Redox changes of ferredoxin, P700, and plastocyanin measured simultaneously in intact leaves

Ulrich Schreiber

doi:10.1007/s11120-017-0394-7

Abstract

Properties and performance of the recently introduced Dual/KLAS-NIR spectrophotometer for simultaneous measurements of ferredoxin (Fd), P700, and plastocyanin (PC) redox changes, together with whole leaf chlorophyll a (Chl) fluorescence (emission >760, 540 nm excitation) are outlined. Spectral information on in vivo Fd, P700, and PC in the near-infrared region (NIR, 780–1000 nm) is presented, on which the new approach is based. Examples of application focus on dark–light and light–dark transitions, where maximal redox changes of Fd occur. After dark-adaptation, Fd reduction induced by moderate light parallels the Kautsky effect of Chl fluorescence induction. Both signals are affected analogously by removal of O2. A rapid type of Fd reoxidation, observed after a short pulse of light before light activation of linear electron transport (LET), is more pronounced in C4 compared to C3 leaves and interpreted to reflect cyclic PS I (CET). Light activation of LET, as assessed via the rate of Fd reoxidation after short light pulses, occurs at very low intensities and is slowly reversed (half-time ca. 20 min). Illumination with strong far-red light (FR, 740 nm) reveals two fractions of PS I, PS I (LET), and PS I (CET), differing in the rates of Fd reoxidation upon FR-off and the apparent equilibrium constants between P700 and PC. Parallel information on oxidation of Fd and reduction of P700 plus PC proves essential for identification of CET. Comparison of maize (C4) with sunflower and ivy (C3) responses leads to the conclusion that segregation of two types of PS I may not only exist in C4 (mesophyll and bundle sheath cells), but also in C3 photosynthesis (grana margins plus end membranes and stroma lamellae).

Highlights

Ferredoxin (Fd) is located at the ‘end of the line’ of the photosynthetic light reactions (Goss and Hanke 2014), playing a pivotal role as distributor of electrons originating from the splitting of water in photosystem II (PS II) between several metabolic pathways at the acceptor side of photosystem I (PS I)
Within the PS I core complex charge separation is stabilized via a cascade of rapid electron transfer reactions in the ps to ns time range from P700 via A0 and A1 to the [4Fe–4S] centers Fx, FA, and FB, with the latter corresponding to P430 of Hiyama and Ke (1971). FB is the distal stromal FeS cluster that transfers electrons to Fd, a small soluble [2Fe–2S] cluster (Vassiliev et al 1998; Diaz-Quintana et al 1998)
The Dual/KLAS-NIR spectrophotometer is the most recent member of a family of pulse-amplitude-modulated (PAM) devices, development of which was initiated more than 30 years ago, first for measuring chlorophyll a (Chl) fluorescence (Schreiber 1986; Schreiber et al 1986), 830 nm absorbance changes for assessment of P700 (Schreiber et al 1988), and absorbance changes in the green spectral region for differentiation of cytochrome redox changes from the much larger overlapping changes caused by P515, ‘light scattering,’ and zeaxanthin (Klughammer et al 1990)

Summary

Introduction

Ferredoxin (Fd) is located at the ‘end of the line’ of the photosynthetic light reactions (Goss and Hanke 2014), playing a pivotal role as distributor of electrons originating from the splitting of water in photosystem II (PS II) between several metabolic pathways at the acceptor side of photosystem I (PS I). Besides binding close to FB to the PS I complex, soluble Fd can bind to various stromal enzymes, channeling the electrons received via PS I charge separation into various metabolic pathways. These include the ferredoxin–NADP reductase (FNR) catalyzed reduction of NADP (Shin et al 1963; Carillo and Ceccarelli 2003), reduction of O 2 and H2O2 in the Mehler-ascorbate-peroxidase (MAP) cycle (Asada and Badger 1984; Schreiber et al 1995; Asada 1999; Miyake 2010), nitrite reduction (Anderson and Done 1978), various types of cyclic electron transport (CET) (Arnon and Chain 1975; Bendall and Manasse 1995; Miyake et al 1995; Munekage et al 2002; Joliot and Joliot 2006; Shikanai 2007; Laisk et al 2010), and reduction of thioredoxin, the key redox regulator of numerous processes at various levels of chloroplast metabolism (Buchanan 1980; Knaff 1996; Buchanan et al 2002)

Methods

Results

Conclusion