Plant Form Chapter 36. 2 Plant Body Organization A vascular plant consists of: 1. Root system, which is underground -Anchors the plant, and is used to.

Plant Form

Chapter 36

2

Plant Body Organization

A vascular plant consists of:

1. Root system, which is underground

-Anchors the plant, and is used to absorb water and minerals

2. Shoot system, which is above ground

-Consists of supporting stems, photosynthetic leaves and reproductive flowers

Each has an apex that extends growth

3

Shoot apex

Flower

Stipule

AxillarybudInternode

NodeVascular system

Primary root

Lateral root

Root apex

Root

Shoot

Petiole

Vein

BladeLeaflet Leaf

Tendril

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4

Plant Body Organization

Plant cell walls consist of cellulose

-Primary cell wall

-Found in all cells

-Cellulose fibers parallel to microtubules

-Secondary cell wall

-Found in some cells

-Additional layers of cellulose and lignin

-Increase mechanical strength of wall

5

a. b.

Cellulose fiberCell membrane

Cytosol

Microtubule

Cellulose-formingrosettes

Cytosol

Cell membrane

Parallelcellulosefibers

Primary cell wall

Time

Primary cell wallremains outside as inner layersare laid down

Secondarycell wall 1

Secondarycell wall 2

Plant Body Organization

6

Plant Body Organization

Roots, shoots and leaves contain three basic tissue systems:-Dermal tissue – For protection

-Wax and bark-Ground tissue – For storage, photosynthesis and secretion-Vascular tissue – For conduction

-Xylem – Water and dissolved minerals

-Phloem – Nutrient-containing solution

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Plant Body Organization

Meristems are clumps of small cells with dense cytoplasm and large nuclei

They act as stem cells do in animals

-One cell divides producing a differentiating cell and another that remains meristematic

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Meristem cell

Meristem cell

Differentiated cell

Cell division

Meristem cell

Cell division

Meristem cell Differentiated cell

Cell division

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Differentiated cell

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Plant Body Organization

Apical meristems are located at the tips of stems and roots

-Give rise to primary tissues which are collectively called the primary plant body

-Three primary meristems

-Protoderm Epidermis

-Procambium 1o vascular tissue

-Ground meristem Ground tissue

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Plant Body Organization

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Plant Body Organization

Lateral meristems are found in plants that exhibit secondary growth

-Give rise to secondary tissues which are collectively called the secondary plant body

-Woody plants have two types

-Cork cambium Outer bark

-Vascular cambium 2o vascular tissue

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Apicalgrowth

Ground meristem

Procambium

Primaryxylem

Primaryphloem

Lateralgrowth

Secondaryxylem

Secondaryphloem

Primaryphloem

Primaryphloem

Primaryxylem

Primaryxylem

Vascular cambium

Cork cambium

Lateralgrowth

Vascular cambium

Secondaryxylem

Secondaryphloem

Apicalgrowth

Primaryxylem

Primaryphloem

Ground meristem

Procambium

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Plant Tissues

As mentioned earlier, plants contain three main types of tissue

-Dermal

-Ground

-Vascular

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Dermal Tissue

Forms the epidermis, which is usually one cell layer thick

Covered with a fatty cutin layer constituting the cuticle

Contains special cells, including guard cells, trichomes and root hairs

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Dermal Tissue

Guard cells are paired sausage-shaped cells

-Flank a stoma, which is the passageway for oxygen and carbon dioxide

Guard cell formation is the result of an asymmetrical cell division that produces:

-A guard cell

-A subsidiary cell

-Aids in stoma opening and closing

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Dermal Tissue

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Dermal Tissue

Trichomes are cellular or multicellular hairlike outgrowths of the epidermis

-Keep leaf surfaces cool and reduce evaporation by covering stomatal openings

-Some are glandular, secreting substances that deter herbivory

Trichome patterning is under genetic control

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Dermal Tissue

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Dermal Tissue

Roots hairs are tubular extensions of individual epidermal cells

-Greatly increase the root’s surface area and efficiency of absorption

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Ground Tissue

Consist of three types of cells

-Parenchyma

-Collenchyma

-Sclerenchyma

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Ground Tissue

Parenchyma cells are the most common type of plant cell -May live for many years, functioning in storage, photosynthesis and secretion-Some contain chloroplasts and are called chlorenchyma

Collenchyma cells provide support for plant organs, allowing bending but not breaking-Have living protoplasts and may live for many years

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Ground Tissue

Sclerenchyma cells have tough thick walls

-Lack living walls at maturity

-Two general types

-Fibers: Long, slender cells that are usually grouped in strands

-Sclereids: Variable shape; branched; may occur singly or in groups

-Both strengthen tissues

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Ground Tissue

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Vascular Tissue

Xylem

-Constitutes the main water- and mineral-conducting tissue

-Vessels: Continuous tubes of dead cylindrical cells arranged end-to-end

-Tracheids: Dead cells that taper at the end and overlap one another

-Vessels are shorter & wider than tracheids

-And conduct water more efficiently

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Vascular Tissue

Xylem

-Also conducts inorganic ions such as nitrates, and supports the plant body

-Typically includes parenchyma cells in horizontal rows called rays

-Function in lateral conduction and food storage

Note: The diffusion of water vapor from a plant is termed transpiration

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Vascular Tissue

Phloem -Constitutes the main food-conducting tissue in vascular plants-Contains two types of elongated cells: sieve cells and sieve tube members

-Living cells that contain clusters of pores called sieve areas or sieve plates-Sieve-tube members are more

specialized -Associated with companion cells

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Roots

Roots have a simpler pattern of organization and development than stems

Four regions are commonly recognized:

-Root cap

-Zone of cell division

-Zone of elongation

-Zone of maturation

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Zone ofmaturation

Zone ofelongation

Zone ofcell division

Epidermis

Ground meristemProcambium

Columella cells

Protoderm

Endodermis

GroundtissueVasculartissue

Quiescentcenter

Root incross-section

Apical meristem Root cap

dermal tissueground tissuevascular tissue

Root hair

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Roots

Root cap

-Contains two types of cells that are formed continuously by the root apical meristem

-Columella cells: Inner

-Root cap cells: Outer and lateral

-Functions mainly in protection of the delicate tissues behind it

-Also in the perception of gravity

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Roots

Zone of cell division

-Contains mostly cuboidal cells, with small vacuoles and large central nuclei

-Derived from rapid divisions of the root apical meristem

-Quiescent center cells divide very infrequently

-Apical meristem daughter cells soon subdivide into the three primary tissues

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Roots

Zone of cell division

-Patterning of these tissues begins in this zone

-WEREWOLF (WER) gene

-Suppresses root hair development

-SCARECROW (SCR) gene

-Necessary for differentiation of endodermal and ground cells

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a.

WER (wild type) wer (mutant)

Root tip Epidermal cell

WER

NoWER

NoWER

NoWER

Nonhair

Hair will develop inzone of maturation

Hair will develop inzone of maturation

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a.

SCR (wild type) scr (mutant)

Root tip

Endodermalcell

SCR

Cell withground andendodermaltraitsAsymmetrical

division

Groundcell

Groundmeristem

cell

2 layers of cells

Root tip

Groundmeristem

cell

SCR

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Roots

Zone of elongation

-Roots lengthen because cells become several times longer than wide

-No further increase occurs above this zone

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Roots

Zone of maturation

-The elongated cells become differentiated into specific cell types

-Epidermal cells: Have very thin cuticle

-Include root hair and nonhair cells

-Cortex: Interior to the epidermis

-Parenchyma cells used for storage

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Roots

Zone of maturation

-Endodermis: Single-layered cylinder

-Impregnated with bands of suberin called the Casparian strips

-Stele: All tissues interior to endodermis

-Pericycle: Multiple-layered cylinder

-Gives rise to lateral (branch) roots or the two lateral meristems

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Casparian strip

Endodermal cellH2O

Xylem

Phloem

Cortex

Pericycle

H2O

Roots

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Zygote Embryo

Shoot apical meristem

Root apical meristem

Cork cambium

Vascular cambium

Leaf primordia

Bud primordia

Shoot elongation

Outer barkPhloemXylem

Inner bark

Wood

Bark

Bark

Leaves

Lateral shoots

Cork cambium

Vascular cambium

Pericycle

Phloem

Xylem

Lateral roots

Root elongation

Outer bark

Inner bark

Wood

Plant Tissue Differentiation

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Modified Roots

Most plants produce either/or:

-Taproot system: Single large root with small branch roots

-Fibrous root system: Many small roots of similar diameter

Some plants, however, produce modified roots with specific functions

-Adventitious roots arise from any place other than the plant’s root

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Modified Roots

Prop roots: Keep the plant upright

Aerial roots: Obtain water from the air

Pneumatophores: Facilitate oxygen uptake

Contractile roots: Pull plant deeper into soil

Parasitic roots: Penetrate host plants

Food storage roots: Store carbohydrates

Water storage roots: Weigh 50 or more kg

Buttress roots: Provide considerable stability

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Prop roots Aerial roots

Pneumatophores Water storage roots Buttress roots

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Stems

Like roots, stems contain the three types of plant tissue

-Also undergo growth from cell division in apical and lateral stems

Shoot apical meristem initiates stem tissue and intermittently produces primordia

-Develop into leaves, other shoots and even flowers

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Stems

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Stems

Leaves may be arranged in one of three ways

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Stems

The spiral (alternate) arrangement is the most common

-Sequential leaves tend to be placed 137.5o apart

-This is termed phyllotaxy

-May optimize the exposure of leaves to the sun

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External Stem Structure

Node = Point of attachment of leaf to stem Internode = Area of stem between two nodesBlade = Flattened part of leafPetiole = Stalk of leafAxil = Angle between petiole/blade and stemAxillary bud = Develops into branches with

leaves or may form flowersTerminal bud = Extends the shoot system

during the growing season

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Internal Stem Structure

Monocot vascular bundles are usually scattered throughout ground tissue system

Eudicot vascular tissue is arranged in a ring with internal ground tissue (pith) and external ground tissue (cortex)

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Internal Stem Structure

Vascular tissue arrangement is directly related to the stem’s ability for secondary growth

-In eudicots, a vascular cambium develops between the primary xylem and phloem

-Connects the ring of primary vascular bundles

-In monocots, there is no vascular cambium

-Therefore, no secondary growth

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a.

b.

c.

Primary xylemSecondary xylem

Primary phloemSecondary phloem

Vascular cambium(lateral meristem)

Vascular cambium(lateral meristem)

Primary xylemSecondary xylem

Primary phloemSecondary phloem

Annual growth layers

EpidermisPrimary xylem Primary phloem

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Internal Stem Structure

Rings in the stump of a tree reveal annual patterns of vascular cambium growth

-Cell size depends on growth conditions

In woody eudicots and gymnosperms, the cork cambium arises in the outer cortex

-Produces boxlike cork cells on outside and parenchyma-like phelloderm cells on inside

-Collectively called the periderm

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Internal Stem Structure

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Internal Stem Structure

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Internal Stem Structure

Cork tissue cells get impregnated with suberin shortly after they are formed

-They then die and constitute the outer bark

The cork cambium also produces unsuberized cells called lenticels

-Permit gas exchange to continue

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Internal Stem Structure

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Modified Stems

Bulbs = Swollen underground stems, consisting of fleshy leaves

Corms = Superficially resemble bulbs, but have no fleshy leaves

Rhizomes = Horizontal underground stems, with adventitious roots

Runners and stolons = Horizontal stems with long internodes that grow along the surface of the ground

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Modified Stems

Tubers = Swollen tips of rhizomes that contain carbohydrates

Tendrils = Twine around supports and aid in climbing

Cladophylls = Flattened photosynthetic stems resembling leaves

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Modified Stems

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Leaves

Leaves are the main site of photosynthesis

-They are determinate structures whose growth stops at maturity

Exist in two morphologies

-Microphyll = Have one vein which does not extend the full length of the leaf

-Found mainly in the phylum Lycophyta

-Megaphylls = Have several to many veins

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Leaves

The flattening of the leaf blade reflects a shift from radial to dorsal-ventral symmetry

-It increases the photosynthetic surface

The mechanism of this shift is becoming clearer through the analysis of mutants that lack distinct tops and bottoms

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PHABULOSA

KANADI

PHAVOLUTAYABBY

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Leaves

Veins consist of both xylem and phloem and are distributed throughout the leaf blades

-Monocot leaves have parallel veins

-Eudicot leaves have netted or reticulate veins

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Leaves

Leaf blades come in a variety of forms

-Simple leaves contain undivided blades

-May have teeth, indentations or lobes

-Compound leaves have blades that are divided into leaflets

-Pinnate = Leaflets in pairs along an axis

-Palmate = Leaflets radiate out from a common point

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Leaves

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Leaves

The leaf’s surface is covered by transparent epidermal cells, most having no chloroplasts

Epidermis has a waxy cuticle

-The lower epidermis contains numerous mouth-shaped stomata flanked by guard cells

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Leaves

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Leaves

The mesophyll is the tissue between the upper and lower epidermis

-Most eudicot leaves have two types

-Palisade mesophyll = Usually two rows of tightly packed chlorenchyma cells

-Spongy mesophyll = Loosely arranged cells with many air spaces in between

-Monocot leaves mesophyll is usually not differentiated into palisade/spongy layers

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Leaves

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Modified Leaves

Floral leaves (bracts) = Surround true flowers and behave as showy petals

Spines = Reduce water loss and may deter predators

Reproductive leaves = Plantlets capable of growing independently into full-sized plant

Window leaves = Succulent, cone-shaped leaves that allow photosynthesis underground

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Modified Leaves

Shade leaves = Larger in surface area but with less mesophyll than sun-lit leaves

Insectivorous leaves = Trap insects

-Pitcher plants have cone-shaped leaves that accumulate rainwater

-Sundews have glands that secrete sticky mucilage

-Venus flytrap have hinged leaves that snap shut