Ch 31 plant structure growth and differentiation
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Ch. 31 – Plant Structure, Growth and Differentiation. Plant Body. Root system Underground Anchor and absorb Shoot system Vertical stem, leaves (flowers, fruits w/seeds) photosynthesis. Fig. 35-2. Reproductive shoot (flower). Apical bud. Node. Internode. Apical bud. Shoot system.

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Plant body
Plant Body

  • Root system

    • Underground

    • Anchor and absorb

  • Shoot system

    • Vertical stem, leaves (flowers, fruits w/seeds)

    • photosynthesis


Ch 31 plant structure growth and differentiation

Fig. 35-2

Reproductive shoot (flower)

Apical bud

Node

Internode

Apical

bud

Shoot

system

Vegetative

shoot

Blade

Leaf

Petiole

Axillary

bud

Stem

Taproot

Lateral

branch

roots

Root

system


Plant cells and tissues
Plant Cells and Tissues

  • Ground tissue system – majority

    • Photosynthesis, storage, support

  • Vascular tissue system

    • Conduction, strength, support

  • Dermal tissue system

    • Covering, protection

      All 3 are Interconnected throughout the plant


Ch 31 plant structure growth and differentiation

Fig. 35-8

Dermal

tissue

Ground

tissue

Vascular

tissue


Ground tissue system
Ground Tissue System

  • Parenchyma, collenchyma, sclerenchyma tissue

  • Primary cell wall – secreted by growing cell; stretches and expands as cell grows

  • Secondary cell wall – secreted when cell stops growing; thick and strong (inside primary)


Parenchyma
Parenchyma

  • Living, metabolizing

  • Most common

  • Soft parts

  • Function

    • Photosynthesis – green chloroplasts

    • Storage – starch, oil, water, salt

    • Secretion – resins, tannins, hormones, enzymes, nectar

  • Can differentiate if plant injured (i.e. xylem cells)


Ch 31 plant structure growth and differentiation

Fig. 35-10a

Parenchyma cells in Elodea leaf,

with chloroplasts (LM)

60 µm



Collenchyma
Collenchyma

  • Flexible, structural support (nonwoody parts)

  • Elongated cells

  • Alive at maturity

  • Primary CW – unevenly thick, thicker in corners

  • Near stem surface, leaf veins


Ch 31 plant structure growth and differentiation

Fig. 35-10b

5 µm

Collenchyma cells (in Helianthus stem) (LM)



Sclerenchyma
Sclerenchyma

  • Structural support

  • Primary and secondary CW (strong and hard, extreme thickening, so can’t stretch, elongate)

  • Cells dead at maturity

  • 2 types:

    • Sclereids – variable shape, nut shells, pits of stone fruits, pears gritty (clusters of sclereids)

    • Fibers – long, tapered – patches, clumps; wood, inner bark, leaf veins



Ch 31 plant structure growth and differentiation

Fig. 35-10c

5 µm

Sclereid cells in pear (LM)

25 µm

Cell wall

Fiber cells (cross section from ash tree) (LM)


Vascular tissue
Vascular tissue

  • Embedded in ground tissue

  • Transport

  • Xylem and phloem


Xylem
Xylem

  • Conducts water, dissolved nutrient minerals roots  stems, leaves

  • Support

  • Angiosperms –

    • tracheids, vessel elements - conduct

    • parenchyma cells - storage

    • fibers - support


Tracheids and vessel elements
Tracheids and vessel elements

  • Dead at maturity  hollow, CW remain

  • Tracheids – long, tapering, patches/clumps; water passes from 1 tracheid to another by pits (thin areas where sec. wall did not form)

  • Vessel elements – larger in diameter than tracheid; end walls have perforations; stacked  water goes between; stack = vessel; pits in side walls for lateral water transport


Ch 31 plant structure growth and differentiation

Fig. 35-10d

100 µm

Vessel

Tracheids

Pits

Tracheids and vessels

(colorized SEM)

Perforation

plate

Vessel

element

Vessel elements, with

perforated end walls

Tracheids


Phloem
Phloem

  • Conducts food

  • Support

  • Angiosperms

    • Sieve tube members, companion cells – conduct

    • Fibers – support

    • Parenchyma cells


Sieve tube members
Sieve tube members

  • Conduct food in solution

  • Joined end-to-end  long tubes

  • CW ends = sieve plates; cytoplasm extends between cells

  • Living at maturity – many organelles shrink/disintegrate

  • Can function w/o nuclei


Companion cells
Companion cells

  • Adjacent to each sieve tube member (stm)

  • Assists stm

  • Living w/ nucleus – directs activities of both cells

  • Plasmodesmata between stm and companion

  • Helps move sugar into stm


Ch 31 plant structure growth and differentiation

Fig. 35-10e

Sieve-tube elements:

longitudinal view (LM)

3 µm

Sieve plate

Sieve-tube element (left)

and companion cell:

cross section (TEM)

Companion

cells

Sieve-tube

elements

Plasmodesma

Sieve

plate

30 µm

10 µm

Nucleus of

companion

cells

Sieve-tube elements:

longitudinal view

Sieve plate with pores (SEM)



Dermal tissue system
Dermal tissue system

  • Epidermis and periderm

  • Protective covering

  • Herbaceous – single layer = epidermis

  • Woody – epidermis splits w/ growth

    • Periderm – layers thick, under epidermis; replaces epidermis in stems, roots, composing outer bark


Epidermis
Epidermis

  • Unspecialized dermal cells

  • Special guard cells + trichomes

  • Single layer, flat cells

  • Usually no chloroplasts  transparent

    • Allow light through


Ch 31 plant structure growth and differentiation

Fig. 35-18a

Key

to labels

Dermal

Ground

Cuticle

Sclerenchyma

fibers

Vascular

Stoma

Upper

epidermis

Palisade

mesophyll

Spongy

mesophyll

Bundle-

sheath

cell

Lower

epidermis

Cuticle

Xylem

Vein

Phloem

Guard

cells

(a) Cutaway drawing of leaf tissues


Ch 31 plant structure growth and differentiation

Fig. 35-18b

Guard

cells

Stomata

pore

50 µm

Epidermal

cell

(b)

Surface view of a spiderwort

(Tradescantia) leaf (LM)


Ch 31 plant structure growth and differentiation

Fig. 35-18c

Upper

epidermis

Key

to labels

Palisade

mesophyll

Dermal

Ground

Vascular

Spongy

mesophyll

Lower

epidermis

100 µm

Air spaces

Guard cells

Vein

(c)

Cross section of a lilac

(Syringa) leaf (LM)


Cuticle
Cuticle

  • Aerial parts

  • Secreted by epidermal cells

  • Waxy – water loss

  • Slows diffusion of CO2 – stomata help

  • Stomata

    • Open – day – photosynthesis, evaporative cooling

    • Closed – night

    • Closed in day if drought


Trichomes
Trichomes

  • Outgrowths or hairs

  • Many shape, sizes, functions

  • Ex:

    • Roots hairs – increase SA

    • Salty env. – remove excess salt

    • Aerial parts – increase light reflection, cooler

    • Protections – stinging nettles


Growth at meristems
Growth at Meristems

  • Cell division

    • Increase # cells

  • Cell elongation

    • Vacuole fills, increase pressure on CW, expands

  • Cell differentiation

    • Specialize into cell types

  • Meristems = where plant cells divide, mitosis

    • No differentiation


2 kinds of growth
2 kinds of Growth

  • Primary growth

    • Increase stem, root length

    • All plants, soft tissues

  • Secondary growth

    • Increase width

    • Gymnosperms, woody dicots

    • Wood + bark


Ch 31 plant structure growth and differentiation

Fig. 35-11

Primary growth in stems

Epidermis

Cortex

Shoot tip (shoot

apical meristem

and young leaves)

Primary phloem

Primary xylem

Pith

Lateral meristems:

Vascular cambium

Secondary growth in stems

Cork cambium

Periderm

Axillary bud

meristem

Cork

cambium

Cortex

Primary

phloem

Pith

Primary

xylem

Secondary

phloem

Root apical

meristems

Secondary

xylem

Vascular cambium


Primary growth
Primary growth

  • Increase in length

  • Apical meristem – tips of roots + shoots (buds)

  • Buds = dormant embryonic shoot (develop into branches next spring

  • Root tip

    • Root cap – protective layer of cells, covers root tip

    • Root apical meristem – directly behind root cap

    • Cell elongation – behind meristem, push tip ahead, some differentiation


Ch 31 plant structure growth and differentiation

Fig. 35-13

Cortex

Vascular cylinder

Epidermis

Key

to labels

Zone of

differentiation

Root hair

Dermal

Ground

Vascular

Zone of

elongation

Apical

meristem

Zone of cell

division

Root cap

100 µm


Ch 31 plant structure growth and differentiation

Fig. 35-14a1

Epidermis

Key

to labels

Cortex

Dermal

Ground

Endodermis

Vascular

Vascular

cylinder

Pericycle

Xylem

100 µm

Phloem

(a)

Root with xylem and phloem in the center

(typical of eudicots)


Ch 31 plant structure growth and differentiation

Fig. 35-14a2

(a)

Root with xylem and phloem in the center

(typical of eudicots)

Endodermis

Key

to labels

Pericycle

Dermal

Ground

Vascular

Xylem

Phloem

50 µm


Ch 31 plant structure growth and differentiation

Fig. 35-14b

Epidermis

Cortex

Endodermis

Vascular

cylinder

Key

to labels

Pericycle

Dermal

Core of

parenchyma

cells

Ground

Vascular

Xylem

Phloem

100 µm

(b)

Root with parenchyma in the center (typical of

monocots)


Ch 31 plant structure growth and differentiation


Ch 31 plant structure growth and differentiation

Fig. 35-16

Leaf primordia

Shoot apical meristem

Young

leaf

Developing

vascular

strand

Axillary bud

meristems

0.25 mm


Ch 31 plant structure growth and differentiation

Fig. 35-17a

Phloem

Xylem

Sclerenchyma

(fiber cells)

Ground tissue

connecting

pith to cortex

Pith

Key

to labels

Cortex

Epidermis

Dermal

Vascular

bundle

Ground

Vascular

1 mm

(a)

Cross section of stem with vascular bundles forming

a ring (typical of eudicots)


Ch 31 plant structure growth and differentiation

Fig. 35-17b

Ground

tissue

Epidermis

Key

to labels

Vascular

bundles

Dermal

Ground

Vascular

1 mm

(b)

Cross section of stem with scattered vascular bundles

(typical of monocots)


Secondary growth
Secondary Growth

  • Increase in width

  • Make secondary tissues: sec. xylem, sec. phloem, periderm

  • Lateral meristem – cells divide, not elongate

  • 2 types:

    • Vascular cambium

      • Between wood and bark

      • Make sec. xylem (wood) + sec. phloem (inner bark)


Ch 31 plant structure growth and differentiation

Fig. 35-20

Growth

Vascular cambium

Vascular

cambium

X

X

C

P

P

Secondary

phloem

Secondary

xylem

X

C

P

X

C

X

P

C

C

C

C

X

C

C

C

After one year

of growth

After two years

of growth

C

C

C


Ch 31 plant structure growth and differentiation

Fig. 35-22

Growth

ring

Vascular

ray

Heartwood

Secondary

xylem

Sapwood

Vascular cambium

Secondary phloem

Bark

Layers of periderm


Ch 31 plant structure growth and differentiation

  • Cork cambium

    • In outer bark

    • Form cork to outside +parenchyma (storage)

    • Periderm = cork, parenchyma, cork cambium


Ch 31 plant structure growth and differentiation


Ch 31 plant structure growth and differentiation

Fig. 35-19a3

Pith

(a)

Primary and secondary growth

in a two-year-old stem

Primary xylem

Vascular cambium

Epidermis

Primary phloem

Cortex

Cortex

Primary phloem

Epidermis

Vascular cambium

Growth

Vascular ray

Primary xylem

Secondary xylem

Pith

Secondary phloem

First cork cambium

Cork

Periderm (mainly

cork cambia

and cork)

Most recent cork

cambium

Cork

Bark

Secondary phloem

Layers of

periderm

Secondary

xylem


Ch 31 plant structure growth and differentiation

Fig. 35-19b

Secondary phloem

Bark

Vascular cambium

Cork

cambium

Late wood

Secondary xylem

Periderm

Early wood

Cork

0.5 mm

Vascular ray

Growth ring

(b)

Cross section of a three-year-

old Tilia (linden) stem (LM)

0.5 mm


You should now be able to
You should now be able to:

  • Compare the following structures or cells:

    • Dermal, vascular, and ground tissues

    • Parenchyma, collenchyma, sclerenchyma, water-conducting cells of the xylem, and sugar-conducting cells of the phloem

    • Sieve-tube element and companion cell

  • Describe in detail the primary and secondary growth of the tissues of roots and shoots

  • Describe the composition of wood and bark