title: Fungal-associated NO is involved in the regulation of oxidative stress during rehydration in lichen symbiosis.
abstract: BACKGROUND
  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).
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Universidad Rey Juan Carlos, Dpto. Biología y Geología, ESCET, Madrid, Spain. myriam.catala@urjc.es
authors.forename: Myriam
authors.initials: M
authors.lastname: Catalá
authors.forename: Francisco
authors.initials: F
authors.lastname: Gasulla
authors.forename: Ana E
authors.initials: AE
authors.lastname: Pradas del Real
authors.forename: Francisco
authors.initials: F
authors.lastname: García-Breijo
authors.forename: Jose
authors.initials: J
authors.lastname: Reig-Armiñana
authors.forename: Eva
authors.initials: E
authors.lastname: Barreno
mesh_terms: D000460:Chlorophyta / Q000502:physiology*; D005658:Fungi / Q000502:physiology*; D008011:Lichens / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism*; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism; D013559:Symbiosis; D014867:Water / Q000378:metabolism*
chemical_list: D017382:Reactive Oxygen Species; D014867:Water; D009569:Nitric Oxide