The signal transduction pathway uses a network of interactions within cells, among cells, and throughout plant. The external signals that affect plant growth and development include many aspects of the plant’s physical, chemical, and biological environments. Some external signals come from other plants. Many signals interact cooperatively and synergistically with each other to produce the final response. Signal combinations that induce such complex plant responses include red and blue light, gravity and light, growth regulators and mineral nutrients . For example the overall regulation of seed germination involves control by both external factors and internal signals.

1. SIGNAL TRANSDUCTION PRINCIPLE
AND MECHANISM IN PLANTS
:Rajendra Bhatt

2. INTRODUCTION
Signal
(Any function that
conveys some
information)
Transduction
(To forward)
Signal
Transduction
 “Signal transduction is the process by which a chemical or physical signal is transmitted
through a cell as a series of molecular events”.
 It also known as cell signaling in which the transmission of molecular signals from a cell's
exterior to its interior.

3. SIGNAL TRANSDUCTION IN PLANTS
• The signal transduction pathway uses a network of interactions within cells,
among cells, and throughout plant.
• The external signals that affect plant growth and development include many
aspects of the plant’s physical, chemical, and biological environments. Some
external signals come from other plants.
• Many signals interact cooperatively and synergistically with each other to
produce the final response. Signal combinations that induce such complex
plant responses include red and blue light, gravity and light, growth
regulators and mineral nutrients .
• For example the overall regulation of seed germination involves control by
both external factors and internal signals.

4. PRINCIPLE OF SIGNAL TRANSDUCTION
• Signal transduction is a very specific and very sensitive bio-chemical process. Signals received by cells must be transmitted
effectively into the cell to ensure an appropriate response. A particular type of signal is received by a particular type of
only. The interaction’s specificity is almost similar to that of substrate-enzyme interaction or antigen-antibody interaction.
• In multicellular organisms, the specificity is a little bit more complex. This is because in multicellular organisms, a particular
of signal is received by a particular type of receptor only and these receptors are present on specific cells only.
• This step is initiated by cell-surface receptors which triggers a biochemical chain of events inside the cell, creating a response.

5. MECHANISM OF SIGNAL
TRANSDUCTION IN PLANTS
• The trigger for each signal transduction system is different but the general features are
common to all.
• A signal interacts with a receptor  the activated receptor interacts with the cellular
machinery, producing a second signal or changing the activity of cellular protein  the
metabolic activity of the cell under goes a change and finally the transduction ends.
• Proteins responsible for detecting stimuli are generally termed as receptors.
• The ligand is signaling molecules that binds to receptors is known as primary messenger
and secondary messengers are produced within the target cell.
• Second messengers relay the signal from one location to another (such as from plasma
membrane to nucleus) leading to cascade of events/changes within a cell.

7. COMPONENTS OF SINGLE TRANSDUCTION
I. Stimulus: Physical environment.
II. Receptor: On the plasma membrane, or internal
III. Secondary messengers: Ca2+, G-proteins, Inositol Phosphate
IV. Effector molecules: Protein kinases or phosphatases, Transcription factors
V. Response: Germination, leaf formation, flowering, tolerance

8. 1. Reception 2. Transduction 3. Response
A GENERAL MODEL FOR SIGNAL
TRANSDUCTION PATHWAYS
Cell
Wall
Environmental
stimulus
Plasma
membrane
Receptor
Cytoplasm
Activation of
cellular
responses
Relay proteins and
second messengers
1. Reception 2. Transduction 3. Response
Cell
Wall
Environmental
stimulus
Plasma
membrane
Receptor
Cytoplasm
Activation of
cellular
responses
Relay proteins and
second messengers

9. SIGNALS FROM THE ENVIRONMENT
• Numerous environmental factors influence plant development. Temperature, light, touch, water, and gravity
are among the stimuli that serve as signals for the activation of endogenous developmental programs.
RECEPTORS
• To initiate transduction, a signal must first be sensed by a receptor. Most known receptors are present
in the plasma membrane, although some are located in the cytosol or other cellular compartments.
• Receptors can be roughly divided into two major classes: intracellular receptors and extracellular
receptors.
EXTRACELLULAR RECEPTORS
• Extracellular receptors are integral transmembrane proteins and make up most receptors. They span
the plasma membrane of the cell, with one part of the receptor on the outside of the cell and the other
on the inside.
• Signal transduction occurs as a result of a ligand binding to the outside region of the receptor (the
ligand does not pass through the membrane).

10. AN OVERVIEW OF MAJOR
SIGNALLING PATHWAYS BY
WHICH EXTRACELLULAR
MESSENGER MOLECULE
CAN ELICIT
INTRACELLULAR
RESPONSES

11. VARIOUS EXTRACELLULAR RECEPTORS
• G protein-coupled receptors.
• Receptors with Kinase activity
• Integrin receptors.
• Toll gate receptors.
• Ligand-gated ion channel receptors.
G PROTEIN–COUPLED RECEPTORS (GPCRS)
• Also known as seven-transmembrane domain receptors, heptahelical receptors, and G
protein–linked receptors (GPLR) because they pass through the cell membrane seven
times..
• These constitute a large protein family of receptors that sense molecules outside the
cell and activate inside signal transduction pathways and, ultimately, cellular responses.

12. THE MEMBRANE-BOUND MACHINERY FOR TRANSDUCING
SIGNALS BY MEANS OF A SEVEN TRANSMEMBRANE
RECEPTOR AND A HETEROTRIMERIC G PROTEIN
Intracellular second
messengers

13. • G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that
act as molecular switches inside cells, and are involved in transmitting signals from a variety of
stimuli outside a cell to its interior.
• When they are bound to GTP
, they are 'on', and, when they are bound to GDP
, they are 'off'.
• G proteins belong to the larger group of enzymes called GTPases.
Two classes of G proteins
• The first function as monomeric small GTPases.
• The second form and function as heterotrimeric G protein complexes.
• Heterotrimeric class of complexes is made up of alpha (α), beta (β) and gamma (γ) subunits.
The beta and gamma subunits can form a stable dimeric complex referred to as the beta-
gamma complex while alpha subunit dissociates on activation.

14. • There are two principal signal transduction pathways involving the G protein–coupled receptors:
A. Cyclic adenosine monophosphate (cAMP) signal pathway
B. Phosphatidylinositol signal pathway.
A. Cyclic adenosine monophosphate (cAMP)-DEPENDENT PATHWAY
• It is also known as the adenylyl cyclase pathway.
• In a cAMP-dependent pathway, the activated Gs alpha subunit binds to and activates an enzyme called adenylyl
cyclase, which, in turn, catalyzes the conversion of ATP into cyclic adenosine monophosphate (cAMP).
MECHANISM
• It is known that in the inactive state, the GPCR is bound to a heterotrimeric G protein complex.
• Binding of primary messenger to the GPCR results in a conformation change in the receptor that is transmitted to the
bound Gα subunit of the heterotrimeric G protein.
• The activated Gα subunit exchanges GTP in place of GDP which in turn triggers the dissociation of Gα subunit from
the Gβγ dimer and from the receptor.
• The dissociated Gα and Gβγ subunits interact with other intracellular proteins to continue the signal transduction
cascade.
• While the freed GPCR is able to rebind to another heterotrimeric G protein to form a new complex that is ready to
initiate another round of signal transduction.

15. THE MECHANISM OF RECEPTOR-MEDIATED
ACTIVATION (OR
INHIBITION) OF EFFECTORS BY MEANS OF
HETEROTRIMERIC G PROTEINS.

16. B. PHOSPHATIDYLINOSITOL SIGNAL
PATHWAY
• In the phosphatidylinositol signal
pathway, the extracellular signal
molecule binds with the G-protein
receptor (Gq) on the cell surface and
activates secondary messenger
phospholipase C, which hydrolyzes
PIP2.
• IP3 binds with the IP3 receptor in
the membrane of the smooth
endoplasmic reticulum and
mitochondria to open Ca2+
channels.
• DAG helps activate protein kinase C
(PKC), which phosphorylates many
other proteins, changing their
catalytic activities, leading to cellular
responses.
PIP2 (phosphatidylinositol
4, 5 bisphosphate)
IP3 (inositol 1, 4, 5,
trisphosphate)
DAG (diacylglycerol)
phospholipase C

17. DURING SIGNAL TRANSDUCTION, CALCIUM CAN
BE RELEASED INTO THE CYTOPLASM: PERCEPTION

18. • The effects of Ca2+ are also remarkable.
• It cooperates with DAG in activating PKC and can activate the calmodulin (CaM) kinase pathway, in which
calcium-modulated protein calmodulin (CaM) binds Ca2+, undergoes a change in conformation, and
activates CaM kinase.
• The kinase then phosphorylates target enzymes, regulating their activities. The two signal pathways are
connected together by Ca2+-CaM, which is also a regulatory subunit of adenylyl cyclase and
phosphodiesterase in the cAMP signal pathway.
• A wide variety of cellular effects have been linked to the activation of protein kinase C, including the
stimulation of cell growth, the regulation of ion channels, changes in the cytoskeleton, increases in
cellular pH, and effects on secretion of proteins and other substances.

19. RECEPTORS WITH KINASE ACTIVITY
• It is a large family of plasma membrane receptors with intrinsic protein kinase activity.
• Receptor tyrosine kinase have a ligand binding domain on the extra cellular face of the
plasma membrane and an enzyme active site on the cytoplasmic phase.
• Receptor tyrosine kinases transmit signals across the plasma membrane, from the cell
exterior to the cytoplasm.
• The interaction of the external domain of a receptor tyrosine kinase with the ligand, often a
growth factor, up-regulates the enzymatic activity of the intracellular catalytic domain, which
causes tyrosine phosphorylation of cytoplasmic signalling molecules.

20.  INTRACELLULAR RECEPTORS
• Intracellular receptors are receptors located inside the cell rather than on its cell membrane.
Examples:
Class of nuclear receptors located in the cell nucleus and cytoplasm
IP3 receptor located on the endoplasmic reticulum.

21. THANK
YOU