Plant Tissues

Chapter 28 Part 1

Impacts, IssuesDrought Versus Civilization

Without plants, we would die – prolonged drought can destroy crops and civilizations

28.1 Components of the Plant Body

The unique organization of tissues in flowering plants is part of the reason why they are the dominant group of the plant kingdom

The Basic Body Plan

Shoots• Aboveground plant parts such as stems, leaves,

and flowers

Roots• Structures that absorb water and dissolved

minerals, store food, and support the plant• Usually grow down and outward in the soil

Plant Tissue Systems

Ground tissue system• Photosynthesis, storage, and structural support of

other tissues

Vascular tissue system• Distributes absorbed water and mineral ions and

products of photosynthesis

Dermal tissue system• Covers and protects exposed plant surfaces

Body Plan: Tomato Plant

Fig. 28-2, p. 476

shoot tip (terminal bud)lateral (axillary) bud young leaf

flower

nodeinternode

dermal tissuenode

vascular tissuesleaf

seeds in fruit

ground tissues withered seed leaf (cotyledon)stemSHOOTS

ROOTS

primary rootlateral root root hairs

root tiproot cap

Animation: Tissue systems of a tomato plant

Eudicots and Monocots

Flowering plants are divided into two classes with tissues organized into different patterns

Eudicots have two cotyledons (seed leaves)

Monocots have one cotyledon

Eudicots and Monocots

Fig. 28-3, p. 477

A

Vascular bundles organized in a ring in ground tissue

In seeds, two cotyledons (seed leaves of embryo)

Flower parts in fours or fives (or multiples of four or five)

Leaf veins usually forming a netlike array

Pollen grains with three pores or furrows

B

Vascular bundles throughout ground tissue

In seeds, one cotyledon (seed leaf of embryo)

Flower parts in threes (or multiples of three)

Leaf veins usually running parallel with one another

Pollen grains with one pore or furrow

Animation: Eudicots and monocots

Introducing Meristems

All plants tissues arise at meristems (regions of rapidly dividing, undifferentiated cells)

Growth in apical meristems at tips of shoots and roots (primary growth) increases length

In some plants, growth in lateral meristems (secondary growth) thickens roots and shoots

Apical and Lateral Meristems

Fig. 28-4a, p. 477

Fig. 28-4a, p. 477

shoot apical meristem (new cells forming)

cells dividing, differentiating

three tissue systems developing

three tissue systems developing

cells dividing, differentiating

root apical meristem (new cells forming)

a Many cellular descendants of apical meristems are the start of lineages of differentiated cells that grow, divide, and lengthen shoots and roots.

Fig. 28-4b, p. 477

Fig. 28-4b, p. 477

vascular cambium

cork cambium

thickening

b In woody plants, the activity of two lateral meristems—vascular cambium and cork cambium—result in secondary growth that thickens older stems and roots.

28.2 Components of Plant Tissues

Different plant tissues form just behind shoot and root tips, and on older stem and root parts

Tissue systems are organized as simple tissues (one cell type) or complex tissues (two or more cell types)

Simple Tissues

Parenchyma makes up most primary growth• Functions in secretion, storage, photosynthesis

(mesophyll), and tissue repair

Collenchyma supports growing plant parts• Pectin provides flexibility

Sclerenchyma contains lignin for support• Cells (fibers, sclereids) are dead at maturity

Simple Tissues

Fig. 28-7a, p. 479

collenchyma parenchyma

Fig. 28-7c, p. 479

lignified secondary wall

Complex Tissues: Vascular Tissues

Xylem carries water and ions through the plant• Consists of two types of cells that are dead at

maturity: tracheids and vessel members• Lignin-filled secondary walls

Phloem conducts sugars, other organic solutes• Sieve tubes connect end to end at sieve plates• Companion cells load sugars into sieve tubes

Vascular Tissues

Fig. 28-8, p. 479

one cell’s wall

sieve plate of sieve-tube cell

pit in wall companion

cell

a b c

parenchyma vessel of xylem

phloem fibers of sclerenchyma

Complex Tissues: Dermal Tissues

Epidermis• Usually a single outer layer of cells that secrete a

waxy, protective cuticle• May contain specialized cells that form stomata

for gas exchange

Periderm• Replaces epidermis in woody stems and roots

Plant Cuticle

Fig. 28-9, p. 479

leaf surface cuticle epidermal cell photosynthetic cell

Flowering Plant Tissues

Studying Plant Parts: Tissue Specimens

Tissue specimens are cut along standard planes

Fig. 28-6, p. 478

radial: tangential: transverse:

Tissues in a Buttercup Stem

Fig. 28-5, p. 478

sclerenchyma (fibers) parenchyma epidermis

xylem phloem

28.1-28.2 Key Concepts Overview of Plant Tissues

Seed-bearing vascular plants have a shoot system, which includes stems, leaves, and reproductive parts; most also have a root system

Such plants have ground, vascular, and dermal tissues

Plants lengthen or thicken only at active meristems

28.3 Primary Structure of Shoots

Inside the soft, young stems and leaves of both eudicots and monocots, the ground, vascular, and dermal tissue systems are organized in predictable patterns

Behind the Apical Meristem

Terminal buds• Main zones of primary growth in shoots • Naked or encased in modified leaves (bud scales)• Form leaves at nodes

Lateral buds (axillary buds)• Dormant shoots in leaf axils• Form side branches, leaves, or flowers

Apical Meristem and Primary Growth

Fig. 28-10 (a-c), p. 480

Fig. 28-10 (a-c), p. 480

immature leaf

shoot apical meristem

a Sketch of the shoot tip in the micrograph at right, tangential cut. The descendant meristematic cells are color-coded orange .

b Same tissue region later on, after the shoot tip lengthened above it

cortex

c Same tissue region later still, with lineages of cells lengthening and differentiating

primary phloem

primary xylem pith

Fig. 28-10d (1), p. 480

Fig. 28-10d (1), p. 480

immature leaf

youngest immature

leaf

apical meristem

epidermis forming

lateral bud forming

vascular tissues

forming

pith

Fig. 28-10d (2), p. 480

Inside the Stem

Vascular bundles• Multistranded cords of vascular tissues threaded

lengthwise through ground tissues of all shoots

Two distinct patterns of vascular bundles• Eudicot stems: Cylinders run parallel with stem,

divide ground tissue into cortex and pith• Monocot stems: Bundles distributed throughout

ground tissue

Eudicot and Monocot Stems

Fig. 28-11a, p. 481

Fig. 28-11a, p. 481

meristem cell

epidermis

cortex

vascular bundle

pith

sieve tube in phloem

companion cell in

phloemA Stem fine structure for alfalfa (Medicago), a eudicot

vessel in xylem

Fig. 28-11b, p. 481

Fig. 28-11b, p. 481

collenchyma sheath cell

air space

vessel in xylem

epidermisvascular bundle

pith

sieve tube in phloem

companion cell in phloemB Stem fine structure for corn (Zea mays), a monocot

Animation: Stem organization

Animation: Apical meristems

Animation: Cutting tissue specimens

Animation: Ground tissues

Animation: Vascular tissues