Polyols and UV-sunscreens in the Prasiola-clade (Trebouxiophyceae, Chlorophyta) as metabolites for stress response and chemotaxonomy.

Vivien Hotter,Ulf Karsten,Markus Ganzera,Anja Hartmann,Karin Glaser,W Henley

doi:10.1111/jpy.12619

Vivien Hotter, Ulf Karsten + Show 4 more

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https://doi.org/10.1111/jpy.12619

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Abstract

In many regions of the world, aeroterrestrial green algae of the Trebouxiophyceae (Chlorophyta) represent very abundant soil microorganisms, and hence their taxonomy is crucial to investigate their physiological performance and ecological importance. Due to a lack in morphological features, taxonomic and phylogenetic studies of Trebouxiophycean algae can be a challenging task. Since chemotaxonomic markers could be a great assistance in this regard, 22 strains of aeroterrestrial Trebouxiophyceae were chemically screened for their polyol‐patterns as well as for mycosporine‐like amino acids (MAAs) in their aqueous extracts using RP‐HPLC and LC‐MS. d‐sorbitol was exclusively detected in members of the Prasiolaceae family. The novel MAA prasiolin and a related compound (“prasiolin‐like”) were present in all investigated members of the Prasiola‐clade, but missing in all other tested Trebouxiophyceae. While prasiolin could only be detected in field material directly after extraction, the “prasiolin‐like” compound present in the other algae was fully converted into prasiolin after 24 h. These findings suggest d‐sorbitol and prasiolin‐like compounds are suitable chemotaxonomic markers for the Prasiolaceae and Prasiola‐clade, respectively. Additional UV‐exposure experiments with selected strains show that MAA formation and accumulation can be induced, supporting their role as UV‐sunscreen.

Highlights

In contrast to their aquatic relatives, aeroterrestrial algae are directly exposed to the atmosphere and thereby subject to harsh environmental conditions, such as strong diurnal and seasonal changes of ultraviolet radiation (UVR; Hartmann et al 2016) and strong differences between cellular and atmospheric water potential (Holzinger and Karsten 2013)
Polyol and other low molecular weight carbohydrate patterns can be used for chemotaxonomy (Karsten et al 1999)
To oppose UVR damage, aeroterrestrial Trebouxiophyceae belonging to the Lobosphaera, Watanabeaand Prasiola-clade biosynthesize and accumulate mycosporine-like amino acids (MAAs; Karsten et al 2005, 2007b)

Summary

Introduction

In contrast to their aquatic relatives, aeroterrestrial algae are directly exposed to the atmosphere and thereby subject to harsh environmental conditions, such as strong diurnal and seasonal changes of ultraviolet radiation (UVR; Hartmann et al 2016) and strong differences between cellular and atmospheric water potential (Holzinger and Karsten 2013). Green algal members of the class Trebouxiophyceae are capable of synthesizing and accumulating polyols These low molecular weight carbohydrates exhibit multiple functions. To oppose UVR damage, aeroterrestrial Trebouxiophyceae belonging to the Lobosphaera-, Watanabeaand Prasiola-clade biosynthesize and accumulate mycosporine-like amino acids (MAAs; Karsten et al 2005, 2007b). These sunscreen compounds absorb UVR and re-emit it as harmless heat, thereby shielding intracellular structures and biomolecules (Bandaranayake 1998). Hartmann et al (2016) elucidated the chemical structure of this putative 324 nm-MAA in the closely related Prasiola calophylla as N-[5,6 hydroxy-5(hydroxymethyl)-2-methoxy-3-oxo-1-cycohexen-1-yl] glutamic acid, which represents a novel MAA Only a few members of the Trebouxiophyceae have been studied for the presence of this and other MAAs and until now the occurrence of prasiolin is experimentally proven only in P. calophylla

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