9.3 plant growth

Essential idea: Plants adapt their growth to
environmental conditions.
9.3: Plant Growth

Understandings
Statement Guidance
9.3 U.1 Undifferentiated cells in the meristems of plants allow
indeterminate growth.
9.3 U.2 Mitosis and cell division in the shoot apex provide cells
needed for extension of the stem and development of
leaves.
9.3 U.3 Plant hormones control growth in the shoot apex
9.3 U.4 Plant shoots respond to the environment by tropisms.
9.3 U.5 Auxin efflux pumps can set up concentration gradients
of auxin in plant tissue.
9.3 U.6 Auxin influences cell growth rates by changing the
pattern of gene expression.

Applications and Skills
Statement Guidance
9.3 A.1 Application: Micropropagation of plants using tissue
from the shoot apex, nutrient agar gels and growth
hormones.
9.3 A.2 Application: Use of micropropagation for rapid bulking
up of new varieties, production of virus-free strains of
existing varieties and propagation of orchids and other
rare species.

Dicotyledon Structure
1. Root system extracts minerals
(nitrates & phosphates) along
with water from the soil. The
main root has lateral divisions
that are either shallow or deep
depending on the water
availability of water.
2. Stem structure supports leaf and
contains the vascular tissue that
transports substances around
the plant.
3. Petioles divisions of the stem.
They support the leaf and
contains branches of the vascular
tissues.
www.click4biology.com

4. Leaf large surface area to
absorb light energy for
photosynthesis. Concentrated
within the palisade tissue of
the leaf is chlorophyll to
absorb the photons of light.
5. Auxiliary bud provide the
tissues for the growth of
lateral branches in future
growing seasons.
6. Terminal bud contains the
structures for the growth and
elongation of the main stem.

Dicotyledonous stem
Tissue types of the plant stem:
• Epidermis: surface of the stem
made of a number of layers
often with a waxy cuticle to
reduce water loss.
• Cortex Tissue: Forming a
cylinder of tissue around the
outer edge of the stem. Often
contains cells with secondary
thickening in the cell walls
which provides additional
support.
• Vascular bundle: contains
xylem, phloem and cambium
tissue.

Dicotyledonous stem
• Xylem: a longitudinal set of tubes that
conduct water from the roots upward
through the stem to the leaves.
• Phloem (sieve elements) transports sap
through the plant tissue in a number of
possible directions.
• Vascular cambium is a type of lateral
meristem that forms a vertical cylinder in
the stem. The cambium produces the
secondary xylem and phloem through
cell division in the vertical plane.
• In the center of the stem can be found
the pith tissue composed of thin walled
cells called parenchyma. In some plants
this section can degenerate to leave a
hollow stem

9.3 U.1 Undifferentiated cells in the meristems of plants allow
• Plants growth is restricted to
'embryonic' regions called
meristems. Having specific
regions for growth and
development (restricted to
just the meristematic
tissue).
• Meristems composed of
undifferentiated cells that
are undergoing active cell
division
Growth Occurs:
• Terminal & Axillary buds
• Tap and Lateral roots
• Cambium (stem thickness)

9.3.U.1 Undifferentiated cells in the meristems of plants allow
• Apical Meristems – found at the tips of stems and roots
• Lateral Meristems – responsible for thickness of the stems
Apical meristem

• Auxins (hormone) – initiating
the growth of roots,
influencing the development
of fruits and regulating leaf
development.
• Auxin influences cell division
growth rates and patterns.
• Auxins also influence cell
elongation.
(a) Shoot apical meristem
(b) Leaf primordial
(c) Auxiliary bud primordium
(d) leaf
(e) Stem tissue
http://www.geraniumsonline.com/apex1.jpg
Apical meristem at the top of the plant
9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth.
9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression

Root apical meristem:
(a) Root cap.
(b) Root apical meristem.
(c) Ground meristem.
(d) Protoderm.
(e) Epidermal tissue of the root.
(f) Vascular tissue (central stele).
Apical Meristem
Apical meristem at the root of the plant

Apical meristem : Axillary Bud Growth
• Stem differentiation at
the apical meristem
creates branching.
• The diagram illustrate
that the tissue added at
the apical meristem
differentiates into the
various primary plant
body structure (AB)

1. Cambium that produces secondary xylem and
phloem
2. Cork cambium produces some of the bark layer of
a stem.
*secondary growth adding thickness usually in the
following years in a perennial plant.
Lateral meristem is secondary growth

• Cells in meristems are small, therefore they go through the cycle quicker to
produce more cells through mitosis and cytokinesis
• These new cell absorb nutrients and water which increase their volume &
mass http://www.navitar.com/images/bf2.jpg
9.3 U.2 Mitosis and cell division in the shoot apex provide cells needed
for extension of the stem and development of leaves.

PLANT GROWTH REGULATORS (aka PLANT HORMONES)PLANT GROWTH REGULATORS (aka PLANT HORMONES)
Plant hormones differ from animal hormones in that:
 Unlike animal hormones, plant hormones are not made in tissues specialized for
hormone production. (e.g., sex hormones made in the gonads, human growth hormone
- pituitary gland)
 Unlike animal hormones, plant hormones do not have definite target areas (e.g., auxins
can stimulate adventitious root development in a cut shoot, or shoot elongation or
apical dominance, or differentiation of vascular tissue, etc.).
 There a several hormones found in plants. Auxins. Auxins (cell elongation), GibberellinsGibberellins (cell
elongation + cell division), CytokininsCytokinins (cell division), Abscisic acidAbscisic acid (Controls guard cells)
and EthyleneEthylene (promotes fruit ripening)
9.3 U.3 Plant hormones control growth in the shoot apex.

Cytokinins
•Hormones that stimulate cell
division, leaf aging (leaf
senescence) and leaf enlargement
•Cytokinins, in combination with
auxin, stimulate cell division and
differentiation.
•Produced in roots and travel
upward in xylem sap.
*The hormone has no direct effect
on the cell wall. For this reason it
work best with the plant hormone
Auxin
The plant, below left has been genetic
modification to increase levels of
cytokinin
Nicotiana (Solanaceae family)

Increasing auxin concentration
Increasing
Cytokinin
concentration
Cytokinin and auxin interactions
Callus of Nicotiana
(Solanaceae family)

Auxin
• Increases the flexibility of the cell wall. A more flexible wall will
stretch more as the cell is actively growing.
• Auxin accumulates in the apical meristem. Allows selective cell
elongation.
• By interacting with other hormones, Auxin also induces cell
width
.

Acid Growth
hypothesis• Plant cell growth dependent on the growth hormone auxin.
• Auxin activates a plasma membrane proton pump, which acidifies the cell wall.
• The lower pH, in turn, activates growth-specific enzymes that hydrolyze the bonds holding
to cellulose. Breaking of these bonds results in the loosening of the cell wall. Causes
uptake of water – which leads to a passive increase in cell size.
Loosening of cell wallLoosening of cell wall

Enzymes break the bonds holding
xyloglucan to cellulose.
Enzymes break the xyloglucan
molecules.
Other enzymes break the pectin
Molecules (NOT SHOWN).
From: Biochemistry and Molecular Biology of plants
The cell is now free to expand
in a given direction.

When expansion has stopped:
Cell wall proteins lock the cells
new shape as these new wall
components are being made.
Enzymes form new xyloglucan
Molecules which re-attach to the
Cellulose microfibrils.
Also form New cross-links
with newly formed Cellulose
microfibrils.

For a plant to grow:
•new wall material has to be laid down as the cell expands
New cellulose microfibrils are
made as the cell expands. Plasma
membrane
These line up perpendicular
to the direction of growth.
As this happens the existing wall
has to be loosened.

• Darwin’s studied the of effects auxin on movement.
• Darwin studied phototropism using the germinating stem of the
canary grass.
• The cylindrical shoot is enclosed in a sheath of cells called the
coleoptile.
http://semoneapbiofinalexamreview.wikispaces.com/file/view/39_05bColeoptileDarwins-L.jpg/289955863/560x411/39_05bColeoptileDarwins-L.jpg
9.3 A.1: Micropropagation of plants using tissue from the shoot
apex, nutrient agar gels and growth hormones.

9.3 A.1: Micropropagation of plants using tissue from the shoot
apex, nutrient agar gels and growth hormones.
Auxin was first isolated by F. W. Went
(m) Went isolated the growth medium auxin onto agar gel.
(n) The gel was cut up into block as a way of quantifying the dose of
auxin used.
(o) The agar block (containing auxin) are placed asymmetrically on the
stem.
(p) The angle of bending-growth was measured
http://plantphys.info/plant_physiology/images/paaltip.gif

9.3 A.1: Micropropagation of plants using tissue from the shoot apex,
nutrient agar gels and growth hormones.
• Since Auxin (IAA3) was synthetically
produced more rigorous quantitative
bio-assay can be performed
• This graph measures the bending-
growth against the concentration of
IAA3.
Graph suggests:
• Increasing IAA3 increases the bending-
growth angle.
• Optimal angle of bending-growth is
achieved between 0.2- 0.25 mg
• Higher levels seem to have reduced-
bending growth

Tropisms: External Factors that Regulate Plant Development
• a change in the growth pattern or
movement of a plant in response to an
external stimulus that mainly come from
one direction.
• As tropisms effect the growth pattern of
plants, they greatly effect the plant cell
wall.
Best known:
Phototropism
Induces cells AWAY from light to elongate.
Cell wall expands in a specific direction.

Phototropism
•Phototropism is the growth of stems of plants toward light - it is probably the best
known of the plant tropisms - phototropism is caused by elongation of the cells on the
shaded part of the plant - so that entire plant bends or curves toward the light
•This growth pattern is caused by the hormone auxin - auxin migrates to the shaded part
of the plant and stimulates increased cell growth and elongation on the shaded part of
the plant
IAA = Auxin

http://upload.wikimedia.org/wikipedia/commons/8/8d/Sunflower_Field_near_Raichur,_India.jpg

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Museo_Larreta_Yatay.jpg/1280px-Museo_Larreta_Yatay.jpg

Gravitropism:
Response of a plant to gravity. Causes roots to grow downwards
and stems to grow upwards. This response is governed by Auxin.
Auxin builds up in the cells of the upper surface of root
This induces localized cell
elongation and re-orientation
of the cell walls to allow the
root to grow downwards.
9.3 U.5: Auxin efflux pumps can set up concentration gradients of
auxin in plant tissue.

Gravitropism = GeotropismGravitropism = Geotropism
http://gp1.wac.edgecastcdn.net/802892/production_public/Artist/150029/image/Gravitropism_pos.jpg

9.3.A.2 Use of micropropagation for rapid bulking up of new varieties,
production of virus-free strains of existing varieties and propagation of
orchids and other rare species.
• Stock plant is identified for a
desirable feature.
• Micropropagation depends on
totipotent cells which retain the
ability to differentiate.
• Tissue from the stock plant are
sterilized and cut into pieces called
explant.
• The explant is placed into a growth
media along with plant hormones.
This undifferentiate mass is called a
callus.
• Once roots and shoots are
developed the cloned plant can be
transferred to soil.
• This technique is used to overcome
plant viruses or to produce large
numbers of rare plants.
http://www.toptenz.net/wp-content/uploads/2012/04/ghostorchid-570x427.jpg

9.3 A.2 Use of micropropagation for rapid bulking up of new varieties,
Sugar Cain
http://www.sciencephoto.com/image/212210/350wm/G28002
82Cereal_plants_being_grown_from_tissue_culture-SPL.jpg http://php.med.unsw.edu.au/cellbiology/images/6/6e/Plant_Tis
sue_Culture_Lab.jpg

9.3 A.2 Use of micropropagation for rapid bulking up of new varieties,
Sugar Cain
http://vsisugar.com/gallery/tissueculture-gallery/img/photo15.jpghttp://3.imimg.com/data3/IQ/AA/WSITE-5570267/files-resized-
199442-470-353-aebeec90aa3a60f977156f626701cf17c8bb5439-
250x250.jpg

9.3 plant growth

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie 9.3 plant growth

Ähnlich wie 9.3 plant growth (20)

Mehr von Bob Smullen

Mehr von Bob Smullen (20)

9.3 plant growth