Role of chlorophyll fluorescence in crop improvement

1. By: Neha Gupta
Chlorophyll fluorescence and its role in
crop improvement

2. Objective
To utilize the information on fluorescence parameters
for understanding PSII photochemistry

3. Outlines
 Photosynthesis- light reaction and photosystems
 Chlorophyll fluorescence
 Measurement of Chl fluorescence
 Role in crop improvement

4. Photosynthesis
6CO2+ 12 H2O C6H12O6+ 6H2O
Chlorophyll
sunlight
Two reactions of photosynthesis: Light reaction
Carbon assimilation reaction
(Dark rxn)

5. Photosystems- light reaction
•Photosynthetic pigments absorb the light that
powers photosynthesis
• Two photosystems: PSI (P700)- stromal lamellae
PSII (P680)- granal lamellae
• No strict one to one stoichiometery between the
two PSs (PSII to PSI is about 1.5:1)
• PS: Complex containing light harvesting/antenna
complex and photochemical reaction centers.
• Reaction center consist of protein complex with a
specialized chlorophyll capable of electron transfer
to acceptor molecule

6. Photosystems- light reaction

7. Chlorophyll fluorescence
The light energy absorbed by chlorophyll molecule can have three fates
1) Derive the electron transport to carry out the redox chemical
reaction - production ATP and NADPH- Photochemistry
2) Excess of energy is lost as heat-----Thermal deactivation /nonradiative
decay
3) Some portion of the absorbed energy is reemitted as radiation of
longer wavelength -----Fluorescence
These three processes do not act in isolation, rather compete with each other

8. Quenching of fluorescence signals
Photochemical quenching- Electronic excitations of Chl is utilized in
production of ATP and NADPH (electron transport from P680 to QA ).
Non photochemical quenching (NPQ): Excitation energy of reaction
center chlorophyll is lost as heat.
Regulation of NPQ: Acidification of thylakoid lumen
Activation of violaxanthin depoxidase
Retention of zeaxanthin

9. Z-scheme of photo-phosphorylation

10. Mechanism of quenching of excitation energy by
NPQ

11. Open and closed reaction centers
Excitation
from LHCII
P680 QA
P680* QA
P680
+ QA
P680
+ QA
-
e-
Open centre
Closed center
 PSII reaction centers- open state- capable of photochemistry since QA
-primary quinone acceptor of PSII is maximally oxidized.
 PSII – closed state- QA is maximally reduced
 Kautsky effect- A sudden rise in chl fluorescence for few seconds when a
dark adapted leaf is exposed to light condition which later on declines and
reaches to steady state.

12. Measurement of chlorophyll fluorescence
Chlorophyll fluorometers- Instrument that helps in measuring chlorophyll
fluorescence
Kautsky fluorometers – Measure fv/fm but are not capable of estimating
quenching coefficients.
Use of DCMU in fluorescence studies to separate components of
photochemical and non photochemical quenching.
Advanced Pulse Amplitude Mediated fluorometers- light doubling
technique.
Fluorescence measurements: Dark adapted state
light adapted state

13. Fluorescence quenching analysis using modulated fluorometer

14. Commonly used fluorescence parameters
Parameter Definition Physiological relevance
Fv/Fm
Maximum quantum efficiency
of PSII photochemistry
Maximum efficiency at which light absorbed by
PSII is used for reduction of QA.
Fq’/Fm’ PSII operating efficiency
Estimates the efficiency at which light absorbed
by PSII is used for QA reduction. This
parameter has previously been termed ∆F’/Fm’
and φPSII in the literature.
Fv’/Fm’ PSII maximum efficiency
Provides an estimate of the maximum efficiency
of PSII photochemistry at a given PPFD, which
is the PSII operating efficiency if all the PSII
centers were ‘open’ (QA oxidized).
Fq’/Fv’ PSII efficiency factor
Relates the PSII maximum efficiency to the
PSII operating efficiency. Nonlinearly related to
the proportion of PSII centers that are ‘open’
(QA oxidized). Mathematically identical to the
coefficient of photochemical quenching, qP.
NPQ Nonphotochemical quenching
Estimates the nonphotochemical quenching
from Fm to Fm’. Monitors the apparent rate
constant for heat loss from PSII. Calculated
from (Fm/Fm’) -1)

15. Role of chlorophyll fluorescence in crop improvement
Points to be considered
Whether to dark adapt or not
Intensity of measuring beam and saturating pulse
Optical property of leaf
Use of weak far red light and contribution of PSI to fluorescence
Stress studies: Selection for stress tolerance
Non stressed healthy leaf exhibit fv/fm =0.83. When plants are exposed
to biotic/abiotic stress, decline in fv/fm are frequently observed
in Fv/Fm = Fm-F0/Fm ……….. F0 increase due to photoinactivation of PSII
Fm decrease due to increase in NPQ

16. • Determination of linear electron flux
Fluorescence can be used to measure efficiency of PSII
photochemistry (PSII operating efficiency Fq/Fm)
Rate of electron transport J= I. A. fractionPSII. Fq/Fm
I is the intensity of actinic light, A is proportion of light absorbed by leaf (0.84),
fraction PSII for leaves is frequently assumed to be 0.5.
• Relationship to CO2 assimilation –
Linear relationship between Fq/Fm and rates of CO2 assimilation
under controlled environment conditions
In C3 plants – this close correlation can be observed best when
photorespiration is inhibited by lowering O2 level at 2%. But the
relationship in C4 plants is much more easily achieved due to the
suppression of photorespiration by CO2 concentrating mechanism
Role of chlorophyll fluorescence in crop improvement

17. Thanks