Some observations on the fine structure of the marine brown alga Phaeostrophion irregulare

In a fine-structure study of Phaeostrophion irregulare (Dictyosiphonales) most characteristics of the organelles and their interrelationships were found to be similar to those previously reported for other brown algae. However, there was an interesting variation regarding the pyrenoid and the nucleus–chloroplast association in the macroscopic thallus. The pyrenoid is present in the cells of the sporeling but absent from the thallus which grows directly from it. In addition, there is no evidence of any connection between the outer membranes of the nucleus and the chloroplast in the cells of the blade. The significance of these findings is discussed in relation to the phyletic importance of the pyrenoid and the possible implications of observing a limited number of heterogeneous tissue types, such as spore, sporeling, and mature thallus, in comparative studies.