The green alga Zygogonium ericetorum (Zygnematophyceae, Charophyta) shows high iron and aluminium tolerance: protection mechanisms and photosynthetic performance.

Klaus Herburger,Daniel Remias,Andreas Holzinger

doi:10.1093/femsec/fiw103

Klaus Herburger, Daniel Remias + Show 1 more

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https://doi.org/10.1093/femsec/fiw103

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Abstract

Streptophyte green algae, ancestors of Embryophytes, occur frequently in terrestrial habitats being exposed to high light intensities, water scarcity and potentially toxic metal cations under acidic conditions. The filamentous Zygogonium ericetorum synthesizes a purple vacuolar ferrous pigment, which is lost after aplanospore formation. However, it is unknown whether this cellular reorganization also removes excessive iron from the protoplast and how Z. ericetorum copes with high concentrations of aluminium. Here we show that aplanospore formation shifts iron into the extracellular space of the algal filament. Upon germination of aplanospores, aluminium is bound in the parental cell wall. Both processes reduce iron and aluminium in unpigmented filaments. Comparison of the photosynthetic oxygen production in response to light and temperature gradients in two different Z. ericetorum strains from an Austrian alpine and a Scottish highland habitat revealed lower values in the latter strain. In contrast, the Scottish strain showed a higher optimum quantum yield of PSII during desiccation stress followed by rehydration. Furthermore, pigmented filaments of both strains exhibited a higher light and temperature dependent oxygen production when compared to the unpigmented phenotype. Our results demonstrate a high metal tolerance of Z. ericetorum, which is crucial for surviving in acidic terrestrial habitats.

Highlights

Based on their primary adaptation to freshwater, distinct streptophyte green algae belonging to the Zygnematophyceae moved to the limnetic transition zone and further to dry land, which gave rise to the evolution of land plants in the Mid-Ordovician period (Becker and Marin 2009; Wickett et al 2014)
The role of cellular reorganization processes to cope with iron, aluminium and zinc stress as well as the photosynthetic response to light, temperature and desiccation gradients was investigated in laboratory experiments
These multicellular land plants are characterized by a high level of functional specialization allowing them to partition complementary tasks among different cells, tissues or organs simultaneously

Summary

Introduction

Based on their primary adaptation to freshwater, distinct streptophyte green algae belonging to the Zygnematophyceae moved to the limnetic transition zone and further to dry land, which gave rise to the evolution of land plants in the Mid-Ordovician period (Becker and Marin 2009; Wickett et al 2014). Zygnematophyceae occur worldwide in limnetic, hydro- and Received: 21 January 2016; Accepted: 27 April 2016 C FEMS 2016. The role of cellular reorganization processes (i.e. accumulation of purple pigmentation or formation of aplanospores) to cope with iron, aluminium and zinc stress as well as the photosynthetic response to light, temperature and desiccation gradients was investigated in laboratory experiments. We tested if (iii) the two Z. ericetorum isolates obtained from two different habitats exhibit distinct responses to light, temperature and desiccation gradients, which would imply a high adaptive capacity and phenotypic plasticity of this species. We investigated whether (iv) the ‘purple morphs’ of both Z. ericetorum isolates show higher photosynthetic oxygen productions in response to increasing light and temperature when compared with the respective ‘green morphs’

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