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Transcript
3/1/2011 Overview of the seed plants First seed plants or spermatophytes evolved from earlier seedless vascular plants similar to modern lycophytes p y p y and pteridophytes Following the early diversification of gymnosperms, one ancestral gymnosperm lineage gave rise to the angiosperms, the flowering plants Section 4 S i Professor Donald McFarlane Lecture 11 Higher Plants: Domination of the Land 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Seed plants (spermatophytes) Critical innovations Angiosperms A Gnetophytes Conifers allows seed plants to disperse male gametophytes Ovules O l allows ll seed d plants l t tto di disperse male l gametophytes Seeds allow plants to reproduce in diverse habitats Wood strengthens plants, allowing them to grow tall and produce many branches, leaves, and seeds KEY Gymnosperms Cycads Pollen Pteridophytes Shared by all seed plants Lycophytes Seedless vascular plants Ginkgo Major critical innovations Flowers; fruits; endosperm; vessels common Wood; ovules, seeds, pollen Euphylls having broad leaves with branched veins Supportive vascular tissue; dominant branched sporophyte generation 3 4 1 3/1/2011 Gymnosperms Wood Produce seeds that are exposed rather than enclosed in fruits “Naked seeds” Most modern forms are woody shrubs or trees Seeds and wood are adaptations that allow gymnosperms to cope with global climate changes and to live in relatively cold and dry habitats Tissue composed of numerous empty waterconducting cells strengthened by lignin Allows woody tissue to transport water upward for greatt distances di t Also provides structural support Vascular cambium Produces thick layer of wood and thin layer of inner bark Inner bark used for transporting watery solutions of organic compounds 5 Progymnosperms 6 Phylum Cycadophyta First wood Vascular tissue in a ring (eustele) Produces vascular cambium and wood Reproduced by means of spores, not seeds Wood came before seeds 300 cycad species today Primarily tropical and subtropical Many species rare Habitats threatened by human activities Nonwoody stems may emerge like tree trunks or be underground Leaves palm-like 7 8 2 3/1/2011 Produce corraloid roots Roots are above ground and resemble corals cyanobacteria for nitrogen fixation Harbor Produce toxins to deter herbivorous animals Distinctive reproduction Conelike structures bearing ovules and seeds or pollen Cones emit odors that attract beetles Beetles carry pollen to ovules 9 10 Phylum Ginkgophyta Ginkgo biloba single remaining species Nearly extinct in the wild Widely planted along city streets (only males) Individual trees produce either ovules and seeds or pollen Flagellate sperm 11 12 3 3/1/2011 Phylum Coniferophyta Named for seed cones 500 species in 50 genera Particularly common in mountain and high highlatitude forests Ginkgos are long-lived- individuals can live for more than a thousand years and grow to 30 m in height 13 14 Simple pollen cones Leaflike structures bearing microsporangia producing pollen More complex ovule-bearing cones Composed of short branch system that bears ovules 15 Mature pollen released to the wind 16 4 3/1/2011 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cone scale Megaspore Scale Ovule cone Mature sporophyte (2n) Egg (n) Ovule Integument Megasporangium Meiosis Female gametophyte (n) Mitosis Megasporangium (2n) Seed coat Microspores Archegonium (n) Pollen grain (n) Pollen cone Section of cone Microsporangium KEY Haploid Diploid S dli Seedling Seed coats may develop wings for wind dispersal Others produce seeds or cones with bright-colored, have fleshy coatings to attract birds for dispersal Scale Ovule Seed Sperm Male gametophyte (n) Embryo (2n) Mitosis 17 18 Wood contains tracheids for water transport Pits on side and end walls through which water moves Valve-like torus to prevent spread of air bubbles Cold climate adaptations Conical shape and flexible branches Scale-like or needle-shaped needle shaped leaves Thick waxy cuticle Resin ducts – resin helps prevent attack by pathogens and herbivores 19 Fertilization Most conifers are evergreens 20 5 3/1/2011 Modern angiosperms Flowers Defining features are flowers and fruits “Enclosed seeds” Presence of seeds within fruits Seed endosperm another defining feature Complex reproductive structures Specialized for efficient production of pollen and seeds 4 types of organs 1. 2. 3. 4. 21 Sepals Petals Stamens – produce pollen Carpels – produce ovules 22 Flower organs supported by receptacle Pedicel – tip of the flower stalk Perinath – petals and sepals Complete flowers – all 4 flower organs Incomplete p flowers – lack one or more organs Perfect flowers – contain both stamens and carpels Imperfect flowers – lack either stamens or carpels 23 24 6 3/1/2011 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pollen grains (n) (immature male gametophytes) Single and compound carpels called pistil Pistil anatomy Stigma Meiosis Microspores Anther Mitosis Male gametophyte – receives and recognizes pollen Ovule Stigma Only appropriate pollen will be allowed to germinate Two sperm (n) Megasporangium Style Ovary Pollen tube Integuments Surviving Megaspore precursor megaspore (n) in megasporangium Gametophyte nuclei Embryo (2n) Egg (n) Mitosis First endosperm cell (3n) Sporophyte (2n) – encloses and protects ovules Style KEY Female gametophyte Pollen tube delivers sperm to ovule Ovaries develop into fruits Double fertilization Seed coat Endosperm Haploid Diploid Zygote (2n) Pollen tube 25 26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Early flowers Front view Microsporangia Anther Filament Stamen Anther Early stamen First appeared 140 mya Flowers were a critical innovation that led to extensive angiosperm diversification Stamen development Filament Cross section (a) Stamen evolution Stigma Front view Early flowers had broad leaf-shaped stamens Narrowed to form filaments and anthers (clusters or microsporangia producing pollen) Ovules Early carpel to protect ovules Fused seam Style Secretion Ovules Carpels also developed from leaf-like structures Folded Leaf Pistil composed of one carpel Compound pistil with multiple carpels Ovary Cross section (b) Carpel evolution 27 28 7 3/1/2011 Eudicots Monocots Magnoliids and relatives Star anise and relatives Water lilies Amborella Extinct gymn nosperm ancestor Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Monocots and eudicots are named for differences in the number of embryonic leaves called cotyledons Monocots differ from eudicots in several additional ways 29 30 Whole Genome Duplication Influenced Flowering Plant Diversification Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. An estimated 40–70% of all plants are polyploid 2 majors types of polyploidy Autoploidy – nondisjunction results in extra chromosomes in gametes Alloploidy – hybridization between 2 species with different chromosome counts followed by whole genome duplication Plants are also known to obtain mitochondrial genes from other plant species by horizontal gene transfer (a) Zinnia flower and butterfly (b) Hibiscus flower and hummingbird (c) Saguaro cactus flower and bat Floral tubes and coevolved pollinators 32 8 3/1/2011 Fruits Develop from ovary walls Aid the dispersal of enclosed seeds Dispersal prevents competition and aids in colonization Fruits may be adapted to Attract animals to eat them, wind dispersal, attach to animal fur or float in water 33 34 Secondary metabolites Synthesis of molecules that are not essential for cell structure and growth Three major classes in plants 1. 2. 3. 35 Terpenes and terpenoids Phenolics (flavonoids and related compounds) Alkaloids 36 9 3/1/2011 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. Terpenes and terpenoids 2. 3. Taxol, citronella, rubber, turpentine, rosin and amber Phenolics (flavonoids and related compounds) Alkaloids Some flower and fruit colors Flavors cinnamon, nutmeg, ginger, clove, chilies, vanilla Prevent UV damage Some are antioxidants Contain nitrogen Potent effects on animal nervous system Caffeine nicotine, Caffeine, nicotine morphine, ephedrine, cocaine, and codeine Alkaloid O H3C CH3 N N H O N N CH3 Caffeine (c) Caffeine produced by Coffea arabica is an example of an alkaloid. 37 38 39 10