A Comparative Morphometrical Study of the Ultrastructural Organization in Six Dinoflagellate Species Using Stereology

A comparative Ultrastructural study of six dinoflagellate species, Prorocentrum triestinum, Prorocentrum micans, Scrippsiella trochoideat Gonyaulax excavata, Gonyaulax polyedra and Gymnodinium sp, wich represent the main phylogenetic groups of this phylum, was carried out using stereological procedures. Even though the size of cell and organelles was very variable, the general organization of the cell (proportions of different compartments analyzed) was less variable than the absolute volumes. Thus, the use of relative stereological parameters is preferable because they allow comparison of ultrastructure organization among cells of very different size. Distance coefficients show that the Ultrastructural organization of a species is more related to its phylogeny than it is to its size. Species within a same genus showed small differences while clones of a same species were nearly identical. For all species studied, the number of mitochondria per unit of cell volume remains constant at around 0.09 mitochondria/μιη. Nucleoli showed a high relative variation while the volume of chromosomes related to nucleus volume showed a low degree of variation. It seems that dinoflagellates can occur with very different relative proportions of nucleolus but with a similar number of mitochondria. The species with a higher relative nuclear volume showed a lower growth rate, while species with a higher thylakoid surface showed the higher growth rates. Introduction tmm micans Ehrenberg and Prorocentrum triestinum Dinoflagellate ultrastructure has been widely deSchiller. They also compared morphometrically the scribed at the qualitative level (Dodge 1973, Steidinger nuclear ultrastructure of six dinoflagellate species and Cox 1980). However, morphometrical analyses (Costas and Goyanes 1988). Furthermore, Costas et at the quantitative level on dinophyceae ultrastructure al. (1988), described quantitatively the ultrastructure are scarce. In a pioneer work, Steidinger (1979) deof P. micans using stereology. scribed the quantitative Ultrastructural variation in Quantitative Ultrastructural studies are more frequent Ptychodiscus brevis Stein. Recently Costas and Goyin diatoms. Stoermer and Sicko-Goad (1985) carried anes (1987) analysed stereologically the nuclear and out a comparative morphometrical analysis of six chromosome ultrastructure and division of Prorocenspecies of the diatom genus Stephanodiscus. SickoGoad and Stoermer (1979) and Sicko-Goad (1982) 1 Supported by CA1CYT Grant n° 2409/83 also evaluated morphometrically Ultrastructural Botanica Marina / Vol. 31 / 1988 / Fasc. 6 Copyright © 1988 Walter dc Gruyter · Berlin · New York 556 Costas ei aL: Ultrastructural organization in six dinoflagellate species changes induced by heavy metal exposure in diatoms. Previously Sicko-Goad et al (1977), developed a morphometrical procedure for quantitative volume estimation of cell organelles in phytoplankton organisms. In the work described here we carried out a morphometrical comparative study of the ultrastructure of six dinoflagellate species, by stereology. We analysed interspecific differences in ultrastructural organization and correlated interspecific quantitative variations in cell organelles with the size and growth rate of each species. Material and Methods Dinoflagellate cultures The isolation and culture procedures, as well as the characteristics and growth rates of the clones used have been previously described in more detail (Costas 1986). Clonal cultures of Prorocentrum triestinum Schiller (Pt); Prorocentrum micans Ehrenberg (Pm 1 and Pm2); Gonyaulax excavata (Braarud) Balech (Ge), Scrippsiella trochoidea Stein (St l and St2); Gonyaulax polyedra (Gp) and Gymnodinium sp. (Gym) were isolated from La Coruna Bay (NW Spain) and were grown in f/2 medium under continuous 25 μΕίη m~ sec"", light and temperature of 20 ± 1 °C. The growth rates of these clones in these environmental conditions are summarized in Table I. Table I. Growth rates (in doublings day — 1) of the clones used (mean ± SE)