1 image – the angel oak lecture #4 – plant structure, growth and development

1

Image – the Angel Oak

Lecture #4 – Plant Structure, Growth And Development

2

Key Concepts:

• What is a kingdom?• Why study plants?• What makes a plant a plant?• The hierarchy of structure – plant cells,

tissues and organs• Growth• Primary growth – elongation• Secondary growth – diameter expansion• Morphogenesis occurs during growth

3

Image – Linnaeus

Carolus Linnaeus

(1707-1778)

The founder of modern taxonomy defined kingdoms by morphological

similarity

4

Linnaeus’ Taxonomic Hierarchy

Taxonomic Category Example (taxon)

Kingdom Plantae, also Metaphyta = all plants

Division (phylum) Magnoliophyta = all angiosperms

Class Liliopsida = all monocots

Order Asparagales = related families (Orchidaceae, Iridaceae, etc)

Family Orchidaceae = related genera (Platanthera, Spiranthes, etc)

Genus Platanthera = related species (P. ciliaris, P. integra, etc)

Specific name/epithet ciliaris = one species

5

Linnaeus’ Taxonomic Hierarchy

Taxonomic Category Example (taxon)








6

Images – the yellow fringed orchid

Platanthera ciliaris

7

Images – the 3 multicellular kingdoms, animals, fungi and plants

Linnaeus recognized only 2 kingdoms• If it moved – animal; if it didn’t – plant• Fungi were lumped with plants• The microscopic world was largely unknown

8

Diagram – the 5 kingdom system

The 5 kingdom system – developed in the 1960’s and used until recently

9

Diagram – 3 domain system of classification

Molecular data supports 3 domain classification scheme

Kingdoms are defined by monophyletic lineage

10

Diagram – transition from 5 kingdom to 3 domain system indicating dynamic nature of classification

Classification is Dynamic!

Multicellular eukaryotes remain fairly well defined – the plants, fungi and animals. Classification of single

celled organisms is still underway.

11

Current Taxonomic HierarchyTaxonomic Category Example (taxon)

Domain Eukarya = all eukaryotic organisms








12

Why Plants?

13

Image – shooting stars

Why Plants?

• Food• Pharmaceuticals• Building materials• Furniture• Paper• Chemicals• Horticulture/Floriculture• etc…..

14

What makes a plant a plant???• multicellular, eukaryotic organisms with extensive specialization

• almost all are photosynthetic, with chloroplasts (= green)– some obtain additional nutrition through parasitism or carnivory– some are saprophytic, entirely without chlorophyll (eat dead OM)

• excess carbohydrates stored as starch (coiled, branched polymer of glucose)

• cell walls of cellulose = fibrous (not branched) polysaccharide = accounts for the relative rigidity of the cell wall

• cell division by formation of cell plate

• most extant plant species are terrestrial (many characteristics that are adapted for terrestrial life)

• separated from cyanobacteria by chloroplasts

• separated from green algae by various adaptations to terrestrial life

15

Images and diagrams – characteristics that separate plants from other kingdoms

16

What makes a plant a plant???• Multicellular, eukaryotic organisms with extensive

specialization • Almost all are photosynthetic, with chloroplasts (= green)

Some obtain additional nutrition through parasitism or carnivory Some are saprophytic, entirely without chlorophyll (absorb dead

OM)• Excess carbohydrates stored as starch (coiled, branched

polymer of glucose)• Cell walls of cellulose = fibrous (not branched)

polysaccharide = accounts for the relative rigidity of the cell wall

• Cell division by formation of cell plate• Most extant plant species are terrestrial (many

characteristics that are adapted for terrestrial life)• Separated from cyanobacteria by chloroplasts• Separated from green algae by various adaptations to

terrestrial life Read this later….

17

Plants were the first organisms to move onto land

• Occurred about 475mya• Very different conditions from former

marine habitat• Many new traits emerged in adaptation to

life on dry land• Extensive adaptive radiation into many

new ecological niches

18

Diagram – phylogeny of land plants; same on next slide

Four major groups of plants have emerged

since plants took to land

19

We will focus on

angiosperms

Next semester in 211 you will learn more about the transition from water to land,

and the evolution of reproductive strategies in all

plants

20

Images – flowering plants

Angiosperms – the flowering plants:90% of the Earth’s modern flora

21

Diagram – plant cell; same on next slide

Basic Structure of the Plant Cell – what’s unique???

22

Basic Structure of the Plant Cell

23

Critical Thinking

• Do all plant cells have chloroplasts???• How can you tell???

24

Critical Thinking

• Do all plant cells have chloroplasts???• NO!!!• How can you tell???

25

Image – chloroplast free white bracts on white-top sedge

Critical Thinking

• Do all plant cells have chloroplasts???

• NO!!!• How can you tell???• Chlorophyll reflects

green lightGreen tissues have

chloroplastsNon-green tissues

don’t

26

Diagram – primary and secondary cell walls; same on next slide

More on the cell wall:

• All cell walls are produced by the cell membrane, outside

• Primary wall is produced firstMostly cellulose

• Secondary walls are produced laterLignified, so ???

• Secondary walls are interior to primary walls

27

More on the cell wall:

• All cell walls are produced by the cell membrane

• Primary wall is produced firstMostly cellulose

• Secondary walls are produced laterLignified, so rigid!

• Secondary walls are interior to primary walls

28

Micrographs – plant cell types

Five Major Plant Cell

Types

• Parenchyma

• Collenchyma

• Sclerenchyma

• Xylem elements

• Phloem elements

29

Micrographs – parenchyma cells

Parenchyma

• Thin primary wall• No secondary wall• Many metabolic and storage functions• Bulk of the plant body

30

Micrograph – collenchyma cells; same on next slide

Collenchyma

• Thick primary wall

• No secondary wallImplications???

• Support growing tissues

31

Collenchyma

• Thick primary wall

• No secondary wall Extensible – no

lignin means they can elongate

• Support growing tissues

32

Micrograph – sclerenchma cells; same on next slide

Sclerenchyma

• Thick secondary wall• Secondary walls are

lignifiedImplications???

• Support mature plant parts

• Often dead at maturity

33

Sclerenchyma

• Thick secondary wall• Secondary walls are

lignifiedLignified cells are rigid

and fixed in size• Support mature plant

parts• Often dead at maturity

34

Micrographs – collenchyma and sclerenchyma cell comparison

Collenchyma vs. Sclerenchyma• Both provide structural support• Both have thick walls• Collenchyma = thick primary wall, no lignin• Sclerenchyma = thick secondary wall, lignified

35

Diagrams and micrograph – tracheids and vessel elements

Xylem Elements

• Lignified secondary walls

• Always dead at maturity (open)

• Function to transport water and dissolved nutrients, and to support the plant

• Tracheids and vessel elements

36

Micrograph – rings of lignin in developing vessel element; same on next slide

Critical Thinking

• Vessel elements and the convergent evolution of rings

• What else looks like this????

• What is the function????

37

Critical Thinking

• Vessel elements and the convergent evolution of rings

• What else looks like this????

• What is the function????

• Stiff rings hold the “tube” openTrachea in both

vertebrates and inverts

38

Micrograph – phloem elements

Phloem Elements

• Sieve tube members + companion cells

• STM lack nucleus, ribosomes – their metabolism is controlled by the companion cells

• Function to transport the products of metabolism

• Non-angiosperms have more primitive phloem elements

39

Diagram – phloem elements

Critical Thinking

• What might be the functional advantage of a cell with no nucleus???

40

Critical Thinking

• What might be the functional advantage of a cell with no nucleus???

• Sieve plates are very open• Plus, function is to move large volumes of

sap around the plantNucleus and other organelles get in the way

• But, phloem transport requires ATP and thus a living cell

41


Plants are Simple

Only Five Major Cell Types

• Parenchyma

• Collenchyma

• Sclerenchyma

• Xylem elements

• Phloem elements

42

Hands On• Use thin sections and stains to see

different plant cells (Page 13)• Sections must be VERY thin to allow light

to pass through• Use toluidine blue to increase contrast• With a fresh section, use phloroglucinol to

see lignified areas of the tissues• Follow instructions for staining in manual,

and take notes to answer questions on handout – label and keep your samples

43


Five Major Plant Cell

Types

• Parenchyma

• Collenchyma

• Sclerenchyma

• Xylem elements

• Phloem elements

44

Diagram – plant tissue types

Tissue Systems

• Epidermis• Vascular• Ground• Meristem

45

Micrograph and diagram – epidermis

Epidermis Tissue:• Covers the outer surface of all

plant parts• Shoot surfaces covered with

waxy cuticleHelps to protect the plant and

prevent desiccation• Usually a single, transparent

cell layer• Tight joints; stomata allow for

gas exchange

46

Critical Thinking

• Do roots have a waxy cuticle???• Why or why not???

47

Critical Thinking

• Do roots have a waxy cuticle???• No• Why or why not???• Wax is waterproof

Roots absorb water from the soilA waxy coating would be a functional

DISadvantage

Never forget the importance of natural selection!!!!!

48

Hands On

• Look at your leaf cross sections• Can you see the epidermis?• Can you see the waxy cuticle?

Diagram of leaf tissue arrangement

49

Micrograph – vascular bundle in cross section

Vascular Tissue:

• Transports water, solutes, and metabolic products throughout the plant

• Confers structural support• Includes xylem elements,

phloem elements, parenchyma and sclerenchyma fibers

50

Critical Thinking

• Why does vascular tissue give structural support to a plant???

51

Critical Thinking

• Why does vascular tissue give structural support to a plant???

• LIGNIN• Xylem and sclerenchyma fibers are

lignified!

52

Hands On

• Look at your cross sections – leaf and stem

• Can you see the vascular tissues?

Diagram of leaf tissue arrangement

53

Micrograph and diagram – ground tissues in stems and leaves

Ground Tissue:

• Bulk of the plant body – pith, cortex and mesophyll

• Mostly parenchyma• Most metabolic,

structural and storage functions

54

Hands On

• Look at the stem cross sections• Can you see the ground tissues?• The potatoes are mostly ground tissue

What characteristics do they share with other stems?

What differences?What function???

55

Micrograph – herbaceous dicot stem

Critical Thinking

• Is this what the inside of a tree looks like???

56

Micrograph of herbaceous eudicot stem; image of woody stem; diagram of woody stem tissue organization

Critical Thinking

• Is this what the inside of a tree looks like???

• No – wood is xylem tissueThe bulk of a tree is wood, not ground tissue

57

Image – new growth at tip of stem

Meristem Tissue:

• How the plant grows• Cells divide constantly during the growing

season to make new tissues• More details later

58

Diagram – plant tissue systems

Plants are Simple

Only Four Major Tissue Types

• Epidermis• Vascular• Ground• Meristem

59

Tissues Make Organs:

• Roots – anchor the plant, absorb water and nutrients

• Stems – support the leaves• Leaves – main site of photosynthesis• Reproductive organs (flowers, cones, etc –

more later)

All organs have additional functions – hormone synthesis, transport, etc…

60

Diagram – root and shoot systems

Plant Organ Systems

61

Hands On

• Show ‘n’ Tell• What plant parts did you bring???• Discuss your plants with your team• Focus on visible tissues and organs• Be prepared to demonstrate your findings

to the whole class

62

ancestral

paleoherbs magnoliids eudicots monocots

Modern molecular evidence indicates four classes of angiosperms

Not all plants have the same tissue organization in their organs

63

Images – water lily and magnolia

Paleoherbs and Magnoliids comprise about 3% of angiosperms

Paleoherbs• Aristolochiaceae, Nymphaeaceae, etc

Magnoliids• Magnoliaceae, Lauraceae, nutmeg, black

pepper, etc

64

ancestral

paleoherbs magnoliids eudicots monocots

Modern evidence indicates 4 classes of angiosperms

~ 97% of angiosperms

65

Images – monocots

Monocots include grasses, sedges, iris, orchids, lilies, palms, etc…..

66

Critical Thinking

• Grasses are arguably the most important plant family

• Why???

67

Critical Thinking

• Grasses are arguably the most important plant family

• Why???• They feed the world

Direct nutrition for most of the world – grains such as rice, wheat and corn

Indirect nutrition by feeding the animals we eat

68

Images – eudicots

Eudicots include 70+% of all angiosperms:

• Most broadleaf trees and shrubs• Most fruit and vegetable crops• Most herbaceous flowering plants

69

Monocots vs. Eudicots

Monocots• Flower parts in multiples of 3• Parallel leaf venation• Single cotyledon• Vascular bundles in a ring in the roots• Vascular bundles in complex arrangement in the

stem

• ~90,000 species

Eudicots• Flower parts in multiples

of 4 or 5• Netted leaf venation• Two cotyledons• Vascular tissues in a

solid core in the roots• Vascular bundles in a

ring around the stem• Modern classification

indicates 2 small primitive groups + eudicots

• 200,000+ species

70

Micrographs – cross sections of eudicot and moncot roots; same on next 3 slides

Root System Tissue OrganizationEudicots Monocots

Epidermis, ground, endodermis, pericycle, vascular tissues

71

Eudicot root – closeup

Epidermis

Cortex

Endodermis

Pericycle

Vascular tissues – in solid core

72

Monocot root – closeup

Epidermis

Cortex

Endodermis

Pericycle

Vascular tissues – in ring

Pith in the very center

73

Critical Thinking

• Where do branch roots form???

74

Micrograph – root emerging from pericycle

Critical Thinking

• Where do branch roots form???• The pericycle is the meristem tissue• Roots branch from the inside and push

their way out

75

Micrograph – eudicot and monocot stem tissue organization; same on next 4 slides

Stem System Tissue Organization

Eudicots Monocots

Epidermis, ground, vascular tissues

76

Eudicot stem – closeup

Epidermis

Cortex

Vascular tissues – bundles in a ring

Pith

77

Monocot stem – closeup

Epidermis

Cortex

Vascular tissues – bundles are scattered

78

Wood forms from a meristem that links the vascular bundles:

79

Stem System Tissue Organization

Eudicots Monocots

Monocots cannot make woodMore on wood formation later

80

Various images and a micrograph of a monocot stem – an example of one influence of plants on American history

Monocots, Palmetto Trees, Ft. Moultrie and the SC State Flag

81

Hands On

• Examine the micrographs and discuss with your team (switch PowerPoints)

• What is the tissue organization in each slide, and how does that tell you what plant part is represented?

82

Micrograph – cross-section of leaf tissue arrangement

Leaf Tissue Arrangement

Epidermis, ground, vascular tissues

83

Diagram – leaf tissue arrangement

Leaf closeup

Epidermis

Cortex – palisade mesophyll

Cortex – spongy mesophyll

Vascular tissues

84

Micrograph – epidermis tissue showing stomata

Stomata – pores to allow for gas exchange and transpiration

85

Hands On

• Make a cross section of both monocot and eudicot leaves

• Stain with T-blue• Position both on the slide for side-by-side

comparison• Note the similarities and differences in

tissue organization

86

Diagram – shoot and root systems

See, plants really are simple

• 5 cell types• 4 tissue types• 4 organ types

87

Plant Growth

• Remember, most plants are anchored by roots

• They can’t move to escape or take advantage of changes in their environment

• Plants adjust to their environment• Simple structure + lots of developmental

flexibility allow plants to alter when and how they grow

Developmental flexibility comes from meristems

88

Meristem Tissues

• Actively dividing cells that generate all other cells in the plant body

• Cause indeterminate growthStems and roots elongate throughout the

plant’s life (indeterminate primary growth)Trees continually expand in diameter

(indeterminate secondary growth)Branches form in roots and stems

89

Not all plant parts have indeterminate growth patterns

Indeterminate:Rootsand

StemsThese parts grow

throughout the life of the plant, exploring

new environments or responding to

damage

Determinate:LeavesFlowersFruits

These parts grow to a genetically +/-

predetermined size and shape and then stop – cannot repair

damage

90

Some mature cells can de-differentiate to become meristematic once more!!!

• Primarily occurs in the indeterminate partsStems and roots

• A process that very seldom occurs in other kingdoms

• Allows stems and roots to repair damage and form branches and sprouts

91

Critical Thinking

• Not all stem and root cells can de-differentiate….

• What would control this???

92

Critical Thinking

• Not all stem and root cells can de-differentiate…

• What would control this???• Lignin!!!

Lignin is strong and rigidOnce a cell is lignified, it cannot expand or

divide

93

Growth in Plants:an irreversible increase in size due to

metabolic processes(processes that use ATP energy)

• Cell division produces new cells = function of meristem

• Cell expansion increases the size of the new cells = up to 80% of size increase

• Cell differentiation occurs during and after expansion

94

Diagram – planes of cell division and the effect on morphogenesis

The plane of cell division contributes to morphogenesis

95

Division in one plane results in files of cells

96

Division in two planes results in sheets of cells

97

Division in three planes results in 3-D masses of cells

98

Critical Thinking

• What tissues are files of cells???• What tissues are sheets of cells???• What tissues are 3-D bulky???

99

Critical Thinking

• What tissues are files of cells???Primary vascular tissues, sclerenchyma fibers

• What tissues are sheets of cells???Epidermis, secondary vascular tissues

• What tissues are 3-D bulky???Ground tissues – pith and cortex

100

Hands On

• Use pasta wheels to build all three tissue types

• Each wheel = one cell

101






102

Diagram – how auxin works to promote cell expansion

Auxin-mediated cell expansion

ATP is usedUse the index to find the figure on the

acid growth hypothesis

103

Diagram – cellulose orientation in primary wall and the effects on morphogenesis

The direction of cell expansion depends on cellulose orientation, and contributes to morphogenesis

104






105

Diagram – patterns of growth in roots

Expansion and differentiation occur in an overlapping

zone in all plant parts

106

REVIEW: Growth in Plants:an irreversible increase in size due to





107

Diagram – location of meristems on the plant body; next slide also

Location of the meristems

determines the pattern of plant

growth

Most common meristems:

apical, axillary and lateral

108

Apical meristems

cause elongation of

roots and stems

109

Micrograph – longitudinal section showing distribution of tissues in root

110

Root Cap• Protects the meristem• Determines geotropism• Secretes mucigel

Eases movement of roots through soilSecretes chemicals that enhance nutrient

uptake• Constantly shedding cells

Mechanical abrasion as roots grow through soil

• Constantly being replenished by meristem

111

Images – root cap and mucigel

112

Diagram – longitudinal section of root showing zones of growth; same on next 2 slides

Primary Growth in Roots

113


114


115

Micrograph – root hairs extending from epidermis; same on next few slides

Root Hairs• Form as the epidermis

fully differentiates• Extensions off epidermal

cellsNOT files of cellsPart of an epidermal cell

• Hugely increase the surface area of the epidermis

• 10 cubic cm (double handful) of soil might contain 1 m of plant rootsMostly root hairs

116

Critical Thinking

• What is the selective advantage of root hairs???

117

Critical Thinking

• What is the selective advantage of root hairs???

• Increased surface area allows for more absorption of water and nutrients

• Fine diameter allows roots to ramify throughout the soil environment

118

Root Hairs• By contrast, 10 cc of soil

may contain up to 1000 m of fungal hyphae (1km!)These serve a similar

function for the fungusRamify throughout the

substrate for maximum absorption

Some fungi form symbiotic associations with plant roots and both organisms benefit from this huge absorptive surface area!

More in 211…..

119

Diagram – location of apical meristems

Apical meristems

cause elongation of

roots and stems

120

Micrograph – longitudinal section of stem showing apical and axillary meristems

Apical Meristems in Shoots

121

Critical Thinking

• There is no “shoot cap” – why not???

122

Critical Thinking

• There is no “shoot cap” – why not???• No selective advantage! Shoots “push”

through air – essentially no friction

123

Diagram – meristem locations

Axillary meristems allow for

branching – similar in

structure and function to

apical meristems

Remember, pericycle in roots has same function

124

Micrograph – longitudinal section of stem showing apical and axillary meristems; same on next two slides

Axillary Meristems in Shoots

125

Primary Growth in Shoots

• Apical meristem• Leaf primordia• Axillary buds

126

As with roots – cell division occurs first; zones of expansion and differentiation

overlap

Axillary buds may activate to make branches, or may remain dormant

127

Diagram – how stems elongate during primary growth

Primary growth of a shoot – elongation from the tip

128

Hands On

• Start some seedsDampen a paper towelAdd seedsKeep lightly covered – why???

• Keep a “journal”

129

Diagram – primary vs. secondary growth

Remember:

Elongation is primary growth

Diameter expansion is

secondary growth

130

Diagram – meristem locations

Lateral meristems

cause diameter

expansion

Roots also expand in diameter, but it’s more complicated – we’ll save that for

BIOL 300

131

Diagram – lateral meristems

Lateral Meristems = Cambiums

132

Images – cross section of wood and whole tree

Secondary growth – diameter

expansion

133

Micrograph – cross section of a eudicot stem; same on next 2 slides

Eudicot Stem – recall the arrangement of vascular bundles

134


Vascular cambium

forms here:

135


Vascular cambium

forms here: a cylinder of

meristem tissue between

the xylem to the interior and the phloem to the exterior

136

Diagram – location of the vascular cambium relative to other tree tissues

Secondary xylem and phloem form through cell division by the vascular cambium

137

Diagram – transition from primary growth to secondary growth; same on next slide

During primary growth the vascular tissues form in bundles from the apical meristem

During secondary growth the vascular tissues form in cylinders from the vascular cambium

2o xylem to the inside

2o phloem to the outside

138

Secondary xylem

accumulates

139

Micrograph – cross section of woody plant showing secondary tissues; same on next slide

Secondary Xylem = Wood!

140

Annual growth rings are accumulating rings of secondary xylem

Vascular cambium divides essentially in two planes and remains only a single cell layer thick

Divisions make 2o xylem and 2o phloem and also increase the diameter of the cambium itself

One layer of cambium, continuously increasing in

diameter

141

Year 1 Year 2 Year 3 Year 4

Wood accumulates with each year’s elongationStep 1: Primary growth elongates the tip

Step 2: Vascular cambium forms connecting the bundlesStep 3: Secondary growth builds diameter

142

Diagram – pattern of accumulation of secondary xylem as a tree grows; same on next slide

Critical Thinking

• Why do eudicot trees taper???

143

Critical Thinking• Why do eudicot trees taper???• Elongation occurs from the tip• Every year adds height to the stem• Each new section of stem has just

one layer of secondary growthThe section below that has +1 layersThe section below that has +2 layersThe section below that has +3 layersetc, etc, etcThe bottom of the tree has as many

rings as the tree is old

144

Bark• All tissues external to the vascular

cambium• Diameter expansion splits original

epidermisBark structurally and functionally replaces

epidermis• Inner bark

Functional secondary phloem• Outer bark

Composition varies as tree matures

145

Micrograph – cross section of a tree showing bark formation

Bark Formation

146

Cork Cambium

• Meristematic tissue• Forms in a cylinder during 2o growth• Divides to produce cork cells

Cells filled with waxy, waterproof suberin• Eventually cork cambium becomes cork

itself

147

More on cork cambium

• First layer develops from cortexDe-differentiation!!!

• Second layer forms from cortex – same process

• Third layer forms from cortex…..• Cortex eventually runs out• Then what???

148





149





150





151

Diagram – lateral meristems and the secondary tissues in a tree; same on next slide

Critical Thinking

• What is the next available layer of tissue???

152

Critical Thinking

• What is the next available layer of tissue???

• Secondary phloem!

153




• Third layer forms from cortex…..• Cortex eventually runs out• Then what???• Cork cambium forms from 2o phloem once

all the cortex is used up

154




• Third layer forms from cortex…..• Cortex eventually runs out• Then what???• Cork cambium forms from 2o phloem

2o phloem does NOT accumulate like 2o xylem

155

Diagram – how undifferentiated cells develop into the tissues of the plant body

Stem Tissue Derivations and Fates:

Cells divide, expand and differentiate

156

Review: Key Concepts:

• What is a kingdom? • Why study plants?• What makes a plant a plant?• The hierarchy of structure – plant cells,

tissues and organs• Growth• Primary growth – elongation• Secondary growth – diameter expansion• Morphogenesis occurs during growth

157

Hands On

• Go downstairs and find a living woody plant

• Snap off a twig – be gentle!• Locate bark – peel off and describe

1 image – the angel oak lecture #4 – plant structure, growth and development

Documents

growth slide

related species

development slide

unknown slide

plants linnaeus

related genera platanthera

morphological similarity

monophyletic lineage