Detailed PPT about Photomorphogenesis & Photoreceptors .

1. Control of growth & development by light
Presented By –
Hemanga Choudhury &
Hakimuddin SK
[Bachelor of Science (Hons.)
Batch 2020-2023
Department of Botany
B.H College, Howly]

2.  INTRODUCTION
 PHOTORECEPTORS
1. PHYTOCHROME
A. INTRODUCTION
B. DIFFERENT FORMS
C. STRUCTURE
D. FUNCTIONS
E. MODE OF ACTION
2. CRYPTOCHROME
A. INTRODUCTION
B. STRUCTURE
C. FUNCTIONS
D. MODE OF ACTION
3. PHOTOTROPIN
A. INTRODUCTION
B. STRUCTURE
C. FUNCTIONS
D. MODE OF ACTION

3.  Photomorphogenesis is the process by
which plants grow & developed in
response to light .
 It is the light–induced control of plant
growth & differentiation .
 The process of photomorphogenesis is
mediated by network of photoreceptor.
 Absorption of light causes conformational
change in the pigment or associated protein
causes photochemical oxidation-reduction.
 Certain wavelengths function as a signal
causing the generation of an information within
the cell that is used for the selective activation
of certain genes .
 Plants can sence light gradients and detect
subtle differences in spectral composition .

4.  The Photoreceptors involve in the process of
photomorphogenesis are ---
1. PHYTOCHROME
2. CRYPTOCHROME
3. PHOTOTROPIN

6. Phytochrome was
discovered by Sterling
Hendricks & Harry
Borthwick

7. WHAT IS PHYTOCHROME ?
Phytochrome is a blue-green pigment protein which acts as a photoreceptor
that absorb Red & Far-red light .
Phytochrome is found in green & red algae , desmids , bryophytes ,
gymnosperms & angiosperms .
It has been detected from roots , stems , coleoptiles , hypocotyls , cotyledons
, petiols & blades of leaves , vegetative buds , floral tissues , seeds &
developing fruits of higher plants .
The pigment responsible for the inhibition of flowering in Short day plants
and stimulation of flowering in Long day plants .
It also helps in the process of absorbing lights & showing its effects on
various developmental & morphogenetic processes .
Phytochromes are generally interconvertible .
It absorbs red & far-red light most strongly 600-700nm .
It absorbs blue light at 350-500nm .
It also absorbs UV radiation at 320-400nm.

8. DIFFERENT FORMS OF PHYTOCHROME :
Phytochromes are generally found in two photoreversible forms .
These are -----
1. Red light absorbing forms or Pr forms .
2. Far red light absorbing forms or Pfr forms .

9. Pr form Pfr form
1. It is an inactive form of
phytochrome .
2. Being inactive , it doesn’t
show phytochrome
mediated responses .
3. It has an absorption
maximum in red region
(about 680 nm ).
4. It is found difused
throughout the cytosol .
5. It is converted into Pfr form
in presence of red light (
660-665nm ) .
6. It shows activity in presence
of urea , metal ions Cu2+ ,
Co2+ , Zn2+ etc. .
1. It is active form of
phytochrome .
2. Being active , it shows
phytochrome mediated
responses .
3. It has an absorption
maximum in far red region
(about 730nm).
4. Iis usually found in discrete
areas of cytosol .
5. It is converted into Pr form
in presence of far red light
(730-735 nm) .
6. It shows comparatively
more activity in presence of
these chemicals .

16. CRYPTOCHROME

17.  It is a blue-light photoreceptor, class of flavorproteins & chromophore is
Flavin & pterin .
 It also absorbs UV light at a wavelength of 320-400nm .
 It is found in ferns , algae , cyanobacteria , fruit flies , mice & humans .
 Cryptochromes are structuraly related to photolyase , a blue-light
activated enzyme that repairs pyrimidime dimer in DNA .
 The cryptochrome don’t have a DNA repair activity , but they are thought
to have evolve from the photolyase enzyme .
 Cryptochrome receptor is localized in the nucleus & have a regulatory
role in plant photomorphogenesis .

18. STRUCTURE OF CRYPTOCHROME
 Most cryptochromes are composed of two
domains , an amino-terminal photolyase
homology region(PHR) & a carboxy-terminal
domain of varying size .
 The PHR regions of cryptochromes posses
two chromophores : Flavin (FAD , which
absorbs at 450nm) & pterin (5,10-
methyltetrahydrofolate , MTHF , which
absorbs at 380nm) .
 Cryptochromes are dimeric proteins .
 Cryptochromes bind with a
Flavinadininedinucleotide(FAD) , the pterin
(MTHF) as chromophore that is light
absorbing derivatives often found in
pigmented cells of insect , fishes , birds etc. .

19.  It plays a primary role in inhibition of stem
elongation.
 It plays primary role in leaf expansion.
 CRY1 helps in enthocyanin production.
 CRY1 promotes cotyledons expansion.
 CRY1 inhibits petiole elongation.
 It helps in membrane depolarization.
 CRY2 plays a primary role in Promotion of
photoperiodic flowering.
 CRY2 promotes photoperiodic flowering in
Arabidopsis.

20. MODE OF ACTION
 Cryptochromes signals regulate plant
growth & development by undergoing
a blue-light dependent
phosphorylation that affects the
conformation , intermolecular
interactions , physiological activities &
protein abundance of the
photoreceptors.
 The unique C – terminal domain , DAS
(DQXVP-acidic- STAES) , Transduces
the light signal by interacting with the
E3 ubiquitin ligase , COP1
(Constitutive a photomorphogenic 1) .

22. PHOTOTROPIN
PHOTOTROPIN was discovered by
Winslow R. Briggs

23. It is a flavoprotein which acts as a blue-light photoreceptor & light
activating protein kinase .
One of the mutant , nph1 ( non phptotropic hypocotyl) mutant lacks a
phototropic response in the hypocotyl.
Recently , the nph1 gene was renemed as phot1 & the protein, it encosed
as named as phototropin .
Phototropin receptors are associated with the plasmamembrane , where
they function as light activated serine or threonine kinase.
It helps in phototropisms , light induce stomatal opening & chloroplast
movement in response to changes in light intensity , leaf expansion etc. .