Drought-induced fluorescence quencher in a poikilohydric moss, Breum argenteum, is formed in the photosystem II core complex

Yutaka Shibataa, Ahmed Mohameda, Koichiro Taniyamaa, Kentaro Kanatania, Makiko Kosugib, and Hiroshi Fukumuraa
aDepartmet of Chemistry, Graduate School of Science, Tohoku university, aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan; bDepartment of Biology, Graduate School of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-Ku, Tokyo 112-8551, Japan

When the light intensity exceeds the capacity of the photosynthetic consumption, excessive amount of excited chlorophylls (Chls) generates harmful species like reactive oxygen species (ROS) [1]. Therefore, plants have developed an ability to dissipate the excessive excitation energy to heat, as well as those to scavenge generated ROS. Some kinds of mosses are extremely tolerant to the drought stress. Their high drought tolerances rely on their abilities to effectively dissipate the absorbed light energy to heat under dry conditions. The mechanism of the energy dissipation in a drought-tolerant moss, Breum argenteum, has been investigated by the low-temperature picosecond time-resolved fluorescence spectroscopy.

Surprisingly, the moss thalli harvested in both the Antarctica and Japan showed almost the same quenching properties, suggesting the identical mechanism of the drought tolerance for this moss species with the two completely different habitats. As shown in figure, the fluorescence quenching in the photosystem II (PS II) spectral region at 691 nm is equally active for the 430-nm (mainly excites Chl-a, shown in blue) and 460-nm (excites Chl-b and carotenoids, shown in red) excitations in the temperature region from 5 K to 77 K. This result excludes the possibility of the quencher induced in the peripheral antenna. The fluorescence quenching is active even at 5 K, where a wide-range excitation-energy migration is inhibited. This excludes the possibility that the spillover mechanism from PS II to PS I plays a main role in this plant. Instead, a model assuming the quencher formed in the PS II core complex, originally proposed by Heber et al. [2], is consistent with the present observation.

Figure 1: Fluorescence decay curves of dry (circles) and wet (solid lines) Breum argenteum thalli at 691 nm excited at 430 nm (blue) and 460 nm (red).

References

[1] B. Demmig-Adams, W.W. Adams, Nature 2000, 403, 371–374.
[2] U. Heber, W. Bilger, V.A. Shuvalov, J. Exp. Botany 2006, 57, 2993–3006.