Plant Tissues

Angiosperms – flowering plants

• The angiosperms are seed-bearing vascular plants

• In terms of distribution and diversity, they are the most successful plants on Earth

• The structure and function of this plant group help explain its success

Monocots and Dicots – same tissues, different features

Parallel veinsNetlike veins

3 pores1 pore

4 or 5 floral parts

3 floral parts

1 cotyledon 2 cotyledons

Vascular bundles dispersed

Vascular bundles in ring

Flowering Plant Life

Cycle Double fertilization Meiosis Meiosis

microspores

Female gametophyte

pollination

Mitosis without cytoplasmic division

Two sperms enter ovule

Diploid

Haploid

Plant Life Histories• Annuals complete life cycle in one growing season

• Biennials live for two seasons; flowers form in second

season

• Perennials grow and produce seeds year after year

Meristems – Where Tissues Originate• Regions where cell divisions produce plant growth• Apical meristems

– Responsible for primary growth (length)• Lateral meristems

– Responsible for secondary growth (width)

Apical Meristems

activity atmeristems

new cellselongateand start todifferentiateinto primarytissues

procambium primary vascular tissues

protoderm epidermis

Cells that form at apical meristems:

ground meristem ground tissues

Lengthen shoots and roots:StemAM and RootAM

Lateral Meristems

vascular cambium secondary vascular tissues

periderm cork cambium

thickening

Increases girth of older roots and stems

Cylindrical arrays of cells

Plant Tissue Systems

VASCULAR TISSUES

GROUND TISSUES

SHOOT SYSTEM

ROOT SYSTEM

EPIDERMIS

• Ground tissue system

• Vascular tissue system

• Dermal tissue system

Ground Tissue• fills space b/t dermis & vascular Parenchyma: Primary metabolic function

(photosynthesis)– Found in roots, stems & leaves– Least specialized, thin flexible walls, don’t divide unless

specializing, respire, store food & water

Schlerenchyma: support w/ thick 2o wall strengthened by lignin– Found in stems & leaves generally lack protoplasts– Very rigid cell wall, dead at maturity, cannot lengthen

scaffolding “fibers” & “Sclereids”

Collenchyma:child support– Found in stems and leaves– Grow and elongate with stems and leaves they support,

flexible in young parts of plant

collenchymaparenchyma sclerenchyma

Morphology of three simple tissue types

Complex Tissues

Composed of a mix of cell

types

Xylem

Phloem

Epidermis

Simple Tissues

Made up of only one

type of cell

Parenchyma

Collenchyma

Sclerenchyma

Vascular Tissue  

Phloem: Phood conduction, carries products of photosynthesis to non-photo cells– Found in roots, stems, leaves– Sieve cells, albuminous cells, companion cells, parenchyma– Gymnospersm: sieve, angiosperms, sieve-tube members, connected

vertically by sieve plates– Alive at maturity

Xylem: provides water & ion transport from roots to leaves– Vessel elements, tracheids, fibers, wood parenchymal– tracheids & vessel members, thick w/ secondary wall with lignin– Dead at maturity– Seedless vascular & gymnosperms have tracheids w/ tapered ends– Angiospersm have both tracheids and vessel members wh are

continuous

Xylem

• Conducts water and dissolved minerals

• Conducting cells are dead and hollow at maturity

vessel membertracheids

Phloem: A Complex Vascular Tissue

• Transports sugars

• Main conducting cells are sieve-tube members

• Companion cells assist in the loading of sugars

sieve plate

sieve-tubemember

companioncell

Epidermis: A Complex Plant Tissue

- Covers and protects plant surfaces

-Secretes a waxy, waterproof cuticle

-In plants with secondary growth,

periderm replaces epidermis

-protection, increase absorption area

in roots, reduces H2O loss in stem &

leaves,

-Regulates gas exchange in leaves

Signaling between Plants and Pathogens

water & minerals

sugar

SHOOT SYSTEM

ROOT SYSTEMRoot system

- anchors the plant

- penetrates the soil and absorbs water and minerals

- stores food

Shoot system

- produces sugars by photosynthesis

- carries out reproduction

Shoot and Root Systems:

Not independent

Shoot Development

ground meristem

primary xylempithprocambriumcortex

procambriumprotoderm

shoot apicalmeristem

primary phloem

Roots also have meristems

Leaf Gross Structure-Adapted for Photosynthesis

petiole

blade

axillarybud

node

blade

sheath

node

DICOT MONOCOT

• Leaves are usually thin

– High surface area-to-volume ratio

– Promotes diffusion of carbon dioxide in, oxygen out

• Leaves are arranged to capture sunlight

– Are held perpendicular to rays of sun

– Arrange so they don’t shade one another

Leaf StructureUPPER

EPIDERMIS

PALISADEMESOPHYLL

SPONGYMESOPHYLL

LOWEREPIDERMIS

one stoma

cuticle

O2CO2

xylem

phloem

Parenchyma

Collenchyma

Mesophyll: Photosynthetic Tissue

• A type of parenchyma tissue

• Cells have chloroplasts

• Two layers in dicots

– Palisade mesophyll

– Spongy mesophyll

Leaf Veins: Vascular Bundles

• Xylem and phloem –

often strengthened with fibers

• In dicots, veins are netlike

• In monocots, they are parallel

Internal Structure of a Dicot Stem

- Outermost layer is epidermis

- Cortex lies beneath epidermis

- Ring of vascular bundles separates the cortex from the pith

- The pith lies in the center of the stem

Internal Structure

of a Monocot

Stem

• The vascular bundles

are distributed

throughout the ground

tissue

• No division of ground

tissue into cortex and

pith

Dicots

Dicots and Monocots have different stem and root anatomies

Ground tissuesystem

Vascular tissue system

Dermal tissuesystem

Monocots

Stems

Monocot stems differ from dicot stems in that they lack secondary growth

• No vascular cambium nor cork cambium

• Stems usually uniform in diameter

• Scattered vascular bundles (not in a ring like dicot stems)

The Translocation of Phloem • the process of moving

photosynthetic product through the phloem

• In angiosperms, the specialized cells that transport food in the plant are called sieve-tube members, arranged end to end to form large sieve tubes

• Phloem sap is very different from xylem sap

– sugar (sucrose) can be concentrated up to 30% by weight

• Phloem transport is bidirectional – Phloem moves from a sugar source

(a place where sugar is produce by photosynthesis or by the breakdown of sugars) to a sugar sink (an organ which consumes or stores sugar)

– What are some organs which would be sugar sinks?

Transport in Plants:

The Pressure Flow Model , 2

Root Systems

Root Structure• Root cap covers tip

• Apical meristem produces the cap

• Cell divisions and elongation at the apical meristem cause the root to lengthen

• Farther up, cells differentiate and mature

root apical meristem

root cap

pericycle

phloem

xylem

root hair

endodermis

epidermis

cortex

Primary Root Growth

Root Cap •Secretes polysaccharide slime that lubricates the soil •Constantly sloughed off and replaced

Apical Meristem •Region of rapid cell division of undifferentiated cells •Most cell division is directed away from the root cap

Quiescent Center •Populations of cells in apical meristem which reproduce much more slowly than other meristematic cells •Resistant to radiation and chemical damage •Possibly a reserve which can be called into action if the apical meristem becomes damaged

The Zone of Cell Division - Primary Meristems •Three areas just above the apical meristem that continue to divide for some time

•Protoderm•Ground meristem•Procambium

The Zone of Elongation •Cells elongate up to ten times their original length •This growth pushes the root further downward into the soil

The Zone of Maturation •Region of the root where completely functional cells are found

Internal Structure of a Root• Outermost layer is epidermis• Root cortex is beneath the epidermis• Endodermis, then pericycle surround the vascular cylinder• In some plants, there is a central pith

Root Anatomy - Dicot Roots Epidermis • Dermal tissue • Protection of the root Cortex • Ground tissue • Storage of photosynthetic products • Active in the uptake of water and minerals Endodermis • cylinder once cell thick that forms a boundary between the

cortex and the stele contains the casparian strip, Pericycle • found just inside of the endodermis • may become meristematic • responsible for the formation of lateral roots Vascular Tissue • Xylem and Phloem Root Anatomy - Monocot Roots Epidermis • Dermal tissue • Protection of the root Cortex • Ground tissue • Storage of photosynthetic products • Active in the uptake of water and minerals Endodermis • cylinder once cell thick that forms a boundary between the

cortex and the stele even more distinct than dicot counterpart contains the casparian strip,

Pericycle• monocot roots rarely branch, but can, and this branch will

originate from the pericycle Vascular Tissue • Xylem and Phloem • Forms a ring near center of plant Pith • Center most region of root

Root Hairs and Lateral Roots• Both increase the surface area of a root

system

• Root hairs are tiny extensions of

epidermal cells

• Lateral roots arise from the pericycle

and must push through the cortex and

epidermis to reach the soil• Root of a single rye plant (fibrous system) measure and

counted 6400 roots w/ 12.5 million root hairs = 250 km, dist

from Memphis, TN to Atlanta, GA

newlateralroot

Symplastic Movement • Movement of water and solutes through the continuous

connection of cytoplasm (though plasmodesmata) • No crossing of the plasma membrane (once it is in the

symplast) Apoplastic Movement • Movement of water and solutes through the cell walls and the

intercellular spaces • No crossing of the plasma membrane • More rapid - less resistance to the flow of water

Net flow in whole plants

Fig. 39.12b

•transpirational pull•flow from greater to lower water concentration

•relies on cohesion & adhesion of water

–cavitation breaks chain of water molecules

Ascent of xylem sap

Fig. 39.11

The availability of soil water and minerals

Long-distance transport of water from roots to leaves

Net flow in whole plants

Key Concepts:• Diffusion: movement

of molecules from high to low concentration.

• Osmosis: diffusion of water across a semi-permeable membrane.

• Mass or bulk flow: movement of fluid due to pressure or gravity differences.

Long-distance movement of water• Plants mostly obtain water & minerals from soil.• Water moves up the xylem by bulk flow.• Movement of water depends on transpiration pull, cohesion &

adhesion of water molecules, capillary forces, and strong cell walls.

Other mechanisms of water transport not as important:

• Diffusion (note mosses, etc.)• Capillary forces (cohesions & adhesion)• Osmotic pressure (guttation)

Fig. 39.11

Water – pushed or pulled?

• Pushing of the xylem sap occurs via root pressure – root cells expend energy to pump mineral into the xylem. Minerals accumulate in the xylem sap lowering water potential there. Thus water flows into the xylem, generating a positive pressure that pushes fluid up the xylem.

Guttation – from root pressure

The availability of soil water and minerals

Long-distance transport of water from roots to leaves

But root pressure can only push sap up a few meters and many plants generate no root pressure at all. How does water reach leaves of 100 m tall trees?Xylem sap is pulled up the plant via transpirational pull. Leaves actually generate the negative pressure necessary to bring water to them.

Translocation• The transport of food throughout a plant is

known as translocation. • Sugar from mesophyll cells in the leaves

and other sources must be loaded before it can be moved.

• Often sieve tube members accumulate very high sucrose concentrations – 2 to 3 times higher than concentrations in the mesophyll – so phloem requires active transport using proton pumps

• At the sink end of a sieve tube, the phloem unloads its sugar. Phloem unloading is a highly variable process; its mechanism depends upon the plant species and the type of organ. In any case, the concentration of sugar in the sink cells is lower than in the phloem because the sugar is either consumed or converted into insoluble polymers like starch.

• Phloem moves at up to 1 m/hour – too fast to be by diffusion. So phloem also moves via bulk flow – pressure drives it.

Secondary Growth

The Plant Body: Secondary Growth: The Vascular Cambium

• Occurs in perennials

• A ring of vascular cambium produces secondary xylem and phloem

• Wood is the accumulation of these secondary tissues, especially

xylem

Woody Stem

periderm (consists ofcork, cork cambium,and secondary cortex)

secondaryphloem

BARK

HEARTWOOD SAPWOOD

vascular cambium

Annual Rings

• Concentric rings of secondary xylem

• Alternating bands of early and late wood

• Early wood– Xylem cells with large diameter, thin walls

• Late wood– Xylem cells with smaller diameter, thicker

walls

Types of Wood

• Hardwood (oak, hickory)– Dicot wood– Xylem composed of vessels, tracheids,

and fibers

• Softwood (pine, redwood)– Gymnosperm wood– Xylem composed mostly of tracheids– Grows more quickly

Resources• Plants in Motion:

• Movement of Water in Plants

• Transport in Plants

• Root Pressure

• Water Transport in 3 Parts