摘要:

ABSTRACTEthmodiscus rex(Rattray) Wiseman and Hendey cells from near surface net tows in the Southwest Atlantic Ocean and Caribbean Sea were examined for chemical composition, internal nutrient pool concentrations, and oxygen evolution characteristics. Elemental ratios indicated nitrogen limitation with C:N:P ratios of 125:9:1 (atoms), and carbon: chlorophyll (chl) ratios of 129:1 (weight). However, internal nitrate pools (1.4–27.1 mM) suggested that cells were notN‐limited. Intracellular NO3−accounted for up to 54% (range = 3–54%) of the total N quota in some samples. Photosynthetic parameters were consistent with a high‐light‐adapted population and suggested an instantaneous maximum chl‐specific photosynthetic rate (PBmax) of 4.8–12.4 nmol O2·μg chl−1· h−1. Respiration rates varied ten‐fold and were inversely related to PBmaxEthmodiscuschemical composition and buoyancy characteristics are similar to vertically migratingRhizosoleniamats and the non‐motile dinoflagellatePyrocystis noctilucaMurray (Schuett). The presence of internal NO3−pools inEthmodiscussuggests that this genus is also vertically migrating to exploit sub‐surface nitrogen pools. Such behavior may be widespread in large, non‐motile oceanic phytoplankton. Based on ascent rate data, chemical composition, and photosynthetic rates, we estimate that the entire division–migration cycle forEthm

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00001.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTNitzschia seriataCleve, a common member of marine bottom ice communities in the Arctic, was grown in unialgal batch cultures to test for compensatory mechanisms for the low temperatures (−1.8° C) typical of its natural habitat. The upper lethal limit for growth was between 12° and 15°C, and the optimum was between 6° and 12° C. The Arrhenius function adequately(R2=73%) fitted the relationship between growth rate and temperature from – 1.6° up to 10° C, with an average Q10of 1.9 over the entire range. Light‐saturated and light‐limited rates of photosynthesis (normalized to chlorophyll a or cell carbon) showed complete compensation from 12° to 4° C. Photosynthetic rates, especially at light saturation, declined rapidly at temperatures below 4° C. Susceptibility to photoinhibition was greatest at the lowest growth temperatures. Cellular composition (chlorophyll a, protein, polysaccharide, and lipid contents) was not systematically related to temperature in any simple way, although cell size (carbon per cell) was maximal at the lowest growth temperature. Dark respiration was unmeasurably low (<0.015 day−1) at all growth temperatures. The strategy of adaptation inN. seriatamay be characterized as optimizing efficiency and compensation, rather than maximizat

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00008.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTCatalase activity increased inPeridinium gatunense(formerlyP. cinctumfa.westii) cells during the decline of the seasonal spring bloom period in Lake Kinneret. This was correlated with the low ambient total CO2concentration. The relationship was confirmed in laboratory experiments where maximum catalase activity occurred under an atmosphere composed of 30% O2and 0.003% CO2. Conversely, high CO2concentrations inhibited catalase activity. The rise in catalase activity was not directly due to increasing environmental pH, asin vitroandin vivomeasurements showed a characteristic broad pH curve with a constant activity from pH 6–10 for catalase.Photoinhibition of catalase occurred above 250 μmol photons · m−2· s−1. However, at high photoinactivating irradiances, photoinhibition was ameliorated under high pO2/pCO2. Such conditions prevail in the Kinneret at the end of the spring. We propose that the enhancement of photorespiration (under high pO2/pCO2) induces a temporary burst in catalase activity despite the progressively photoinhibitory conditions of earl

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00017.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTMicrotubular elements in the chloroplasts (chl‐MTs) ofOedogonium capilliformeWittrock were examined by conventional electron microscopy and immunoelectron microscopy. Chl‐MTs were frequently seen in the terminal, convex, and concave peripheral regions of the chloroplasts. Each bundle of chl‐MTs was composed of 2–25 tubular elements. Some chl‐MTs were located in the stroma. Chl‐MTs frequently bridged two areas of the envelope membrane near the apex of convex regions of chloroplasts. Some chl‐MTs were closely associated with the envelope membrane via apparent anchors along their length. The distribution patterns of chl‐MTs and their appearance suggest that chl‐MTs are involved in the maintenance of the outer shape of chloroplasts. However, immunoelectron microscopy with an antibody against α‐tubulin indicated that the chl‐MTs are n

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00023.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe flagellar apparatus and presumptive vestigial feeding apparatuses of a cold‐water, photosynthetic, quadriflagellate euglenoid is described. The organism possesses two similar sets of flagella each consisting of one short and one long flagellum. Each pair of flagella is associated with three microtubular roots for a total of six roots in the basal apparatus. At the level of the ventral basal bodies, each intermediate root is nine‐membered, while the ventral roots are composed of eight to nine microtubules. Only one of the ventral roots lines the single microtubule reinforced pocket. A four‐membered dorsal root attaches to each dorsal basal body, and at the level of the reservoir each gives rise to a dorsal band. An additional bundle of microtubules, not arising from the microtubular roots of the basal apparatus, begins posterior to the basal apparatus as a small group of a few microtubules and extends anteriorly on the right ventral side of the reservoir ending at the canal. At the level of the stigma, the microtubules are organized into a multi‐layered bundle that continues to increase in size and eventually splits to form two bundles at the level of the canal. We postulate that these bundles may represent the remnants of a rod‐and‐vane‐type feeding apparatus like that found in many phagotroph

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00028.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTNumerous spherical bodies containing electron‐dense material, fibrous material, and membranous material are present in the cytoplasm of two dinoflagellate species,Prorocentrum lima(Ehr.) Dodge andProrocentrum maculosumFaust. Similar bodies have been observed in other dinoflagellates and have been termed accumulation bodies or PAS bodies. In bothProrocentrumspecies, these bodies autofluoresce under blue light excitation and increase in size with cell culture age. They possess acid phosphatase activity, react positively with the periodic acid/Schiff reagent, and stain with acridine orange. All these properties are characteristic of eukaryotic lysosomes; thus, we propose that dinoflagellate accumulation bodies and PAS bodies are identical organelles and are, in fact, dinoflagellate lysosome

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00039.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe relatively non‐toxic dye, rhodamine 123 (R123), was incorporated into the frustule ofThalassiosira weissflogiiGrun. clone ACTIN in direct proportion to biogenic silica (BSi). R123 was used together with the DNA stain propidium iodide to track and quantify Si deposition during the cell cycle ofT. weissflogiiusing flow cytometry. Silicon deposition was not continuous through the cell cycle. Deposition of the valves occurred during M phase. The hypocingulum was largely deposited during G1 with some suggestion of minor girdle band deposition during G2. Silicon deposition did not occur during S phase. Assuming that a complete frustule consists of an epivalve, epicingulum, hypocingulum, and hypovalve, then 40% of cellular BSi was contained within the cingulum ofT. weissflogiiwith 60% present in the valves. These percentages correspond to 0.38 pmol Si in the two cingula and 0.57 pmol Si in the valves. Temporal differences in the timing of silicic acid uptake and deposition during the cell cycle ofT. weissflogiisuggested that deposition of both the new valves and the cingulum is supported by an internal pool of dissolved Si acquired during G

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00045.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTFertilization of cultured microscopic female gametophytes by spermatia from field‐collected male gametophytes ofPalmariasp. was observed by light and transmission electron microscopy. Liberated spermatia had a prophase‐arrested nucleus with a pair of polar rings. The protoplast of spermatia was covered with ca. a 3‐μm‐thick hyaline covering. After spermatium inoculation, the spermatial covering was attached specifically to the coat surrounding the cell wall of the trichogyne. The spermatial covering was eliminated only at the site of gamete attachment, resulting in direct attachment of the spermatial plasma membrane to the trichogyne within 5 min after spermatium inoculation. This direct attachment was followed by completion of spermatial nuclear division and cell wall formation. The polar rings disappeared before prometaphase. The cytoplasm of the binucleate spermatium invaded the trichogyne cell wall and subsequently fused with the trichogyne cytoplasm. The trichogyne could fuse with many spermatia, and many male nuclei (the derivative nuclei of spermatial nuclear division) could enter the trichogyne c

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00055.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTPhylogenetic relationships in the Arctic‐Antarctic disjunct seaweed speciesAcrosiphonia arcta(Dillwyn) J. G. Agardh (Acrosiphoniales, Chlorophyta) were examined using restriction fragment‐length polymorphism analysis of the fast‐evolving nuclear ribosomal intergenic spacer (IGS) region and random amplified polymorphic DNA (RAPD) markers. Twenty‐two isolates collected from 10 different locations in both hemispheres were compared. Five IGS length classes were identified among the 10 locations. Throughout the North Atlantic, IGS regions were found to be extremely homogeneous whereas RAPD patterns revealed subdivided populations that suggest founder effects.Acrosiphonia arctapopulations found in the Arctic and North Atlantic oceans are hypothesized to be of Pacific origin. Extensive differences found between Arctic Greenland populations and those in the North Atlantic suggest that colonization of Arctic Greenland occurred as an independent event. Recolonization of the Antarctic peninsula from Southern Chile is favored, whereas the directionality of transequatorial passage along the western coast of the Americas could be in either di

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00067.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTTwo species of the colonial green flagellate family Volvocaceae are worldwide in distribution yet exhibit contrasting species structure. Geographically disparate isolatesof Gonium pectoraleMueller can interbreed while isolates ofPandorina morumBory 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.morumand ofG. pectorale.Members of syngens ofP. morumwith 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 eitherP. morumis a more ancient species thanG. pectoraleor thatP. morumhas a less stable genome. In either case, the biogeographic distribution of certain syngens may reflect climatological changes of the p

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00080.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY