Effects of hydroxylamine and silicomolybdate on the decay in delayed light emission in the 6?100 ?s range after a single 10 ns flash in pea thylakoids

Abstract

Measurements are reported on μs delayed light emission, following a single 10 ns excitation flash, in Alaska pea thylakoids treated with hydroxylamine (NH2OH) or with silicomolybdate. 1. In thylakoids treated with 2 mM NH2OH in the light, or in the dark, the quantum yield of delayed light emission is considerably enhanced. A 10 μs lifetime component of delayed light emission is not significantly changed, whereas a 50-70 μs lifetime component is increased. MnCl2 and diphenylcarbazide are unable to reverse the above effects of NH2OH treatment. Thus Mn(2+) and diphenylcarbazide must not donate electrons directly to reaction center II but on the oxygen-evolution side of the NH2OH block. 2. When the closed form of photosystem II reaction centers (P680Q(-)), where P680 is the reaction center chlorophyll and Q is a 'stable' electron acceptor, is generated by preillumination of NH2OH-treated thylakoids with diuron present, the μs delayed light emission is inhibited, but a low level residual delayed light emission remains. Possible origins of this emission are discussed. It is believed that the best explanation for residual DLE is the existence of another acceptor besides Q that partakes in charge separation and rapid dissipative recombination when the reaction center is in the P680Q(-) state. 3. The quantum yield of delayed light emission from 'closed' reaction centers (P680 (+)Q(-)) that have all charge stabilization reactions (i.e., flow of electrons to P680 (+) and out of Q(-)) blocked by NH2OH treatment and addition of diuron is 1.1×10(-3) for components measured in a range from 6 to 400 μs and extrapolated to zero time. 4. The addition of silicomolybdate, which accepts electron from Q(-), causes delayed light emission in the μs range to be greatly inhibited.

Frequently asked questions about chlorophyll fluorescence, the sequel

“…Half-times for the recombination between Q A − and P680 + determined for samples with a destroyed donor side (Tris-washed) give a half-time of about 120–130 µs (Conjeaud and Mathis 1980; de Wijn and van Gorkom 2002). This type of fluorescence emission is called delayed fluorescence (DF) (e.g., Wraight and Crofts 1971; Goltsev et al 2009) or delayed light emission (DLE) (e.g., Arnold and Thompson 1956; Srivastava et al 1999) and is much weaker (about 100-fold) than PF (Jursinic and Govindjee 1982; Arnold 1991). In summary, the lifetime of different DF components is determined by the lifetime of the corresponding PSII state (charge pair).…”

Temperature Effects on Pea Plants Probed by Simultaneous Measurements of the Kinetics of Prompt Fluorescence, Delayed Fluorescence and Modulated 820 nm Reflection

“…It was followed by a middle, sub ms component, that was characterized by L 2  = 86.0±1.9 and τ 2  = 300.9±23.4 µs. The possible origin of the fast DF component is charge recombination in the PSII reaction center in state ZP680 + Q A – [32], [40]. This DF is considered to be a leakage type luminescence decay; it is a result of separated charge stabilization by re-reduction of P 680 + by Yz.…”

Delayed fluorescence in photosynthesis

“…When Q A is reduced, three light emission components are observed, with lifetimes of 1 ls (Van Best and Duysens 1977), 5-10 ls, and 35-40 ls (Jursinic and Govindjee 1982); these are suggested to arise as a result of charge recombination in the ZP 680…”

“…PheoQ A -state (Sonneveld ? Pheo -] S states (Jursinic and Govindjee 1982;Jursinic 1986). However, triplet exciton model for DF has not been supported (Stacy et al 1971).…”