title: Localization and Quantification of Callose in the Streptophyte Green Algae Zygnema and Klebsormidium: Correlation with Desiccation Tolerance.
abstract: Freshwater green algae started to colonize terrestrial habitats about 460 million years ago, giving rise to the evolution of land plants. Today, several streptophyte green algae occur in aero-terrestrial habitats with unpredictable fluctuations in water availability, serving as ideal models for investigating desiccation tolerance. We tested the hypothesis that callose, a β-d-1,3-glucan, is incorporated specifically in strained areas of the cell wall due to cellular water loss, implicating a contribution to desiccation tolerance. In the early diverging genus Klebsormidium, callose was drastically increased already after 30 min of desiccation stress. Localization studies demonstrated an increase in callose in the undulating cross cell walls during cellular water loss, allowing a regulated shrinkage and expansion after rehydration. This correlates with a high desiccation tolerance demonstrated by a full recovery of the photosynthetic yield visualized at the subcellular level by Imaging-PAM. Furthermore, abundant callose in terminal cell walls might facilitate cell detachment to release dispersal units. In contrast, in the late diverging Zygnema, the callose content did not change upon desiccation for up to 3.5 h and was primarily localized in the corners between individual cells and at terminal cells. While these callose deposits still imply reduction of mechanical damage, the photosynthetic yield did not recover fully in the investigated young cultures of Zygnema upon rehydration. The abundance and specific localization of callose correlates with the higher desiccation tolerance in Klebsormidium when compared with Zygnema.
authors.affiliation: University of Innsbruck, Institute of Botany, Functional Plant Biology, Sternwartestrasse 15, 6020 Innsbruck, Austria.
authors.forename: Klaus
authors.initials: K
authors.lastname: Herburger
authors.affiliation: University of Innsbruck, Institute of Botany, Functional Plant Biology, Sternwartestrasse 15, 6020 Innsbruck, Austria Andreas.Holzinger@uibk.ac.at.
authors.forename: Andreas
authors.initials: A
authors.lastname: Holzinger
mesh_terms: D000814:Aniline Compounds; D001557:Benzenesulfonates; D005075:Biological Evolution; D002473:Cell Wall / Q000737:chemistry; D000460:Chlorophyta / Q000737:chemistry* / Q000145:classification / Q000502:physiology* / Q000648:ultrastructure; D003890:Desiccation; D005936:Glucans / Q000032:analysis*; D013194:Staining and Labeling
chemical_list: D000814:Aniline Compounds; D001557:Benzenesulfonates; D005936:Glucans; C007061:C.I. Fluorescent Brightening Agent 28; C017006:aniline blue; C048306:callose
keywords: Aero-terrestrial green algae; Cell wall; Evolutionary biology; Imaging-PAM; Phylogeny; Terrestrialization