Ultra-fast dissipation of excess excitation energy by multiple pathways in dry mosses and lichens with algal/cyanobacterial symbionts

Shigeru Itoha, Masayuki Komuraa, Hisanori Yamakawab, Urlich Heberc, Tomoki Satod, Ikuko Iwasakid
aCenter Gene Res, Nagoya University, Nagoya, Japan; cUniv. Wurzburg, Germany; dBioresources, Akita Prefecture University, Japan

Sun light kills ordinary plants under dehydration where electron transfer stops. On the other hand, dried mosses and lichens stay green and survive even under strong sunshine. In these organisms we found that the excess excitation energy is dissipated by the strong quencher into heat (a-c). The dissipation mechanisms were studied by measuring the fluorescence lifetime of pigments with a laser-streak camera system at 300 and 77 K. Most (40/45 species collected) of drought-tolerant lichens showed strong quenching of PS II fluorescence when dehydrated, giving the very short 1/2-1/6 fluorescence lifetimes at 77K with sever quenching of F0 level. 2) One species showed no quenching upon the dehydration. 3) Some species showed lowered fluorescence yield without lifetime shortening. 4) Cyanobacterial-type lichens showed the accelerated fluorescence decays in both phycocyanin and Chls suggesting the quenching inside PBS and PSII core Chls. 5) Nostoc sp. isolated and cultured showed strong quenching upon drying. 6) Similar quenching was also found in drought-tolerant mosses. It is in contrast to the plants like spinach, Vicia faba, etc, which did not change fluorescence upon desiccation. 7) It is concluded that drought-tolerant algae, lichens and some mosses, drying induces the strong quenchers in phycocyanin


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