title: The terrestrial green macroalga Prasiola calophylla (Trebouxiophyceae, Chlorophyta): ecophysiological performance under water-limiting conditions.
abstract: The phylogenetic placement of Prasiola calophylla, from an anthropogenic habitat previously shown to contain a novel UV sunscreen compound, was confirmed by analysis of its rbcL gene. This alga has the capacity to tolerate strong water-limiting conditions. The photosynthetic performance and ultrastructural changes under desiccation and osmotic stress were investigated. Freshly harvested thalli showed an effective quantum yield of PSII [Y(II)] of 0.52 ± 0.06 that decreased to ∼60% of the initial value at 3000 mM sorbitol, and 4000 mM sorbitol led to a complete loss of Y(II). The Y(II) of thalli exposed to controlled desiccating conditions at 60% relative humidity (RH) ceased within 240 min, whereas zero values were reached after 120 min at 20% RH. All investigated samples completely recovered Y(II) within ∼100 min after rehydration. Relative electron transport rates (rETR) were temperature dependent, increasing from 5, 10, to 25 °C but strongly declining at 45 °C. Transmission electron microscopy of samples desiccated for 2.5 h showed an electron dense appearance of the entire cytoplasm when compared to control samples. Thylakoid membranes were still visible in desiccated cells, corroborating the ability to recover. Control and desiccated cells contained numerous storage lipids and starch grains, providing reserves. Overall, P. calophylla showed a high capacity to cope with water-limiting conditions on a physiological and structural basis. A lipophilic outer layer of the cell walls might contribute to reduce water evaporation in this poikilohydric organism.
authors.affiliation: Functional Plant Biology, Institute of Botany, University of Innsbruck, Sternwartestrasse 15, 6020, Innsbruck, Austria. Andreas.Holzinger@uibk.ac.at.
authors.forename: Andreas
authors.identifier: http://orcid.org/0000-0002-7745-3978
authors.initials: A
authors.lastname: Holzinger
authors.affiliation: Functional Plant Biology, Institute of Botany, University of Innsbruck, Sternwartestrasse 15, 6020, Innsbruck, Austria.
authors.forename: Klaus
authors.initials: K
authors.lastname: Herburger
authors.affiliation: Functional Plant Biology, Institute of Botany, University of Innsbruck, Sternwartestrasse 15, 6020, Innsbruck, Austria.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Blaas
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, 06269-3043, USA.
authors.forename: Louise A
authors.initials: LA
authors.lastname: Lewis
authors.affiliation: Institute of Biological Sciences, Applied Ecology and Phycology, University of Rostock, Albert-Einstein-Straße 3, 18059, Rostock, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Karsten
mesh_terms: D000460:Chlorophyta / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D003681:Dehydration / Q000378:metabolism; D010788:Photosynthesis; D010802:Phylogeny; D020524:Thylakoids / Q000378:metabolism / Q000648:ultrastructure
keywords: Chlorophyll fluorescence; Desiccation; Light; Photosynthesis; Temperature