LSM3261_Lecture 2 Leaf

8/3/2019 LSM3261_Lecture 2 Leaf

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LSM 3261 Life Form and Function

Leaf Structure


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Lecture 2 Topics

Reference Definition of the leaf

Leaf variation in structure

Leaf arrangement

Lamina venation

Lamina organization

Epidermis Mesophyll

Leaf structure to function

Stomatal o enin and closin Transpiration

Guttation

Leaf abscission

Leaf modifications


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Reference

Solomon, E.P., L.R. Bergand D.W. Martin. 2011.

Biology. 9th ed.

Cha ter 34


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Definition of the Leaf 1

A leaf is typically the main photosynthetic organ of a

plant and accordingly, it has a broad lamina of one or

more parts an s supp e w t m nera s n so ut on, v a

xylem elements and supplies organic food compounds to,

phloem forming veins throughout the lamina. The veins

communicate with the vascular tissue of the stem.

However modified a leaf may be, it can be recognized bythe presence of at least one axillary budbetween its leaf

ase an t e stem. owever, t s u may e re at ve y

undeveloped.

A flat, food factory subtending an axillary bud


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Definition of the Leaf 2Classical conce t

of the leaf:

subtend at least one

axillar bud in its

axil. If a leaf-like

structure (e.g.,

leaflet) has none,then it is not a leaf.

Latin axilla, armpit

Coffee plants can have up to

15 axillary buds per leaf!


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Leaf Morphology Can be ver s ecific and used

for identification

Stipules (optional)

Outgrowths at base

Petiole/leaf stalk (optional) ttac es a e to stem

Lamina/blade (optional)

roa , a co ec s g

Veins (vascular tissue)

Upper surface =

adaxial/ventral Lower surface =

abaxial/dorsalmnemon c: =

bottom)


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Di ression: Identification with Limited Data

What is this structure? The less data to constrain the identification, the more the

possibilities

Real-life situations often do not provide sufficient data forconclusive identifications

Identifications are necessarily tentative in such situations

an nc u e more poss t es


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Leaf Structure Varies 1

mp e Only one blade per petiole (although often lobed)

ompoun

Each blade divided into smaller leaflets Kinds of compound leaf

Palmate: leaflets arise from a common origin on the rachis

nnate: ea ets ar se a ong s es o t e rac s, t e extens on

of the petiole


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Leaf Structure Varies 2

nnate ea ypes Simply pinnate (once pinnate)

p nnate tw ce p nnate

Tripinnate (thrice pinnate)

Paripinnate = With opposite leaflets

and no terminal leaflet

=

leaflets and a terminal leaflet


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Leaf Arrangement

ea per no e: ternate or sp ra Leaves arise from alternating attachment site,

leaves arise)

Leaves are opposite each other on the stem


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Lamina Venation

Parallel Veins run approximately parallel to each other

Pinnately netted

Veins branch off a central midvein Palmately netted

Several major veins radiate out from a point


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Lamina Organization

ayers

Epidermis esop y

Epidermis


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Epidermis Cuticle

Made of waxy layer called cutin = an insolublemixture containing waxes, fatty acids, soaps, andresinous material that forms a continuous layer on theouter epidermal wall of a plant

Reduces water loss

Thicker in upper epidermis

Epidermis Usually clear, nonphotosynthetic, outer cell wall thick

compared to inner cell wall

Upper

Covers the upper surface

Covers lower surface


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Epidermal Cell Adaptations 1

Trichomes

Hairs on leaves

Credit: David Sieren/Visuals Unlimited


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unct ons o tr c omes May reduce water loss retaining humid region

-

interface)

Stinging hairs (covered in Lecture 1)

Salt secretion (covered in Lecture 1) windspeedhigher here

zero here

lamina epidermis


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Stomata (singular stoma) Pores in leaf

For gas exchange


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The Mesophyll 1

Major mass of mostly photosynthetic tissue

Tissue types

ypo erm s

Palisade mesophyll

pongy mesop y

Vascular

ypo erm s usua y cons sts o parenc yma

cells without chloroplasts (rare) Water storage

Water seal


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The Mesophyll 2

a sa e an spongy mesop y cons st oparenchyma cells containing chloroplasts

volume

Near upper epidermis,palisade

Longer parallel cells

,

environment

Ma or site of hotos nthesis Lower cells called spongy mesophyll

Allow for as exchan e and as

movement within leaf Also hotos nthetic


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Palisade

meso h ll

Vein

(vascular

bundle)

Cuticle

Spongy

mesophyll

Upper

epidermis

X lem

Bundle

sheath

Stoma

Air space

Phloem

Lower

epidermis

Stoma Guard cells


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The Mesophyll 3

Extensively branched so that veinsare close to any cell in the leaf

Xylem is usually located in upper

part, near upper surface Transports water + mineral

nutrients

central and lower regions of the leaf Transports sugars + water


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The Mesophyll 4

Bundle sheath

cells

structuresbundle

Extend throughmesophyll fromupper to lowerepidermis

Submarine

cable


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Eudicot and Monocot Leaf Structure

Characteristic Monocot EudicotVenation Usually parallel

Usually net-veined

Vascular arrangement in

veins

Closed bundles always

without fascicular

Usually open bundles (with

fascicular cambium

cambium) Fascicle = bundle

Mistletoe leaf

Dumb cane leaf


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Structure and Function of the Leaf 1

Primary light harvesting organ responsible for

location of photosynthesis

,

area for interception of light

ncrease sur ace area an s oma a open ngs o

the flat lamina lead to water transport through the

p an u requ res a ap a ons o preven unnecessary

water loss

Leaves produce glucose and other sugars from

photosynthesis


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Structure and Function of the Leaf 2 The upper epidermis is clear to allow light to pass through; has waxy cuticle to

prevent excessive water loss

ere s a gra en o g n ens y rom e upper o ower sur ace o e am na;

if chloroplasts are fixed in position in the cytoplasm of each cell, those at the top

will get bleached chlorophyll, and those at the bottom get too little light;cytoplasmic streaming moves the chloroplasts from top to bottom of the cell

Mesophyll contains the bulk ofchloroplasts for photosynthesis

Air s aces between meso h ll cells o en to the o en air throu h the stomata CO

diffuses into thin water layer on mesophyll cell walls The flexing of the lamina pumps air (including CO2) into the leaf

,

through the plant, bringing nutrients to the plant cells via the xylem; similarly water

flowing back to the stem and roots carries sugar via the phloem Water moves from the vascular tissues to the mesophyll by diffusion or via the

bundle sheath cells to the epidermis to move back down to the other mesophyll cells

Bundle sheath cells rovide leaf su ort and movement of water to meso h ll cells

(also important in C4

metabolism)


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Structure and Function in Leaves

cell

wall

cytoplasm

chloroplasts

vacuole

palisade

mesophyll

cell


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Lecture 1 Questions

Hope all of you have attempted this by now!

You find out how well you understand the material

You obtain practice in answer questions

You obtain the answers (non-participants do not get

the answers)


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Practical 1

T u, 25 Aug, 2.00 to 4.45 pm At LS Lab 7 Blk S2 Level 3

DETAILED pre-lab briefing at 2.00 pm sharp Bring

Schedule

Textbook Lecture notes

Notebook

Mechanical encil B, 0.5 or 0.3 nib size

Concentrate on the important points first:


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Mechanism of Stomatal Opening and Closing 1

Chan es in osmotic concentration of uard cells make them

turgid (opening stoma) or less turgid (closing stoma)

Please visit this website for an animation on osmosis:http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html


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Blue light (400 to 500 nm) is absorbed by yellowpigment in guard cell, probably in the plasma

membrane, triggering the activation of proton pumps

Blue li ht also tri ers Malic acid synthesis

H drol sis s littin of starch

Blue light

activates proton

pumps

h i f S l O i d Cl i 3


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Proton pumps use ATP energy to actively transport the protons (H+) out of the


guard cells These H+ are from the H+ which form when malic acid ionizes to form H+ and

Because H+ are pumped out of the guard cell, an electrochemical gradient

(charge and concentration difference) forms on two sides of the guard cellp asma mem rane

activates proton

pumps

M h i f S l O i d Cl i 4


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The electrochemical gradient drives the facilitateddiffusion of potassium ions (K+) into the guard cellst roug vo tage-act vate potass um c anne s n t e

plasma membranes

Blue li ht

activates proton

pumps

M h i f St t l O i d Cl i 5


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or e ons

are a so ta en nto guar ce sthrough the ion channels in the guard cell plasma

mem rane

These negatively charged Cl

and malate ionse ectr ca y a ance t e pos t ve y c arge

These osmotically active ions increase the solute

concentration in the guard cell vacuoles

activates proton

pumps



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esu t ng osmot c movement o water nto guarcells causes them to become turgid, causing them

to e ongate so caus ng to orm an open ng etween

the two guard cells (stoma)

activates proton

pumps



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Mechanism of Stomatal Opening and Closing 7 ys o og ca c anges con nue

As the day progresses, potassium ions slowly leave guard cells (K+

concentration declines) but counteracted by starch beinghydrolyzed to sucrose, which increases in concentration in theguard cells so turgidity maintained

Later in the day, stomata close when water leaves guard cellsowing to decline in concentration of sucrose (osmotically activesolute) because (1) less to no photosynthesis because of low tozero light level, and sucrose is converted to starch (osmoticallyinactive; no ionizaton because relatively insoluble)

Some environmental factors affecting stomatal opening andclosing

Light (open) or darkness (close)

CO2 concentration in leaf (low: open; high: close) Water stress (close to reduce water loss)

Plants circadian rhythm (open/close timing)

T i ti 1


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Transpiration 1

Transpiration is the loss of water through aerialplant parts

It is the process that brings water into and through

the plant from the root system Accounts for the loss of ~99% of the water that

enters the plant through the roots. Loss is mainly

via the leaves, through stomata Cools the plant by evaporation (like perspiration

in humans)

Carries nutrients through the plant

Evapotranspiration = loss of water from the soil both by

evapora on an y ransp ra on rom e p an s grow ng

thereon

Transpiration 2


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Transpiration 2

Too much transpiration causes first temporary wilting,from which the plant can recover

Add water

Transpiration 3


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Transpiration 3

Prolonged excessive transpiration, as during a drought,causespermanent wilting, which will kill the plant

Coleus lant Plectranthus

Credit: Jack Bostrack/Visuals Unlimited

scutellarioides) under water

stress

Transpiration 4


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Transpiration 4

Provides moisture to the atmosphere; in many places (e.g.the Amazon) is critical to local climate

climate control everywhere on the planet

G tt tiStrawberry (Fragaria


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Guttation ananassa)

Guttation = Releaseof liquid water

from leaves of

some plants, occurs

roug y a o es

when

negligible and

moisture is high

=typically at the margins

of the lamina with

ermanentl o en stoma

and water secretory

tissue

L f Ab i i 1


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Leaf Abscission 1

ants ose t e r eaves Part of natural cycle of life and deatho eaves n any spec es

Plant-wide loss of leaves that often

With approach of winter (temperate

climates; water is solid (ice or snow),

ence ry env ronment

At beginning of dry period (subtropicalclimates with wet and dry seasons)

Complex process involving

chan es occurrin rior to leaf fall Physiological

Anatomical

Why not allow leaves to overwinter?

Leaf Abscission 2Credit: David Sieren/Visuals

Unlimited


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Leaf Abscission 2 Unlimited

Physiological processes

and reveals the accessory

i ments and the red Maple leavesanthocyanins; hence brightcolors in the fall

cersp.

From leaves to other plantparts, the following are

ecyc ng o

nutrients

Sugars

Amino acids Many essential minerals

Chlorophyll breaks down

Caroteno s an ant ocyan ns

become evident

Leaf Abscission 3


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Leaf Abscission 3 natom ca processes

Abscission zone develops

where etiole detaches from

stem

Here, enzymes dissolve the

, -

substance

Allows the leaf to snap off at

the base of the petiole with

disturbance from the wind

Abscission

zone = self-

Credit: Dr. Ken Wagner/Visuals Unlimitedsealing break

Leaf Modifications


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Leaf Modifications

Leaves are highly plastic organs

,

Attractive leaves

Plastic = liable =

Food storage

Ph llode

adjustable to

varying conditions

Carnivorous leaves Reproductive leaves

Sensitive leaves

Spines Tendrils

Water storage leaves

Attractive Leaves


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Attractive Leaves

Attractive leaves = Leaves that are brightly coloredto attract pollinators

Has humming

bird pollinator

Bougainvillea inflorescence (Bougainvillea hybrid)

Bud Scales Maple (Acersp.)


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Bud Scales

Bud scale =

o e ea a

protects the delicate

the bud from injury,

freezing or drying out

Food Storage Leaves


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Food Storage Leaves

Food stora e leaf =

Leaf modified to be fleshy

materials and water

n on um cepa u nsection

Phyllode


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Phyllode

Phyllode =

lamina, the petiole3expan s an a es

the functions of the

1

1 2 3 4

Carnivorous Leaves 1


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Carnivorous leaf =

Leaf modified to be an active or passive

trap to catch animals and digest them tosupplement the nutrients taken up by the

roots

Credit: David Sieren/Visuals Unlimited

Pitcher plant

(Sarracenia

Carnivorous Leaves 2a


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Carnivorous Leaves 2a

Lower

pitcher (left);

upper pitcher

(right)

Slender itcher lant Ne enthes

gracilis) pitchers, . . . . .

carnivorous plants of Singapore. Singapore

Science Centre, Singapore. 176 pages.

Carnivorous Leaves 2b


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Ca vo ous eaves b

Nectaries under lid attract insects (mainly ants) with sugary

solution which may lead to fungal growth. Spiders may also

exploit the trap to catch insect prey (parasitism).

Carnivorous Leaves 2c


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.

breakdown products absorbed by the plant.



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(a) (b)

Venus fly trap (Dionaea muscipula) leaf in action

Reproductive Leaves


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p

Reproductive leaves =Leaves with meristems in their mar ins from

which small plants develop when the leaves fall to

the ground

Leaf ofKalanchoepinnata with young

plantlets

Sensitive Leaves


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Se s t ve eaves

Sensitive leaves =Leaves which are sensitive to touch and fold up

when touched. Pulvini at the leaf bases are

responsible for the movements.

Open and closed

leaves of touch-me-

not ( imosa

pudica)

Spines Pincushion cactus (Mammilaria sp.)


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p ( p )

S ine =

Modified leaf that is

defence

How do you know the

Tendril Leaves


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=

Modified leaf to form a thin,

co e s ruc ure use or

attaching to support

structures to enable the lantto climb

Credit: Wally Eberhart/Visuals Unlimited

Pea Pisum sativum

Flame lily (Gloriosa superba)

Water Storage Leaves 1


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Water storage leaf= Thick, succulent leaf for photosynthesisand modified for storage of water.

String-of-beads plant (Senecio

rowleyanus)

Why are

the leaves

of this

eser

species

s herical?

Water Storage Leaves 2


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Water storage leaf= Thick, succulent leaf for photosynthesisand modified for storage of water.

Aloe (Aloe vera)

broken leaf

LSM3261_Lecture 2 Leaf

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