Fungal-associated NO is involved in the regulation of oxidative stress during rehydration in lichen symbiosis

Universidad Rey Juan Carlos, Dpto. Biología y Geología, ESCET, Madrid, Spain.
BMC Microbiology (Impact Factor: 2.73). 11/2010; 10:297. DOI: 10.1186/1471-2180-10-297
Source: PubMed


Reactive oxygen species (ROS) are normally produced in respiratory and photosynthetic electron chains and their production is enhanced during desiccation/rehydration. Nitric oxide (NO) is a ubiquitous and multifaceted molecule involved in cell signaling and abiotic stress. Lichens are poikilohydrous organisms that can survive continuous cycles of desiccation and rehydration. Although the production of ROS and NO was recently demonstrated during lichen rehydration, the functions of these compounds are unknown. The aim of this study was to analyze the role of NO during rehydration of the lichen Ramalina farinacea (L.) Ach., its isolated photobiont partner Trebouxia sp. and Asterochloris erici (Ahmadjian) Skaloud et Peksa (SAG 32.85 = UTEX 911).
Rehydration of R. farinacea caused the release of ROS and NO evidenced by the fluorescent probes DCFH₂-DA and DAN respectively. However, a minimum in lipid peroxidation (MDA) was observed 2 h post-rehydration. The inhibition of NO in lichen thalli with c-PTIO resulted in increases in both ROS production and lipid peroxidation, which now peaked at 3 h, together with decreases in chlorophyll autofluorescence and algal photobleaching upon confocal laser incidence. Trebouxia sp. photobionts generate peaks of NO-endproducts in suspension and show high rates of photobleaching and ROS production under NO inhibition which also caused a significant decrease in photosynthetic activity of A. erici axenic cultures, probably due to the higher levels of photo-oxidative stress.
Mycobiont derived NO has an important role in the regulation of oxidative stress and in the photo-oxidative protection of photobionts in lichen thalli. The results point to the importance of NO in the early stages of lichen rehydration.

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Available from: Myriam Catalá,
    • "Notwithstanding the low PPFD to which LT was actually exposed, LT showed an increased ''oxidative burst'' upon rehydration. This phenomenon was already observed in lichens (Weissman et al. 2005; Catalá et al. 2010) and in mosses (Minibayeva and Beckett 2001; Cruz de Carvalho et al. 2012), but the influence of the illumination in the time span prior to rehydration was not tested before. Protracted periods under photo-oxidative conditions cause an inevitable impairment of the antioxidant machinery (Kranner et al. 2005; Vráblíková et al. 2005) which can leave the cells unprotected against the subsequent oxidative burst derived from the sudden metabolism reactivation (Weissman et al. 2005). "
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    • "Interestingly, the histochemical localization of ROS was congruent with the quantitative measurements of O 2 @BULLET− and, to a lesser extent, of H 2 O 2 . Previous studies detected ROS in both symbionts (Weissmann et al., 2005a; Catalá et al., 2010), but the photobiont of F. caperata seems to scavenge ROS better than the mycobiont. Therefore, it can be argued that the accumulation of ROS measured quantitatively (see Fig. 3) derives totally from the latter. "
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