Skotomorphogenesis & Photomorphogenesis

Here is the presentation about Skotomorphogenesis & Photomorphogensis.
A seedling that emerge in darkness is known as skotomorphogenesis which is characterized by etiolation. A seedling that emerge in light is known as photomorphogenesis which is characterized by de-etiolation. effect of duration of photoperiod on floral indication is known as Photoperiodism. Phytochrome present in the chloroplast is responsible for the photoperiodic responses. Phytochromes in chloroplast exist in two interconvertible forms. That is PR and PFR. The sunlight converts PR into PFR that results to initiate transcription of a variety of genes that eventually effect the process of photoperiodism.

1. SYSTEM PHYSIOLOGY

SKOTOMORPHOGENESIS
&
PHOTOMORPHOGENESIS
-By,
HEMA PRIYA B
(BIOTECHNOLOGY)

2. INTRODUCTION
•Generally plants use light energy to make
sugar and oxygen (O2) gas from
carbondioxide (CO2) and water during
Photosysthesis.

•In the seedling process, there is no light in
the land.

•That time seed germinated without light.

3. SEED GERMINATION
•Light has profound effects on the development of plants.
•Normally the seedling radicle (root) emerges first from the seed, and the
shoot appears as the root becomes established.
•Later, with growth of the shoot (particularly when it emerges into the light)
there is increased secondary root formation and branching.
•In the absence of light, plants develop an etiolated growth pattern.

4. SKOTOMORPHOGENESIS
•Skotomorphogenesis is when a
seedling develops in the dark.

•Seedling that have undergone
growth in the dark is described as
being an etiolated seedling.
Distinct apical hook (dicot) or
coleoptile (monocot)
No leaf growth
No chlorophyll
Rapid stem elongation
Limited radial expansion of
stem
Limited root elongation
Limited production of lateral
roots.
Etiolated characteristics:

5. PHOTOMORPHOGENESIS
• Photomorphogenesis is when a seedling
develops in the light.

•Seedlings that have undergone growth
in the presence of light are described as
being a de-etiolated seedling.
De-etiolated characteristics:
Apical hook opens or
coleoptile splits open
Leaf growth promoted
Chlorophyll produced
Stem elongation
suppressed
Radial expansion of stem
Root elongation promoted
Lateral root development
accelerated

7. Characteristics Skotomorphogenesis Photomorphogenesis
Hypocotyl Long Short
Apical hook Closed Open
Cotyledons Closed Expanded
Chloroplasts Proplastids Fully developed
Photosynthesis No Yes
Difference between Skotomorphogenesis
& Photomorphogenesis

8. PLANT GROWTH IN DARK
•Kramer’s team made use of Arabidopsis mutants that use photomorphogenesis even in
the dark, ending up with longer roots and fuller, greener leaves than they would
through skotomorphogenesis.

•In these seedlings, the researchers found that pectin, a cell wall component had
chemical modifications including more ethylcarboxyester groups and less acetylation.

•Although the genetics and molecular mechanics of these mutants varied, the unifying
theme was pectin alterations and Kramer reasoned that these were responsible for
allowing photomorphogenesis to proceed in the dark.

•By this logic, normal pectin components might be the signal that wild-type seedlings
use to pass information about the absence of light to other cells.
Plant cell wall can control growth in the Dark

9. To test this idea, the researchers began supplying
mutants with normal pectin fragments in their
growth medium to see if they could restore
skotomorphogenesis.
1)First they tried adding a chunk of protein
backbone called Galacturonic acid, initially as a
monomer. But nothing happened.
2)So they tried a dimer. Again, no change.
3)They adding a trimer of Galacturonic acid, they
looked just like normal plants that had been
grown in the dark.

•In the dark, the plants generate pectin compound,
and this compound is recognized by a receptor
that then acts through signal transduction to
repress the light type of seedling development
and therefore the dark type is maintained.

10. PHOTOMORPHOGENESIS
•Photomorphogenesis is the light-
induced control of plant growth and
differentiation.

•Certain wave lengths function as a
signal causing the generation of an
information within the cell that is used
for the selective activation of certain
genes.

11. PHOTOPERIODISM
•Some plants relay on light signals to determine when to switch from the
vegetative to the flowering stage of the plant development.
•This type of photomorphogenesis is known as Photoperiodism.
•Simply, effect of duration of photoperiod on floral indication is known as
Photoperiodism.

□ Long day plant needs long day to start flowering.
(More than Critical day length).
□ Short day plant needs short day to making flowers.
(Less than Critical day length).

•Minimum duration of photoperiod for floral initiation is known as critical day
length or photoperiod.

12. PHYTOCHROME
•Photoperiodic stimulus is perceived by leaf.
•Phytochrome present in the chloroplast is
responsible for the photoperiodic responses.
•Phytochromes in chloroplast exist in two
interconvertible forms.
P
R : absorbs red light (R) 660nm
P
FR : absorbs far red light (FR) 730nm

13. P
R and P
FR relationship:
Absorption of red light P
R by converts it into P
FR.
Absorption of far red light P
FR by converts it into P
R .

In the dark, P
FR spontaneously converts back to P
R.
P
FR is active & P
R is inactive.
Conversion of P
R into P
FR is fast but P
FR converts back to P
R slowly.
R FR

15. PHYTOCHROME WORK
1)When sunlight converts P
R
into P
FR
,the
moves from the cytoplasm into the
nucleus.

2)There it binds to a protein called PIF3
(Phytochrome Interacting Factor 3)

3)It turns on promoters that encode
transcription factors.

4)It in turn, initiate transcription of a
variety of genes that eventually effect
the process of photoperiodism.

16. Difference in phytochrome gene family structure
VLFR – Very Low Fluence Responses, LFR – Low Fluence Responses, HIR – High Irradiance Responses
(Response to very low light intensity is called as VLFR. Response to high light intensities is called as HIR.)

17. Summary
A seedling that emerge in darkness is known as skotomorphogenesis
which is characterized by etiolation. A seedling that emerge in light is
known as photomorphogenesis which is characterized by de-etiolation.
effect of duration of photoperiod on floral indication is known as
Photoperiodism. Phytochrome present in the chloroplast is responsible for
the photoperiodic responses. Phytochromes in chloroplast exist in two
interconvertible forms. That is P
R and P
FR. The sunlight converts P
R into
P
FR that results to initiate transcription of a variety of genes that eventually
effect the process of photoperiodism.

18. REFERENCES
Parks, B. M. (2003). “The red side of photomorphogenesis”. Plant
physiology, 133(4), 1437-1444.
Takimoto, A., & Saji, H. (1984). “A role of phytochrome in photoperiodic
induction: Two‐phytochrome‐pool theory”. Physiologia Plantarum, 61(4),
675-682.
Kerry Grens (2018) “Plant cell walls can control growth in the dark” The
Scientist – exploring life, inspiring Innovation.
Mohr, H. (2012) ”Lectures on photomorphogenesis”. (Pg. No: 178, 183 -
184)Springer Science & Business Media.
Josse, E. M., & Halliday, K. J. (2008). “Skotomorphogenesis: the dark side
of light signalling”. Current Biology, 18(24), R1144-R1146.