Ultrastructure and assembly of the scale case in Synura (Synurophyceae Andersen)

Abstract

Scale cases of Synura petersenii and S. echinulata are made up of diagonal rows of scales arranged with a precise and consistent imbrication. Scales of one row overlap the rims of those in the row in front. In the mid-region of the cell each scale is surrounded by six others, the three posterior scales overlap the rim of the central scale and the anterior end of this scale overlaps the rims of the three scales in front. Scales are produced intracellularly in silica deposition vesicles which are arranged in rows over the surface of one of the two chloroplasts. During interphase new scales are interpolated into an existing case without apparently disturbing the existing scale arrangement. It is proposed that rows of scales mature intracellularly more or less in the region in which they will be incorporated into the overlying scale case, and that scales emerge from the protoplast in the order in which they overlap each other in a row, that is from the posterior forwards. The pattern of intracellular scale deposition and extracellular insertion of scales into a case is discussed in the light of previous studies and what is known about the construction of the case.