3/1/2011

Overview of the seed

„ First seed plants or spermatophytes evolved from earlier seedless vascular ppypylants similar to modern lycophytes and SSiection 4 pteridophytes Professor Donald McFarlane „ Following the early diversification of gymnosperms, one ancestral gymnosperm Lecture 11 Higher Plants: lineage gave rise to the angiosperms, the Domination of the Land flowering plants

2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Seed plants (spermatophytes) KEY Critical innovations Major critical innovations Seedless vascular plants Gymnosperms

„ Shared by all seed plants

Pollen allows seed plants to disperse male Ginkgo Cycads Conifers

gametophytes Lycophytes ngiosperms Gnetophytes Pteridophytes A OlOvules all ows see dlttdid plants to disperse ma le gametophytes Flowers; fruits; endosperm; Seeds allow plants to reproduce in diverse habitats vessels common Wood strengthens plants, allowing them to grow tall Wood; ovules, seeds, pollen and produce many branches, leaves, and seeds

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 „ Tissue composed of numerous empty water- enclosed in fruits conducting cells strengthened by lignin „ “Naked seeds” Allows woody tissue to transport water upward for greatditt distances „ Most modern forms are woody or Also provides structural support „ Seeds and wood are adaptations that allow „ Vascular cambium gymnosperms to cope with global climate changes and to live in relatively cold and dry Produces thick layer of wood and thin layer of inner bark habitats Inner bark used for transporting watery solutions of organic compounds

5 6

„ Progymnosperms Phylum Cycadophyta First wood Vascular tissue in a ring (eustele) „ 300 cycad species today Produces vascular „ Primarily tropical and subtropical cambium and wood „ Many species rare Reproduced by „ Habitats threatened by human activities means of spores, not seeds „ Nonwoody stems may emerge like Wood came before trunks or be underground seeds „ Leaves palm-like

7 8

2 3/1/2011

„ Produce corraloid roots Roots are above ground and resemble corals Harbor cyanobacteria for nitrogen fixation „ 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- latitude 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 „ Mature pollen released to the wind

15 16

4 3/1/2011

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cone scale Megaspore Egg (n) Ovule Scale cone Ovule Mature Integument sporophyte Megasporangium (2n) Meiosis Mitosis Female gametophyte (n) Megasporangium (2n) Seed coat Microspores Archegonium (n) Pollen grain (n) Pollen Section KEY cone of cone Microsporangium Haploid SdliSeedling Diploid

Scale „ Seed coats may develop wings for wind Ovule Seed dispersal Sperm „ Others produce seeds or cones with bright-colored, have fleshy coatings to Male gametophyte (n) Embryo (2n) Mitosis Fertilization attract birds for dispersal

17 18

„ Wood contains tracheids for water transport „ Cold climate Pits on side and end walls through which water moves adaptations Valve-like torus to prevent spread of air bubbles Conical shape „ Resin ducts – resin helps prevent attack by and flexible pathogens and herbivores branches Scale-like or needle-shaped leaves Thick waxy cuticle „ Most conifers are evergreens

19 20

5 3/1/2011

Modern angiosperms Flowers

„ Defining features are „ Complex reproductive structures flowers and fruits „ Specialized for efficient production of „ “Enclosed seeds” pollen and seeds „ Presence of seeds within fruits „ 4 types of organs 1. Sepals „ Seed endosperm another defining 2. Petals feature 3. Stamens – produce pollen 4. Carpels – produce ovules

21 22

„ Flower organs supported by receptacle „ Pedicel – tip of the flower stalk „ Perinath – petals and sepals „ Complete flowers – all 4 flower organs „ Incomplete 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 Microspores Meiosis Anther „ Pistil anatomy Mitosis Male gametophyte Stigma – receives and recognizes pollen Ovule Stigma „ Only appropriate pollen will be allowed to Two sperm (n) germinate Megasporangium Integuments Pollen tube Surviving Megaspore precursor megaspore (n) Style Sporophyte (2n) in megasporangium Style Gametophyte nuclei Embryo (2n) Mitosis Egg (n) First endosperm cell (3n) KEY Ovary – encloses and protects ovules Haploid Female Diploid „ Pollen tube delivers sperm to ovule gametophyte

„ Ovaries develop into fruits Double Seed fertilization Endosperm coat Zygote (2n)

Pollen tube 25 26

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Anther Early flowers Front Microsporangia Stamen Filament view Early Anther stamen

„ First appeared 140 mya Filament Cross „ Flowers were a critical innovation that led to section

extensive angiosperm diversification (a) Stamen evolution

„ Stamen development Stigma Pistil Compound Front Early carpel pistil with Leaf Fused composed view multiple seam Style of one Early flowers had broad leaf-shaped stamens carpels Ovules Secretion carpel Ovules Narrowed to form filaments and anthers (clusters or Ovary microsporangia producing pollen)

„ Carpels also developed from leaf-like structures Cross section Folded to protect ovules (b) Carpel evolution

27 28

7 3/1/2011

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Monocots Amborella Water lilies Water Magnoliids and relatives and Star anise Star relatives and osperm ancestor osperm n

„ Monocots and eudicots are named for

Extinct gym differences in the number of embryonic leaves called cotyledons „ Monocots differ from eudicots in several additional ways

29 30

Whole Genome Duplication Influenced Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Flowering Diversification

„ 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 (a) Zinnia flower and butterfly (b) Hibiscus flower and hummingbird (c) Saguaro cactus flower and bat „ Plants are also known to obtain mitochondrial genes from other plant species by horizontal gene „ Floral tubes and coevolved pollinators transfer

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. Terpenes and terpenoids 2. Phenolics (flavonoids and related compounds) 3. Alkaloids

35 36

9 3/1/2011

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

3. Alkaloids Alkaloid 1. Terpenes and terpenoids Contain nitrogen Taxol, citronella, rubber, turpentine, rosin O CH Potent effects on 3 and amber H3C N animal nervous N H 2. Phenolics (flavonoids and related system O N compounds) N Caffeine, nicotine , CH Some flower and fruit colors morphine, 3 Caffeine Flavors cinnamon, nutmeg, ginger, clove, ephedrine, chilies, vanilla cocaine, and Prevent UV damage codeine Some are antioxidants (c) Caffeine produced by Coffea arabica is an example of an alkaloid.

37 38

39

10