Different sensitivity of photosynthetic electron transport of plant species to lichen acids

摘要

The lichens are the unique symbiont of algae and fungi in nature. Usually, specific pair of lichen photobiont (algae) and lichen mycobiont (fungi) form the thallus. Majority of the lichen photobionts (about 60 percent) belong to the genus Trebouxia,unicellular green algae (Ahmadjian 1993), and the major lichen mycobionts are ascomycete (Poelt 1973). The lichen mycobiont produces the lichen-specific secondary metabolites such as lichen acids from glucose and ribitol, photosynthetic products of lichen photobionts. However, the research on the ecological and physiological roles of these secondary metabolites are very limited. After Inoue et al. (1987) reported the inhibition of oxidizing side of P680 in PSII in spinach by lichen acid, no similar research was published until we reported the more detailed characterization of the inhibition in photosynthetic electron transport by the lichen acids in spinach (Endo et al. 1998). Barbatic acid, one of the most abundant lichen acids, primarily inhibited at the reducing side of P680, possibly Qb, but also at the oxidizing side of P680, suggesting Yz as the target. Because we found the different inhibitory activity among a variety of lichen acids, we have been also interested in characterizing the differences in the sensitivity among different species of photosynthetic organisms to lichen acids. Here we report that PSII of cultured tobacco cells, Chlamydomonas reinhardtii and lichen photobionts showed different sensitivity to lichen acids.