Maximum fluorescence and electron transport kinetics determined by light-induced fluorescence transients (LIFT) for photosynthesis phenotyping

Beat Keller,Shizue Matsubara,Christoph Jedmowski,Imre Vass,Onno Muller,Ladislav Nedbal,Uwe Rascher,Roland Pieruschka,Kenny Paul

doi:10.1007/s11120-018-0594-9

Abstract

Photosynthetic phenotyping requires quick characterization of dynamic traits when measuring large plant numbers in a fluctuating environment. Here, we evaluated the light-induced fluorescence transient (LIFT) method for its capacity to yield rapidly fluorometric parameters from 0.6 m distance. The close approximation of LIFT to conventional chlorophyll fluorescence (ChlF) parameters is shown under controlled conditions in spinach leaves and isolated thylakoids when electron transport was impaired by anoxic conditions or chemical inhibitors. The ChlF rise from minimum fluorescence (Fo) to maximum fluorescence induced by fast repetition rate (Fm−FRR) flashes was dominated by reduction of the primary electron acceptor in photosystem II (QA). The subsequent reoxidation of QA− was quantified using the relaxation of ChlF in 0.65 ms (Fr1) and 120 ms (Fr2) phases. Reoxidation efficiency of QA− (Fr1/Fv, where Fv = Fm−FRR − Fo) decreased when electron transport was impaired, while quantum efficiency of photosystem II (Fv/Fm) showed often no significant effect. ChlF relaxations of the LIFT were similar to an independent other method. Under increasing light intensities, Fr2′/Fq′ (where Fr2′ and Fq′ represent Fr2 and Fv in the light-adapted state, respectively) was hardly affected, whereas the operating efficiency of photosystem II (Fq′/Fm′) decreased due to non-photochemical quenching. Fm−FRR was significantly lower than the ChlF maximum induced by multiple turnover (Fm−MT) flashes. However, the resulting Fv/Fm and Fq′/Fm′ from both flashes were highly correlated. The LIFT method complements Fv/Fm with information about efficiency of electron transport. Measurements in situ and from a distance facilitate application in high-throughput and automated phenotyping.

Highlights

Photosynthetic processes, from light absorption by the chlorophyll-based pigments through charge separation in the photosystem II (PSII) reaction centers and sequential electron transport, are related to the redox state of the primary quinone electron acceptor (QA) and coupled to the signature of chlorophyll fluorescence (ChlF) (Kautsky and Hirsch 1931; Baker 2008; Müh et al 2012)
Based on ChlF, parameters such as the maximum quantum efficiency of PSII (Fv/Fm) and non-photochemical quenching (NPQ) estimating the proportion of absorbed light energy utilized for PSII photochemistry and non-photochemical energy dissipation, respectively, were established (Butler 1978; Baker 2008; Lazár 2013)
Photosynthetic characteristics were studied by measuring light-induced ChlF transients using both the modulated light-induced fluorescence transient (LIFT) and the double-modulated FL3000 device with an emphasis on the properties of electron transport from PSII towards Photosystem I (PSI)

Summary

Introduction

Photosynthetic processes, from light absorption by the chlorophyll-based pigments through charge separation in the photosystem II (PSII) reaction centers and sequential electron transport, are related to the redox state of the primary quinone electron acceptor (QA) and coupled to the signature of chlorophyll fluorescence (ChlF) (Kautsky and Hirsch 1931; Baker 2008; Müh et al 2012). A saturating STF has to provide high enough excitation power to induce one single charge separation in all PSII reaction centers and fully reduce QA in order to yield maximum ChlF level (Fm−ST) (Malkin and Kok 1966; Schreiber 1986a; Samson and Bruce 1996; Kolber et al 1998; Steffen et al 2001). A saturating MTF requires at least 0.2-s duration of excitation at a few 1000 μmol photons m−2 s−1 (Ögren and Baker 1985; Schreiber et al 1986b; Schreiber 2004) Within this time range, QA is reduced and reoxidized several times followed by reduction of the plastoquinone (PQ) pool and electron transfer to Photosystem I (PSI) (Vernotte et al 1979; Schansker et al 2005). The origin of the thermal phase is not yet localized due to the complex and overlying kinetics of different electron transport processes (Rascher and Nedbal 2006; Müh et al 2012) and the probable involvement of additional ChlF quenchers (Schansker et al 2011, 2014; Prášil et al 2018; Magyar et al 2018)

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Conclusion