Abstracts of papers read at the Winter Meeting, 1961

Herdmania litoralis is a heterotrophic, sand-dwelling dinoflagellate with morphological characters that do not provide clear evidence for its systematic position in any existing family of dinoflagellates. Protoperidinium minutum is a heterotrophic, planktonic species that has a typical tabulation for the genus Protoperidinium. In order to infer the phylogenetic positions of these two species more confidently, we characterized the thecal plate patterns and determined small-subunit and large-subunit ribosomal DNA sequences (SSU rDNA and LSU rDNA, respectively) from both species. Intraindividual and intraspecific diversity of SSU and LSU rDNA data were characterized in H. litoralis using a combination of single-cell PCR approaches and analyses of PCR clones derived from multi-cell DNA extractions. The results of the molecular phylogenetic analyses demonstrated a novel, well-supported clade comprising both sand-dwelling species (H. litoralis and Thecadinium dragescoi) and planktonic species (P. minutum). Because the establishment of this clade also demonstrated that P. minutum is not a member of Protoperidinium, we reinstated and emended the genus Archaeperidinium Jörgensen 1912 Jörgensen, E. 1912. Bericht über die von der schwedischen hydrographisch-biologischen Kommission in den schwedischen Gewässern in den Jahren 1909–10 eingesammelten Planktonproben. Svenska Hydrograph.-Biol. Komm. Skr., 4: 1–20.  [Google Scholar].     

Abstracts of papers read at the Winter Meeting, 1962

The effect of a range of inhibitors on the carotenoid biosynthetic pathway of the microalga Haematococcus pluvialis has been studied during normal growth and during the induction of astaxanthin synthesis. Diflufenican and norflurazon had similar effects and resulted in the almost complete inhibition of secondary carotenoid synthesis together with a build up of the acyclic carotenoid precursor, phytoene. In contrast, the inhibitor CPTA blocked cyclisation of lycopene and was seen to act differentially on the β- and ?-cyclases. Both diphenylamine and 1-aminobenzotriazole had the effect of blocking the synthesis of astaxanthin and the other secondary carotenoids by preventing the introduction of oxygen functions. As a direct result treated cells accumulated large levels of β-carotene instead. Selective use of inhibitors of carotenogenesis demonstrated that the accumulated lycopene and β-carotene could act as a precursor for astaxanthin synthesis.     

Abstracts of papers read at the Winter Meeting at the University of Surrey

A novel member of the Calyptrosphaeraceae surrounded by a hyaline sheath, with only one chloroplast and without an emergent haptonema, is tentatively described as a species of Calyptrosphaera Lohmann. It has an interrupted body to its single pyrenoid and a unique microtubular root complement with only one crystalline root (CR) nucleating on root 2 (R2). At preprophase it produces a CR1, lending support to the idea that these crystalline roots contribute to the mitotic spindle. It shares numerous ultrastructural traits with the heterococcolithophorid Cruciplacolithus neohelis but, although it is tempting to consider it a haploid phase of this organism, is distinct from it.     

Abstracts of Papers Read at the Winter Meeting at the University of Liverpool

Previous investigations with planktonic cyanobacteria have suggested that these organisms do not form new gas vesicles in the dark. This study, on Microcystis sp., confirmed that cells that had been preincubated at low photon irradiances (< 15 μmol m^-2 s^-1) formed negligible amounts of gas vesicles in the dark. Significant gas vesicle formation occurred, however, in cells preincubated continuously at higher irradiances, and particularly within the range 65 to 105 μmol m^-2 s^-1. The results suggest that gas vesicle formation in the dark is dependent on the prior accumulation of energy reserves. The amount of gas vesicles formed in continuous light was linearly related to irradiance over the range 0 to 20 μmol m^-2 s^-1, and reached a maximum at only 30 μmol m^-2 s^-1 that was over five times the amount formed at higher irradiances. This suggests that the rate of gas vesicle formation, regulated directly in response to irradiance, has a role in the light-mediated buoyancy regulation of this cyanobacterium.