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Chapter 35. Plant Structure, Growth, and Development. Figure 35.1 Fanwort (Cabomba caroliniana). Reproductive shoot (flower). Terminal bud. Node. Internode. Terminal bud. Shoot system. Vegetative shoot. Blade Petiole. Leaf. Axillary bud. Stem. Taproot. Root system.

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chapter 35

Chapter 35

Plant Structure, Growth, and Development

figure 35 2 an overview of a flowering plant

Reproductive shoot (flower)

Terminal bud

Node

Internode

Terminal

bud

Shoot

system

Vegetative

shoot

Blade

Petiole

Leaf

Axillary

bud

Stem

Taproot

Root

system

Lateral roots

Figure 35.2 An overview of a flowering plant
figure 35 4 modified roots

(c) “Strangling” aerialroots

(a) Prop roots

(b) Storage roots

(d) Buttress roots

(e) Pneumatophores

Figure 35.4 Modified roots
figure 35 5 modified stems

(a)

Stolons. Shown here on a

strawberry plant, stolons are horizontal stems that grow

along the surface. These “runners”

enable a plant to reproduce

asexually, as plantlets form at

nodes along each runner.

Storage leaves

(d)

Rhizomes. The edible base

of this ginger plant is an example

of a rhizome, a horizontal stem

that grows just below the surface

or emerges and grows along the

surface.

Stem

Node

Root

(b)

Bulbs. Bulbs are vertical,

underground shoots consisting

mostly of the enlarged bases

of leaves that store food. You

can see the many layers of

modified leaves attached

to the short stem by slicing an

onion bulb lengthwise.

Rhizome

(c)

Tubers. Tubers, such as these

red potatoes, are enlarged

ends of rhizomes specialized

for storing food. The “eyes”

arranged in a spiral pattern

around a potato are clusters

of axillary buds that mark

the nodes.

Root

Figure 35.5 Modified stems
figure 35 6 simple versus compound leaves

(a) Simple leaf. A simple leafis a single, undivided blade.Some simple leaves are deeply lobed, as in anoak leaf.

Petiole

Axillary bud

(b) Compound leaf. In acompound leaf, theblade consists of multiple leaflets.Notice that a leaflethas no axillary budat its base.

Leaflet

Petiole

Axillary bud

(c) Doubly compound leaf.In a doubly compound leaf, each leaflet is divided into smaller leaflets.

Leaflet

Petiole

Axillary bud

Figure 35.6 Simple versus compound leaves
figure 35 7 modified leaves

(a) Tendrils. The tendrils by which thispea plant clings to a support are modified leaves. After it has “lassoed” a support, a tendril forms a coil that brings the plant closer to the support. Tendrils are typically modified leaves, but some tendrils are modified stems, as in grapevines.

(b) Spines. The spines of cacti, such as this prickly pear, are actually leaves, and photosynthesis is carried out mainly by the fleshy green stems.

(c) Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water.

(d) Bracts. Red parts of the poinsettia are often mistaken for petals but are actually modified leaves called bracts that surround a group of flowers. Such brightly colored leaves attract pollinators.

(e) Reproductive leaves. The leaves of some succulents, such as Kalanchoe daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil.

Figure 35.7 Modified leaves
figure 35 8 the three tissue systems

Dermal

tissue

Ground

tissue

Vascular

tissue

Figure 35.8 The three tissue systems
figure 35 9 examples of differentiated plant cells

PARENCHYMA CELLS

WATER-CONDUCTING CELLS OF THE XYLEM

Tracheids

Vessel

100 m

Pits

Parenchyma cells

60 m

COLLENCHYMA CELLS

Tracheids and vessels

Cortical parenchyma cells

80 m

Vessel

element

Vessel elements with

partially perforated

end walls

Tracheids

SUGAR-CONDUCTING CELLS OF THE PHLOEM

Sieve-tube members:

longitudinal view

Collenchyma cells

SCLERENCHYMA CELLS

5 m

Companion

cell

Sclereid cellsin pear

Sieve-tube

member

25 m

Sieve

plate

Nucleus

Cell wall

30 m

15 m

Companion

cell

Cytoplasm

Fiber cells

Figure 35.9 Examples of Differentiated Plant Cells
figure 35 10 an overview of primary and secondary growth

Primary growth in stems

Shoot apical

meristems

(in buds)

Epidermis

Cortex

In woody plants,

there are lateral

meristems that

add secondary

growth, increasing

the girth of

roots and stems.

Primary phloem

Primary xylem

Vascular

cambium

Lateral

meristems

Pith

Cork

cambium

Secondary growth in stems

Apical meristems

add primary growth,

or growth in length.

Periderm

Cork

cambium

Pith

The Cork

cambium adds

secondary

dermal tissue.

Primary

xylem

Cortex

Primary

phloem

Root apical

meristems

Secondary

xylem

The vascular

cambium adds

secondary

xylem and

phloem.

Secondary

phloem

Vascular cambium

Figure 35.10 An overview of primary and secondary growth
figure 35 11 three years past growth evident in a winter twig

Terminal bud

Bud scale

Axillary buds

Leaf scar

Node

This year’s growth

(one year old)

Stem

Internode

One-year-old side

branch formed

from axillary bud

near shoot apex

Leaf scar

Last year’s growth

(two years old)

Scars left by terminal

bud scales of previous

winters

Leaf scar

Growth of two

years ago (three

years old)

Figure 35.11 Three years’ past growth evident in a winter twig
figure 35 12 primary growth of a root

Cortex

Vascular cylinder

Epidermis

Key

Zone of

maturation

Root hair

Dermal

Ground

Vascular

Zone of

elongation

Apical

meristem

Zone of cell

division

Root cap

100 m

Figure 35.12 Primary growth of a root
figure 35 13 organization of primary tissues in young roots

Epidermis

Cortex

Vascular

cylinder

Endodermis

Pericycle

Core of

Parenchyma

cells

Xylem

Phloem

100 m

100 m

(a)

Transverse section of a typical root. In the

roots of typical gymnosperms and eudicots, as

well as some monocots, the stele is a vascular

cylinder consisting of a lobed core of xylem

with phloem between the lobes.

Transverse section of a root with parenchyma

in the center. The stele of many monocot roots

is a vascular cylinder with a core of parenchyma

surrounded by a ring of alternating xylem and phloem.

(b)

Endodermis

Key

Dermal

Pericycle

Ground

Vascular

Xylem

Phloem

50 m

Figure 35.13 Organization of primary tissues in young roots
figure 35 14 the formation of a lateral root

100 m

Emerging

lateral

root

Cortex

Vascular

cylinder

1

2

3

4

Epidermis

Lateral root

Figure 35.14 The formation of a lateral root
figure 35 15 the terminal bud and primary growth of a shoot

Apical meristem

Leaf primordia

Developing

vascular

strand

Axillary bud

meristems

0.25 mm

Figure 35.15 The terminal bud and primary growth of a shoot
figure 35 16 organization of primary tissues in young stems

Phloem

Xylem

Groundtissue

Sclerenchyma(fiber cells)

Ground tissueconnecting pith to cortex

Pith

Epidermis

Key

Vascularbundles

Cortex

Epidermis

Dermal

Vascularbundle

Ground

Vascular

1 mm

1 mm

(b) A monocot stem. A monocot stem (maize) with vascularbundles scattered throughout the ground tissue. In such anarrangement, ground tissue is not partitioned into pith andcortex. (LM of transverse section)

(a) A eudicot stem. A eudicot stem (sunflower), withvascular bundles forming a ring. Ground tissue towardthe inside is called pith, and ground tissue toward theoutside is called cortex. (LM of transverse section)

Figure 35.16 Organization of primary tissues in young stems
figure 35 17 leaf anatomy

Key

to labels

Guard

cells

Dermal

Stomatal pore

Ground

Vascular

Epidermal

cell

Sclerenchyma

fibers

50 µm

Cuticle

(b)

Surface view of a spiderwort

(Tradescantia) leaf (LM)

Stoma

Upper

epidermis

Palisade

mesophyll

Bundle-

sheath

cell

Spongy

mesophyll

Lower

epidermis

Guard

cells

Cuticle

Vein

Xylem

Vein

Air spaces

Guard cells

Guard

cells

Phloem

100 µm

Transverse section of a lilac

(Syringa) leaf (LM)

(c)

(a)

Cutaway drawing of leaf tissues

Figure 35.17 Leaf anatomy
figure 35 18 primary and secondary growth of a stem layer 2

(a) Primary and secondary growth in a two-year-old stem

3

1

2

4

Pith

Primary xylem

Epidermis

Vascular cambium

Cortex

Primary phloem

Xylem ray

Growth

Phloem ray

Cork

Primary xylem

First cork cambium

Secondary xylem

Primary phloem

Vascular cambium

Secondary phloem

Figure 35.18 Primary and secondary growth of a stem (layer 2)
figure 35 18 primary and secondary growth of a stem layer 3

(a) Primary and secondary growth in a two-year-old stem

6

5

7

8

9

2

3

4

1

Pith

Epidermis

Cortex

Primary xylem

Epidermis

Vascular cambium

Cortex

Primary xylem

Xylem ray

Growth

Phloem ray

Cork

Primary xylem

First cork cambium

Secondary xylem

Primary phloem

Vascular cambium

Secondary phloem

Secondary phloem

Periderm(mainly cork cambiaand cork)

Growth

Bark

Primary phloem

Primary phloem

Layers of periderm

Secondary xylem(two years ofproduction)

Secondary phloem

Vascular cambium

Vascular cambium

Cork

Secondary xylem

Most recentcork cambium

Primary xylem

Primary xylem

Pith

Pith

Vascular cambium

Figure 35.18 Primary and secondary growth of a stem (layer 3)
slide23

Secondary phloem

Cork

cambium

Vascular cambium

Late wood

Secondary

xylem

Periderm

Early wood

Cork

(b) Transverse sectionof a three-year-old stem (LM)

Xylem ray

Bark

0.5 mm

0.5 mm

figure 35 19 cell division in the vascular cambium

Vascular

cambium

C

X

C

C

C

P

(a)

Types of cell division. An initial can divide

transversely to form two cambial initials (C)

or radially to form an initial and either a

xylem (X) or phloem (P) cell.

X

X

C

X

P

X

P

C

X

P

C

P

X

C

C

(b)

Accumulation of secondary growth. Although shown here

as alternately adding xylem and phloem, a cambial initial usually

produces much more xylem.

Figure 35.19 Cell division in the vascular cambium
figure 35 20 anatomy of a tree trunk

Growth ring

Vascular

ray

Heartwood

Secondary

xylem

Sapwood

Vascular cambium

Secondary phloem

Bark

Layers of periderm

Figure 35.20 Anatomy of a tree trunk
figure 35 21 arabidopsis thaliana

Cell organization and biogenesis (1.7%)

DNA metabolism (1.8%)

Carbohydrate metabolism (2.4%)

Signal transduction (2.6%)

Unknown

(36.6%)

Protein biosynthesis (2.7%)

Electron transport

(3%)

Protein

modification (3.7%)

Protein

metabolism (5.7%)

Transcription (6.1%)

Other metabolism (6.6%)

Other biological

processes (18.6%)

Transport (8.5%)

Figure 35.21 Arabidopsis thaliana
figure 35 22 the plane and symmetry of cell division influence development of form

Division in

same plane

Single file of cells forms

Plane of

cell division

Division in

three planes

Cube forms

Nucleus

(a)

Cell divisions in the same plane produce a single file of cells, whereas cell divisions in three planes give rise to a cube.

Asymmetrical

Developing

guard cells

cell division

Unspecialized

epidermal cell

Unspecialized

epidermal cell

Unspecialized

epidermal cell

Guard cell

“mother cell”

(b)

An asymmetrical cell division precedes the development of epidermal guard cells, the cells that border stomata (see Figure 35.17).

Figure 35.22 The plane and symmetry of cell division influence development of form
slide30

fass seedling

(b)

(a)

Wild-type seedling

(c)

Mature fass mutant

Figure 35.25 The fass mutant of Arabidopsis confirms the importance of cytoplasmic microtubules to plant growth
figure 35 28 control of root hair differentiation by a homeotic gene

When epidermal cells border a single cortical

cell, the homeotic gene GLABRA-2 is selectively

expressed, and these cells will remain hairless.

(The blue color in this light micrograph indi-

cates cells in which GLABRA-2 is expressed.)

Here an epidermal cell borders two

cortical cells. GLABRA-2 is not expressed,

and the cell will develop a root hair.

Cortical

cells

20 µm

The ring of cells external to the epi-

dermal layer is composed of root

cap cells that will be sloughed off as

the root hairs start to differentiate.

Figure 35.28 Control of root hair differentiation by a homeotic gene
figure 35 29 phase change in the shoot system of acacia koa

Leaves produced

by adult phase

of apical meristem

Leaves produced

by juvenile phase

of apical meristem

Figure 35.29 Phase change in the shoot system of Acacia koa
figure 35 30 organ identity genes and pattern formation in flower development

Pe

Ca

St

Se

Pe

Se

Pe

(a)

Normal Arabidopsis flower.Arabidopsis

normally has four whorls of flower parts: sepals

(Se), petals (Pe), stamens (St), and carpels (Ca).

Pe

(b)

Abnormal Arabidopsis flower. Reseachers have

identified several mutations of organ identity

genes that cause abnormal flowers to develop.

This flower has an extra set of petals in place of

stamens and an internal flower where normal

plants have carpels.

Se

Figure 35.30 Organ identity genes and pattern formation in flower development
figure 35 31 the abc hypothesis for the functioning of organ identity genes in flower development

Sepals

Petals

Stamens

Carpels

A

B

(a) A schematic diagram of the ABChypothesis. Studies of plant mutationsreveal that three classes of organ identitygenes are responsible for the spatial patternof floral parts. These genes are designated A,B, and C in this schematic diagram of a floralmeristem in transverse view. These genesregulate expression of other genesresponsible for development of sepals,petals, stamens, and carpels. Sepals developfrom the meristematic region where only Agenes are active. Petals develop where bothA and B genes are expressed. Stamens arisewhere B and C genes are active. Carpels arisewhere only C genes are expressed.

C

C gene

activity

B + C

gene

activity

A + B

gene

activity

A gene

activity

A

B

B

A

B

A

A

Active

genes:

B

B

B

B

B

C

A

C

A

C

A

B

A

C

A

B

A

A

A

C

A

A

C

B

C

B

C

C

C

C

C

C

C

C

C

A

A

Whorls:

Carpel

Stamen

Petal

Sepal

Wild type

Mutant lacking A

Mutant lacking B

Mutant lacking C

missing, the other activity spreads through all four whorls, we can explain the

phenotypes of mutants lacking a functional A, B, or C organ identity gene.

(b) Side view of organ identity mutant flowers. Combining the modelshown in part (a) with the rule that if A gene or C gene activity is

Figure 35.31 The ABC hypothesis for the functioning of organ identity genes in flower development