Nonetheless, much remains to be learned about lichen metabolism of ROS during dehydration/rehydration cycles, since it has been recently reported that classical antioxidant mechanisms play a limited role in the strategies that facilitate transition of photobionts to the desiccated state [7]. Reactive oxygen species are produced in the respiratory selleck compound and photosynthetic

electron chains of many organisms. In photosynthetic organisms, the production of ROS is enhanced during desiccation and/or rehydration because carbon fixation is impaired, whereas chlorophyll electrons continue to be excited. ROS result from the uncontrolled donation of electrons from electron transport chains in chloroplasts and mitochondria to molecular oxygen, initiating an indiscriminate chain reaction.

If antioxidant defenses are overcome by ROS production, the uncontrolled free radicals cause widespread cellular damage by provoking protein alterations, lipid peroxidation, and the formation of DNA adducts [8]. The bioactive gas nitric oxide (NO) has multiple biological functions in a very broad range of organisms. These functions include signal transduction, cell death, transport, basic metabolism, ROS production and degradation [9, 10], among others (reviewed in [11]). It is well-known that NO exerts both pro-oxidant and antioxidant effects, depending on the ambient redox status, the presence of other reactants, and the LY294002 solubility dmso nature of the reaction (for a review of the antioxidant actions of NO, see [12]). In plants, Clomifene ROS and reactive nitrogen species have been shown to be involved in the defensive response of plants to biotic or abiotic stresses such as pathogens [13], drought [14], and air pollutants or UV-B radiation [15]. In the latter study, the authors found support for the hypothesis that NO reactive species, together with the glutathione system, play a key role in the coordination of gene expression during plant symbiosis. NO has been

postulated as one of the first antioxidant mechanisms to have evolved in aerobic cells [16, 17]. This idea builds on the work of Feelisch and Martin [18], who suggested a role for NO in both the early evolution of aerobic cells and in symbiotic relationships involving NO efficacy in neutralizing ROS. In addition, NO is involved in the abiotic stress response of green algae such as Chlorella pyrenoidosa Pringsheim, by reducing the damage produced by photo-oxidative stress [19]. The first work that focused on NO production in lichens was published in 2005, by Weissman and co-workers [20], who carried out a microscopy study of Ramalina lacera (With.) J.R. Laundon. These authors described the occurrence of intracellular oxidative stress during rehydration together with the release of NO by the mycobiont, but not by the photobiont. We have recently reported evidence that NO is involved in oxidative stress in lichens exposed to the oxidative pollutant cumene hydroperoxide [21].