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Home , Archegonium, Bulb, Capsule (fruit), Corm, Cortex (botany), Double fertilization

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• Study of the Kingdom... Our Essential Partners in Life • INTRODUCTION ALTERNATION OF GENERATIONS What’s so special about ? A unique evolutionary strategy for repro- • They are photosynthetic, using the ultimate energy duction where a single plant has Haploid source, the sun, to make their own . For this reason two phases to its life history. they are called . Plants power most (n) ecosystems and are thus essential to life on Earth. • Gametophyte – Haploid, multicelled Have you thanked a plant today? individual produces via . Dominant form in lower plants. n n • – Diploid, multicelled individual n n from fusion (); produce haploid Syngamy GAMETE EVOLUTION spores via meiosis for dispersal; spores Plants have developed different strategies for gamete germinate via mitosis to produce gameto- 2n 2n Spore mother cell Zygote production and fusion. phytes. Dominant form in higher plants. • Isomorphic A/G – Gametophyte and sporo- 2n • – Gametes are equally motile and of similar phyte individuals are morphologically indis- Sporangia size. tinguishable. Sporophyte • – One gamete • Heteromorphic A/G – Gametophyte and is large and less motile, (+) Male(-) (2n) sporophyte individuals are morphologically Diploid with reserves, distinct. while the other is smaller and more motile, with few nutrient reserves. Isogamy • Oogamy – One gamete is PLANT CLASSIFICATION NONVASCULAR PLANTS non-motile and large, with 1st Plants on Land large nutrient reserves , VASCULAR • Lack vascular tissues (egg), while the other is Anisogamy • Gametophyte is dominant, sporophyte nutritionally smaller and motile Angiosperms dependent on gametophyte. (sperm) and must • Small; live in moist environments; gametes released locate the larger into . gamete. Oogamy a. Division Hepatophyta (Liverworts) b. Division Anthocerophyta () c. Division Bryophyta () (a) (b) Plant evolution: Land colonization occurred about 400 SEEDLESS, VASCULAR mya, likely from aquatic, green ancestor.

Ferns • New problems on land: Plants must adapt to living Club Mosses in the air, a non-aquatic, dry medium. This presents some problems: Sporophyte - Obtaining water and preventing water loss. - Transporting water and . Horsetails Gametophyte - (requires moisture) Growing - Gravity region - Reproduction when gametes swimming in water is Foot of limited. Whisk sporophyte - Temperature flux of air is more rapid than in water. (c)

Plant adaptations/solutions NONVASCULAR • A & B, to capture sunlight – similar to Sporophyte chlorophyll. • storage, for prolonged inactive periods during Mosses seasonal variations. • Gametes protected and kept moist inside plant Foot tissues. • Stomata ( openings) to regulate gas exchange. Gametophyte • surfaces to prevent excess water loss. Liverworts • system to pull in water and nutrients from . • Conduction tissues to transport water, nutrients and food. Hornworts • Support tissues to battle gravity for vertical growth. • All of these adaptations have greatly enhanced the success of plants on land today. GREEN ALGAL ANCESTOR

1 SEEDLESS VASCULAR PLANTS “Ferns” Seedless Vascular plants Microphyll Evolution Extinct fossil forms that • Possess & for transport of materials. • Sporophyte is dominant. Stem may show transition from Microphyll seedless vascular plants • Evolution of leaf for efficient light capture. Vascular - Microphylls, megaphylls (In , the prefixes (e.g., ferns) to vascular "micro" and "mega" generally refer to similar seed plants (e.g., structures in male and female parts of the plant, Unbranched Vascular Leaf with gymnosperms and respectively). stem Projection supply to one vein angiosperms). • Division Lycophyta (Club Mosses) projection - present. Megaphyll Evolution - present (microphylls). • Division Psilophyta (Whisk Ferns) No roots or leaves Main axis of stem • Division Sphenophyta ( Horsetails) - Roots present. Overtopping • Most plants are angiosperms and thus produce - Stems contain silica. (one becomes Dichotomously flowers with both male and female reproductive - Leaves present (microphylls). branching stems Side main axis of stem) - Division Pterophyta (Ferns) branch structures. - Roots present. Megaphylls • - Leaves (= fronds) - , - Fronds present (megaphylls). - (Male Portion): Anther, filament

- life history (see fig. below) - Pistil (Carpel, Female Portion): , style,

- Sporophyte, sori, sporangia, spores, gametophyte , (= ), archegonium with and antheridium with sperm Leaves with The pistil Stigma { many veins Anthers • The Plant Scene (300 mya): Many seedless vascular contains Style The stamen Webbing of side (micro- contains plants and some nonvascular plants exhibited lush, branch systems the female Ovary organs {Ovule sporangia) the male dense growth covering large expanses in Earth’s history. organs • Much of today’s oil, coal and gas deposits were formed by these plants. OVULE TO SEED Evolution of the "seed" plants • Terrestrial adaptations of seed plants. Megasporangium (2n) Seed coat (2n) (derived from integument) - protected in moist sporophytic, Integument (2n) Female reproductive tissues. gametophyte (n) Food Spore case (n) supply - replaced swimming for sperm delivery to egg. Egg Filament (derived nucleus - The seed evolved - a dormant embryo with tube (n) from surrounding nutrients protected from environ- (n) female mental conditions. Seeds replaced spores as gameto- phyte dispersal agents, using wind, water or animals. Micropyle tissue) • The seed - a fertilized egg - Inside an ovule. Discharged sperm nucleus (n) - Integument, megasporangium ➔ Megaspore (n) Embryo (2n) (new sporophyte) ‘gametophyte ➔ egg sperm (a) Ovule (b) Fertilized ovule (c) Seed FERN LIFE HISTORY The sporophyte • Angiosperms have dominated the plant scene since the (still attached to demise of dinosaurs and many gymnosperms the gametophyte) (Cenozoic era, 65 mya to present). grows, develops • Seed in a protective container or • Angiosperm life cycle: - mother cell ➔ ➔ pollen grain (male gametophyte)which includes tube cell and generative cell (sperm) - Megaspore mother cell ➔ megaspore ➔ embryo zygote Diploid Stage sorus sac with 7 cells and 8 nuclei (female gametophyte) fertilization meiosis ➔ egg Haploid Stage Archegonium Sporangia - Two sperm move through the and Spores develop The spores are engage in a (where one sperm egg released from a producing Prothallus fuses with the egg to form a zygote/embryo, and the egg spore chamber structure mature other sperm fuses with a large, central cell to form gametophyte sperm (underside) A spore /nutrient reserve for the embryo) until it producing germinates and can produce its first leaves and begin photosyn- sperm structure grows into a gametophyte thesis. Antheridium - Pollination and fertilization occur within hours to days, making angiosperms quick reproducers, compared to gymnosperms. TRENDS IN ALTERNATION OF GENERATIONS • Flowers ensure pollination by insects, birds and . Gametophyte (n) Sporophyte (2n) - Flowers and co-evolved. Gametophyte (n) • Sporophyte (2n) - Important because plants may drop seeds close by, Sporophyte (2n) but new individuals will possibly compete with parent plants. - Wind, water and animals are common dispersal agents. - can entice animals to aid in dispersal. • Fruits – ripened ovary (see fig.) • Monocots and Dicots - two major groups of Gametophyte (n) • Sporophyte dependent on gametophyte (e.g., ) angiosperms (see fig. for differences) - Monocots include grasses, corn, cane, palm • Large sporophyte and small, independent gametophyte (e.g., ferns) , lilies and orchids. • Reduced gametophyte dependent on sporophyte (seed plants) - Dicots include most trees, , and cacti. 2 THE GYMNOSPERMS - “naked seed” plants • Dominant plant when dinosuars ruled (Mesozoic era, 220 - 65 mya). LIFE CYCLE • Do not produce flowers. • /seeds exposed. Megaspore(n) • Division Cycadophyta Scale of - Slow-growing palm-like trees found female cone primarily in tropics and sub-tropics. Female cone HAPLOID • Division Ginkgophyta Gametophyte - Only one living member. generation - biloba (common diet Megasporangium Pollen chamber supplement) Micropyle • Division Ovule Male cones Note that the same plant has both Female - Closest living relatives of angiosperms pollen-producing male cones and MEIOSIS gametophyte(n) - Ephedra egg-producing female cones Egg - Drug ephedrine originally derived from this Microspore Microspores(n) plant. mother cells(2n) Reduced Germinating pollen - Cells resemble xylem vessel cells of arche- produces pollen tubes to reach the egg. angiosperms. gonium Male gametophyte - Cone clusters resemble flowers. Pollen (germinating pollen • Division Coniferophyta (, grain grain) Evergreens) FERTILIZATION The gametophytes - Oldest, tallest, most massive plants (e.g., Sporophyte(2n) Scale of are tiny male cone DIPLOID 380 ft. tall Redwood ). Sporophyte Female - Leaves form needles, which slow desiccation generation gametophyte(n) and are resistant to grazing by herbivores. Seed coat - Important economically as /paper Suspensors source, , and Christmas Seed trees Female (2n) gametophyte • life cycle: Winged seed - Ovulate cone = megastrobilus with megas- Embryo porophylls (scales) - Micropyle, where pollen lands on ovulate cone. Female cone - Pollen cone = microstrobilus with microsporphylls Developing embryo Wing Scale of - The process from pollination to fertilization female cone The seed protects can take over a year, which proved slow the embryo once the angiosperms evolved.

THE ANGIOSPERMS - “enclosed seed” plants DEVELOPMENT Endosperm ANGIOSPERM LIFE CYCLE Primary endosperm Pollen grains (n) cell

Anther Generative cell Fruit flesh Ovary Meiosis Seed coat Integument Tube cell Embryo Zygote Microspores (n) Fruit Flower Pollen mother Anther cells (2n) Pollen MONOCOTS VS DICOTS Stigma tube Functional 8-nucleate MONOCOTS DICOTS megaspore (n) embryo sac Sperm Megaspore (megagametophyte) cells mother cell (2n) (n)

Floral parts in Florals parts in multiples of three multiples of 4 of 5 Meiosis LEAVES

Ovule Ovary Seed (2n) Adult Formation of Long tapering blades Broad to narrow leaves pollen tube (n) with parallel venation with netted venation sporophyte Double Endosperm (3n) STEMS (2n) with fertilization flowers Seed coat Egg

Vascular bundles Vascular bundles are scattered arranged in a circle Endosperm (3n) SEEDS

Embryo (2n)

Contain 1 cotyledon Contain 2

3 PLANT ARCHITECTURE STEM STRUCTURE • Plant needs and solutions: • -based cell walls for support and growth toward sunlight - Leaves - Collection and conversion of solar energy • - Stems - Positioning and support of leaves • Dicots with and separated by ring of vascular bundles. - Roots - Anchorage and absorption • Monocots with with scattered vascular bundles. Vessels Meristematic cell - Vascular system - Transport in xylem (brick-shaped cells)

Axillary tip (terminal bud) Epidermis Vascular Cortex bundle Young leaf

Flower Pith

Node Internode Epidermis Node Leaf Transverse section of a stem, with enlargement of a vascular Ring of shown to the right bundles divides Sieve-tube members Fibers in phloem Vascular ground tissue into and companion cells tissues cortex and pith in phloem Seeds (inside fruit) Vessel in xylem Epidermis Air space Thick-walled Ground sclerenchyma tissue cells forming a sheath Vascular around the Ground tissues Withered bundle mature cotyledon vascular Shoot system bundle Root system

Root

Primary root Root tip Root cap Groundvascular bundles distributed through Transverse section of a stem, ground tissue with enlargement of a vascular Sieve-tube member Companion cell bundle shown to the right in phloem in phloem

LEAF STRUCTURE ROOT STRUCTURE • Epidermis • Cuticle with wax to resist desiccation (produced by epidermis). Epidermis • Guard cells with stomata to regulate gas exchange. Endodermis • Mesophyll - Photosynthetic layer. • Dicots with palisade and spongy layers; monocots with one layer. • Vein - Vascular bundle for transport of materials.

Root section

Palisade Cortex mesophyll

Vein Casparian vascular strip bundle Endodermis Upper epidermis Movement of water through the endodermis to the center Cuticle of the root

Bundle • Epidermis - Has root hairs for increased absorption area for water/minerals. sheath • Cortex • Endodermis - With casparian wax strips Xylem • - Central cylinder with vascular tissues inside • Apoplastic pathway vs. symplastic pathway: Water enters through root Lower epidermis and passes in the spaces "between" cortex cells apoplastically unti epidermis reaching the endodermis. Casparian strips prevent water from passing between endodermal cells. Thus, water is forced through the cell membranes symplastically where it is filtered before reaching the vascular tissues within Spongy the stele. In this way, potentially harmful substances might be removed by the Stoma Guard cells mesophyll selectively-permeable membranes of the endodermal cells. 4 VASCULAR TISSUES

• Xylem, used for water/mineral transport. Pits in wall Sieve plate - - Thin, hollow, dead cells One vessel member MERISTEMATIC TISSUES with perforated, tapered ends. - Vessel members (element) - Thick, • Growth after germination Apical hollow, dead cells with large holes no • Upward growth on end. cytoplasm sieve- (cells are tube - Epicotyl or • Phloem used for sugar/food transport. dead at member - Sieve tube members (element), maturity) (alive) - - Plant companion growth and movement in hollow, living cells with perforated ends. cell Protoderm - Companion cells, living cells that (alive) response to light. help keep sieve tube member cells Portions of Portion of Portion of • Downward growth one sieve tube alive. tracheids one vessel Ground - or meristem - - Plant growth response to gravity Procambium IMPORTANT SYMBIOSES WITH PLANTS via statolith sensors. Three Primary : • Root nodules & • Meristematic tissues form all - Bacteria fix nitrogen and are housed in root nodules to supply tissues of adult plant (similar "fertilizer," thus allowing the plant to thrive, even in that to germ tissues of animals). are nutrient poor. • Apical meristems • Mycorrhizae - Responsible for increase - Most plants today have an association between their roots and in plant height. Vascular bundle fungi in the soil. This association, or mycorrhizae, is critical in • Lateral meristem aiding water/mineral uptake by the plant. - Responsible for increase Vascular in plant diameter (girth). cambium • Three primary meristems: VEGETATIVE (asexual) REPRODUCTION - Protoderm - Epidermis - Ground meristem - Plants typically produce new Fleshy leaves Cortex and ground tissues parts/structures without sexual repro- - Procambium - Vascular duction, thus allowing the quick spread Stem Stem of Lateral Meristems Stem bundles with xylem and of the plant into the immediate habitat. primary (their location in phloem. plant body stems showing )

Bulb DEVELOPMENT

New plant Foliage leaves

Stolon (runner) Cotyledon Epicotyl Rhizome Cotyledon Root Hypocotyl Cotyledon Hypocotyl

Asexual Reproductive Modes of Flowering Plants Mechanism Representative Characteristics on modified stems Radicle Seed coat Runner () New plants arise at nodes on an above ground horizontal stem Bean Foliage leaves Rhizome Bermuda New plants arise at nodes of grass underground horizontal stem Hypocotyl Epicotyl Corm New plant arises from axillary bud on short, thick, vertical Cotyledon New arise from axillary on Hypocotyl (enlarged tips of slender Radicle underground ) lily New bulb arises from axillary bud on short underground stem Orange tree, Embryo develops without nuclear or cellular fusion (e.g., from unfertilized Coleoptile Foliage haploid egg; or develops leaves adventitiously, from tissue surrounding embryo sac) Vegetative Jade plant, New plant develops from propagation African tissue or (e.g., a leaf) violet that drops or is separated from plant Radicle Tissue Orchids, New plant induced to arise culture lily, , from cell of a parent plant that propagation , rice, is not irreversibly differentiated corn Corn

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Plant development continued: • - Produces xylem inward and phloem outward SECONDARY GROWTH • - Cork Xylem • Wood is produced from xylem: - Annual rings (see fig.) Heartwood Sapwood Cork (with cambium) Phloem - Heartwood vs. sapwood (see fig.) - Heartwood - Clogged xylem, little water transport - Sapwood - Newer xylem, free flowing water transport • is produced from phloem, cork cambium, cork - are cracks in the bark to facilitate gas exchange. - " plants" or a horizontal band around the circumference of the plant, can be deadly because the vascular cambium, in which nutrients and water travel vertically, can be damaged. Lawn equipment (especially weed whackers) is a "Bark" potential source of this kind of plant damage. • Exchange and Transport - Plants obtain gases, nutrients, minerals and water via internal Vascular cambium fluids. - Gas exchange- stomata, roots, lenticels - Internal transport- xylem and phloem ANNUAL RINGS - Fluids move in xylem via adhesion, cohesion, evaporation and . 1993 • Theories of upward movement: - Capillary action - Some water moves up small vascular cells naturally. 1992 - - Solutes inside the root tissues draw some water up. Annual ring 1991 - pull (cohesion-adhesion-tension)- The main motive force for transporting water up to the top of a plant (sometimes several hundred feet). - Essentially, as water evaporates from the leaf surface, the 1990 cohesive and properties of water pull water molecules 250 um from below, establishing a water tension/pressure. One drawback is it requires loss of water from the plant. In dry conditions or arid environments, this water loss for vertical transport can be critical to plants – thus, a replenishing water supply in the roots is vital. • Fluid movement in phloem (see fig.) INTERNAL TRANSPORT IN PHLOEM - produced by the leaves via must be Xylem Phloem distributed to the rest of the plant. Gravity can assist this basically downward movement. However, getting the sugars into the cells of the phloem requires energy (i.e. active transport). Sometimes large quantities of sugars/starch are stored in special Companion cell vegetative structures (e.g., tubers).

This QUICKSTUDY ¨ guide is an outline of the basic topics taught in Botany courses. Due to its condensed format, use it as a Botany guide but not as a replacement for assigned class work. Leaf All rights reserved. No part of this publication may be reproduced or transmitted in any form, or by any means, electronic or mechanical, including photocopy, recording, or any information (source of ) storage and retrieval system, without written permission from the publisher. © 2001 BarCharts, Inc., Boca Raton, FL 1007

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