Ondrej Flashcards
Cuteness overload
What is the processes under fluorescence excitation?
- Photon capture (absorption) raises electron from the ground state (S0) to the S1level (a) or the S2level in one or two steps (band c).
- S2decays rapidly to S1and excess energy is released as heat (band c).
- In vivo, the excitation energy can migrate between the S1levels of adjacent Chlamolecules (d) (via resonance transfer not involving electron transfer). Migration to a reaction centreis the first step in photosynthesis.
- When this is not possible, the energy decays to the ground state, releasing fluorescence (e).
What is photochemistry?
provides chemical energy in the form of ATP and NADPH for CO2fixation in the Calvin-Benson cycle. Photosystem II (PSII) extracts electrons from water releasing O2in the process .Efficiency 60-85% of the absorbed excitation energy
What are non-photochemical processes?
mainly dissipation of energy as heat (10-40% of absorbed energy).
What is fluorescence?
re-release of energy as light (a very small percentage 1-5% of excitation energy); because some energy of the excitation light is lost in this process, the fluorescent light has a longer wavelength (it is red).
What is the relationship between photosynthesis and chl fluorescence?
Inverse relation between the rate of photosynthesis and chl fluorescence yield
What will be the color of the fluorescence of an electron is excited to S2 level?
Blue
What will be the color of the fluorescence of an electron is excited to S1 level?
Red
What processes happen when there is fluorescence excitation with carotenoids?
- Photon absorption by a carotenoid raises an electron to the S2level
- The electron rapidly returns to the S1level. This is symmetry-forbidden and there is no corresponding absorbance band.
- Carotenoids with an S1level higher than that of Chla(PSC) can transfer energy to Chla(c).
- Carotenoids with an S1level lower than that of Chla(PPC) cannot transfer energy to Chla but can accept energy (d). This energy is then lost with decay to the S0state as heat.
Note heat is infrared radiation (IR), which has a longer wavelength than Chla fluorescence.
What are the practical use of fluorescence in aquatic environment?
- In vivofluorescence detectors for the estimation of phytoplankton biomass
- Flow cytometry
- Spectrofluorometry
- Variable fluorescence
- Sun-Induced Chlorophyll Fluorescence
What effect has light on fluorescence?
Fluorescence is quenched (declines) in high light, so that light intensity and fluorescence intensity are inversely related.
Why does fluorescence decline with increasing irradiance?
Extended periods of high light activate non-photochemical fluorescence quenching due to photoprotectivemechanisms that avoid adverse effect of excess light. Processes that cause non-photochemical quenching (NPQ)are
•
Dissipation of access energy by photoprotectivepigments (xanthophylls) as heat
•
State transitions (shifts from the antenna systems from PSII to PSI so that e-are drawn out of the electron transfer chain
•
Photoinhibition(damage and regeneration of the PSII-D1 protein).
How do you measure chla fluorescence in extracts?
A light emitting diode (LED) emits blue excitation (485nm) light; a photodiode array detects the of emission of red (685nm) Chlafluorescence.
After careful calibration, this will also give you a Chla concentration
What is the effect of nutrient on fluorescence?
Increasing nutrient stress canlead to an increase in the fluorescence yield because photochemical quenching of excitation energy declines
WHAT IS PHYTOPLANKTON FLUORESCENCE USED FOR IN FLOW CYTOMETRY? (sorry for Caps lock)
Distinguish phytoplankton from bacteria and other particles, on a cell basis
Distinguish phycobilin-containing phytoplankton from other chl-containing cells
What happen when dark-adapted photosynthesising cells are illuminated with continuous light?
the induced chlorophyll fluorescence displays characteristic changes in intensity accompanying the induction of photosynthetic activity
- Fluorescence is minimal in dark-acclimated cells, F0. All reaction centers are open.
- When these cells are illuminated with continuous (actinic) light, photosynthesis is induced and fluorescence rises to an intermediate level, F.
- When all the reaction centers are closed, fluorescence is maximal, Fm.
- The difference between Fm and F0 is variable fluorescence, Fv.
- Some fluorometers measure F0, Fm and Fv. Most simple fluorometers induce some photosynthesis and measure something between F0and Fm.
What is a single turnover fluorescence induction?
In the dark (RC are open), QAis oxidized and strongly quenches fluorescence.
When a dark-acclimated sample is exposed to a high-energy flash of light that causes a single reduction of all the QA acceptors, fluorescence rises from F0 to Fm.
requires a short flash (fraction of 1 ms).
What is a multiple turnover fluorescence induction?
When a dark-acclimated sample is exposed to a longer (50-1000 ms), high-energy flash of light, fluorescence rises even higher (to Fm(MT)because the QA acceptors are reduced multiple times.
What can the maximum photosynthetic efficiency used for?
Maximum photosynthetic efficiency (Fv/Fm or ΔΦm) can be used as a diagnostic for nutrient and light stress.
What is F?
F steady-state fluorescence in the light (sometimes also referred to F’)
What is Fm’(ST/MT)?
maximum fluorescence in the light acclimated state
What is F0’(ST/MT?
minimal fluorescence in the light acclimated state (can be difficult to measure).
what are the 5 fluorescence levels?
*Fo–intrinsic level in dark
*Fm-maximal level in dark
*F (Ft) –momentary level in light
*Fm’ –maximal level in light
*Fo’ –minimal level in light acclimated sample. Can be measured using FR light or calculated:
Fo’ = 1/ (1/Fo+1/Fm+ 1/Fm’)
What is the maximal photochemical yield of photosystem II?
- Fv/Fm= (Fm–Fo)/Fm
- Values 0-0.85
- Gives the maximum fraction of photons absorbed by PSII that can be used for photochemistry in PSII
- Reference state for NPQ…
What is the effective quantum yield of photosysteme II?
-Y(II) = ΦPSII= (Fm’ –Ft)/Fm’
-Values 0-0.85, Y(II) < Fv/Fm
-Gives the fraction of photons absorbed by PSII that canbeused for photochemistry in PSII when exposed to given light conditions
-Changes with irradiance
and level of stress.
What is the coefficient for photochemical quenching in PSII?
- qp= (Fm’ –Ft)/(Fm’–Fo’)
- Does not require dark measurements(Fo, Fm)
- Values 0-1
- Estimates the fraction of open reaction centers of PSII
What is the coefficient for non-photochemical quenching in PSII?
- qN = 1 -(Fm’ –Ft)/(Fm’–Fo’)
- Values 0-1
- Tells the fraction of photons absorbed by PSII that are dissipated as heat
What is the Stern-volmer type non-photochemical quenhing NPQ?
- NPQ = (Fm’/Fm) -1
- Values 0-∞
- Proportional to heat dissipation
How do you calculate de losses of absorbed energy by heat and fluorescence?
-Y(NO) = 1/(Fm/Fm’ + (Fm’ –Ft)/(Fm’–Fo’)x ((Fm/Fo)-1))
-Y(NO) = 1/(NPQ +1 + qpx Fv/Fo)
-Y(NO) = F/Fm
-Values 0-1
-Tells the fraction of photons
absorbed by PSII that are dissipated as heat in the dark,
“non-regulatory” quenching
What is the quantum yield of light induced non-photochemical quenching?
- Y(NPQ) = 1 –Y(NO) –Y(II)
- Y(NPQ) = F/Fm’ –F/Fm
- Values 0-1
- Tells the fraction of photons absorbed by PSII that are dissipated as heat due to response to stress (regulatory quenching)
How do you calculate de relative electron transport rate through PSII?
-ETR = PAR · ETR-Factor · PS2/PS1 · Y(II)
-Values 0-∞
-PAR = incident light intensity
-ETR-factor: how much PAR is
absorbed by sample
- PPS2/PPS1: ratio of PS2/PS1
RELATIVE ELECTRON TRANSPORT RATE THROUGH PSII
