A STUDY OF WALL ORNAMENTATION IN CULTURES OF SCENEDESMUS

In a comparative study, six strains of Scenedesmus isolated from one small pond were examined in culture. Three of the isolates, S. denticulatus, S. dispar, and S. abundans, proved to be morphologically quite stable when studied in the laboratory. In an axenic culture of any one of the three pleomorphic strains one could find coenobia which resemble S. longispina or S. armatus. High percentages of four-celled coenobia with several ridges but with only two spines (the S. semipulcher type) were found typically in older cultures of two of the pleomorphic cultures. Long, delicate appendages (bristles) were easily detected on most coenobia in desiccated preparations of all but the S. dispar culture. The use of cultures in identifying Scenedesmus coenobia is discussed.     

SPINE DISTRIBUTION IN SEVERAL SCENEDESMUS CULTURES

In a comparative study of several cultures of species of Scenedesmus, it was determined that some were morphologically quite stable. These included 1 culture each of S. abundans, S. bijugatus and S. quadricauda. Three isolates were pleomorphic. In an axenic culture of one of the pleomorphic organisms one can find coenobia which resemble S. longus, S. abundans, S. bijugatus and S. acutiformis. The value of pure-culture studies is emphasized, and the identification of members of the genus based solely upon microscopic observation of organisms from nature is discouraged.     

THE CELL WALL OF SCENEDESMUS QUADRICAUDA

Bisalputra, T., and T. E. Weier. (U. California, Davis.) The cell wall of Scenedesmus quadricauda. Amer. Jour. Bot. 50(10): 1011–1019. Illus. 1963.—Fine structure of the cell wall of Scenedesmus quadricauda fixed in both KMnO₄ and osmium tetroxide is described. The cell wall consists of 3 layers: the inner cellulosic layer which delimits individual cells; the outer pectic layer which binds the cells of the coenobium together; and a thin middle layer, bounded by membranes on either side, which is electron-dense in osmium-fixed material but of medium electron density in KMnO₄. The structure of the outer pectic layer is similar in both fixatives; it consists of a hexagonal network of electron-dense material on the surface, and a system of tubules or “props” which radiate out from the middle layer of the wall to support the net. The pectic layer appears in the daughter coenobia before their liberation from the parent colony.     

THE PECTIC LAYER OF THE CELL WALL OF SCENEDESMUS QUADRICAUDA

Further evidence from shadow casting techniques of the empty cells of Scenedesmus quadricauda confirms the structure of the pectic layer presented in an earlier work which was based entirely on reconstruction from thin sections. The structure of the net and props and their relationship are clearly seen and the inner boundary of the pectic layer is demonstrated by staining techniques.     

SCENEDESMUS MORPHOGENESIS. COLONY CONTROL IN DILUTE MEDIA1

Morphological stability, with the elimination of the unicellular singe, was achieved by culturing several strains of Scenedesmus in media with, low inorganic salt levels. Organisms stabilize and form only colonies at specific nutrient levels. One became colonial only when the salt level was dropped to 3.07 mg inorganic salts per liter, with N and P at levels found in nature.     

SCENEDESMUS MORPHOLOGY AND FLOTATION1

Various flotation studies were conducted on several strains of Scenedesmus. Inverted microscope flotation experiments run on culture 614 with bristles, culture 614 centrifuged to remove bristles, and bristle-less strain 76 revealed that bristles aid in flotation. Cultures grown in NH₄NO₃-Bristol's compared to cultures grown in Bristol's medium exhibited a positive buoyancy as do cells transferred, to fresh media. Differential centrifugation procedures demonstrate that colonies with bristles and spines exhibit a greater buoyancy than spineless and bristle less colonies, and furthermore that unicells and newly released colonies exhibit greater buoyancy than older cultures and large, granular, dividing cells.     

CELL DIVISION IN BULBOCHAETE. I. DIVISIONS UTILIZING THE WALL RING1

Cell division in Bulbochaete closely resembles that of Oedogonium, particularly in the involvement of a ring in cell elongation, the structure of the spindle, the existence of complex kinetochores, and the method of cross-wall formation using a phycoplast. Some minor differences between the 2 genera are found. In contrast to Oedogonium, the filaments of Bulbochaete are branched. The site and direction of branching are initially determined by a subtle change in the morphology of the wall, which invariably (if the cell divides) leads to the asymmetrc division that forms a hair cell (these events will be described separately). The position of the wall ring is always precisely determined as in Oedogonium, by the position of a very characteristic weakening in the wall; once a hair cell has been formed, this weakening is located underneath the hair, and all subsequent division and elongation in the cell subtending the hair will necessarily be in the direction of that hair (ie, thereby forming and increasing the length of a branch).     

SCENEDESMUS MORPHOGENESIS. TRACE ELEMENTS AND SPINE FORMATION1

When Scenedesmus culture 16, a soil organism with numerous long spines, was grown in axenic culture in a dilute laboratory medium (with approximately 30 mg/liter total salts), spines were not formed. In this medium the organism resembled S. bijugatus, whereas S. longus and S. abundans colonies were typically formed in more concentrated media. Spines were formed on daughter colonies upon transfer to the dilute medium plus additional Fe EDTA or Ca EDTA. No other individual components of the medium did this. Spineless colonies were healthy and green with a well-defined chloroplast, provided the culture was transferred often. In addition to the absence of spines, cultures in the dilute medium had a linear arrangement of cells within a colony, along with terminal cells 20% shorter than median cells. With 4-celled spiny colonies all cells were the same length and were alternately arranged.     

PHENOTYPIC PLASTICITY IN SCENEDESMUS COMMUNIS (CHLOROPHYCEAE). I. RELATIONSHIP OF S. COMMUNIS TO S. KOMAREKII1

When scenedesmus communis Hegew. (UTEX 76) was transferred daily in dilute media and a low cell density was maintained (ca. 1000 cells · mL^?1), up to 30% unicells were produced in that population. Unlike previously described uncell-coenobium-unicell transformation with other species, these unicells never produced S. communis coenobia (large coenobium type, LCT) but rather small coenobium type (SCT) resembling S. komarekii Hegew. Growth and morphological development of the paratype strain of S. komarekii (UTEX 1236) was compared with an isolated SCT strain (SCT 76–8). SCT 76–8 never produced LCTs and grew significantly faster than UTEX 1236. Both SCT 76–8 and UTEX 1236 produced uncells at low cell densities. Coenobia formed when cell densities increased over time in batch cultures. SCT 76–8 and UTEX 1236 did not differ morphologically when viewed with the light microscope. Under scanning electron microscopy, an outer opaque layer covered an inner warty layer on unicells. The outer layer was reduced or absent in coenobia from batch cultures in stationary growth. In addition, long spikelets, not present on the walls of unicells, were prominent on coenobial walls. The spikelets of UTEX 1236 appeared smaller and more uniformly distributed than in strain 76–8. In contrast, the surface wall morphology of LCT S. communis was composed of an outer reticulate layer supported by spikelets and appeared as a pentagonal meshwork covering the cell walls. This phenotypic plasticity, as demonstrated by SEM and light microscopy, provides further evidence needed for an understanding of Scenedesmus evolution.     

PLASTID FUNCTION IN PLANT TISSUE CULTURES. I. PORPHYRIN SYNTHESIS BY DARK-GROWN HAPLOID AND DIPLOID ALBINO CULTURES

Tissue cultures lacking chlorophyll formed porphyrins when fed δ-aminolevulinic acid, a precursor of tetrapyrroles. When grown in the dark tissues from Ginkgo biloba L., Taxus, and Rosa formed protoporphyrin and several unidentified compounds. When grown in the light cultures did not form these pigments. The protoporphyrin was detected in the tissues after 3–6 hours incubation with δ-aminolevulinic acid; it was localized in the plastids by ultraviolet light microscopy and was identified by extraction procedures, chromatography, and absorption spectroscopy. No magnesium protoporphyrins were found, suggesting that chlorophyll synthesis was blocked at this point. Both male and female haploid albino tissues from Ginkgo formed protoporphyrin. The female albino tissue was derived from a chlorophyll-containing tissue culture from the female gametophyte by serially subculturing the green tissue in the dark. Upon exposing the female albino tissue to light, no greening occurred. The treatments used thus far have not caused chloroplasts to develop in the haploid albino tissues, even though the tissues contain many amyloplasts. Concurrent with the loss of chloroplasts, the female tissue loses all capacity to differentiate specialized cells, such as tracheids, resin cells, and chlorenchyma.     

CAPITATE APPENDAGES ON SCENEDESMUS CULTURE 16 WALLS1

A capitate appendage was detected on the cell wall of Scenedesmus strain 16 with the electron microscope, using the negative staining technique. The mushroom-like structures, from 450 to 650 mμ long, possessed an elongate stipe and a circular cap. These are attached to ridges or the cell wall of both spiny and spineless colonies.     

LAGERHEIMIA HINDAKII IS THE UNICELLULAR STAGE OF A SCENEDESMUS1

Extensive variability in spine number and position was emphasized in the protologue for the spiny unicell Lagerheimia hindakii Hegew. et A. Schmidt. Using an axenic clone established from culture Hindk 1975/95, which provided the type material of that organism, we initiated a morphogenetic study. While in the unicellular stage, three short spines were usually formed at each cell pole. A colonial morph was first observed during the initial isolation procedure after unicells were dispersed on firm agar and allowed to grow. We propose that L. hindakii is a Scenedesmus, close to S. subspicatus R. Chod. This organism is unlike most representatives of the genus Scenedesmus because colonies do not readily appear in dilute media; they also fail to form in Bristol's liquid medium unless there is an organic supplement, e.g. glucose. Hindk 1975/95 may be more closely related to truly unicellular taxa than to other Scenedesmus.     

VARIATIONS OF MORPHOGENETIC BEHAVIOR IN PLANT TISSUE CULTURES I. CICHORIUM ENDIVIA

Several-years-old callus tissue derived from mature embryos of endive (Cichorium endivia Linn., Compositae) was grown on synthetic liquid and/or agar nutrient media. Incorporation of yeast extract or high concentrations of inositol, kinetin, casein hydrolysates (pancreatic and acid hydrolysates), etc., improved growth and organ formation. Rosettes of leaves, shoots and roots were differentiated on synthetic media. On agar media shoots arose first and were from marginal meristematic areas, while the roots arose later and were from pockets of meristematic tissue located in the deeper regions of the callus. In liquid media embryoids from single cells were formed which first developed roots and then shoots.     

MYCOLOGICAL SYNTHESIS OF FAT FROM WHEY. I. PRELIMINARY STUDIES WITH STATIONARY CULTURES

SUMMARY: Forty mould species, 30 of which were from the genera Aspergillus, Penicillium, Fusarium and Mucor , were examined for their ability to utilize the lactose in whey and to produce fat in the mycelium in stationary cultures.
In terms of lactose consumed and weight of mycelial felt produced the most promising species were A. ustus, P. frequentans, P. oxalicum and P. notatum. The first three of these warrant further study as fat producers.     

FINE STRUCTURE OF PARKINSONIA ACULEATA POLLEN. I. THE POLLEN WALL

Larson , Donald A., and C. Willard Lewis , Jr . (U. Texas, Austin.) Fine structure of Parki nsonia aculeata pollen. I. The pollen wa ll. Amer. Jour. Bot. 48(10): 934–943. Illus. 1961.—Fresh pollen samples and chemically fossilized pollen samples were fixed in either potassium permanganate or osmium tetroxide and some sectioned material was poststained in an effort to demonstrate the various wall components existing in pollen of P. aculeata. The exine was observed to be consistently 2-layered with the layers corresponding to the endexine and ektexine demonstrated with basic fuchsin staining by optical microscopy. The exine also contained an extensive system of internal channels. Aperture membranes contained laminate-globulate fine structure, and this has been interpreted as a modification for the maintenance of membrane continuity through changes in pollen grain volume.     

SURVIVAL OF SCENEDESMUS ACUMINATUS (CHLOROPHYCEAE) IN DARKNESS1

Survival of the green alga Scenedesmus acuminatus Lagerh. in complete darkness was studied in axenic batch cultures at 7°C and 22°C for three months. The decrease in cell numbers was insensitive to temperature and slower than the loss of dry weight. However, the lag phase before cells began to lyse was more than twice as long at 7° C than at 22°C. The decline in cellular carbohydrates and proteins occurred in two phases. During the first 3-4 days, the decrease in cellular carbohydrate levels was significantly accelerated and temperature-sensitive. Pyrenoids disappeared within 5 days of darkness. Proteins showed 20-fold higher degradation rates at 22°C than at 7°C during the first 4 days. Thereafter, the rates of carbohydrate and protein decomposition were slow and temperature-independent. By contrast, lipids degraded only little at virtually constant and temperature-insensitive rates over the entire experimental period. After three months of dark incubation, about 40% of the remaining cells had retained their growth potential. However, the lag phase, after which cell division was resumed when exposed to light, increased with the duration of the previous dark period. The decrease in photo synthetic potential, which was more pronounced at 22° C than at 7° C, was apparent both in declining maximum assimilation numbers and maximum quantum yields. Cellular chlorophyll a concentrations in surviving cells decreased only slightly. We conclude that the primary means by which S. acuminatus survives extended dark periods is by reduction of catabolic reactions. This was suggested by the slow loss of cell weight. No evidence of significant heterotrophic acetate uptake was found. The initial temperature-dependence of most observed processes indicates that in natural environments chances for survival of algae are augmented by the prevailing low water temperatures.     

REGULATION OF GAMETOGENESIS IN SCENEDESMUS OBLIQUUS (CHLOROPHYCEAE)1

The effects of nutrients, temperature and light on gametogenesis in Scenedesmus obliquus (Turp.) Kütz, were studied in culture. Concentrations of nitrogen in the medium employed showed a marked influence on gamete production. Gametogenesis is inhibited by N excess but is not a response to N starvation or depletion. A drop in N level from that of the growth medium is not required, nor does it per se trigger gametogenesis. The N concentration satisfying growth requirements insufficiently low to permit sexual differentiation. Nitrogen level in the growth medium has no effect on subsequent N to maintain a typical culture. Number of gametes present at maximum production time is inversely related to N concentration, but neither time of onset of gametogenesis, nor time of maximum gamete production is affected by N concentration. Cultures incubated at 15 C in medium lacking N take a minimum of 20—24 h to develop cells irreversibly committed to gamete formation. At the concentrations tested, no medium component other than the N-containing salt affected gametogenesis. Temperature influences both time of maximum production and numbers present at maximum production time. Time of maximum production is inversely related to incubation temperature; a 15 C incubation temperature yielded highest gamete production. Light enhances gametogenesis but gamete formation can occur in absence of light. Achievement of a light-saturated response is dependent upon illumination given at two critical periods: one occurs shortly after N withdrawal; the other occurs later, when cells are becoming irreversibly committed to gamete formation. Ability to produce gametes diminished with prolonged laboratory culture.