LSM3261_Lecture 4 --- Roots and Mineral Nutrition

8/3/2019 LSM3261_Lecture 4 --- Roots and Mineral Nutrition

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LSM 3261 — Life Form and Function

Roots and Mineral Nutrition



Lecture 4 Topics• Reference

• Definition of the root

• Main functions

• Root types

• Taproot• Fibrous root

• Root structure• Tissues

• oo cap

• Root hairs

• Herbaceous eudicot or monocot root structure

• Cortex (including endodermis)

• Stele

• Water movement in the root

• Vascular cambium

• Periderm

•

• Root modifications



Reference

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

Biology. 9th ed.

• Chapter 36



Definition of the Root

A root is typically a subterranean or

aquatic multicellular axis or

appendage of a plant the function of

which is the absorption of mineral saltsin solution and anchora e of the lant.

(There are exceptions to this.)

Water hyacinth, with roots growing into

water.

Taeniophyllum obtusum, a “shootless,leafless” orchid



Main Functions

• Anchor plants

materials from the soil

materials to the rest of the plant

•

• Serve as food reserves for

the lant roots s ecialized

for even more storage are

covered later under rootmodifications)



Root Types

•

• Fibrous root



Taproot 1• Taproot = primary root

• In gymnosperms and eudicots

• Forms from the enlarged seedling radicle

• Radicle is the embryonic or primary root

• Travels directly down into the soil

• Usually travel deeply into the soil to capturewa er

• Collects water and nutrients from deep in soil



Taproot 2• Most large trees lose their ta root and develo a shallow

root system that sends branchesdeep into the soil

roots

• Secon ary root = t ose w cdirectly arise from the tap root

=

trun

directly arise from the secondaryroot

Fallen casuarina tree (Casuarina equisetifolia)

secondary

root

tertiary rootTongkat Ali ( Eurycoma longifolia)



• In monocots

• Primary root dies quicklyFibrous Root 1

• Roots develop from the stem or

leaves― called adventitious

roots (adventitious organs are

those that arise in unexpected



• Cling strongly to the soil― prevent

surface soil erosionFibrous Root 2

• Collects surface water and nutrients

• =

directly arise from the fibrous root

• Tertiar root = those which directl

arise from the secondary root

secondary

root

tertiary rootfibrous root



Root Tissues

• Mature t ssues• Dermal system

• E idermis

• Root cap

• Root hairs• er erm

• Ground/fundamental system

• Cortex

• Stele• Vascular system

• Primary vascular tissues

• Secondary vascular tissues• Meristematic tissues

• Apical meristem

•

• Cork cambium• Anomalous forms (not covered in this module)



Root Cap

• Hollow conicallayer of multiplela ers of tou h

Root apicalmeristem

(area of

cells

• Cells are sloughedoff as the rootforces its way

replaced by cellsthe divide and grow

Root cap

ns e e roo cap

• May aid in

―

removal‘disorients’ theap ca mer s em

250 µm



Root Hairs • Tubular extensions of single epidermal cells

• No cuticle―

soabsorptive

•

• A modified trichome

―much longer than

most tr c omes yetstill relatively short― maximally ~1 cm

• Very numerous• Have very close

particles

• Increase the surfacearea of the root

• Increase the absorptive



Herbaceous Eudicot and Monocot Roots

Epidermis

• Roots in a primary

state of growth,

Cortex

. .,

herbaceous eudicot

or monocotStele

• Have three basiclayers of

tissues/zones

• Epidermis• Cortex

• Stele250 µm

Eudicot Root



Monocot Roots

variable in internal

structure

Stele

• Usually with a pith in

the center

Epidermiscell

• All monocots have no

vascular cambium but

may have other formsof secondary growth,

Pericyclecell

Pith cell. ., ,

anomalous forms (not

covered in this module

Xylemvessel

element

Phloem cell

250 µmMonocot Root



Cortex (including Endodermis)• Cortex = Tissues immediately below the epidermis up to

and including the endodermis• Parenchyma cells (storage)

• Collenchyma (rare in roots)

• Innermost layer of tightly packed endodermis connectedtogether by casparian strips, which are rich in waxysuberin

Pandan (Pandanus sp.)

has persistent roots



Stele

• Stele = Central cylinder of tissues consisting of

• er cyc e = ng e ayer of parenchyma cells insidethe endodermis which

filled withamyloplasts

Endodermis

separates the vascular tissues from the

cell

Pericycle cell

• Vascular tissues = Xylemand hloem in alternatin

Phloem cell

Xylem vesselelements

and radial patches

• Intervascular regions =Intercellular

s aceGroun t ssues o

parenchyma and/or sclerench ma between the

25 µm

xylem and phloem patches



Stele

• Stele (continued)• Pith = Centermost tissue

Stele

cons s ng o grountissues of parenchyma

and/or sclerenchyma and

Epidermiscell

usually absent in dicotroots

Pericyclecell

Pith cell

Xylemvessel

element

Phloem cell

250 µmMonocot Root



Announcements and Discussion

• Practical 2 on Roots and Reproductive Structures• 2-4 pm at LS Lab 7 on Thursday, 8 Sep 2011

• Come punctually for the detailed pre-lab briefing

• Bring the usual items as for Practical 1• Tutorial 2 on a structure to function experiment

• Download it after 5 Sep

• Appeal for help with field work• Assist my three Honours students with their final year projects

• Abandoned rubber plantations

• Wasteland vegetation

• uteco ogy o potent a y nvas ve tree

• Chance to see what ecological research involves

-



Water Movement in the Root 1

• Water and minerals move into root by four athwa s:• Apoplastic: via porous connected cell walls extending

from the root hairs• ymp ast c: v a p asmo esmata― nterconnecte

cytoplasm of adjacent cells

•

membranes and cell walls of the cells along the pathway (not in main text)

• Combination of the above pathways (not in main text)

http://www.youtube.com/watch?v=o32jqyIpoHg




• The casparian strip of each endodermal cell blocks the passage of water and nutrient minerals past the cell walls

etween t e en o erma ce s an rects water nto

endodermal cytoplasm to the phloem or xylem from the

• Xylem conducts water and dissolved nutrient minerals

from the root hairs

• Phloem conducts sugars from the leaves as well as sugar from stored nutrients in the root cortex

ftp://tdata.atu.edu/cindy.jacobs/Intro%20to%20Biology/Biol%201014%20Unit%202%20Spr%2007/Ch%2018/animations/root_functioning.html




Root hair/ground epidermal cellcortex including endodermis pericycle root xylem

. .

not illustrated here



Learning Tip: Using Analogies

• Analogy = A likeness between two entities, not based on

e resem ance o e wo ngs, u o a ew o e

key attributes of those things• e more ey attr utes n common, t e etter

• Helps in understanding new concepts or ideas, but has

limitations• Example

• Analogy for a stoma• Hole in a wall

• Automated window in a wall

•

better than others



Vascular Cambium 1

• Found in most older eudicot and all older

• Develops in the

intervascular region

between the primary

Precursor of vascular cambium

xylem and primary phloem (cell divisions

start

• When cell division

pericycle, the vascular

cambium is full

developed



Vascular Cambium 2

divides to form xyleminside, phloem outside

• Primary phloem pushedoutward

• Primary xylem stayswhere it is

• Ring of vascular

circular by extra divisionsof vascular cambium

• Primary phloem,epidermis and cortex

outer bark

• Periderm replaces epidermisw ncrease n ame er o

root



Periderm 1

parenchyma cells just below the epidermis

• Like the periderm in the stem

Precursor of vascular cambium



Periderm 2•

form the cork cambium toform columns of cells:• Those outwards become cork

cells or phellem which are

dead a maturity and have amec an ca protect on aninsulating functions

• Those inwards becomephelloderm or corkparenchyma and have astorage or cork cambiumreserve unct on. en growtstops as during a the dry season

or winter, cells differentiaten o cor or p e o erm. engrowth resumes, the

phelloderm cells start dividing.

id 3



Periderm 3

• Several sequent periderms form the bulk of the bark whichis all the tissues outside the vascular cambium

cork cork cork

cork cambium

cork

cork cambium

cork parenchyma cork parenchyma cork parenchyma

cork

cork parenchyma

cork

cork cambium

cork parenchyma

cork cambium

cork parenchyma

cork cambium

cork parenchyma

cork

cork cambium

cork

cork cambium

cork arench ma

cork

cork cambium

cork parenchyma

R t d id i d t



Lateral RootRuptured epidermis and cortex

Lateral root Cortex

eve opment• Originate in the pericycle

• Cells in one portiondivide and pushes

through the endodermis,the rest of the cortex andepidermis

• Each lateral root has allthe parts of the larger root from which itoriginates

• Root cap

• Root hairs

• Epidermis• Cortex (including

endodermis)

• Stele (with connectionsto the main root

developing) 100 µm



Root Modifications

• Aerial roots

• u

• Contractile roots

• Haustorial roots• Pneumatophores

• Prop roots

• Storage rootso Food

o Water

Di i Al i Cl ifi i



Digression: Alternative Classifications

• Classification = Hierachical set of groups and subgroups

• Same set of entities will produce different classifications

based on different criteria• Classification of roots

• Based on origin

• Primary (tap), adventitious (including fibrous),secondary, tertiary

• Based on modifications or not

• Aerial, buttress, haustorial, pneumatophore, prop,

‘ ’s orage, norma = unmo e

• Using categories from one classification to fit into those of

classification is being used at any one time



Aerial Roots

Aerial roots =

vent t ous roots w c

arise in the aerial parts of the

not

Aerial roots

Phalaenopsis hybrid

Wh are aerial roots

Money plant ( Epipremnum aureum) considered adventitious?

B R 1



Buttress Roots 1

uttress roots =Roots with a board-like or plank-

e growt on t e r upper s es,

presumably for a supporting

Which roots are buttresses outgrowths of?

B R 2



Buttress Roots 2

at are t e unct ons o buttress roots?

gravity pulls

tension u n k

e ree

downwards

strut

compressionstrut t

r e e

t

20 m

C t til R t



Contractile Roots

Contractile roots =

becoming broader to pull the corm or bulb deeper into the soil

(e.g., gladiolus (Gladiolus sp.))

root broaden when it

becomes shorter? (Hint:

The volume of the cellstays the same.)

Contractile roots

H i l R



Haustorial Roots

Haustorial roots =

oots o paras t c spec es w c

grow into the host

Mistletoe ( Macrosolen

cochinchinensis)

P h 2



Pneumatophores 2

Pneumatophores =

in marshes or swamps

Api api ( Avicennia sp.)

Do pneumatophores branch off from secondary roots?

P R t



Prop Roots

Adventitious roots

lower nodes of the

stem which have asupporting function

Maize ( Zea

mays) 1.93 m

Bakau Rhizo hora s .

F d St R t



Food Storage Roots =

Roots modified

storage

parenchymacontaining

starch or other

pro uc s

Chinese radish

Sweet potato

Food Storage Roots



Food Storage Roots =

Roots modified

storage

parenchymacontaining

starch or other

pro uc s

Left to right: carrot ( Daucus

carota), sweet potato

( Ipomoea batatas), Chinese

ra s ap anus sat vus

‘Longipinnatus’, bangkwang

or yam bean (Pachyrrhizus

erosus ta ioca Manihot

esculenta)

Record Breaking Carrots



Record-Breaking Carrots

'’ .grown by Joe Atherton (UK). The carrot was

measured at the UK National Giant Vegetablecarrot, at 8.61 kg in 1998 in Alaska,

USA., ,

2007.

Water Storage Roots



Water Storage Roots

• Water storage stems and roots

• Will see this sp. during Botanic

ar ens e r p

• Auspicious plant of the Chinese

LSM3261_Lecture 4 --- Roots and Mineral Nutrition

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