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

Abstract

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.