Photosynthetic efficiency, desiccation tolerance and ultrastructure in two phylogenetically distinct strains of alpine Zygnema sp. (Zygnematophyceae, Streptophyta): role of pre-akinete formation.

K Herburger,L A Lewis,A Holzinger

doi:10.1007/s00709-014-0703-3

Abstract

Two newly isolated strains of green algae from alpine regions were compared physiologically at different culture ages (1, 6, 9 and 15 months). The strains of Zygnema sp. were from different altitudes (‘Saalach’ (S), 440 m above sea level (a.s.l.), SAG 2419 and ‘Elmau-Alm’ (E-A), 1,500 m a.s.l., SAG 2418). Phylogenetic analysis of rbcL sequences grouped the strains into different major subclades of the genus. The mean diameters of the cells were 23.2 μm (Zygnema S) and 18.7 μm (Zygnema E-A) but were reduced significantly with culture age. The photophysiological response between the strains differed significantly; Zygnema S had a maximal relative electron transport rate (rETR max) of 103.4 μmol electrons m−2 s−1, Zygnema E-A only 61.7 μmol electrons m−2 s−1, and decreased significantly with culture age. Both strains showed a low-light adaption and the absence of strong photoinhibition up to 2,000 μmol photons m−2 s−1. Photosynthetic oxygen production showed similar results (P max Zygnema S, 527.2 μmol O2 h−1 mg−1 chlorophyll (chl.) a, Zygnema E-A, 390.7 μmol O2 h−1 mg−1 chl. a); the temperature optimum was at 35 °C for Zygnema S and 30 °C for Zygnema E-A. Increasing culture age moreover leads to the formation of pre-akinetes, which accumulate storage products as revealed by light and transmission electron microscopy. Desiccation at 84 % relative air humidity (RH) lead to a reduction of the effective quantum yield of photosystem II (PSII) (ΔFv/Fm′) to zero between 90 to 120 min (Zygnema S) and between 30 to 60 min (Zygnema E-A), depending on the culture age. A partial recovery of ΔFv/Fm′ was only observed in older cultures. We conclude that pre-akinetes are crucial for the aeroterrestrial lifestyle of Zygnema.

Highlights

IntroductionZygnema (Zygnematophyceae), a streptophyte green alga, occurs in freshwater (Ettl and Gärtner 1995; Hawes 1989) and hydroterrestrial habitats (Ettl and Gärtner 1995; Elster and Benson 2004; Holzinger et al 2009), including shallow puddles, streams and well-hydrated soils in alpine, Arctic and Antarctic regions (Davey 1991; Holzinger et al 2009; Stancheva et al 2012; Kaplan et al 2013; Pichrtová et al 2013, 2014)
We conclude that the two phylogenetically distinct Zygnema isolates are adapted to low light conditions, but are not strongly photoinhibited under high light conditions
Temperature regimes needed for positive net carbon gain are likely related to the different habitats from which the algae were obtained

Summary

Introduction

Zygnema (Zygnematophyceae), a streptophyte green alga, occurs in freshwater (Ettl and Gärtner 1995; Hawes 1989) and hydroterrestrial habitats (Ettl and Gärtner 1995; Elster and Benson 2004; Holzinger et al 2009), including shallow puddles, streams and well-hydrated soils in alpine, Arctic and Antarctic regions (Davey 1991; Holzinger et al 2009; Stancheva et al 2012; Kaplan et al 2013; Pichrtová et al 2013, 2014). Gray et al 2007; Karsten et al 2010, 2014; Holzinger et al 2011; Karsten and Holzinger 2012; Aigner et al 2013), for example, caused by decreasing rates of repair of D1 protein in photosystem II (PSII) resulting from direct inactivation of the translation machinery (Takahashi and Murata 2008) This leads to interrupted carbon fixation and the creation of reactive oxygen species (ROS), which can cause severe cellular damages by membrane lipid peroxidation and hydroxylation of DNA (Kranner and Birtic 2005). The effects of plasmolysis were tested recently in arctic field samples of Zygnema (Pichrtová et al 2014)

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