title: Towards clarifying what distinguishes cyanobacteria able to resurrect after desiccation from those that cannot: The photosynthetic aspect.
abstract: Organisms inhabiting biological soil crusts (BSCs) are able to cope with extreme environmental conditions including daily hydration/dehydration cycles, high irradiance and extreme temperatures. The photosynthetic machinery, potentially the main source of damaging reactive oxygen species during cessation of CO(2) fixation in desiccating cells, must be protected to avoid sustained photodamage. We compared certain photosynthetic parameters and the response to excess light of BCS-inhabiting, desiccation-tolerant cyanobacteria Leptolyngbya ohadii and Nostoc reinholdii with those observed in the "model" organisms Nostoc sp. PCC 7120, able to resurrect after mild desiccation, and Synechococcus elongatus PCC 7942 and Synechocystis sp. PCC 6803 that are unable to recover from dehydration. Desiccation-tolerant strains exhibited a transient decline in the photosynthetic rate at light intensities corresponding to the inflection point in the PI curve relating the O(2) evolution rate to light intensity. They also exhibited a faster and larger loss of variable fluorescence and profoundly faster Q(A)(-) re-oxidation rates after exposure to high illumination. Finally, a smaller difference was found in the temperature of maximal thermoluminescence signal in the absence or presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) than observed in "model" cyanobacteria. These parameters indicate specific functional differences of photosystem II (PSII) between desiccation tolerant and sensitive cyanobacteria. We propose that exposure to excess irradiation activates a non-radiative electron recombination route inside PSII that minimizes formation of damaging singlet oxygen in the desiccation-tolerant cyanobacteria and thereby reduces photodamage.
authors.affiliation: Dept. of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
authors.forename: Hagai
authors.initials: H
authors.lastname: Raanan
authors.affiliation: Dept. of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
authors.forename: Nadav
authors.initials: N
authors.lastname: Oren
authors.affiliation: Dept. of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
authors.forename: Haim
authors.initials: H
authors.lastname: Treves
authors.affiliation: Dept. of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
authors.forename: Nir
authors.initials: N
authors.lastname: Keren
authors.affiliation: Dept. of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
authors.forename: Itzhak
authors.initials: I
authors.lastname: Ohad
authors.affiliation: Dept. of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel; Arid Ecosystems Research Center, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Berkowicz
authors.affiliation: Universität Rostock, Institut für Biowissenschaften, Abteilung Pflanzenphysiologie, A.-Einstein-Str. 3, D-18059 Rostock, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Hagemann
authors.affiliation: Dept. of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
authors.forename: Moriz
authors.initials: M
authors.lastname: Koch
authors.affiliation: Department of Chemical Engineering, Shamoon College of Engineering, Beer Sheva, 84100, Israel.
authors.forename: Yoram
authors.initials: Y
authors.lastname: Shotland
authors.affiliation: Dept. of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel; Arid Ecosystems Research Center, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel. Electronic address: aaron.kaplan@mail.huji.ac.il.
authors.forename: Aaron
authors.initials: A
authors.lastname: Kaplan
mesh_terms: D000458:Cyanobacteria / Q000145:classification / Q000254:growth & development* / Q000378:metabolism*; D003890:Desiccation / Q000379:methods*; D007700:Kinetics; D008027:Light; D046937:Nostoc / Q000254:growth & development / Q000378:metabolism; D010084:Oxidation-Reduction / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D013045:Species Specificity; D046940:Synechococcus / Q000254:growth & development / Q000378:metabolism; D046939:Synechocystis / Q000254:growth & development / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
chemical_list: D045332:Photosystem II Protein Complex; D010100:Oxygen
keywords: Dehydration; Drought stress; Fluorescence; Photosynthetic activity; Photosystem II; Q(A)-reoxidation