Ultrastructure of the cyst wall of Haematococcus pluvialis (Chlorophyceae): wall development and behaviour during cyst germination

Abstract

M.C. Damiani, P.I. Leonardi, O.I. Pieroni and E.J. Cáceres. 2006. Ultrastructure of the cyst wall of Haematococcus pluvialis (Chlorophyceae): wall development and behaviour during cyst germination. Phycologia 45: 616–623. DOI: 10.2216/05-27.1

The cell wall structure and behaviour of cysts of Argentinian strains of Haematococcus pluvialis were studied during cyst germination and zooid release. The cyst wall is composed of an outer primary wall, a trilaminar sheath, a secondary wall, and a tertiary wall. The primary wall disintegrates as the cyst ages. During germination the trilaminar sheath breaks down, carrying the adjacent secondary wall with it and the extensible tertiary wall accompanies the cyst in its size increase and shape changes. Zooid release subsequently follows as a result of the apical breakage of this third wall. Although the secondary and tertiary walls exhibit the same conformation in mature cysts, the arrangement of their components during their formation is different. This could be the reason why the behaviour of the two walls is different during germination. The chemical characterization carried out in the present research showed that the external trilaminar sheath of the wall is formed by algaenan, while fluorescence labelling suggested the presence of mannose and cellulose in the secondary and tertiary walls. Because of the physical difficulty of breaking cysts during astaxanthin extraction, cyst germination may provide a natural, alternative wall-breaking mechanism.

Key Words::

• Algaenan
• Astaxanthin
• Cell wall
• Chlorophyceae
• Cyst
• Germination
• Haematococcus pluvialis
• Ultrastructure

ACKNOWLEDGMENTS

Financial support for the present research was provided by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina, through grants PEI 6024 and PIP 0949/98 to PIL and EJC, as well as by the Secretaría de Ciencia y Tecnología of the Universidad Nacional del Sur through grant PGI 488/03 to EJC. Thanks Dr C. Rodríguez for assistance with the fluorescence micrographs and for comments on the manuscript. We also thank Dr T. Motomura and reviewers for helpful suggestions to improve the manuscript. PIL is a researcher from the CONICET and EJC is a researcher from the Comisión de Investigaciones Científicas de la Provincia de Buenos Aires, Argentina.