Methylviologen and dibromothymoquinone treatments of pea leaves reveal the role of photosystem I in the Chl a fluorescence rise OJIP

Abstract

The effects of dibromothymoquinone (DBMIB) and methylviologen (MV) on the Chl a fluorescence induction transient (OJIP) were studied in vivo. Simultaneously measured 820-nm transmission kinetics were used to monitor electron flow through photosystem I (PSI). DBMIB inhibits the reoxidation of plastoquinol by binding to the cytochrome b(6)/f complex. MV accepts electrons from the FeS clusters of PSI and it allows electrons to bypass the block that is transiently imposed by ferredoxin-NADP(+)-reductase (FNR) (inactive in dark-adapted leaves). We show that the IP phase of the OJIP transient disappears in the presence of DBMIB without affecting F(m). MV suppresses the IP phase by lowering the P level compared to untreated leaves. These observations indicate that PSI activity plays an important role in the kinetics of the OJIP transient. Two requirements for the IP phase are electron transfer beyond the cytochrome b(6)/f complex (blocked by DBMIB) and a transient block at the acceptor side of PSI (bypassed by MV). It is also observed that in leaves, just like in thylakoid membranes, DBMIB can bypass its own block at the cytochrome b(6)/f complex and donate electrons directly to PC(+) and P700(+) with a donation time tau of 4.3 s. Further, alternative explanations of the IP phase that have been proposed in the literature are discussed.

Different effects of dark treatment on pigment composition and photosystem I and II activities in intact cotyledons and primary leaves of Cucurbita pepo (zucchini)

“…The contribution of PSI cyclic electron transport as the reason for decreased DA 830 can be excluded because of the similarity in the decay kinetics between dark-treated and control leaves after switching off the far-red light (data not shown). As judged by u R 0 , the lower P 700 oxidation levels in the darktreated leaves could be associated with a rise in PSI reaction center recombinations as a result of reduced electron transport activity in the PSI acceptor side (Schansker et al 2005). Moreover, a close correlation between the changes in Chl content and the DA 830 signal in the primary leaves was observed, thus indicating that the changes in P 700 activity were determined to a greater extent by the changes in pigment content.…”

Application of chlorophyll fluorescence performance indices to assess the wheat photosynthetic functions influenced by nitrogen deficiency

“…Recently introduced parameter total performance index (Smit et al 2009) extended the recorded effects also to the capacity of electron transport between photosystems (Schansker et al 2005), which is not considered in PI abs . In terms of the mechanism, the nitrogen deficiency was proven to increase the cyclic electron transport and there is less PS I available for accepting electrons from PS II (Antal et al 2010).…”

Non-intrusive Assessment of Photosystem II and Photosystem I in Whole Coral Tissues

“…The OJ, photochemical phase, relates to the reduction of the acceptor side of PSII (Strasser, 1992). The JI phase relates to the transport beyond Q A and IP phase relates to several processes, in particular the electrons reaching PSI (Schansker et al, 2005;Kalaji et al, 2017). The induction curve of the chlorophyll a fluorescence (OJIP transient) was measured at 25 • C using a Multichannel-Plant Efficiency Analyzer 2 (M-PEA, Hansatech Instruments, UK) (for a full description of the instrument refer to Strasser et al, 2010).…”