Stomata w/in epidermis

LE 36-15a

Cells turgid/Stoma open

Changes in guard cell shape and stomatal opening and closing(surface view)

Radially orientedcellulose microfibrils

Vacuole

Cell wall

Guard cell

Cells flaccid/Stoma closed

May have up to 20K/cm2

Global warming has caused a decrease in

their number

LE 36-15b

• Decreased CO2

• Blue light: triggers H+ pumps (moves H+ out & K+ in)• Circadian rhythms• Temperature

• H2O availability/humidity

• ABA: Abscisic Acid – made in roots in response to H2O deficiency, stress hormone, close stomata

Cells turgid/Stoma open

Role of potassium in stomatal opening and closing

Cells flaccid/Stoma closed

H2O

H2O

H2OH2O

H2O

H2O

H2O

H2O

K+

LE 36-12

Upperepidermis

MesophyllAir

space

Cuticle

Lowerepidermis

Cuticle CO2 O2 CO2Xylem

O2

Stoma

Evaporation

EvaporationWater film

Airspace

Cytoplasm

Cell wall

Vacuole

Air-waterinterface

High rate of transpiration

Low rate of transpiration

= –10.00 MPa = –0.15 MPa

Cell wall

Airspace

Palisade

spongy

phloem

Leaves

• The leaf is the main photosynthetic organ of most vascular plants

• Many leaves are modified for various functions• http://www.arkive.org/venus-flytrap/dionaea-muscipula/video-00.html

http://www.youtube.com/watch?v=trWzDlRvv1M

Xerophytes• Reduced leaves• Thick, waxy cuticle• Decrease # stomata• Stomata in pits surrounded by hairs to reduce air flow/tran• Deep roots• Water storage tissue• Short life cycles,• dormant seeds• Smaller• Pep carboxylase & bundle

sheath cells

LE 36-16

100 µm

Halophytes

• Leaves are reduced to small scaly structures or spines• Shed leaves when water is scarce and stem becomes

green and takes over photosynthesis when leaves are absent

• Water storage structures develop in the leaves• Thick cuticle and multiple layered epidermis• Sunken stomata• Long roots, in search of water• Structures for removing salt build-up

LE 35-10

Shoot apicalmeristems(in buds)

Vascularcambium

Corkcambium

Lateralmeristems

Primaryphloem

Periderm

Corkcambium

Secondaryxylem

Primaryxylem

Pith

Pith

Cortex

Secondary growth in stems

Secondaryphloem

Vascular cambium

Primary phloem

Primary xylem

Cortex

Primary growth in stems

Epidermis

Root apicalmeristems

Tracheids

Spiral bands of lignin for supportXylem is nonliving when plant is mature

Living tissue, membranes maintain sucrose concentrations

LE 35-16

Key

Dermal

Ground

Vascular

Epidermis Cortex

A eudicot (sunflower) stem. Vascular bundles form a ring. Ground tissue toward the inside is called pith, and ground tissue toward the outside is called cortex. (LM of transverse section)

XylemPhloem

Pith

Vascularbundles

Epidermis

Vascularbundles

1 mm

Sclerenchyma(fiber cells)

Ground tissueconnectingpith to cortex

Ground tissue

A monocot (maize) stem. Vascular bundles are scattered throughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith and cortex. (LM of transverse section)

1 mm

Dicot stem cross section

LE 35-19

Vascular cambium

Types of cell division

Accumulation of secondary growth

LE 35-18aPrimary and secondary growth in a two-year-old stem

Epidermis

Cortex

GrowthXylemray

Vascularcambium

Primaryphloem

Pith

Primaryxylem Phloem ray

EpidermisCortex

Vascular cambiumPrimary phloem

Pith

Primary xylem

Vascular cambium

Primary phloem

Primaryxylem

Secondary phloem

Secondary xylem

First cork cambium Cork

Growth

Vascular cambium

Primary phloem

Secondary phloem

Secondary xylem

Periderm(mainly corkcambiaand cork)

Primary xylem

Pith

Vascular cambium

Secondary phloem

Secondaryxylem (twoyears ofproduction)

Cork

Bark

Layers ofperiderm

Most recentcork cambium

LE 35-18b

0.5 mm

Vascular cambiumSecondary phloem

Secondaryxylem

Transverse sectionof a three-year-old Tilia (linden)stem (LM)

Late woodEarly wood

0.5 mm

Cork cambium

Cork

Periderm

Xylem rayBark

Tree Age

LE 35-20

Growth ring

Vascularray

Secondaryxylem

Heartwood

Sapwood

Vascular cambium

Secondary phloem

Layers of periderm

Bark

No H2O transport

Transport H2O

Heartwood darker due to resins which clog pores to protect from insects

Girdled Trees

Roots

Roots and fungi form mycorrhizae, symbiotic structures consisting of plant roots united with fungal hyphae

Root Hairs

LE 35-12

Key

Dermal

Ground

Vascular

Epidermis

Root hair

Cortex Vascular cylinder

Zone ofmaturation

Zone ofelongation

Zone of celldivision

Apicalmeristem

Root cap

100 µm

Root Growth time lapse

LE 35-13

Key

Dermal

Ground

Vascular

Epidermis

Cortex

Vascular cylinder

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.

100 µm

Endodermis

Core ofparenchymacells

Pericycle

Xylem

Phloem

Endodermis

Pericycle

Xylem

Phloem

50 µm

100 µm

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.

Active Transport of Minerals in Roots

• Solutes in roots greater than in soil due to active transport

• Protein pumps for different ions

• Mycorrhizae of fungus help absorb minerals from soil particles to root (mutualistic)

LE 36-8b

Transmembrane route

Key

Symplast

Apoplast

Symplastic route

Transport routes between cells

Apoplastic route

Apoplast

Symplast

Symplastic route: via the continuum of cytosolApoplastic route: via the the cell walls and extracellular spaces

LE 36-9Casparian strip

Endodermal cellPathway alongapoplast

Pathway throughsymplast

Casparian strip

Plasmamembrane

Apoplasticroute

Symplasticroute

Roothair

Vessels(xylem)

Cortex

EndodermisEpidermis Vascular cylinder

Media

Transport in root

Minerals from soil

LE 36-18

Vessel(xylem)

Sieve tube(phloem)

Sucrose

Source cell(leaf)

H2O

H2O

Sucrose

Sink cell(storageroot)

H2O

Pre

ssu

refl

ow

Tra

nsp

irat

ion

stre

am

Companion cell

Media: Phloem transport spring/

summer

Sucrose is carb transported because it isn’t easily metabolized by plant during transport

Osmotic pressure: bulk flow

Using the apoplastic route to load sucrose into the phloem seive- tubes with the help of companion cells. Concentration gradient of sucrose is established by active transport. H+ is transported out of companion cells using ATP, build-up of H+ flows down concentration gradient through a co-transport protein which carries the sucrose in

Some plants just use symplastic route

What organelle is common in companion cells? Why?Lots of in folding of plasma membrane of companion cell into sieve tube cell, why?For symplastic route, there must be many of these between companion and sieve tube cells?Rigid cell walls of sieve tube cells allow for establishment of pressure necessary to achieve flow of phloem

Aphids & whitefly have special stylets that can penetrate plant tissues to reach phloem. Experiment anaesthetized aphid and stylet is severed (b). Phloem continues to flow out of stylet (e) and both rate of flow and composition of sap can be analyzed by looking at radioactively labelled CO2. The closer to the sink, the slower the rate of phloem flow.

Phototropism

Sumanas animation

Auxin• Discovered indirectly in the study of phototropism• Produced in apical meristem; moves downward• Influences cell growth by changing pattern of gene

expression to produce PIN3 transporter proteins which transport auxin to where growth is needed

• Promotes:– Stem elongation through acid growth hypothesis cell

expansion– Root growth and development: used w/ cuttings– Fruit development: stimulates seedless tomato plants

w/o fertilzation

LE 39-8a

Cross-linkingcell wallpolysaccharides

Cell wallenzymes

Microfibril

Expansin

CELL WALL

Plasma membrane

CYTOPLASM

ATP

Acid Growth Hypothesis:Auxin stimulates movement of H+ into cell wall which breaks down cellulose, increases osmosis, cells expand

Gravitropism

• Gravity causes statoliths to accumulate on lower side of cells.

• PIN3 transporter proteins direct auxin to bottom of cells

• High auxin inhibits root cell elongation so top cells elongate at higher rate than bottom cells, so root bends downward

Micropropagation of plants using tissue from shoot apex, nutrient agar

gels & growth hormones.• In vitro• Identify stock plant w/

desirable traits• Sterilize plant tissue from

stock plant, cut into explants• Explant placed into sterilized

growth media w plant hormones

• Equal amts of auxin & cytokinins form undifferentiated mass = callus

Depends on totipotency of plants: ability to differentiate into any plant part

Growth medium w/ 10X more auxin than - cytokinins – promotes rooting

If ratio of auxin to cytokinin is less than 10:1 – promotes shoots

Once both develop cloned plant is transferred to soil.

Micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing

varieties and propagation or orchids and other rare species

• Apical meristem usually free of viruses

• Fast process, takes up less space

• Orchid seeds are hard to germinate

• Plantlets can be stored in liquid nitrogen

• Propagate rare species and plant in wild habitat