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

Myriam Catalá,Eva Barreno,Francisco Gasulla,Francisco García-Breijo,Ana E Pradas Del Real,Jose Reig-Armiñana

doi:10.1186/1471-2180-10-297

Abstract

BackgroundReactive 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).ResultsRehydration 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.ConclusionsMycobiont 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.

Highlights

Reactive oxygen species (ROS) are normally produced in respiratory and photosynthetic electron chains and their production is enhanced during desiccation/rehydration
Chemicals The chemicals 2,6-di-tert-buthyl-4-methylphenol trichloroacetic acid (BHT), 2-thiobarbituric acid (TBA), 1,1,3,3, tetraethoxypropane (TEP), cumene hydroperoxide 88% (CP), and bisbenzimide H (Hoechst) were provided by Sigma Aldrich Química S.A (Tres Cantos, Spain); 2,7-dichlorodihydrofluorescein diacetate (DCFH2DA), hydrochloric acid (HCl) and ethanol were purchased from Panreac Química S.A.U (Barcelona, Spain); 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt and 2,3-diaminonaphthalene (DAN) were from Invitrogen S.A (El Prat de Llobregat, Spain); and Triton X-100 was from VWR Prolabo (Barcelona, Spain)
ROS generation, chlorophyll autofluorescence and lipid peroxidation during lichen rehydration several works have described an extracellular oxidative burst during rehydration in some lichen species, virtually nothing is known about intracellular ROS production and its relationship to abiotic stress

Summary

Introduction

Reactive oxygen species (ROS) are normally produced in respiratory and photosynthetic electron chains and their production is enhanced during desiccation/rehydration. Lichens are symbiogenetic organisms composed of fungi (mycobionts) and their photosynthetic partners (photobionts). They are poikilohydrous, subject to repeated desiccation/rehydration cycles, and able to survive in extreme, frequently very dry environments, such as deserts or the arctic tundra. Reactive oxygen species (ROS) are known to be a major cause of damage during desiccation, especially in photosynthetic organisms [1]. Reactive oxygen species are produced in the respiratory and photosynthetic electron chains of many organisms. The production of ROS is enhanced during desiccation and/or rehydration because carbon fixation is impaired, whereas chlorophyll electrons continue to be excited. 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]

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