Comparative ultrastructure of the zoospores of nine species ofNeochloris (Chlorophyta)

Nine species ofNeochloris can be divided into three groups on the basis of comparative ultrastructure of the flagellar apparatus, the cell wall and the pyrenoid of zoospores. In Group I,N. wimmeri andN. minuta, zoospores are thin-walled, pyrenoids are penetrated by stromal channels, and the basal bodies are in the clockwise absolute orientation and connected by the distal and two proximal fibers. In Group II,N. aquatica, N. vigenis, N. terrestris, N. pyenoidosa, andN. pseudostigmatica, zoospores are naked or covered by fuzzy material, pyrenoids are covered by a continuous starch sheath or invaginated by cytoplasmic channels, basal bodies are directly opposed, the distal fiber is differentiated into a ribbed structure at the central region, a striated microtubule-associated component (SMAC) is continuous between opposite two-membered rootlets and connected to the ribbed structure, proximal ends of basal bodies are covered by partial caps, each two-membered rootlet and a basal body are connected by a striated fiber to the X-membered rootlet associated with the opposite basal body, and the basal bodies, when oriented at wide angles, are joined at their proximal ends by core extensions. In Group III,N. pseudoalveolaris andN. cohaerens, zoospores are naked, pyrenoids are traversed by parallel thylakoids, basal bodies are in the counterclockwise absolute orientation and overlapped, and each X-membered rootlet is connected to the end of the opposite basal body by a terminal cap. It is suggested that the genusChlorococcopsis gen. nov. be erected for the Group I species. Group II, which includes the type species,N. aquatica, should be preserved asNeochloris. The group appears to be closely related to the coenobial generaPediastrum, Hydrodictyon, andSorastrum, and to have affinities with the coenocytic generaSphaeroplea andAtractomorpha as well. It is also suggested that the genusParietochloris gen. nov. be erected in thePleurastrophyceae for the species of Group III.     

Ein Beitrag zur Kenntnis vonApatococcus lobatus (Chlorophyta,Chaetophorales, Leptosiroideae)

Comparative investigations on the morphology, life-history, and reproduction of 3 cultivated strains of the atmophytic green algaApatococcus lobatus are presented. Some ultrastructural features are added to the results of earlier investigations, and comments on the systematics and ecology are given. Morphology and cytology of each strain is variable and shows considerable overlapping. The results support the view thatApatococcus consists of a single variable species (A. lobatus) only. For the epiphytic algal associationPleurococcetum vulgaris the more significant termApatococcetum lobati is proposed.

Herrn Prof. Dr.Lothar Geitler zu seinem 90. Geburtstag gewidmet.     

Comparative ultrastructure of pyrenoids inTrebouxia (Microthamniales,Chlorophyta)

Pyrenoid ultrastructure has been investigated from cultures of all 26 species ofTrebouxia with the aim of establishing pyrenoids as a taxonomic character. Different arrangements and forms of thylakoid lamellae within the pyrenoid matrix allow eight pyrenoid types to be distinguished. Each type is characteristic of a group of species. Thegigantea- andimpressa-type are similar, differing only in the form of the tubules: short, branched tubules mark thegigantea-type; ± long and straight invaginations theimpressa-type. Thearboricola-type is characterized by meandering pyrenoid membranes developing from lamellae parallel with each other in young autospores. Pyrenoids of thegelatinosa-type are traversed by thin parallel-arranged tubules. Few thylakoids with a curved profile are typical of theirregularis-type. Thecorticola-type is different from all others in having a distinct starch sheath closely connected with the pyrenoid matrix and no pyrenoglobuli being associated with the pyrenoid membranes. No true pyrenoids have been found inT. magna andT. erici. Within the chloroplast, they have indistinct areas with pyrenoglobuli, but without differentiated thylakoids. Pyrenoid morphology is stable in culture on different media as well as in phycobionts within lichen thalli. Comparing the pyrenoid of a lichenizedTrebouxia with that from cultured species, the identification of the phycobiont within the lichen thallus is possible, without the need of culturing the algae. This has been shown in species ofParmelia andHypogymnia. New aspects for the taxonomy and systematics ofTrebouxia are discussed.Dedicated to Prof. DrLothar Geitler on the occasion of the 90th anniversary of his birthday.     

Deoxyribonucleic acid base composition of simonsiellaceae

The molar percentages of guanine plus cytosine in the DNA of 51 strains of Simonsiellaceae were determined by buoyant density ultracentrifugation of cell lysates in CsCl. The DNA base ratios ranged from 41–55 mole-% guanine plus cytosine. These values fall within the range known for the Order Cytophagales, the non-fruiting gliding bacteria, and are out-side the range of the Order Myxobacterales, the fruiting myxobacteria. Among the strains of the genus Simonsiella, four distinct groups can be delineated on the basis of source of origin (sheep, dog, cat, human) and GC content. The neotype of Alysiella filiformis has a GC content of 45.4 mole-%.     

Zoospore ultrastructure in species ofTrebouxia andPseudotrebouxia (Chlorophyta)

Zoospore ultrastructure (incl. flagellar apparatus) has been investigated in three species ofTrebouxia (T. glomerata, T. erici, T. pyriformis) and one species ofPseudotrebouxia (P. impressa) using an absolute configuration analysis. Zoospores in all taxa studied are nearly identical in ultrastructure and exhibit a very distinctive disposition of cell organelles: cells are naked, biflagellate and considerably flattened along the plane of flagellar beat, the single contractile vacuole is located anteriorly in the ventral region of the cell, the nucleus is anteriorly to centrally located in the dorsal region of the cell. A single dictyosome is located close to the anterior, ventral edge of the nucleus. The chloroplast occupies a posterior position in the cell and usually has an anterior profile in the left region of the cell. There are two branched mitochondria per cell or a single mitochondrial reticulum with profiles anterior to the nucleus (in the dorsal region of the cell), and posterior to the nucleus. In zoospores ofTrebouxia spp. the posterior mitochondrial profile is associated with a microbody, inP. impressa zoospores the anterior mitochondrial profiles are associated with a microbody. The zoospores contain a distinctive system of three ER-cisternae: one system links to both basal bodies and extends to the nucleus, the other two systems subtend the plasmamembrane on the left and right broad cell surfaces and extend to the posterior region of the cell. The flagellar apparatus is structurally identical to that previously described for zoospores ofFriedmannia israelensis and exhibits basal body displacement by one basal body diameter into the 11/5 o'clock direction, a non-striated distal connecting fiber, a cruciate microtubular root system lacking system I fibers and presence of a single system II fiber which connects the basal bodies with the nucleus and runs parallel to one of the ER-strands. The left flagellar roots (X-roots) are subtended by a complex set of amorphous and striated material that connects each left root with both basal bodies.—This study demonstrates the close systematic relationship between the phycobiontsTrebouxia andPseudotrebouxia and the generaFriedmannia, Pleurastrum, andMicrothamnion and supports recent classification schemes which place all these taxa into a single order separate from otherChlorophyta. Dedicated to Prof. DrElisabeth Tschermak-Woess on the occasion of her 70th birthday.     

Carotenoids in the outer cell-wall layer of Scenedesmus (Chlorophyceae)

Scenedesmus obliquus, strain 633, which synthesizes ketocarotenoids and sporopollenin, also forms pink-red-colored cell walls. Both the cell walls left over after autospore liberation and those from homogenates of disrupted green cells have similar carotenoid pigmentation. Canthaxanthin, astaxanthin, an unidentified ketocarotenoid, and lutein were found as integral cell wall components. They are bound to the outer (trilaminar) layer of the complete cell wall which also contains sporopollenin.Abbreviations CWH complete cell walls isolated from the homogenates - CWM maternal cell walls accumulated in the medium - KC ketocarotenoid - SC secondary carotenoids - SP sporopollenin     

Phylogenetic position of the Oedogoniales within the green algae (Chlorophyta) and the evolution of the absolute orientation of the flagellar apparatus

The order Oedogoniales is made up of green algae with an unusual form of cytokinesis, a ring of flagella on the zoids, and a complex sexual reproduction. The genera included in this order, Oedogonium, Oedocladium and Bulbochaete, differ in their type of habit. In this contribution we report a phylogenetic analysis using 18S ribosomal DNA sequences from 66 species of green algae, including ten species of Oedogonium isolated from fresh water bodies in Argentina. The phylogenetic study demonstrates the monophyly of the Oedogoniales within the green algae, and suggests that in this group the flagellar apparatus of the stephanokont zoid could have derived from a DO configuration. It is also found that the genus Oedogonium does not appear to be monophyletic and that the morphological characters traditionally used for the taxonomic classification of Oedogonium species do not define natural groups.     

DNA base composition heterogeneity in some agarophytes (Gracilariales,Rhodophyta) from Mexico and the Philippines

Estimates of nuclear DNA base composition by determination of thermal denaturation temperatures (T_m) indicate guanine + cytosine (G + C) levels of 35.4–46.8% for ten species of the Gracilariaceae, representing the generaGracilaria andHydropuntia. T_m values were found to be reproducible with variation among most samples and replicates of less than 1 °C and 2 mol%. Interspecific variation in G + C values was less than 11.4% amongGracilaria species. Calculation of intragenomic base pair composition distribution based on mid-resolution thermal denaturation (A 1 °C/min with 4s interval H and dT logging) indicated an inverse relationship between maximum similarity values and taxonomic rank. Intraspecific (population level) maximum similarity (homology) values were estimated to range from 79–90% inGracilaria tikvahiae (4 isolates). Interspecific values of 46–69% were found in 13 species ofGracilaria. Nucleotide distribution similarity values for the Gracilariaceae are compared with previous information for genome organization and complexity, genome size and karyotype patterns.Author for correspondence     

A cladistic evaluation of the lower and higher green plants (Viridiplantae)

This paper presents a cladistic analysis and classification of the green plants (Viridiplantae). It is intended to be more balanced than previous treatments because more attention is paid to the lower green plants, or green algae. A major dichotomy is reflected by the structure of the flagellar root system of motile cells. Taxonomically, this justifies recognition of two divisions of green plants, viz.Chlorophyta sensu stricto, andAnthocerotophyta. The latter embraces a portion of the green algae plus all embryophytes. From a cladistic viewpoint it is doubtful whether land plants are strictly monophyletic.     

Notes on the variation,geographical distribution and ecology ofEuastrum insulare var.basichondrum (Chlorophyta,Desmidiaceae)

Euastrum insulare var.basichondrum, morphologically taking an intermediate position in respect ofCosmarium trilobulatum var.basichondrum andEuastrum bipapillatum, appeared to exhibit such a wide range of variation that it may be considered identical to the other two above-mentioned taxa. This taxon, after having been studied with both light- and scanning electron microscopy, is re-diagnosed. This alga occurs in wet moss cushions in weakly acid to neutral environments. The relation between such a terraqueous habitat and the principally arctic-alpine distribution and a conceivably associated process of speciation is discussed.     

Cell shape in the algaPediastrum (Hydrodictyaceae; Chlorophyta)

Summary Species ofPediastrum, a genus in which the colonies assemble from aggregating zoospores, differ in the number and form of prongs on peripheral cells and the amount of space between cells of the colony; cell shape appears to be genetically based. Peripheral cells of theP. boryanum colony, for example, have two prongs per cell;P. simplex has one prong per cell. Prong extension is suppressed in the interior cells ofP. boryanum, but prong sites have been reported in scanning electron micrographs of the cell walls. A mutant unicellular strain in which cells of the colony separate after attaining typical form reveals several prong sites (6 or more) in each cell. Multiple suppressed prong sites are evident inP. simplex cells as well. Polyeders, 4- and 5-pronged unicells, occur in the life cycle ofP. simplex. Based on these observations and a recent report byMarchant (1979) of a microtubule organizing center associated with the prongs, it is suggested that several microtubule organizing centers are to be found in zoospores ofPediastrum species and may be related to species differences in cell shape.Research supported in part by Argonne Center for Educational Affairs, U.S. Department of Energy, under contract No. W-31-109-ENG-38.     

Cell multiplication and ultrastructure ofMicrasterias denticulata (Desmidiaceae) grown under salt stress

Cells ofMicrasterias denticulata Bréb. were kept in nutrient solution of high osmolality (salt stress) for four weeks. In a special cell multiplication test it was established that cell division is gradually inhibited at increasing salt concentrations and totally arrested at the highest concentration (26 mosm/kg). Recovery studies proved that even cells from the highest concentration range start dividing immediately after being placed in aqua bidest. thus indicating the full reversibility of the inhibiting effect. — Cells of the highest concentration range show marked ultrastructural changes. Besides an enormous accumulation of starch and oil bodies and a condensed appearance of the ground plasma, a reduction of mitochondria, ER and the Golgi-system is found. The most striking effect occurs on the vacuolar system which appears extremely reduced and condensed. The cell wall is thickened by the formation of an additional cell wall layer with a spongy electron microscopical appearance. Through the cell wall many droplets of a probably fat-like substance are excreted. — In summary, salt stress induces growth-inhibited akinete cells in the sense ofFritsch; these can be reactivated by decreasing the salt concentration. The salt-induced akinete state seems to be an ecological adaption to unfavourable conditions rather than a degeneration of the cells.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday.23. 12. 1988     

The fine structure of motile cells in the generaUlvaria andMonostroma,with special reference to the taxonomic position ofMonostroma oxyspermum (Ulvophyceae,Chlorophyta)

The zoospores and isogametes ofUlvaria obscura var.blyttii, the isogametes ofMonostroma bullosum, and the anisogametes ofM. grevillei have a flagellar apparatus with counterclockwise absolute orientation and terminal caps, and therefore belong to theUlvophyceae. On the basis of the absence or presence of body scales and the morphologies of certain flagellar apparatus components,Ulvaria obscura var.blyttii is retained in theUlvales, whileM. bullosum, M. grevillei andM. oxyspermum are referred to theUlotrichales. Differences in scale morphology, certain flagellar apparatus components, and early thallus ontogeny support the transfer ofM. oxyspermum to the genusGayralia. Mating structures and their positional relationships within the cell are described from the gametes examined. A plasmalemma-associated plaque that may be a degenerate mating structure occurs in someG. oxysperma motile cells.     

Detection of DNA polymorphisms within the genusCattleya (Orchidaceae)

We have adapted methodology necessary for the detection of molecular polymorphisms in the orchid genusCattleya, namely, randomly amplified polymorphic DNA (RAPD). We report a high level of molecular variability among species; each of eight species examined exhibited a unique DNA fingerprint with nine out of ten arbitrary primers used in single-primer RAPD reactions. Among progeny of an intraspecificCattleya cross, 55 percent of major amplification products were found to segregate. Segregation of these markers facilitated the preliminary identification of several linkage intervals. The identification and mapping of DNA polymorphisms by the RAPD technique will facilitate the use of these taxa for the identification of species-specific and genus-specific traits, allow for the measurement of recombination and introgression in hybrid populations, and enable geneticists to address concordance (or lack thereof) in the processes of speciation, morphological evolution, and molecular change in a large and highly advanced plant family.     

Determination of DNA base composition by small scale acrylamide-CsCl gradient centrifugation

In this paper we describe a simple and rapid protocol for DNA base composition determination by CsCl gradient in the presence of acrylamide. This method permits the determination of GC content in microgram amounts of DNA, and results are easily documented in photographs or graphs. The protocol was applied to the characterization of nematode DNA, but can be used for other organisms. Analyzing several experiments the mean standard deviation observed in the calculated GC content is near 1.3%.     

C-band distribution,DNA content and base composition inAdoxa moschatellina (Adoxaceae), a plant with cold-sensitive chromosome segments

The chromosomes ofAdoxa moschatellina (2n = 36, paleo-4x) contain mostly terminal, occasionally intercalary, negatively heteropycnotic cold-induced regions which correspond to all major C-bands including the satellites, as revealed by sequential analysis. Positively C-stained are also centromeres, the dotlike arms of the 7 telocentric chromosome pairs, and some very narrow intercalary bands; their cold-sensitivity is hardly traceable. There exists a fraction of condensed interphase chromatin, at least after chilling, which is virtually not C-banded (possibly condensed euchromatin).The DNA amount is 14.3 pg (1 C). The heterochromatin content is 13.0%. The thermal melting profile (Tm corresponding to 38.6% GC) does not reveal a particular AT- or GC-rich fraction. Significantly, the heterochromatin respond to the Hy-banding procedure is neutral.The distribution of cold-sensitive regions in plants was analysed with the arm-frame method: Intercalary positions, clearly, are not especially favoured regions. The obvious deficiency at centromeric positions may depend on the action of natural selection against mechanically labile centromeric regions.Dedicated to Univ.-Prof. Dr.Lothar Geitler on the occasion of his 80th birthday.     

Evolution of highly repeated DNA within the genusTriturus (Amphibia,Urodela)

Highly repeated DNA is a main feature of urodele amphibian genomes. InTriturus this class of DNA consists of several sequence families differently arranged at both the molecular and the chromosomal level, showing varying degrees of conservation across species. Present data on highly repeated DNA inTriturus are here summarized and discussed with regard to the evolution and possible functional role of these sequences.     

Variability in nuclear DNA content within pigeonpea,Cajanus cajan (Fabaceae)

4C DNA values have been estimated in 16 cultivars ofCajanus cajan by cytophotometry. The values range between 6.19 pg to 7.97 pg, a 23.6% variation. The cultivars form four groups which differ significantly from each other but have insignificant difference within them. The implications of this variability with respect to the heterogeneity and origin of this legume crop are discussed.     

Nuclear DNA content inCelosia (Amaranthaceae)

Nuclear DNA amount of five species ofCelosia ranging from 2x to 12x varies from 3.26 (2x) to 9.70pg (12x). The diploidC. trigyna has twice as much DNA/basic genome as other taxa, which is commensurate with its taxonomic position and genetic isolation. There is insignificant variation in DNA/basic genome among 4x, 8x, and 12x taxa. Therefore, DNA/nucleus shows a strong positive correlation with ploidy level. The different accessions of 4x taxa show constancy of DNA amounts. There is no correlation of seed weight with DNA amount.     

PCR-identification of Dunaliella salina (Volvocales, Chlorophyta) and its growth characteristics

The saline pond microalga, Dunaliella salina (Dunal) Teod. maintained in De Walne's (basal) medium under laboratory conditions was confirmed by amplifying the chromosomal DNA of the microalga by PCR with specific primers MA1 and MA2. Seaweed extracts obtained from Sargassum wightii and Ulva lactuca were amended separately at 1.0%, 1.5%, 2.0% and 2.5% levels to the basal medium in order to assess their potential on the growth and concentration of pigments, viz. Chl a, Chl b and beta-carotene of the alga. beta-Carotene was isolated and visible absorption spectrum was taken at 443 and 475 nm confirmed the presence of 9-cis-beta-carotene and all-trans-beta-carotene isomers. Maximum yield, highest division rate (mu) and highest pigment concentrations were observed in the cells grown in 1.5% S. wightii and 2.0% U. lactuca amended medium and these cells were subjected to DAPI staining. The results of epifluorescence microscopy and image analysis revealed a significant enhancement of the cell and nuclear area of the microalgae.