Chlorophyll flourescence

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 6CO 2 + 12 H 2 O C 6 H 12 O 6 + 6H 2 O 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 (P 700 )- stromal lamellae PSII (P 680 )- 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 Derive the electron transport to carry out the redox chemical reaction - production ATP and NADPH- Photochemistry Excess of energy is lost as heat----- Thermal deactivation / nonradiative decay 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 P 680 to Q A ). 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 P 680 Q A P 680 * Q A P 680 + Q A P 680 + Q A - e- Open centre Closed center PSII reaction centers- open state- capable of photochemistry since Q A -primary quinone acceptor of PSII is maximally oxidized . PSII – closed state- Q A 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 Q A . Fq’/Fm’ PSII operating efficiency Estimates the efficiency at which light absorbed by PSII is used for Q A reduction. This parameter has previously been termed ∆ F’ / Fm’ and φ PSII 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’ (Q A 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’ (Q A 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 F v /F m = F m -F /F m ……….. F increase due to photoinactivation of PSII F m 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 F q /F m ) Rate of electron transport J= I. A. fractionPSII . F q /F m 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 CO 2 assimilation – Linear relationship between F q /F m and rates of CO 2 assimilation under controlled environment conditions In C 3 plants – this close correlation can be observed best when photorespiration is inhibited by lowering O 2 level at 2%. But the relationship in C 4 plants is much more easily achieved due to the suppression of photorespiration by CO 2 concentrating mechanism Role of chlorophyll fluorescence in crop improvement

17. Thanks