DIFFERENTIATION OF THE GREEN ALGA CODIUM FRAGILE

Clonal cultures of Codium fragile were established from both swimming cells and vegetative filaments. In the laboratory axis primordia differentiate from heterotrichous juveniles only when cultures are agitated on a reciprocating shaker. The shear forces created by mechanical agitation are essential both for initiation and maintenance of primordia. Contact guidance of growing coenocytic filaments indicates mutual adhesion of filaments as the basis for the differentiation process.     

GROWTH OF THE GREEN ALGA CODIUM FRAGILE IN A CONNECTICUT ESTUARY1

An in situ comparison of environmental and physiological factors was undertaken in 1971–72 (15 months) in the Niantic River estuary to elucidate some of the important aspects, of the growth and development of the seaweed Codium fragile. In general, Codium in the estuary has a growing season of from 6 to 9 months. Growth increments during this period are relatively constant. Temperature and salinity are the main limiting factors to growth, although low summer concentrations of inorganic nitrogen may also be involved. Reproduction by means of swarmers occurs only in late summer or autumn. Codium appears highly adapted to the role of a colonizing species. It not only possesses the capability to occupy the harshest of environments, but also a system of reproductive alternatives which facilitates rapid colonization. The availability of substrate for attachment is the chief factor limiting its spread in this estuarine system.     

CURRENT STATUS OF THE INVASIVE GREEN ALGA CODIUM FRAGILE IN EASTERN CANADA

Ten years after the initial discovery of Codium fragile in eastern Canada on the Atlantic coast of Nova Scotia, C. fragile has extended its range considerably to northern Nova Scotia, southern New Brunswick and Prince Edward Island (P.E.I.) in the Gulf of St. Lawrence. In all principal areas C. fragile subsp. tomentosoides is present. In two regions of Prince Edward Island, Codium is becoming extremely abundant, and is known by local fishers as the "oyster thief". A potential second taxon of Codium was collected in 1999 at three sites in Malpeque Bay where it is locally abundant. These plants are distinguished from C. fragile subsp. tomentosoides by their smaller frond size, flatter utricle tops, smaller mucrons, and smaller gametangia. Principal component analysis distinguishes plants of the two types. The abundance of C. fragile on both hard bottom and soft bottom substrata suggests that it will become the dominant alga in many subtidal algal communities in eastern Canada.     

SEPTAL PLUGS IN A GREEN ALGA

Septal plugs, resembling those found in red algae, occur in the transverse wall between all cells in a newly discovered marine green alga, Pilinia earleae Gallagher & Humm.³ No plasmodesmata traverse the cross-wall, and the septal plug blocks cytoplasmic continuity between cells. The septal plug consists of an electron-translucent core bordered at each end by two electron-opaque caps. Cytochemical procedures demonstrate that the plug consists of protein and polysaccharide, but lacks peroxidase. The outer cap is highly proteinaceous while the inner cap is composed primarily of polysaccharide. The plug core is not routinely stained by Coomassie Blue but it is pronase sensitive and probably proteinaceous. Historically, septal plugs have been considered unique to the red algae and the fungi, but ultrastructural and biochemical data provide no support for derivation of the septal plug in this green alga from a symbiotic relationship. The discovery of septal plugs in a green alga makes the hypothesis of an independent origin of this structure in a number of plant groups more likely.     

CHLOROPHYLL A:B RATIOS IN SOME SIPHONOUS GREEN ALGAE IN RELATION TO SPECIES AND ENVIRONMENT1

The chlorophyll a:b ratios measured in several species of Caulerpa and in Bryopsia plumosa (Hudson) C. Ag. gave values close to 2.00 or below. Values obtained for Ulva lactuca L. taken from the same site gave a higher value of 2.44, and the sea-grass Heterozostera tasmanica (Martens ex Aschers) den Hartog a value of 2.98. Although there were changes in a:b ratios observed when Caulerpa plants were, stored for up to 10 days in dim light, the values did not suggest that chlorophyll a:b ratios were directly controlled by light intensity. It is conducted that the a:b ratios described in this paper, are a characteristic of the species themselves and are not a result of their growth in extremely shaded situations.     

A POSSIBLE VIRUS INFECTION IN THE GREEN ALGA OEDOGONIUM1

Developing germlings of the green alga Oedogonium have been sectioned and some were found to contain particles presumed to be those of a virus. Fully formed particles were hexagonal in a 2-dimensional section, about 240 nm in diameter with a densely stained surface layer and core; what appear to be different stages in their assembly were also seen. Many of the particles were clustered together in groups surrounded by aggregations of ribosomes. In cells containing many of the particles, the germlings' cytoplasm and organelles showed considerable evidence of disruption and breakdown. These particles have only been detected in germlings, so infection by this presumed virus was probably initiated in the naked, motile zoospore.     

MOLECULAR DELINEATION OF SPECIES AND SYNGENS IN VOLVOCACEAN GREEN ALGAE (CHLOROPHYTA)1

Two species of the colonial green flagellate family Volvocaceae are worldwide in distribution yet exhibit contrasting species structure. Geographically disparate isolates of Gonium pectorale Mueller can interbreed while isolates of Pandorina morum Bory behave quite differently. More than 20 sexually isolated subpopulations occur within this species; these have been termed “syngens” (sensu Sonneborn). Because prezygotic barriers to mating cause intersyngen pairings to fail, breeding analyses cannot be used to estimate genetic relatedness among the syngens of P. morum. DNA comparisons provide an alternative method of assessing genetic relatedness. We compared the nucleotide sequence of the internal transcribed spacer (ITS) region of the nuclear ribosomal repeat among clones of P. morum and of G. pectorale. Members of syngens of P. morum with distribution restricted to one small geographical area show great similarity. Likewise, members of any syngen of worldwide distribution show near uniformity, even those from different continents. However, the ITS sequence of each syngen differs from that of other syngens. In contrast, G. pectorale, which has an ITS region that is remarkably uniform throughout the world, appears to consist of a single syngen within North America and Europe by mating tests. The molecular data are in complete conformity with previous syngen assignment. Because the latter is based on mating affinity, with two complementary mating types per syngen, the evolution of new mating type pairs appears to be the basis of microevolution in these algae. We infer that either P. morum is a more ancient species than G. pectorale or that P. morum has a less stable genome. In either case, the biogeographic distribution of certain syngens may reflect climatological changes of the past.     

METHYLAMINE UPTAKE IN THE GREEN ALGA CHLORELLA PYRENOIDOSA1

Methylamine uptake in nitrogen-starved Chlorella pyrenoidosa Beij. follows Michaelis-Menten kinetics: maximum uptake is about 1.6 nmol μl^?1· cells · min^?1, half-saturation occurs at 4 μM methylamine, and the slope in the range where uptake is proportional to concentration is 0.4 nmol μl^?1· min^?1·μM^?1. In cells grown in the presence of a non-limiting nitrogen concentration, methylamine uptake is directly proportional to concentration up to at least 0.5 mM, and the slope is 1/500 that for starved cells. Similar uptake kinetics have been reported for Penicillium chrysogenum and attributed to an inducible “ammonium permease.” Apparently, a similar permease occurs in algae.     

PIGMENT COMPOSITION OF THE SCALY GREEN FLAGELLATE MESOSTIGMA VIRIDE (MICROMONADOPHYCEAE) IS SIMILAR TO THAT OF THE SIPHONOUS GREEN ALGA BRYOPIS PLUMOSA (ULVOPHYCEAE)1

Pigments were isolated from Mesostigma viride Lauterborn by reversed-phase high-performance liquid chromatography and compared to standards from Chlamydomonas reinhardtii Dang. and Bryopsis plumose (Huds.) Ag. M. viride possesses chlorophylls a and b, α and β-carotenes, and the xanthophylls siphonaxanthis, siphonein, neoxanthin, violaxanthin and echinenone. In addition, three unidentified xanthophylla were detected. Neither lutein nor zeaxanthin were detected. The pigment composition of M. viride was similar to that of B. plumosa which had chlorophylls a and b, ?- and α-carotenes, siphonaxanthin, siphonein, neoxanthin, violaxanthin, and two of the unidentified xanthophylls found in M. viride. The similarities in the pigments of Mesostigma and Bryopsis and other characters suggest that Mesostigma may be related to a flagellate ancestor of the Ulvophyceae.     

STORAGE AND STRUCTURAL PRODUCTS FORMED DURING PHOTOSYNTHESIS IN THE SIPHONOUS ALGA CAULERPA SIMPLICIUSCULA(CHLOROPHYCEAE)1

The distribution of radioactivity into storage and intermediary metabolites during photosynthesis over periods of up to three hours was followed in the siphonous green alga Caulerpa simpliciuscula C. Ag. After the first hour, almost all the carbon assimilated was recovered as insoluble 1,4-α-glucan. There was rapid movement of carbon into insoluble 1,3-β-glucans during the first 20 min of photosynthesis, but little additional carbon moved into these compounds after that time. This contrasted with the movement of carbon into the soluble 1,3-β-glucan fraction, which continued for 2 h. Sucrose accumulated very little ¹⁴C during the entire period of photosynthesis. There was a very slow transfer of ¹⁴C into lipid throughout the period but the rate was linear. Protein labelling showed a lag of 2 h before it reached the same rate of ¹⁴C accumulation as shown by the lipid initially. It is suggested that the distribution of radioactivity can be explained in part by proposing that the tissue is in the latter stages of recovery from the wounding which look place at the time of dividing the thallus into sections.     

ULTRASTRUCTURE OF MITOSIS AND CYTOKINESIS IN THE MULTINUCLEATE GREEN ALGA ACROSIPHONIA

The processes of mitosis and cytokinesis in the multinucleate green alga Acrosiphonia have been examined in the light and electron microscopes. The course of events in division includes thickening of the chloroplast and migration of numerous nuclei and other cytoplasmic incusions to form a band in which mitosis occurs, while other nuclei in the same cell but not in the band do not divide. Centrioles and microtubules are associated with migrated and dividing nuclei but not with nonmigrated, nondividing nuclei. Cytokinesis is accomplished in the region of the band, by means of an annular furrow which is preceded by a hoop of microtubules. No other microtubules are associated with the furrow. Characteristics of nuclear and cell division in Acrosiphonia are compared with those of other multinucleate cells and with those of other green algae.     

TAXONOMIC SIGNIFICANCE OF NUCLEUS-MICROBODY ASSOCIATIONS,SEGREGATED NUCLEOLI AND OTHER NUCLEAR FEATURES IN SIPHONOUS GREEN ALGAE1

On the basis of fine-structural features of nuclei the “true” siphonous green algae (Eusiphoniidae) are divided into three groups. In the Codium group nuclei are generally similar to those in most other algae. The Penicillus group is characterized by the association of microbodies with nuclei. In the Avrainvillea group nucleoli are segregated into a granular and a fibrillar component. This condition, known as macrosegregation, persists throughout the vegetative phase of the life history and may indicate a peculiar ribosomal RNA cycle. The Penicillus group corresponds to the order Caulerpales Feldmann. Avrainvillea and Cladocephalus probably constitute a new order. Blastophysa, although having a type of segregated nucleoli, is probably more closely related to Siphonocladales than to any order in Eusiphoniidae.     

MICROSENSOR STUDIES OF OXYGEN AND LIGHT DISTRIBUTION IN THE GREEN MACROALGA CODIUM FRAGILE1

Scalar irradiance, oxygen concentration, and oxygenic photosynthesis were measured at 0.1 mm spatial resolution within the tissue of the siphonous green macroalga Codium fragile subsp. tomentosoides (van Goor) Silva by fiber-optic scalar irradiance microsensors and oxygen microelectrodes. The scalar irradiance of visible light was strongly attenuated in the outer 0.2 mm of the tissue but was nearly constant for the subsequent 1.0 mm of photo-synthetic tissue. Far-red scalar irradiance at 750 nm increased below the tissue surface to a maximum of 200% of incident irradiance at 1.2 mm depth due to multiple scattering in the medullary tissue. The constant intensity of visible light below 0.2 mm was thus a result of the combined effects of absorption and backscattering from the medulla. The oxygen exchange between the alga and the surrounding water was diffusion-limited with a steep O₂gradient inside and around the alga. In darkness, the tissue below 0.6 mm became anoxic, and endophytic extracellular space provided an environment where anoxygenic microbial processes may occur. When illuminated at 160 nmol photons·^?2·^?1, O₂ concentrations exceeded ambient levels throughout the thallus, with a maximum of 250% of air saturation just below the surface. The amplitude of oxygen variation was buffered by gas bubbles formed in the medullary tissue.     

CALCIUM OXALATE CRYSTALS IN THE GREEN ALGA SPIROGYRA SP. (ZYGNEMATALES, CHLOROPHYTA)

Specimens of an unidentified species of the freshwater green alga Spirogyra were found to have abundant cruciate cellular inclusions up to 34 micrometers long. A crystalline nature was shown by birefringence in polarized light. Despite their large size and complex shape, these inclusions did not occur free in the large central vacuole. Instead, they were associated with cytoplasmic strands that spanned the space between gyres of the parietal spiral chloroplasts and with strands that suspended the nucleus in a cytoplasmic embayment of the central vacuole. Some crystals moved directionally along the cytoplasmic strands, and their movement was arrested by cytochalasin B, suggesting that actin microfilaments had a role in crystal movement. Solubility tests showed that the inclusions were composed of calcium oxalate; they dissolved rapidly in weak hydrochloric acid without effervescence, but they were not soluble in concentrated acetic acid or sodium hypochlorite. A colorimetric enzymatic test for oxalate was used to demonstrate microscopically the presence of oxalate and to quantify the amounts. The calcium oxalate crystals were surrounded by a water-soluble organic matrix that retained the shape of the crystal even after demineralization. Scanning electron microscopy was used to examine the morphology of isolated crystals.     

A CLASSROOM DEMONSTRATION OF ZOOSPORE PRODUCTION IN THE GREEN ALGA SCHIZOMERIS LEIBLEINII KUETZ.12

Using the parenchymatous ulotrichalean green alga Schizomeris leibleinii, a dependable technique for the classroom demonstration of zoospore production is described. The onset of zoospore release can be predicted accurately by controlling light, temperature, and medium. Large numbers of zoospores are released.     

FINE STRUCTURE OF CAPITULAR FILAMENTS IN THE COENOCYTIC GREEN ALGA PENICILLUS1,2,3

Capitular filaments of Penicillus capitatus contain a large central vacuole. The parietal cytoplasm is densely packed, devoid of chloroplasts in the growing tip, and becomes convoluted and sponge-like as extensions of the vacuole penetrate the cytoplasm in mature portions of the filament. Structure of organelles and their distribution in the filament are described. The vacuole contains a variety of inclusions, such as membranous configurations, spherical bodies, electron dense bodies, and calcium oxalate monohydrate crystals, each of the latter surrounded by a chamber associated with microtubules. Endophytic bacteria are present throughout the vacuole and occasionally in the tip cytoplasm. Some vacuolar components of P. pyriformis are described for comparison.     

丝状固氮蓝藻柱胞鱼腥藻原生质球的培养再生

丝状固氮蓝藻柱胞鱼腥藻 (Anabaena cylindrica)在含 0 .1mol/ L KCl的 Allen液体培养基中培养7～ 9d,90 %以上细胞转化为原生质球或半原生质球 ,对低渗敏感或抗低渗。此种材料经 0 .1%溶菌酶 ,在 2 8℃下处理 3～ 4h,细胞低渗破裂率约 10 0 % ,成为质量较高的原生质球。用 0 .15mol/ L Ca Cl2 液体无机盐培养基培养 ,原生质球再生和分裂。不同原生质球再生不同步 ,最快培养 3 d分裂。再生分裂的主要方式为均等分裂 ,但有不规则分裂和出芽方式 ,再生率在 2 5%以上。