Plant Tissues

Chapter 26

Jin Hoe Huh

March 28, 2005

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

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

Shoot System

Root System

Root 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

water & minerals

sugar

SHOOT SYSTEM

ROOT SYSTEM

Shoot and root systems are interdependent

Plant Tissue Systems

VASCULAR TISSUES

GROUND TISSUES

SHOOT SYSTEM

ROOT SYSTEM

EPIDERMIS

• Ground tissue system

• Vascular tissue system

• Dermal tissue system

Meristems – Where Tissues Originate

• Regions where cell divisions produce plant growth

• Apical meristems– Lengthen stems and roots– Responsible for primary growth

• Lateral meristems– Increase width of stems– Responsible for secondary growth

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:SAM and RAM

Lateral Meristems

vascular cambium secondary vascular tissues

periderm cork cambium

thickening

Increases girth of older roots and stems

Cylindrical arrays of cells

Simple Tissues

Made up of only one type of cell

Parenchyma

Collenchyma

Sclerenchyma

collenchymaparenchyma sclerenchyma

Morphology of three simple tissue types

Parenchyma: A Simple Tissue

• Comprises most of a plant’s soft primary growth

• Cells are pliable, thin walled, many sided

• Cells remain alive at maturity and retain capacity to divide

• Mesophyll is a type of parenchyma that contains chloroplasts

Collenchyma: A Simple Tissue

• Specialized for support for primary tissues

• Cells are elongated, with walls (especially corners) thickened with pectin

• Makes stems strong but pliable

• Cells are alive at maturity

Sclerenchyma: A Simple Tissue

• Supports mature plant parts• Protects many seeds• Cells have thick, lignified walls and are dead

at maturity• Two types:

– Fibers: Long, tapered cells– Sclereids: Stubbier cells

Complex Tissues

Composed of a mix of cell types

Xylem

Phloem

Epidermis

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

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

Shoot Development

ground meristem

primary xylempithprocambriumcortex

procambriumprotoderm

shoot apicalmeristem

primary phloem

Bud = undeveloped shoot of meristematic tissue

Internode

Leaves

Axillary bud at node

Longitudinal section of terminal bud

Roots also have meristems

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

Leaf Gross Structure

petiole

blade

axillarybud

node

blade

sheath

node

DICOT MONOCOT

Adapted for Photosynthesis

• 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

Mesophyll:Photosynthetic Tissue

• A type of parenchyma tissue

• Cells have chloroplasts

• Two layers in dicots

– Palisade mesophyll

– Spongy mesophyll

Parenchyma

Collenchyma

Leaf Veins: Vascular Bundles

• Xylem and phloem –

often strengthened with fibers

• In dicots, veins are netlike

• In monocots, they are parallel

Root Systems

Root Structure

• Root cap covers tip

• Apical meristem produces the cap

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

• Farther up, cells differentiate and mature

root apical meristem

root cap

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

pericycle

phloem

xylem

root hair

endodermis

epidermis

cortex

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

newlateralroot

Secondary Growth

• Occurs in perennials

• A ring of vascular cambium produces

secondary xylem and phloem

• Wood is the accumulation of these

secondary tissues, especially xylem

Secondary Growth

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