A dip in the chlorophyll fluorescence induction at 0.2–2 s in Trebouxia-possessing lichens reflects a fast reoxidation of photosystem I. A comparison with higher plants

Abstract

An unusual dip (compared to higher plant behaviour under comparable light conditions) in chlorophyll fluorescence induction (FI) at about 0.2-2 s was observed for thalli of several lichen species having Trebouxia species (the most common symbiotic green algae) as their native photobionts and for Trebouxia species cultured separately in nutrient solution. This dip appears after the usual O(J)IP transient at a wide range of excitation light intensities (100-1800 micromol photons m(-2) s(-1)). Simultaneous measurements of FI and 820-nm transmission kinetics (I(820)) with lichen thalli showed that the decreasing part of the fluorescence dip (0.2-0.4 s) is accompanied by a decrease of I(820), i.e., by a reoxidation of electron carriers at photosystem I (PSI), while the subsequent increasing part (0.4-2 s) of the dip is not paralleled by the change in I(820). These results were compared with that measured with pea leaves-representatives of higher plants. In pea, PSI started to reoxidize after 2-s excitation. The simultaneous measurements performed with thalli treated with methylviologen (MV), an efficient electron acceptor from PSI, revealed that the narrow P peak in FI of Trebouxia-possessing lichens (i.e., the I-P-dip phase) gradually disappeared with prolonged MV treatment. Thus, the P peak behaves in a similar way as in higher plants where it reflects a traffic jam of electrons induced by a transient block at the acceptor side of PSI. The increasing part of the dip in FI remained unaffected by the addition of MV. We have found that the fluorescence dip is insensitive to antimycin A, rotenone (inhibitors of cyclic electron flow around PSI), and propyl gallate (an inhibitor of plastid terminal oxidase). The 2-h treatment with 5 microM nigericin, an ionophore effectively dissipating the pH-gradient across the thylakoid membrane, did not lead to significant changes either in FI nor I(820) kinetics. On the basis of the presented results, we suggest that the decreasing part of the fluorescence dip in FI of Trebouxia-lichens reflects the activation of ferredoxin-NADP(+)-oxidoreductase or Mehler-peroxidase reaction leading to the fast reoxidation of electron carriers in thylakoid membranes. The increasing part of the dip probably reflects a transient reduction of plastoquinone (PQ) pool that is not associated with cyclic electron flow around PSI. Possible causes of this MV-insensitive PQ reduction are discussed.

Alterations in photochemical efficiency of photosystem II in wheat plant on hot summer day

“…The P step measured at high intensity of excitation light splits into two steps (H and G) in the fluorescence curve (TsimilliMichael et al 1998). The fluorescence decrease from H step to a dip between H and G steps is caused by a removal of limitation on the acceptor side of PS I (Ilik et al 2006).…”

N-Terminal Structure of Maize Ferredoxin:NADP+ Reductase Determines Recruitment into Different Thylakoid Membrane Complexes

“…As we found Arabidopsis plants expressing maize FNR1, FNR2, and FNR3 are respectively enriched in FNR bound to TROL, Tic62, and in soluble FNR, we compared their PET capacity, to gain further insight into this question. There are early reports that FNR is the likely point of light regulation at the reducing side of PSI on light induction (Satoh and Katoh, 1980;Satoh, 1982), and more recent articles have provided further evidence that FNR may regulate PET (Ilík et al, 2006;Joliot and Johnson, 2011) and that this might be dependent on the NADP + /NADPH ratio (Rajagopal et al, 2003;Hald et al, 2008). In addition, FNR membrane association is known to change during dark-to-light transitions: FNR bound to Tic62 is released at basic pH values that could be generated in PET (Alte et al, 2010), and interaction with thylakoid Tic62-and TROL-mediated complexes is reported to be disrupted in the light (Benz et al, 2009).…”

Chlorophyll Fluorescence in Plant Biology

“…The nomenclature for 'OJIP' is O for origin or F 0 level measured at 20-50µs after illumination, J and I are intermediate states measured after 2ms and 30 ms, and P is the peak or F M (maximal fluorescence). In contrast to the angiosperms, the foraminifers, zooxanthellae and lichens, show an additional G peak and H (=P) peak (Tsimilli-Michael et al, 1998;Ilik et al, 2006). The origin G peak is assigned to an early activation of the ferredoxin-NADP+-reductase, FNR, (Ilik et al, 2006).…”

“…In contrast to the angiosperms, the foraminifers, zooxanthellae and lichens, show an additional G peak and H (=P) peak (Tsimilli-Michael et al, 1998;Ilik et al, 2006). The origin G peak is assigned to an early activation of the ferredoxin-NADP+-reductase, FNR, (Ilik et al, 2006). In heat-stressed samples, another peak arises between F 0 and F J at 300 µs which is designated as K peak (Guisse et al, 1995;Srivastava et al, 1997;Strasser, 1997;Misra et al, 2001bMisra et al, , 2007.…”