Kinetics of delayed chlorophyll a fluorescence registered in milliseconds time range

Abstract

Delayed fluorescence dark decays in the time interval from 0.35 to 5.5 ms are measured during dark to light adaptation in whole barley leaves and isolated thylakoid membranes, using a disc phosphoroscope. The changes in delayed fluorescence features are compared with variable chlorophyll fluorescence simultaneously registered with the same apparatus as well as in parallel by Handy PEA (Hansatech Instruments Ltd.), and absorbance changes at 820 nm. The registered delayed fluorescence signal is a sum of three components - submillisecond with lifetime of about 0.6 ms, millisecond decayed 2-4 ms and slow component with lifetime > >5.5 ms. The submillisecond delayed fluorescence component is proposed to be a result of radiative charge recombination in Photosystem II reaction centers in the state Z+PQA -QB -, and its lifetime is determined by the rate of electron transfer from QA - to QB -. The millisecond delayed fluorescence component is associated with recombination in Z+PQA -QB = centers with a lifetime determined by the sum of the rate constants of electron transfer from the oxygen-evolving complex to Z+ and of the exchange between the reduced and oxidized plastoquinone pool in the QB-site. On the basis of these assumptions and of the different share of the three components in the integral delayed fluorescence during induction, an attempt has been made to interpret the changes in the delayed fluorescence intensity during the transition of the photosynthetic apparatus from dark to light adapted state.

Correlations between delayed fluorescence of chlorophyll, metabolism and yield of plants. II. Influence of moisture of leaf and temperature condition on delayed fluorescence of leaves

“…It was previously assumed that the time course of DF after the maximum (Figure 1) is possibly influenced by a number of dark photosynthetic processes (directly or indirectly modifying the characteristics of PSII) [13,14]. The decay of induction curve was generally explained by a decrease in the membrane energization as a result of secondary cation efflux from thylakoids [13,14]. Our results showed that half time of I decay-τ describe the level of interaction LR with dark processes of plants [10].…”

“…The incubation of detached leaves at 36℃ with further more notable moisture loss resulted in I decline as opposed to variants with other thermal treatment ( Tables 1-3, r IM(T) at incubation of 400 min). I depends on the size of ECP on a membrane [11,13,14] donor availability [11][12][13], as well as possible concentration of active PS II [10]. Our results have shown that half time of I decay-τ describe the level of interaction LR with dark processes of plants [10].…”

“…DF transients have been shown to be driven by many mechanisms, including electrical and pH gradients [11], acceptor availability, donor availability [12], and redox state of the oxygen-evolving system [13,14]. The delayed fluorescence induction curve, registered in a several minutes time period, encompasses two major phases-a fast one, taking place in the first second of induction, and a slow one, that can last for minutes (Figure 1).…”

“…The delayed fluorescence induction curve, registered in a several minutes time period, encompasses two major phases-a fast one, taking place in the first second of induction, and a slow one, that can last for minutes (Figure 1). Each phase is shaped by several processes running at the same time [13,14]. Those initial phases of the induction which many authors attribute to the changes of the electrical potential, depending on the size of ECP on a membrane on the state of the PSII reaction center, since the light induced potential difference and the proton gradient across the thylakoid membrane are thought to reduce the amount of activation energy necessary for the back reaction between QA -and Z + to occur and on the other hand, the I level follows the extent of the variable component of fluorescence and has been suggested to be proportional to the amount of oxidized QA at the beginning of illumination [11,13,14], as well as the concentration of active centers of the PSII [11].…”

“…Each phase is shaped by several processes running at the same time [13,14]. Those initial phases of the induction which many authors attribute to the changes of the electrical potential, depending on the size of ECP on a membrane on the state of the PSII reaction center, since the light induced potential difference and the proton gradient across the thylakoid membrane are thought to reduce the amount of activation energy necessary for the back reaction between QA -and Z + to occur and on the other hand, the I level follows the extent of the variable component of fluorescence and has been suggested to be proportional to the amount of oxidized QA at the beginning of illumination [11,13,14], as well as the concentration of active centers of the PSII [11]. It was previously assumed that the time course of DF after the maximum (Figure 1) is possibly influenced by a number of dark photosynthetic processes (directly or indirectly modifying the characteristics of PSII) [13,14].…”