whmf121 session five plant morphology part ii roots · whmf121 session five plant morphology part...

© Endeavour College of Natural Health endeavour.edu.au

WHMF121

Session Five

Plant Morphology Part IIRoots

(http://commons.wikimedia.org/wiki/Category:Root_vegetables#mediaviewe

r/File:Celeriac_J2.jpg)Celeriac

http://commons.wikimedia.org/wiki/Category:Root_vegetables#mediaviewer/File:Celeriac_J2.jpg


Todays Botany Topics

o Roots and root development

o Root cap

o Root modifications

o Functions of roots

o Vascular Tissue


Rootso “Roots are normally underground structures which are

distinguished from stems by the absence of nodes, buds

and chlorophyll”.

o When a seed germinates, the embryo inside starts to

grow in two directions.

(http://www.newtonsapple.org.uk/wp-

content/uploads/2013/06/root-depth.jpg)


Roots

o First the radicle

(embryonic root) grows

downwards towards the

centre of the earth in

response to gravity.

o Later the plumule

(embryonic shoot) grows

towards the light.

(http://commons.wikimedia.org/wiki/File:Broad_Bean_(Vicia_f

aba)_seed_Germination.jpg)

http://commons.wikimedia.org/wiki/File:Broad_Bean_(Vicia_faba)_seed_Germination.jpg


Roots

o The first tiny root that grows is

the “primary root”.

o In Dicots the primary root

becomes the tap root (eg.,

carrot) with lateral roots

developing from it as it grows

downwards into the soil.

o This forms a tap root system.

o NB: Tap roots are not always

obvious like carrots.

Note the distinctive taproot of Taraxacum

officinal or you might know it from its

common name Dandelion.

/wikipedia/commons/8/8f/Paardenbloem_(Taraxacum_officinale).jpg

/wikipedia/commons/8/8f/Paardenbloem_(Taraxacum_officinale).jpg


Roots

o Some taproots become very swollen and are much

larger than the many lateral roots whereas in other

species such as Achillea millefolium (Yarrow) the

taproot is about the same size as the laterals.

o The important thing to remember is that the tap root

develops from the radicle, which is the embryonic root.

Maca root; Lepedium meyenii

Beetroot: Beta vulgaris


Roots

o In Monocots, the primary

root doesn’t develop into a

tap root.

o Instead a network of

evenly sized roots

develops from

adventitious roots growing

from the base of the stem.

o This forms a fibrous root

system. (e.g. grass roots)

From the family Amaryllidaceae comes Allium sativum, or

common garlic, showing a fibrous root system(http://en.wikipedia.org/wiki/File:Allium_sativum_Woodwill_1793.jpg)

http://upload.wikimedia.org/wikipedia/commons/3/39/Allium_sativum_Woodwill_1793.jpg

http://upload.wikimedia.org/wikipedia/commons/3/39/Allium_sativum_Woodwill_1793.jpg


Roots

o As they have not

originated from pre-

existing roots and are

not radicles they are

called adventitious

roots

o Adventitious roots

increase the root

systems capacity for

absorption and

transportation of water

and nutrients(Mauseth, 2014)

Banyan Tree(https://en.wikipedia.org/wiki/Banyan#/media/File:Big_Banyan_Tree_at_Bangalore.jpg)


Rootso Fibrous root systems consist

of many roots, which are not

derived from a radicle but

originated in the stem tissue.

o The radicle dies during or

straight after germination and

then the first stage of the

fibrous roots are formed.

o Some dicots can also form

adventitious roots i.e. those

with stolons and rhizomes. (Mauseth, 2014)

(http://commons.wikimedia.org/wiki/File:Roots_of_a_hydro

ponically-grown_plant.jpg)


Rootso The root system of a plant constantly provides the stems

and leaves with water and dissolved minerals.

o In order to accomplish this, the roots must grow into new

areas of the soil.

o The growth and metabolism of the plant root system is

supported by the process of photosynthesis occurring in

the leaves

o Other dicots which normally don’t produce adventitious

roots naturally, but they do so if cut.

o This is useful when it comes to asexual propagation or

cloning.(Mauseth, 2014)


Roots

o Both root systems (tap and fibrous) have “feeder roots”

that actively absorb water and nutrients.

o Most feeder roots are found in the uppermost 15cm of

soil where the richest organic matter is found. These fine

roots extend out to where the water falls under the tree's

outermost foliage.

o Nutrients are concentrated in the area beneath the tree's

branches, just 30-60-cm below the soil surface. As

organic matter breaks down on the soil surface, fine

feeder roots recycle the nutrients back to the tree.


Roots

Mangrove roots


Roots

o Tap root systems can penetrate deeper into the soil so

do not rely on surface moisture but they hold the soil in

place and prevent soil erosion.

o However plants with fibrous roots systems are better for

erosion control, because the mass of roots cling to soil

particles.


Roots

o Roots will generally grow in any direction where the

correct environment of air, minerals, nutrients

and water exists to meet the plant's needs.

o Roots will not grow in dry soil. Over time, given the right

conditions, roots can crack foundations, snap water

lines, and lift sidewalks.

© Endeavour College of Natural Health endeavour.edu.auImage credit: Wikipedia, viewed 8 January 2014

http://commons.wikimedia.org/wiki/File:Tree_growing_on_pavement_in_Hong_Kong.JPG


Roots

o Tap and fibrous root systems

have basically the same

structures.

o Lateral roots grow from a

central core through the root’s

outer skin (epidermis).


Roots

o The tip is covered in specialised cells

(the root cap).

o The section of dense root hairs are

responsible for absorption of water and

nutrients.

o The growing tip is covered by a layer of

cells called the “root cap”.


Root Cap

o The root cap is where longitudinal growth occurs and

unlike animals where all parts of the body grow at the

same time, only small sections of the root and stem can

grow at the one time.

o Because the root is in the soil it is impossible for the

whole root body to push its way through.

o Only the tip can push its way through the soil.

o As the cap is forced through the soil ahead of the body, it

is being worn away and therefore needs to be renewed

constantly. (Mauseth, 2014)

18


Root Cap

The root cap helps the root grow through the soil in 3 ways:

1. By protecting the root.

As the root grows the cells behind the root cap divide pushing the cap forward first.

The cells of the root cap provide a physical barrier around the tender growing tip.


Root Cap

2. Lubricating its passage.

The cells at the edge of the root cap get old and die, slough off and become slimy, making a mucilaginous coating around the root that lubricates the tip as it moves through the soil.

3. Directing it’s growth

Roots grow mostly downwards i.e. they exhibit geotropism or gravitropism. Geotropism is growth directed by gravity. The cells of the root cap initiate this.


Geotropism

o A "tropism" is a plant movement triggered by stimuli.

o The mechanism involves little “gravity sensors” that can

move within the cells of the root cap.

o If a root begins to grow upwards or sideways, the gravity

sensors will move to another part of the cell.

o This movement triggers a hormone called auxin that

inhibits elongation of the root on the lower side.

o The upper side grows normally while the lower side

grows less.

o The end result is that the root tip points downwards. (Read Capon, B. pp. 148-166)


Geotropism in a Corn Kernel

(Monocot)

(http://gened.emc.maricopa.edu/bio/bio181/BIOBK/corngeotrop.gif)


Root Hairo Behind the tip of the root is an

area which can is often called the

maturation or root hair zone.

o It contains a dense band

of “root hairs".

o Root hairs are tubular outgrowths of the

epidermal cells of the root.

o Water (and minerals dissolved within it)

seep into the root hairs from the soil and

are carried to special vessels in the

middle of the root (xylem). (Mauseth, 2014)


Roots

o Xylem are vascular tissue that transports water and nutrients

absorbed by the root hairs to the rest of the plant.

o The word xylem comes from the Greek meaning ‘wood’.

o Water is moved in the xylem by a suction like mechanism and only

moves upwards throughout the stem and leaves.

o Apart from transportation of water and nutrients, the xylem is also

used to replace water lost during transpiration and photosynthesis.

(Mauseth, 2014)


Roots

o Many dicots are perennial (live longer than 2 yrs) and

undergo secondary growth. This results in an increase in

healthy xylem in both the roots and stem. This then also

increases the number of leaves and fine new roots.

o In monocots there is no secondary growth, once the

stem is formed and all of the connective tissue has been

established.(Mauseth, 2014)


Rootso Extra leaves and an ever increasing tap root system

cannot be supplied with water or nutrients. However

some monocots do increase their size via stolons or

rhizomes

o These stolons or rhizomes produce their own

adventitious roots.

o Because they have arisen from new stem tissue, the

water and nutrients are transported directly into them

and are not affected by the old shoots.

o By this method monocot shoots can grow larger as long

as they stay close to the original body of the plant. (Mauseth, 2014)


Roots

https://en.wikipedia.org/wiki/File:Xanthorrhoea_trunk

_cross-section.jpg

Campanula spp.


Roots

Think of Cymbopogon citratus (Lemongrass) (http://www.indochinavoyages.com/popularity-of-lemongrass-in-

indochina-dishes-and-its-benefits/)

28


Functions of Roots

1. Anchorage and support

• Roots anchor the plant in the soil, they usually spread

under the ground at least as much as branches

spread above the ground.

(https://en.wikipedia.org/wiki/Root#/media/File:Exposed_mango_tree_roots.jpg)


Functions of Roots

2. Absorption of water and nutrients

• Roots have special adaptations for this, i.e. root

hairs.

• Absorption is vital for plant survival and there must

be correct balance between the surface area of the

roots (for absorption) and the surface area of the

leaves (for photosynthesis).

• Young plants need a higher surface area ratio of

root to leaf than older plants because they are

growing more rapidly.


Functions of Roots

3. Hormone production

• The aerial parts of plants depend on plant growth

hormones.

• A number of these are synthesised in the roots,

especially:

• cytokinins (that stimulate cell division)

• gibberellins (that stimulate stem elongation).


Functions of Roots

o Lack of the plant hormone

auxin can cause abnormal

growth.

o Which plant do you think lacks

the auxin?

(http://en.wikipedia.org/wiki/File:Auxin.jpg)


Functions of Roots4. Storage

• Some roots have certain cells adapted for starch

storage (e.g. carrot Daucus carota and beetroot

Beta vulgaris)

• Food that has been made in the leaves is

transported down to the roots for storage until it is

needed. It may be used by the root or returned to

the rest of the plant.

• Many biennial plants store excess food as starch

during the first year. This is then used by the plant

during the second year when flowering and fruit

production occurs. (Tan, 2013)


RootsWhat type of roots are these?

Daucus carota (Carrot) from Apiaceae family

(http://en.wikipedia.org/wiki/File:Carrots_of_many_colors.jpg)

https://en.wikipedia.org/wiki/Monocotyledon

Roystonea regia palm (Arecales)

stems showing secondary root

growth


Root Modifications

o Most roots grow in the soil but in some plants aerial roots

have evolved.

o Aerial roots are mostly adventitious roots i.e., they grow

from the stem rather than from another root.

o Adventitious or Modified roots can be;

• Prop roots

• Aerial roots

• Pneumatophores

• Buttress roots


Prop Root

o A prop root is an example of an aerial root.

o The stem of a monocot becomes wider and then

produces these roots which go down to the soil.

Common in grasses

o In some larger monocots the roots can take months

growing through the air until they reach the soil.

o Prop roots support the stem and also absorb water and

nutrients from underground as well as stabilising the

plant.


Prop Root

e.g. Zea mays- corn plant.http://www.columbiamagazine.com/index.php?sid=45848)

37


Climbing Root

o Another example of an aerial

root is a climbing root.

o Climbing roots grow away from

light and into cracks.

o They support climbing stems

like Ivy (Hedera helix) on

vertical surfaces (observe the

picture to the right) (Tan, 2013)

(https://commons.wikimedia.org/wiki/Hedera_helix#/media/File:Ip

penburg_Efeu.jpg)38


Climbing Roots

(http://commons.wikimedia.org/wiki/File:Zielona_G%C3%B3ra,_ul._G%C5%82owackiego_7_%284%29.jpg)

39


Aerial Rootso Another example of plants with aerial roots are

epiphytes, such as orchids and bromeliads

o Epiphytic plants use photosynthesis for energy and

obtain moisture from the air or from dampness (rain and

cloud moisture) on the surface of their hosts. They are

not the same as parasitic plants, they do not kill the host.

(https://en.wikipedia.org/wiki/File:Bromeliad_Flower.jpg)


Epiphytes on a tree near Santa Elena in Costa Rica (http://en.wikipedia.org/wiki/File:DirkvdM_epiphytes.jpg)


Aerial Roots

o Roots may develop primarily for attachment, and

specialised structures (e.g. cups and scales) may be

used to collect or hold moisture.

o The green aerial roots of these plants carry out

photosynthesis.

42

Tillandsia spp. – happy growing on

telephone wires – Bolivia

https://upload.wikimedia.org/wikipedia/commons/5/53/Tillan

dsia_sp._telephone_line_%28codiferous%29.jpg


Pneumatophores

o Pneumatophores are another example of aerial roots.

o Pneumatophores have evolved to absorb air as well aswater.

o Roots need oxygen for respiration, therefore mostplants can’t survive in water logged soil because thereare no air spaces.

o Pneumatophores are not adventitious roots becausethey grow from roots, not other parts of the plant.

(Tan, 2013)


Arial roots (Pneumatophores) of the grey mangrove Avicennia marina var resinifera - Barker Inlet, South

Australia

(http://commons.wikimedia.org/wiki/File:Pneumatophore_overkill_-_grey_mangrove.JPG)


Pneumatophores

o Plants like mangrove dwellers have adapted to

swampy habitats by growing extensions of their roots

that poke up out of the water and absorb air allowing

the roots to breathe.

45

http://upload.wikimedia.org/wikipedia/commons/f/f0/Mangroves.jpg

http://upload.wikimedia.org/wikipedia/commons/f/f0/Mangroves.jpg


Pneumatophores

http://upload.wikimedia.org/wikipedia/en/4/42/Mangrove_knees_Yap.jpg

http://upload.wikimedia.org/wikipedia/en/4/42/Mangrove_knees_Yap.jpg


Buttress Roots

https://upload.wikimedia.org/wikipedia/commons/1/16/CeibaTreePeru02.jpg

o Common in rainforest trees.

o Large roots all around a

shallowly rooted tree

o Buttress roots of adjoining

trees may emesh overtime,

creating an ecosystem of

support

o What is seen above ground

may also be reflected below

ground.

o Can grow up to 9 metres high

o Involved in collecting nutrients

for the tree


Buttress Roots

(http://upload.wikimedia.org/wikipedia/commons/0/04/A_Above_ground_root.JPG)

o How do you think this might be of advantage in

rainforests?


Vascular Tissue

o Plants are composed of specific cells arranged in roots,

leaves and stems – these are called vascular tissues.

o These tissues perform specialised activities, for

example:

• Xylem – from the Greek meaning ‘wood’

Xylem moves water and nutrients in an upwards direction from

the roots

• Phloem – from the Greek mean ‘bark’

Phloem moves sugars from photosynthesis in a downward

direction to the roots (Capon, 2010)


Xylem

o Xylem is vascular tissue in the middle of the plant

stem and root.

o Xyleum enables water to move in an upward direction

from the roots, therefore transporting it along with

nutrients that had been absorbed by the root hairs, to

the rest of the plant.

o The main cells in the xylem have thickened walls and

specifically adapted long thin cells placed end to end

that allow water to pass through easily.


Phloemo Phloem is the vascular tissue that carries organic

nutrients, particularly sucrose, down to all parts of the

plant where needed.

o The phloem is concerned mainly with the transport of

soluble organic material made during photosynthesis.

o These cells are especially adapted to enhance flow, but

to minimise leakage if damaged.

o When a plant stem is damaged phloem cells produce

mucilage and resin forming substances that block up the

holes and stop sap leaking out.(Capon, 2010)

51


Phloem is Inner Bark

Pic: Juha Kamarainen

https://commons.wikimedia.org/w/index.php?title=User:Juha_K%C3%A4m%C3%A4r%C3%A4inen&action=edit

&redlink=1


Phloem

o Fluid moves around in the phloem according to supply

and demand or a “source-sink” mechanism.

o Because phloem tube cells sit on the outside of

the xylem in most plants, a tree or other plant can be

effectively killed by stripping away the bark in a ring on

the trunk or stem.

o With the phloem destroyed, nutrients cannot reach the

roots and the tree/plant will die. (Mauseth, 2014)

53


Cross Section of Root Stem

Notice the different representation of the vascular bundles in a stem, which

will typically be similarly represented in the roots. Via conduction, these

vessels transport all the water and nutrients the plant needs

54


Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem

(http://en.wikipedia.org/wiki/File:Celery_cross_section.jpg)

Cross Section – Apium graveloens


Tutorial Session

o Practical: Check on your monocotyledon and

dicotyledon seeds germinating in the cottonwool and

notice the changes since last week

o Be confident that you can draw and label both the fibrous

and tap root systems


Tutorial Option

o Watch a TED video: http://www.ted.com/talks/stefano_mancuso_the_roots_of_plant_intelligence

o Check out Crash Course in Biology – Khan Acadamyo https://www.khanacademy.org/science/biology/crash-course-bio-

ecology/crash-course-biology-science/v/crash-course-biology-136

http://www.ted.com/talks/stefano_mancuso_the_roots_of_plant_intelligence

https://www.khanacademy.org/science/biology/crash-course-bio-ecology/crash-course-biology-science/v/crash-course-biology-136


Next Week

o Preparation:

• Read through the slides for session 7 – stems

• Read the chapter in your textbook on stems


Suggested ReadingsTan, E. (2013). Botany of the flowering plants (4th ed.). (pp. 22- 26). VIC: Northern Melbourne

Institute of TAFE.

Chen, R., Rosen, E., & Masson, P. (1999). Plant physiology, 120(2), pp. 343–350. doi:

dx.doi.org/10.1104/pp.120.2.343

Have a read to learn more about the theory of geotropism.

Clarke, I., & Lee, H. (1987). Name that flower: The identification of flowering plants. (pp. 48-49).

VIC: Melbourne University Press.

(Discusses roots and vascular systems.)

Mauseth, J. (2014). Botany: An introduction to plant biology. (5th ed.). (pp. 151-169). MASS:

Jones & Bartlett Publishers.

Raven, J. A., & Edwards, D. (2001). Roots: Evolutionary origins & biogeochemical

significance. Journal of Experimental Botany 52(suppl_1), pp. 381-401.

doi.org/10.1093/jexbot/52.suppl_1.381

(Read through and focus upon the topics covered in class, but do not concern

yourself over the chemical information discussed.)


References

Capon, B. (2010). Botany for gardeners (3rd ed.). Portland, OR:

Timber Press.

Clarke, I., & Lee, H. (1987). Name that flower: The identification of

flowering plants. Melbourne, VIC: Brown Prior Anderson for

Melbourne University Press.

Mauseth, J. (2014). Botany: An introduction to plant biology (5th ed.).

MASS: Jones & Bartlett Publishers.

Tan, E. (2004). Herbal preparations laboratory manual. Victoria,

Australia: Northern Melbourne Institute of TAFE.

Tan, E. (2013). Botany of the flowering plants (4th ed.). VIC:

Northern Melbourne Institute of TAFE.

Wohlmuth, H. (1992). An introduction to botany and plant

identification (2nd ed.). Lismore, NSW: MacPlatypus

Productions.


COMMONWEALTH OF AUSTRALIA

Copyright Regulations 1969

COMMONWEALTH OF AUSTRALIA

Copyright Regulations 1969

WARNING

This material has been reproduced and communicated to you by or on

behalf of the Australian College of Natural Medicine Pty Ltd (ACNM)

trading as Endeavour College of Natural Health, FIAFitnation, College

of Natural Beauty, Wellnation - Pursuant Part VB of the Copyright Act

1968 (the Act).

The material in this communication may be subject to copyright under

the Act. Any further reproduction or communication of this material by

you may be the subject of copyright protection under the Act.

Do not remove this notice.

whmf121 session five plant morphology part ii roots · whmf121 session five plant morphology part...

Documents