plant body organization plant form...1 plant form chapter 36 2 plant body organization a vascular...

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Plant Form

Chapter 36

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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

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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

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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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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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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 (Cont.)

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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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Plant Tissues

As mentioned earlier, plants contain three main types of tissue

-Dermal

-Ground

-Vascular 15

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 (Cont.)

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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 26

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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Ground Tissue (Cont.)

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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 30

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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 32

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 33

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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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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 39

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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 44

Roots

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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

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Pneumatophores Water storage roots

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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 nodes Blade = Flattened part of leaf Petiole = Stalk of leaf Axil = Angle between petiole/blade and stem Axillary bud = Develops into branches with

leaves or may form flowers Terminal 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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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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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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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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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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Modified Stems (Cont.)

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Modified Stems (Cont.)

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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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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 81

Leaves

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Leaves (Cont.)

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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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Leaves (Cont.)

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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

plant body organization plant form...1 plant form chapter 36 2 plant body organization a vascular...

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