摘要:

ABSTRACTCephaleuros parasiticusKarsten, an endophyte ofMagnolia grandifloraL. has been examined with light, and scanning and transmission electron microscopy. The discoid thalli are composed of filaments which ramify throughout the leaf tissues beneath the epidermis. Algal filaments do not penetrate host cells, but do produce black leaf spots which have been mistaken for those caused by the fungusGlomerella cingulate(Ston.) Spauld. and Schrenk. Two distinct thallus types occur, often simultaneously on a single leaf. One bears clusters of zoosporangiate branches which seasonally emerge through the ventral (and rarely, dorsal) surface of the leaf. In contrast, the other thallus type bears gametangia which break through the dorsal leaf surface. Zoosporangia and gametangia have never been found on the same thallus. The zoosporangia are smaller than, but almost identical in shape to, those ofC. virescensKunze. Simple plasmodesmata are present in crosswalls and acetolysis indicates that little or no sporopollenin is present in the cell walls. The ultrastructure of biflagellate gametes and quadriflagellate zoospores is virtually indistinguishable from that reported forC. virescensand similar to that reported forPhycopeltisandTrentepohlia.In both gametes and zoospores there are keeled flagella, overlapping and parallel basal bodies, two 3‐layered multilayered structures with microtubular splines, and two medial compound microtubular roots. Pyrenoids, eyespots, flagellar and body scales, striated roots (or rhizoplasts), and distal bands are absent. Two presumptive mating structures are present in each biflagellate gamete, and flagellar collars occur in both types of motile cells. The extreme similarity in motile cell ultrastructure revealed in this interspecific comparison parallels that similarity revealed in intergeneric comparison

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00513.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTMitosis and cell division were studied in the green algaCylindrocapsa geminellaWolle with transmission electron microscopy. Vegetative cells possess a parietal, lobed chloroplast, and a central pyrenoid. Prophase and metaphase nuclei are surrounded by 1–3 layers of perinuclear endoplasmic reticulum. At early prophase a small number of perinuclear microtubules (MTs) are present while at late prophase MTs are concentrated at the presumptive spindle poles. At the same time, MTs begin to appear in the nucleoplasm. Metaphase spindles are diamond‐shaped and centric. During telophase, centrioles migrate towards the center of the equatorial zone, presumably guided by a small group of perinuclear MTs. A second system of MTs develops in the equatorial plane, initially consisting of randomly orientated microtubular elements. Later they tend to run in a predominantly radial direction although a common MT focal point or organizing center is not apparent. The two centriole complexes remain at the center of the equatorial plane until well into interphase, facing each other across the newly formed transverse septum. Centrioles are associated with root templates and connecting fibers. The present observations corroborate the view thatC. geminelladoes not form a true filament in the ulotrichalean or chaetophoralean sense, but rather consists of a row of autospores. Its affinity with other “pseudo‐filamentous” green algae and the Chlorococcales is discussed. The interpretation of the cytokinetic MTs inC. geminellaas a phycoplast appears to be pr

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00523.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTThe ultrastructure of the flagellar apparatus in pre‐inversion and inversion stages ofPlatydorinaresembles that ofChlamydomonasin having 180° rotational symmetry and clockwise absolute orientation. Basal bodies are in a “V” configuration and connected by one distal and two proximal fibers. Alternating two‐ and four‐membered microtubular rootlets are cruciately arranged. During maturation, the basal bodies rotate and separate, and 180° rotational symmetry is lost. Simultaneously, each proximal fiber detaches from one of the functional basal bodies, and the distal fiber detaches from both. The mature apparatus has widely separated and nearly parallel basal bodies. Flagellar orientation inPlatydorinais completed just after inversion and a flattening of the colony called intercalation, resulting in the pairs of flagella of neighboring cells extending from the colony in opposite directions in an alternating fashion. Flagellar orientation and separated basal bodies minimize the interference between the flagella of neighboring cells. Basal bodies and rootlets of the two intercalated halves of a colony rotate, resulting in the effective strokes of the flagella of every cell being towards the colonial posterior. The flagella of each cell beat with an effective stroke in the direction of the two inner rootlets. The flagella have an asymmetrical ciliary type beat. The rotated, separated, and parallel basal bodies, together with the nearly parallel rootlets probably are adaptations for movement of this colonial volvocalean alga. The flagellar apparatus in immature stages ofPlatydorinalends support to the suggestion that the alga has evolved from aChlamydomonas‐

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00533.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTGrowth and sexual reproduction of the marine littoral diatomCocconeis scutellumEhrenb. var.ornataGrun. were investigated at 30 different combinations of temperature (5, 10, 14, 18, 22° C), irradiance (20, 60, 100 μE·m−2·s−1) and daylength (14:10 and 10:14 h LD cycle). Growth occurred at all combinations. The optimal growth was observed at 14–18° C, long daylength and highest‐to‐moderate irradiance, and at 18° C, short daylength and highest irradiance. Sexual reproduction on the other hand occurred between 5 and 18° C, and the optimal condition was 10–14° C and short daylength.Annual cyclic, and sesonal changes in the distribution of cell size (valve length) were observed in a field population. These changes were characterized by an annual minimum in mean cell size in autumn, an annual maximum in winter, a slight decrease from the mean in spring–middle summer, a rapid decrease from the mean in late summer–early autumn, and appearance of bimodal distribution of cell size in winter. These changes were caused by sexual reproduction in autumn, rapid growth in late summer–early autumn and slow growth in other seasons, and poor viability of small cells near the lo

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00547.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTA secondarily formed reticulum of cells that encloses axial strands and a carposporophyte that is almost entirely converted to sporangia are the diagnostic features of a new genus,Reticulocaulis(Naccariaceae, Nemaliales), withR. mucosissimusas the type species. A new species ofNaccaria, N. hawaiianapermits close comparison with the new genus and other previously described species ofNaccaria.Until now, no Naccariaceae were known in the Pacific, and these new taxa are part of the sketchily known subtidal marine flora of Hawaii.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00554.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTBiomass, akinete numbers, net photosynthesis, and respiration ofPithophora oedogoniawere monitored over two growing seasons in shallow Surrey Lake, Indiana. Low rates of photosynthesis occurred from late fall to early spring and increased to maximum levels in late spring to summer (29–39 mgO2·g−1dry wt·h−1). Areal biomass increased following the rise in photosynthesis and peaked in autumn (163–206g dry wt·m−2). Photosynthetic rates were directly correlated with temperature, nitrogen, and phosphorus over the entire annual cycle and during the growing season. Differences in photosynthetic activity and biomass between the two growing seasons (1980 and 1981) were apparently related to higher, early spring temperatures and higher levels of NO3‐N and PO4‐P in 1981.Laboratory investigations of temperature and light effects onPithophoraphotosynthesis and respiration indicated that these processes were severely inhibited below 15°C. The highest Pmaxvalue occurred at 35°C (0.602 μmol O2·mg−1chl a·min−1). Rates of dark respiration did not increase above 25°C thus contributing to a favorable balance of photosynthetic production to respiratory utilization at high temperatures. Light was most efficiently utilized at 15°C as indicated by minimum values of Ik(47 μE·m−2·s−1) and Ic(6 μE·m−2·s−1). Comparison of P. oedogonia andCladophora glomerataindicated that the former was more tolerant of temperatures above 30°C.Pithophora'stolerance of high temperature and efficient use of low light intensity appear to be adaptive to conditions found within the dense, floating algal mats and the shallow littora

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00562.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTThe reservoir cytoskeleton ofColaciumEhrenberg is formed of three bands of microtubules. The microtubules of the dorsal band (DMT) become doublets and are continuous with the longitudinal microtubules of the canal and, therefore, of the pellicle. A band of para‐reservoir microtubules (PMT) acts as a linkage between the edges of the dorsal band at the formation of the canal. The third band of microtubules (MTR), more ventral, branches away from the reservoir‐canal transition region and forms a supportive band for a pocket formed from the reservoir membrane. The outer part of the pocket membrane is closely invested with a fibrillar mesh. The pocket ofColacium,a green euglenoid, resembles structurally the cytopharynx of the colorless phagotrophic euglenoids,Isonema papillatumand the bodonid flagellates. The homologies support the hypothesis of euglenoid derivation from the kinetoplastid flagella

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00570.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTHalosaccion americanum,a member of Palmariaceae, was grown in culture from spores and the life history was critically examined by the use of scanning EM and light microscopy. A mature tetrasporangium ofH. americanumproduces four spores that germinate to form two male and two female gametophytes. The male gametophytes grow to maturity in approximately eight months and macroscopically resemble the tetrasporophyte. Following the first division of the tetraspore, the two‐celled female gametophyte consists of a vegetative cell and a carpogonium with trichogynes. Fertilization is accomplished by spermatia from male plants of the preceding generation, as male plants of the same season are immature. Spermatia are formed in a continuous layer over the surface of the mature male gametophytes and, when released, are entrained in long strands of mucous. Spermatia adhere to and fuse with trichogynes and, nuclear fusions presumably follow. The carposporophyte is absent; the new tetrasporophyte develops directly from the fertilized carpogonium. Growth of the sporophyte eventually obliterates the female gametophyte, and development into a mature tetrasporophyte proceeds over a period of approximately eight months. The development ofH. americanum,with its extremely abbreviated female gametophyte stage and direct development of the tetrasporophyte from the zygote, indicates that this rhodophyte has the same life history as reported for other members of the Palmariale

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00578.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTA comparative histochemical study of the nature and distribution of acidic and neutral cell wall polysaccharides was conducted on marine sexual and asexual filaments of the red algaBangia atropurpurea(Roth) C. Ag. Outer and inner walls of this species were clearly partitioned according to staining and transmission electron microscopic characteristics. Neutral polysaccharides were detected in the outer coating (cuticle) but were absent from outer and inner walls of all filaments. Acidic polysaccharides were noted in the outer wall material but not in the inner wall layers of any filaments at any developmental stages. The major staining component of vegetative regions of sexual material and all regions of asexual filaments was a highly sulfated polymer. During sexual reproduction only there was a generalized change in the nature of the acidic component, characterized by a decrease in intensity of staining for sulfates in both male and female filaments and the appearance, in female filaments only, of polysaccharides which presumably were carboxylated. Spermatia attached to both male and female filaments in regions where sexual differentiation was initiated and where changes in the outer wall components commenced.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00585.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY

摘要:

ABSTRACTSelenastrum minutum(Naeg.) Collins was grown over a wide range of growth rates under phosphate or nitrate limitation with non‐limiting nutrients added to great excess. This resulted in saturated luxury consumption. The relationships between growth rate and cell quota for the limiting nutrients were well described by the Droop relationship. The observed variability in N cell quota under N limitation as reflected in kQ·Qmax−1*, was similar in magnitude to previously reported values but kQ·Qmax−1*for P under P limitation was greater than previously reported for other species. These results were evaluated in light of the optimum ratio hypothesis. Our findings support previous work suggesting that the use of a single optimum ratio (kQi·KQj−1) is inappropriate for dealing with a species growing under steady‐state nutrient limitation. Under these conditions the optimum ratio should be viewed as a growth rate dependent variable. Two approaches for testing the growth rate dependency of optimum ratios are proposed.The capacity for luxury consumption differed between nutrients and was growth rate dependent. At low growth rates, the coefficient of luxury consumption (Rsat) for P was ca. four times that for N. The set of all possible relationships between N and P cell quota under these conditions was reported and these values were then used to establish the cellular N:P niche boundaries forS. minutum.Cell quotas of non‐limiting nutrients were not described by the Droop equation. Analysis showed that as the cellular N:P ratio deviates from the optimum ratio, the ability of the Droop equation to describe the relationship between growth rate and non‐limiting cell quotas decreases. When non‐limiting nutrient cell quotas are saturated, the Droop equation appears to be invalid. Previously reported patterns of non‐limiting nutrient utilization are summarized in support of this conclusion. The physiological and ecological consequences of luxury consumption and growth rate dependent optimum r

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1985.00592.x

出版商:Blackwell Science Inc    

年代:1985

数据来源: WILEY