Mechanism of strong quenching of photosystem II chlorophyll fluorescence under drought stress in a lichen, Physciella melanchla, studied by subpicosecond fluorescence spectroscopy

Abstract

The mechanism of the severe quenching of chlorophyll (Chl) fluorescence under drought stress was studied in a lichen Physciella melanchla, which contains a photobiont green alga, Trebouxia sp., using a streak camera and a reflection-mode fluorescence up-conversion system. We detected a large 0.31 ps rise of fluorescence at 715 and 740 nm in the dry lichen suggesting the rapid energy influx to the 715-740 nm bands from the shorter-wavelength Chls with a small contribution from the internal conversion from Soret bands. The fluorescence, then, decayed with time constants of 23 and 112 ps, suggesting the rapid dissipation into heat through the quencher. The result confirms the accelerated 40 ps decay of fluorescence reported in another lichen (Veerman et al., 2007 [36]) and gives a direct evidence for the rapid energy transfer from bulk Chls to the longer-wavelength quencher. We simulated the entire PS II fluorescence kinetics by a global analysis and estimated the 20.2 ns(-1) or 55.0 ns(-1) energy transfer rate to the quencher that is connected either to the LHC II or to the PS II core antenna. The strong quenching with the 3-12 times higher rate compared to the reported NPQ rate, suggests the operation of a new type of quenching, such as the extreme case of Chl-aggregation in LHCII or a new type of quenching in PS II core antenna in dry lichens.

Ideal Osmotic Spaces for Chlorobionts or Cyanobionts Are Differentially Realized by Lichenized Fungi

“…Our data confirm that this phenomenon applies to desiccation-tolerant cyanolichens, chlorolichens, and green algae, which is consistent with the report by Lange et al (1989). The mechanism by which fluorescence is quenched during desiccation has been examined previously (Komura et al, 2006(Komura et al, , 2010Veerman et al, 2007;Miyake et al, 2011;Kosugi et al, 2013). Meanwhile, the mechanism underlying the inability to rereduce P700 + under dry/light conditions in desiccation-tolerant photosynthetic organisms is not well understood.…”

Acclimation to high-light conditions in cyanobacteria: from gene expression to physiological responses

“…However, this is not the case in terrestrial cyanobacteria, as rewetting of dried colonies or crusts results in rapid recovery of photosynthetic activity Harel et al 2004). A decrease in the yield of chlorophyll fluorescence during desiccation has been observed in several cyanobacterial species such as Nostoc commune and Microcoleus vaginatus (Ohad et al 2010), and also in drought-tolerant lichens (Komura et al 2010). In general, this decrease in fluorescence yield can be considered a consequence of the increase in energy dissipation to avoid photodamage.…”

Conservation and dissipation of light energy in desiccation-tolerant photoautotrophs, two sides of the same coin

“…Excitation energy, instead of being trapped in the reaction centres, now migrates energetically ''downhill'' towards the far-red end of the absorption spectrum. It is trapped there efficiently in dissipation centres which are characterized by weak far-red emission (Heber and Shuvalov 2005;Veerman et al 2007;Komura et al 2010;Slavov et al 2011;Yamakawa et al 2012). When excitation energy no longer reaches them, reaction centres are protected.…”