megaspore mother cell MEIOSIS MEIOSIS ovule wall Microspores Megaspores megaspore 3 megaspores disintegrate integument micropyle 13 Life Cycle of Flowering Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. anther Development of the male gametophyte: Development of the female gametophyte: In pollen sacs of the anther, a microspore mother cell undergoes meiosis to produce 4 microspores each In an ovule within an ovary, a megaspore mother cell undergoes meiosis to produce 4 megaspores anther ovule ovary Pollen sac ovary microspore mother cell Sporophyte Ovule megaspore mother cell MEIOSIS MEIOSIS ovule wall tube cell Microspores Megaspores generative cell ovule wall Pollen grain (male gametophyte) antipodals polar nuclei egg cell synergids Microspores develop into male gametophytes (pollen grains). One megaspore becomes the embryo sac (female gametophyte). Embryo sac (mature female gametophyte) (Top): Courtesy Graham Kent; (Bottom): © Ed Reschke megaspore 3 megaspores disintegrate integument micropyle 14 Life Cycle of Flowering Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. anther Mature Seed Development of the male gametophyte: In pollen sacs of the anther , a microspore mother cell undergoes meiosis to produce 4 microspores each seed coat The ovule develops into a seed containing the embryonic sporophyte and endosperm. Development of the female gametophyte: In an ovule within an ovary, a megaspore mother cell undergoes meiosis to Produce 4 megaspores. anther mitosis ovule ovary Pollen sac ovary Ovule embryo microspore mother cell endosperm (3n) Sporophyte Seed megaspore mother cell diploid (2n) MEIOSIS DOUBLE FERTILIZATION MEIOSIS haploid (n) ovule wall tube cell Pollination Microspores During double fertilization, one sperm from the Male gametophyte Will fertilize the egg; another Sperm will join with polar nuclei to produce the 3n endosperm. Development of the sporophyte: pollen tube Pollination occurs; a pollen grain germinates and produces a pollen sperm Mature male gametophyte polar nuclei egg sperm tube cell nucleus generative cell Megaspores ovule wall Pollen grain (male gametophyte) antipodals polar nuclei egg cell Microspores develop into male gametophytes (pollen grains). One megaspore becomes the embryo sac (female gametophyte). megaspore 3 megaspores disintegrate integument micropyle synergids Embryo sac (mature female gametophyte) (Top): Courtesy Graham Kent; (Bottom): © Ed Reschke 15 Sexual Reproductive Strategies • Male Gametophytes – Microspores are produced in anthers – Each anther has four pollen sacs, each with many microspore mother cells • Microspore mother cells undergo meiosis to produce microspores • Microspores undergo mitosis to produce pollen grains 16 Sexual Reproductive Strategies • The ovary contains one or more ovules – An ovule has a central mass of parenchyma cells covered by integuments – One parenchyma cell enlarges to become a megaspore mother cell • The megaspore mother cell undergoes meiosis to produce four haploid megaspores, three of which are nonfunctional • The functional megaspore divides mitotically until there are eight nuclei in the female gametophyte – The female gametophyte (embryo sac) contains • One egg cell associated with two synergid cells • One central cell with two polar nuclei • Three antipodal cells 17 Sexual Reproductive Strategies • Pollination – The transfer of pollen from an anther to the stigma of a carpel • Self-pollination occurs if the pollen is from the same plant • Cross-pollination occurs if the pollen is from a different plant 18 Sexual Reproductive Strategies • Fertilization • When a pollen grain lands on the stigma, it germinates, forming a pollen tube • The pollen tube passes between the stigma and style to reach the micropyle of the ovule • Double fertilization occurs – One sperm nucleus unites with the egg nucleus, producing a 2n zygote – The other sperm nucleus unites with the polar nuclei, forming a 3n endosperm nucleus, which develops into the endosperm • A mature seed contains the embryo, stored food, and the seed coat 19 Plants and Their Pollinators Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b. Ba: © Anthony Mercieca/Photo Researchers, Inc.; Bb: © Merlin D. Tuttle/Bat Conservation International; 20 27.2 Seed Development • Development: – Programmed series of stages from a simple to a more complex form – Development of a eudicot embryo • After double fertilization, the zygote divides repeatedly to form a proembryo and a suspensor – During the globular stage, the proembryo is a ball of cells • The outermost cells will become dermal tissue 21 Seed Development • Heart and Torpedo Stages • The embryo is heart shaped when cotyledons appear • The embryo enlarges, elongates, and takes on a torpedo shape 22 Seed Development • Mature Embryo – The epicotyl is the portion between cotyledons contributing to shoot development – The hypocotyl is the portion below that contributes to stem development – The radicle is the embryonic root 23 Development of an Eudicot Embryo Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Arabidopsis thaliana endosperm endosperm nucleus embryo suspensor zygote 1 zygote Zygote stage: Double fertilization results in zygote (true green) and endosperm. basal cell 2 Proembryo stage: Embryo (green) is multicellular and the suspensor (purple) is functional. (Proembryo): Courtesy Dr. Chun-Ming Liu; (Torpedo): © Biology Media/Photo Researchers, Inc.; (Mature embryo): © Jack Bostrack/Visuals Unlimited 24 Development of an Eudicot Embryo (continued) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A. thaliana A. thaliana endosperm cotyledons appearing Capsella shoot apical meristem Capsella bending cotyledons hypocotyl (root axis) epicotyl (shoot apical meristem) seed coat endosperm root apical meristem 3 Globular stage: Embryo is globe shaped. 4 Heart stage: Embryo is heart shaped. 5 Torpedo stage: Embryo is torpedo shaped; the cotyledons are obvious. radicle (root apical meristem) cotyledons 6 Mature embryo stage: The epicotyl will be the shoot system; the hypocotyl will be the root system. (Proembryo): Courtesy Dr. Chun-Ming Liu; (Torpedo): © Biology Media/Photo Researchers, Inc.; (Mature embryo): © Jack Bostrack/Visuals Unlimited 25 Monocot vs. Eudicot Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. seed coat plumule pericarp hypocotyl endosperm coleoptile radicle cotyledon embryo embryo plumule cotyledon radicle coleorhiza a. b. a: © Dwight Kuhn; b: Courtesy Ray F. Evert/University of Wisconsin Madison 26 27.3 Fruit Types and Seed Dispersal • A fruit is a mature ovary • Simple Fruits – Simple fruits are derived from single ovary with one or several chambers • Compound fruits develop from several groups of ovaries – Aggregate Fruits • Ovaries are from a single flower one receptacle • Blackberry – Multiple Fruits • Ovaries are from separate flowers clustered together • Pineapple 27 Fruit Types and Seed Dispersal • Fruit Development – The ovary wall thickens to become the pericarp, which can have three layers • The exocarp forms the outermost skin • The mesocarp is the fleshy tissue between the exocarp and the endocarp • The endocarp is the boundary around the seeds 28 Fruit Types and Seed Dispersal • Fruit Types – In dry fruits, the pericarp is paper, leathery, or woody when the fruit is mature • Dehiscent - the fruit splits open when ripe – Legumes • Indehiscent - the fruit does not split open when ripe – Grains 29 Fruit Types and Seed Dispersal • Dispersal of Fruits – Many dry fruits are dispersed by wind • Woolly hairs, plumes, wings – Many fruits attract animals and provide them with food • Peaches, cherries, tomatoes 30 Fruit Dispersal by Animals Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b. a: © Marie Read/Animals Animals/Earth Scenes; b: © Scott Camazine/Photo Researchers, Inc. 31 Fruit Types and Seed Dispersal • Seed Germination – When seed germination occurs, the embryo resumes growth and metabolic activity – Length of time seeds retain their viability is quite variable – Some seeds do not germinate until they have been through a dormant period • Temperate zones - Cold Weather 32 Fruit Types and Seed Dispersal • Environmental requirements for seed germination – Availability of oxygen for metabolic needs – Adequate temperature for enzyme activity – Adequate moisture for hydration of cells 33 Eudicot and Monocot Seed Structure and Germination Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pericarp cotyledons plumule (two) endosperm cotyledon (one) coleoptile hypocotyl radicle plumule seed coat radicle cotyledon coleorhiza Corn kernel Seed structure true leaf first true leaves (primary leaves) seed coat epicotyl withered cotyledons cotyledons (two) first leaf hypocotyl coleoptile coleoptile prop root radicle hypocotyl primary root Bean germination and growth a. secondary root primary root adventitious root primary root coleorhiza Corn germination and growth b. a: © Ed Reschke; b: © James Mauseth 34