Vidan biology Famous for making Great slide About Biology

1. 1
Light is vital for photosynthesis but it is also necessary for
plants growth and development.
“The light mediated growth and development in plants
independent of photosynthesis are called Photomorphogenesis”.

2. 2
 Light is important for photosynthesis, but is also necessary
for plant growth and development.
 The light mediated growth and development in the plants is
Photomorphogenesis.
 Light act as a signal to initiate and regulate
photomorphogenesis.

3. 3
TYPES OF PHOTORECEPTORS
1. Phytochrome (Red Light Photoreceptor) Plays a role in seed
germination, flowering and stem elongation etc.
2. Cryptochrome (Blue Light Photoreceptor) Plays a role in flowering,
circadian rhythms and inhibition of stem elongation etc.
3. Phototropin (Blue Light Photoreceptor) Plays a role in chloroplast
movement and phototropism etc
4. Zeitlupe family (Blue Light Photoreceptor) plays a role in circadian
rhythms and control of flowering.
There are 4 major types of photoreceptors involved in photomorphogenesis:

4. 4
Cryptochrome
Phototropin
Zeitlupe
Phytochrome

5. Phytochrome was discovered
by Sterling Hendricks & Harry
Borthwick.

6. Phytochrome is red light photoreceptor of plants synthesize in
dark entirely as Pr form in the cytoplasm.
Phytochrome is a photomorphogenetic chromoprotein that absorbs red
and far red light strongly & causes photomorphogenesis.
It is a blue protein pigment with a molecular mass of about 125 kDa. It is
present in almost all plants, Fungi, some Algae and Bacteria.

7. 7
1.Red light absorbing (666nm) Pr form
2.Far red light absorbing (730nm) Pfr form.
The Phytochrome is present in 2 Photoreversible forms:
Absorption of red light by Pr convert it to
Pfr form and absorption of Far red light
by Pfr convert it to Pr form.

8. 8
Pfr Form (Far-Red Light Absorbing Form)
When Pfr absorbs far red light it is
converted into Pr form
It is the active form which initiates
biological
Pfr form can also spontaneously revert to the
Pr form in the dark (night time) overtime, It is
called Dark Reversion.

9. 9
Red Light
Far Red Light
Initiated
Biological
responses
Dark
Reversion
Phytochrome Also absorb Blue Light, hence phytochrome effects
can also be mediated by blue light Eg- PHY A.

10. Red Light
Far Red Light
Dark
Reversion
Day Event
Active
Inactive

11. 11
• It is a Photomorphogenic pigment.
• Phytochrome consist of chromophore
• Absorb red and far-red light and cause photomorphogenesis.
Chromophore=Phytochromobilin
• Found in most plant, regulate growth and development process like
induction of flowering, seed germination, stem elongation etc.

12. 12
Phytochromobilin
GAF PHY
PAS
PRD PRD HKRD
PAS GAF PHY
PRD PRD HKRD
Phytochromobilin
Photosensory Region Regulatory Region
Thiother linkage Covalent bond
Thiother linkage Covalent bond
N
N
Dimer
Form
C
C
PHY-Phytochrome-specific
GAF related domain.
PRD-PAS Related domain .
HKRD- Histidine kinase related domain

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 The N-terminal half contain PAS domain, GAF domain which binds the
chromophore through a covalent bond and PHY domain which
stabilizes the Phytochrome in Pfr form. The PAS-GAF-PHY domains
comprises Photosensory Region of phytochrome.
 The C-terminal half called Regulatory Region, it contains 2 PAS-related
domains (PRD) that mediates phytochrome dimerization and nuclear
targeting & non-functional Histidine kinase related domain (HKRD).

14. 14
 When chromophore absorbs light there is slight change in its structure this
causes a change in conformation of the protein to the form that initiates
responses.
 N-terminal region perceives photosensory signals and C-terminal region do
the transmission of photosensory signal to signal transduction pathway.
 It has been suggested that phytochrome are Auto phosphorylating
serine/threonine kinases.
 Phytochrome protein are encoded by phytochrome gene family termed PHY.
Its 5 members are PHY A, PHY B, PHY C, PHY D & PHY E.

15. 15
Different Classes Of Phytochrome
Type 1 phytochrome Type 2 Phytochrome
It is abundant in dark grown plant
presence of light its concentration
decreases rapidly as a result of :
PHY A is most abundant
phytochrome in Dark grown
(etiolated) plants.
They are photoreceptor of Far Red
Light. Example- PHY A.
It is stable in Light and present in
both light and dark grown plants
(mainly functions in light)
PHY B is most abundant
phytochrome in light grown
plants
They are photoreceptors of Red
Light. Example- PHY B, PHY C, PHY
D, PHY E.
• Transcriptional inhibition
• mRNA degradation
• Proteolysis

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Functions
Induction of stem elongation.
Promotes induction of flowering.
Leaf Senescence.
Leaf abscission.
Seed Germination.
Nyctinąstic Movements.
 Chloroplast development.
 Promotion of leaf formation & also regulates size, number, shape of Leaves.

17. Phytochrome - Photoactivated Phytochrome Pfr after Autophosporylation migrates into the
nucleus and mediate Photomorphogenic development (de-etiolation) by degrading PIFS and
Inactivating COP1 activity. So the main function of the Phytochrome is the removal of negative
regulators of Photomorphogenesis.
HY5 (Elongated Hypocotyl 5), LAF1 (Long After Far Red Light 1) and HFR1 (Long Hypocotyl in
Far Red 1) – These are Photomorphogenesis promoting transcriptional factors. In which HY5
(bZIP transcriptional factor) is a master regulator of Photomorphogenesis in the light the level
of HY5 protein increases and in dark it decreases.
Positive Regulators of Photomorphogenesis
MECHANISM OF ACTION

18. Negative Regulators of Photomorphogenesis
MECHANISM OF ACTION
 COP1 (Constitutive Photomorphogenic 1)- COP1 is E3 Ubiquitin ligase which
is involve in targeting several photomorphogenesis promoting factor like HY5, LAF1, HFR1
for degradation via. 26S proteasome pathway. In the dark COP1 is present in nucleus but in
the presence of light it is exported to cytoplasm.
 PIFS (Phytochrome Interacting factors) are bHLH transcription factors e.g. PIF3
which promotes Skotomorphogenesis (when grown in dark plants undergo
etiolated growth i.e. elongated hypocotyl, closed cotyledons with apical hook
& pale yellow leaves) in dark by binding to PIFs induced genes.

19. 19
Nucleus
LAF1
HY5
HFR1
COP1
SPA1
COP1
PROTEOSOME
26S
PIFS
PIFS induced Genes
Skotomorphogenesis Photomorphogenesis
Migrates
Degradation
SPA1- suppressor
of PHY A-105 1
Pr
Inactive
DARK

20. 20
Nucleus
LAF1
HY5
HFR1
COP1
SPA1
PIFS
Degradation
SPA1
COP1
Photomorphogenesis
Light
Responsive
Gene
Active
PROTEOSOME
26S
P
P
P
P
P
Pfr
Active
Autophosphorhylation
Light

21. PIFs in the dark accumulates in the nucleus and induces expression of PIFs-Induced Genes &
directly promotes Skotomorphogenesis and also inhibits Photomorphogenesis
In Dark, Phytochrome is synthesize as the inactive Pr form
In the dark, COP1 migrates from the cytoplasm to nucleus & forms complex with
SPA1 and becomes more active
COP1-SPA1 complex constantly degrade the photomorphogenic promoting
transcription factors like HY5, LAF1, HFR1 via ubiquitin mediated 26S proteasome
degradation pathway to prevent photomorphogenesis

22. 22
 It is a Photomorphogenic pigment.
 Absorb red and far-red light and cause
photomorphogenesis.
 Found in most plant,regulate growth and development
process like induction of flowering, seed germination, stem
elongation etc.
PHYTOCHROME

23. 1. COP1 remains in nucleus in dark.
2. COP1 function as an E3 ubiquitin ligase and target
HY5 for degradation by 26S proteasome system.
3. No photomorphogenesis due to lack of transcription
and proteins.
Light
1. COP1 Exported in cytoplasm from nucleus.
2. High amount of HY5,due to lack of degradation by COP1.
3. HY5 involve in successful transcription.
4. Photomorphogenesis occur.