A presentation of Topic 9.3. Growth in plants

1. 9.3. Growth in plants
Miltiadis-Spyridon Kitsos
Platon IB Diploma
https://upload.wikimedia.org/wikipedia/commons/thumb/1/14/Phototropism_Diagram.svg/
2000px-Phototropism_Diagram.svg.png

2. The official IB Diploma Biology guide
Essential idea: Plants adapt their growth to environmental conditions.
https://ibpublishing.ibo.org/server2/rest/app/tsm.xql?doc=d_4_biolo_gui_1402_1_e&pa
rt=4&chapter=3

3. Growth in plants
Undifferentiated cells in the meristems of the plants allow indeterminate growth
In plants growth is indeterminate that is, the
cells have the potential to divide indefinitely.
http://www.b4fa.org/wp-content/uploads/2012/06/How-do-plants-reproduce-
asexually1.png
Whole plants may develop from
differentiated cells. Side stems known as
runners, tubers and bulbs are very good
examples.
http://www.b4fa.org/wp-content/uploads/2012/06/Many-plants-
reproduce-asexually-21.png

4. Growth in plants
Undifferentiated cells in the meristems of the plants allow indeterminate growth
Plant growth is taking place at the meristems. Meristems are areas where
undifferentiated cells undergo division.
http://media-2.web.britannica.com/eb-media/99/5599-004-D6C19960.jpg
http://bio1152.nicerweb.com/Locked/media/ch35/35_10SecondGrowth.jpg
http://www.mhhe.com/biosci/genbio/maderbiol
ogy7/graphics/mader07b/mader_labeling/mader
_labeling_source/mi09-10a.dcr
http://study.com/cimages/multimages/16/stem_cross_section.png

5. Undifferentiated cells in the meristems of the plants allow indeterminate growth

6. Mitosis and plant growth
Mitosis and cell division in the shoot apex provide cell needed for extension for the stem and
development of the leaves
http://www.doctortee.com/dsu/tiftickjian/cse-
img/botany/plant-anat/stem/coleus-stem-tip.jpg
Different meristematic tissues result from the apical meristem which in turn give rise to different
tissues. Chemical signals play a role in differentiation.

7. Hormones and plant growth
Plant hormones control growth in the shoot ape
A hormone is a chemical compound produced and released somewhere in the plant, transported
via the sap and having an effect on another part of the plant.
http://image.slidesharecdn.com/plantresponses-150311200432-conversion-
gate01/95/plant-responses-33-638.jpg?cb=1426122375
http://image.slidesharecdn.com/plantresponses-150311200432-conversion-gate01/95/plant-
responses-33-638.jpg?cb=1426122375
Specific functions of auxin are:
• root and shoot growth
• Flowering
• fruit development
• leaf development
• wound response

8. 9.3.U4 Plant shoots respond to the environment by tropisms.
http://www.kscience.co.uk/animations/aux
in.htm
Gravitropism (aka Geotropism) is the response to
gravity. This response can be both positive and
negative.
Phototropism interactive
animation
Gravitropsim
tutorials &
animations
Edited from: http://www.slideshare.net/gurustip/plant-structure-and-growth-ahl
http://leavingbio.net/plant%2
0responses.htm
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9. Plant tropisms
Plant respond to environment by tropisms
http://4.bp.blogspot.com/-
sgciBSW6tco/UaZFMN23xQI/AAAAAAAADoE/QLmrA44d46k/s1600/Phototropism.png
In this image you can see different experimental setups to investigate the effect of light
on plant grown. Can you deduce the respective results?
Phototropims= Photo (light) + Tropos
(movement)
Gravitropism = Gravity + Tropos
(movement)
Growth following the gravitational
force

10. Plant tropisms
Plant respond to environment by tropisms
https://youtu.be/4-2DZo2ppAY
http://www.kscience.co.uk/animations/auxin.swf
http://www.mhhe.com/biosci/genbio/tlw3/eBridge/Chp18/animations/ch18/demonstrating_
phototropism.swf
http://www.kscience.co.uk/animations/aux
in.htm
Phototropism interactive
animation

11. Auxin affects gene expression in shoots:
• Cells contain an auxin receptor.
• When auxin binds to receptors, transcription of specific genes is promoted.
• The expression of these genes causes secretion of hydrogen ions into cell walls.
• hydrogen ions loosen connections between cellulose fibres, allowing cell
expansion.
http://www.sciencemag.org/content/312/5775/858/F1.medium.gif
Auxin and gene expression
Auxin influences cell growth rates by changing the pattern of gene expression
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12. 9.3.U5 Auxin efflux pumps can set up concentration gradients of auxin in plant tissue. 9.3.U6 Auxin influences cell growth
rates by changing the pattern of gene expression.
Different factors can affect transporter
proteins and hence the direction in which
auxin can move:
• The location of transporter proteins can be
changed as the plasma membrane is fluid,
e.g. efflux transporters can congregate at
the top of cells in roots to move auxin
upwards
• Transporter proteins can be activated
and/or inhibited by stimuli such as light
http://www.sciencemag.org/content/312/5775/858/F1.medium.gif
Concentration gradients of auxin are necessary
to control the direction of plant growth.
Auxin can enter the cell by:
• Diffusion
• influx transporter proteins
Auxin can move out of the cell
by through efflux transporters
(called PIN proteins)
This requires that auxin is unevenly transported amongst plant tissues.
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13. Auxin and gene expression
Auxin efflux pumps can set up concentration gradients of auxin in plant tissue.
Phototropins at the apex receive
the light
They undergo conformational
changes and bind to receptors
within the cell
This binding promotes the
expression of specific genes
which encode for plasma
proteins called PIN3
glycoproteins

14. Intracellular movement of auxin
Auxin efflux pumps can set up concentration gradients of auxin in plant tissue
PIN3 proteins may determine the direction of auxin transport. See
these examples
When the sun moves
sideways PIN3
channels enable the
later movement of
auxin.
http://i.stack.imgur.com/bjH5P.jpg
http://www.mhhe.com/biosci/genbio/tlw3/eBridge/Chp18/animations/ch18/
auxin_mode_of_action.swf

15. Intracellular movement of auxin
Auxin efflux pumps can set up concentration gradients of auxin in plant tissue
Amyloplast statoliths pulled by gravity will change the distribution of PIN3
proteins which accumulate at the bottom of the cells.
Unlike in the stems, high auxin concentration in the roots inhibits cell
elongation.
http://www.mhhe.com/biosci/genbio/tlw3/eBridge/Chp18/animations/ch18/
auxin_mode_of_action.swf
http://3.bp.blogspot.com/-
5UnKO8d2IOg/T7e3jjMwRoI/AAAAAAAAAhM/N1PC4kfPEgw/s320/1-statolith.gif

16. Micropropagation of plants
Micropropagation is an in vitro technique of developing numerous identical
plants on an artificial culture medium under aseptic and controlled
conditions.
 Replaces traditional propagation techniques
 Lead to the development of virus-free plants – selective breeding
 Saves time and labor
http://www.bbc.co.uk/staticarchive/a20f41790254c2ae96c013ef544d1f031ad6fc70.jpg
https://encrypted-
tbn3.gstatic.com/images?q=tbn:ANd9GcRfbXW
nAu6NmehtzbpDCoT2aTKH_jvNRd1GoFj4IyNy8
hrZuVlG

17. Micropropagation of plants
Explants that is sterilized pieces of plants are cut into pieces and placed in
a growth medium along with plant hormones. Sterilise media to prevent
growth of fungi and other microorganisms
Formation of an undifferentiated mass called
the callus (totipotent cells)
Based on the relative proportion of
hormones development of stems or
roots
Hardening process
Transfer to soil
Cytokinins cons > auxin cons
development of shoot
Cytokinins cons < auxin cons
development of roots
https://upload.wikimedia.org/wikipedia/commons/e/e7/Pv_callus_da
rk_3_3-11-2008.jpg

18. Micropropagation of plants
Micropropagation of plants is used for:
• A cost-effective production of a significant number of plants.
• Conservation of species close to extinction.
• Isolation of diseases from plants.
• Development of genetically modified plants.
http://www.bgci.org/news-and-
events/news/0136/?sec=resources&option=com_news&id=0136

19. Nature of Science: Developments in scientific research follow improvements in analysis and deduction - improvements in analytical
techniques allowing the detection of trace amounts of substances has led to advances in the understanding of plant hormones and
their effect on gene expression. (1.8)
http://www.salk.edu/images/pressrelease/2013/619ecker.jpg.png
The interactions between different plant hormones and multiple plant genes
are very complex and not fully understood. Our understanding of this area of
science is steadily growing due to our ability to detect trace (very small)
amounts of molecules.
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20. www.stepsinbiology.com