Absence Of Pyrenoids Research Articles

REPRODUCTION AND SYSTEMATICS OF THE MARINE ALGA DERBESIA (CHLOROPHYCEAE) IN NEW ENGLAND1,2

SUMMARYThe morphology, gross cytology, reproduction, and habitat ecology are described for Derbesia marina based on observations of New England field populations and laboratory cultures of this plant. These data, and additional observations on cultures of several other species of Derbesia from elsewhere and on type and other important collections, have been used to evaluate the systematic relationship of New England Derbesia with other species of this genus. The single Derbesia species in New England is referred to D. marina. The systematic criteria previously used to distinguish species within Derbesia are reviewed and interpreted within the context of the present investigation. In systematic studies, we stress the importance of the use of sporangial and chloroplast morphology, the presence or absence of pyrenoids, and reproductive history.Two types of life history are reported for D. marina in New England: (1) A form of D. marina collected at 20 m reproduces directly with stephanokontous zoospores growing into sporophytic plants of Derbesia morphologically identical to their parent thalli. (2) On the other hand, at least some New England, populations of D. marina have retained the genetic potential for producing a sexual generation (Halicystis ovalis), even though the latter is unknown for the coast of northeastern North America.3 Gametophytes (H. ovalis) were produced directly from enlargement and subsequent differentiation of uncleaved lateral sporangia in 2 cultured populations of New England D. marina. A single female and numerous male vesicles formed in this manner produced gametes, but neither fertilization nor parthenogenesis occurred; thus the entire life history was not completed in culture.The occurrence of the directly reproducing deep water form of D. marina is presented as evidence for speciation of a sporophyte (Derbesia) independent of its alternate gametophyte (Halicystis). An hypothesis is advanced to explain the source and means for expression of genetic variability necessary for speciation in a population of nonsexually reproducing Derbesia.

Distribution of pyrenoids among some brown algae.

The distribution of pyrenoids among some orders of the brown algae has been investigated with the electron microscope and a report on their occurrence is given, with particular reference to the results obtained with the light microscope by Simon (1954). Some illustrated detail of the structure of the pyrenoids and of the chromatophores is included. Pyrenoids were found to be present in the representatives examined of the Ectocarpales, Sphacelariales, Scytosiphonales and Dictyosiphonales. Excepting the Sphacelariales, this is in agreement with the results of Simon. Pyrenoids were found to be definitely absent in all members of the Dictyotales and Laminariales examined, and disagreement is expressed with Bouck (1965) who reported their presence in Chorda filum, a member of the latter order. The situation in the Fucales is the subject of another communication elsewhere. The presence or absence of pyrenoids is regarded as an additional taxonomic character of possible phyletic use when more is known. The results are discussed from the standpoint of their possible value in assessing the relative position of the Phaeophyceae as a whole. Brown algal lamellations are composed of three, or occasionally four, parallel thylakoids which do not cohere and are not aggregated into stacks. This is thought to be more primitive than the condition in some of the other groups of the Chromophyta where there is adherence of thylakoids into stacks of two or three members as, for example, in the Haptophyceae, Xanthophyceae and Chrysophyceae. The Phaeophyceae are, however, regarded as much less primitive than the Rhodophyceae, where the widely spaced parallel thylakoids are arranged singly.

TAXONOMIC PROBLEMS IN THE EUGLENINEAE

SummaryThe Euglenineae form a well‐defined natural group comprising a great number of species, the subdivision of which into families is difficult to make.Among taxonomic features, the basic shape of the cell body is fusiform but often irregular and twisted, with periodical tapering towards the posterior end. It may be concealed by morphological aberrations. The metaboly of many species and the occurrence of dimensional varieties render the use of shape and size as specific features sometimes rather equivocal. Other features have to supplement them for the identification of the species.The shape of the nucleus is sometimes characteristic, but the structure of the plastidome and the presence or absence of pyrenoids are of much greater taxonomic importance. These features vary greatly in the species of Englena, while the other green genera have almost uniform chromatophores. By plastid and other characteristics Trachelomonas and Colacium are related to certain species of Euglena, while Phacus and Lepocinclis are nearer to others.The flagellar apparatus of the Euglenineae is tentatively considered as being composed of two flagellar units throughout the group, the length alone varying according to the genus. Eutreptia with two equal or more or less unequal flagella would be nearest to the hypothetical ancestral form. The other green genera would be derived from it by a further shortening of the minor flagellum. Its near convergence to the long active flagellum gives the impression of bifurcation. Distigma would be the apoplastidic counterpart of Eutreptia, Astasia that of Euglena. All green Euglenineae and some colourless ones have an eye‐spot and opposite to it a thickening of the active flagellum or flagella not found in the species without an eye‐spot.The striation of the periplast varies greatly, without correlation to the degree of cell metaboly. A first attempt at classifying the different types of metaboly is made. Envelopes differ from the periplast by being exudations of inorganic substances.While the distinction between the phototrophic and the saprotrophic Euglenineae seems gradually to disappear, the holozoic forms are more distantly derived. There are no indications as to their evolution, as no zootrophic green Euglenineae are known, and some are similar to saprotrophic forms. The entire class of the Euglenineae is rather uniform, and a rational and at the same time natural classification has not yet been attained.