摘要:

ABSTRACTPEP‐dependent4CO2‐fixation by extracts ofAscophyllum nodosum(L.) Le Jol. is reported. The carboxylation of PEP is Mn2+dependent and ATP is shown to be a product. IDP was found to be less efficient as a phosphate acceptor than ADP and 3‐mercaptopicolinic acid inhibited the carboxylation reaction. Extracts decarboxylated OAA only in the presence of ATP and had high activities of MDH and GOT. This evidence, together with the probable absence of PEPC, PEPCTrP, and PC inA. nodosumextracts, favors the view that PEPCK is responsible for the light‐independent CO2‐fixation observed in

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00001.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe effects of different glutaraldehyde‐osmium fixation schedules on the ultrastructure of the vegetative cells from the meristematic regions ofScytosiphon lomentaria(Lyngbye) Link fronds are described. The best overall preservation of cell structure was obtained with a 2 h fixation in 2.5–3.5% glutaraldehyde in 0.1 M cacodylate buffered seawater (pH 7.0), followed after washing by 1 h post fixation in 1% osmium tetroxide. The addition of 1% caffeine to the glutaraldehyde fixative resulted in better retention and spatial localization of the electron dense phenolic deposits within the cells. Particular attention was paid to the effects of the various fixation schedules on the electron‐dense material within the cells and the images obtained were compared with previous accounts of brown algal cells. It is proposed that the term physode should be restricted to the discrete electron dense spherical bodies within the vacuoles and not applied to electron dense material in general. Although the organization ofScytosiphoncells was similar to that previously reported in the Scytosiphonaceae, the organization of the plasmodesmata into pit fields is at variance with previous acc

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00004.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe apical cells ofSphacelaria tribuloidesMenegh. are larger than other thallus cells, contain more organelles and appear polarized. Their tip portion, where they grow, contains a well developed Golgi apparatus, abundant endoplasmic reticulum (ER) membranes, mitochondria, chloroplasts and a large number of small vacuoles. It seems likely that a continuous flow of membranous material from the ER membranes to the dictyosomes and from the latter to the plasmalemma of the extending tip portion takes place. In contrast, the basal pole possesses fewer organelles and is occupied mainly by large‐sized, sometimes central vacuoles. The apical cells undergo two distinct types of highly asymmetrical differential divisions giving rise to cells of the thallus and hair initials. During the early stages of mitosis the nuclear envelope remains intact, except for fenestrated poles. Microtubules pass through the fenestrae into the nucleoplasm. During meta‐phase, a typical chromosome plate is organized. The sites of attachment of spindle microtubules to the chromosomes are structurally different from the rest of the chromosomes. At late anaphase, the nuclear envelope breaks down completely. During telophase, a new membrane encloses the chromosomes which are decondensed and the nucleoli are reorganized. Cytokinesis proceeds long after mitosis at a stage in which the nuclei have increased in size and have moved farther apart. A membranous furrow develops centripetally, without the participation of microtubules. However, microtubules traverse the thin cytoplasmic strands which, in both interphase and cytokinetic cells, meander among the vacuoles of the basal pole of the cell and the internuclear space. Dictyosomes appear to be involved in the subsequent wall deposit

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00016.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTAdverse weather and resultant turbulence caused sloughing of attached diatom communities during the first two weeks of colonization on artificial substrates. In contrast to Pacific macroalgal systems, older communities (8–12 d) were the most affected by wave action. Ash‐free dry weight of the periphyton and diatom cell density generally increased, except following periods of high turbulence when losses of up to 80% occurred. The maximum cell density (4×105diatoms · cm−2) and ash‐free dry weight (2.9 mg · cm−2) are among the highest reported for similar conditions. Percent transmittance through the growth layer correlated significantly with cell density and ash‐free dry weight and is recommended as a rapid method for measuring the relative accumulation of periphyton. Diatom diversity generally increased throughout the study period and did not clearly reflect the effects of disturbance as did standing crop. Comparisons of diatom diversity and community composition indicated that the three overlapping growth series were not significantly different and samples collected on the same date were not more similar than those of identical age. Combined with previous evidence, the present study indicates that the first two weeks of substrate exposure in the summer represented a colonization phase followed by rapid m

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00030.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe role of microtubules in silicon metabolism leading to valve formation was investigated in the pennate diatomNavicula saprophilaLange‐Bertalot&Bonik. By using synchronized cells blocked after mitosis and cytokinesis but prior to cell wall formation, effects due to inhibition of mitosis were eliminated. Cells were treated with three anti‐microtubule drugs to assess the role of microtubules. Chemical analogs to two of the drugs provided controls for inhibition not related to microtubule disruption. Although all three anti‐microtubule drugs reduced cell separation at high concentrations (1 × 10−3M), podophyllotoxin was the only drug which reduced cell separation at concentrations lower than 1 × 10−5M. None of the drugs at any concentration tested affected cell viability. There was no differential inhibitory effect between the active and inactive drugs on silicic acid transport, total uptake, incorporation, or pool formation. There was no qualitative difference between silica incorporated in treated and untreated cells. A colchicine binding component was isolated fromN. saprophila.The characteristics of colchicine binding suggest this component may be tubulin. Microtubules do not appear to be involved in any of the steps of silicon metabolism leading to valve formation and yet they have profound influence on the symmetry and pattern of the mineralized product, the sili

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00039.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTEucheuma isiforme(C. Agardh) J. Agardh exhibits a combination of vegetative and reproductive features that distinguish it from other critically studied genera in the Solieriaceae. The development of the multiaxial thallus, emphasizing the arrangement of periaxial cells around each axial file; presence of reproductive nemathecia that contain carpogonial branches and auxiliary cells; and post‐diploidization stages, including gonimoblast and pericarp initiation, stages of fusion cell formation, and carposporophyte development are described and illustrated for the first time in this species. The vegetative and reproductive features observed inE. isiformeare not diagnostic of any of the recently erected tribes in the Solieriaceae.Eucheumaappears most closely related to the Indian Ocean genus,Sarconem

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00045.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTTen seaweed species were surveyed for simultaneous photoevolution of hydrogen and oxygen. In an attempt to induce hydrogenase activity (as measured by hydrogen photoproduction) the seaweeds were maintained under anaerobiosis in CO2‐free seawater for varying lengths of time. Although oxygen evolution was observed in every alga studied, hydrogen evolution was not observed. One conclusion of this research is that, in contrast to the microscopic algae, there is not a single example of a macroscopic alga for which the photoevolution of hydrogen has been observed, in spite of the fact that there are now at least nine macroscopic algal species known for which hydrogenase activity has been reported (either by dark hydrogen evolution or light‐activated hydrogen uptake). These results are in conflict with the conventional view that algal hydrogenase can catalyze a multiplicity of reactions, one of which is the photoproduction of molecular hydrogen. Two possible explanations for the lack of hydrogen photoproduction in macroscopic algae are presented. It is postulated that electron acceptors other than carbon dioxide can take up reducing equivalents from Photosystem I to the measurable exclusion of hydrogen photoproduction. Alternatively, the hydrogenase system in macroscopic algae may be primarily a hydrogen‐uptake system with respect to light‐activated reactions. A simple kinetic argument based on recent measurements of the photosynthetic turnover times of simultaneous light‐activated hydrogen and oxygen production is presented that supports the second ex

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00053.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTSeveral environmental factors affected total growth and zygospore production inChlorococcum echinozygotumStarr. The temperature range at which zygospore production occurred was more restricted than the range that supported vegetative growth. Light intensity had little effect upon zygospore formation: gamete production and gamete pairing occurred in darkness. Zygospore production occurred over a wide pH range; bicarbonate had a minor effect upon zygospore formation. Nitrogen concentration was the factor of primary importance. As the level of nitrogen supplied as nitrate, ammonia, urea and asparagine in the medium was increased, zygospore production first increased (over no nitrogen) at low levels and then decreased at high levels. All levels of glutamine supplied reduced zygospore production. A possible way in which nitrogen concentration in the medium and sexual expression are linked is discussed.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00057.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTMany chrysophycean species produce resting cysts (statospores) with purportedly species‐specific morphology. I investigated variation in the cyst morphology of a single species that may result from genetic differences among the vegetative clones involved and from variation in the temperature of the environment during cyst development. Populations ofDinobryon cylindricumImhof cysts were produced under defined conditions in vitro and then sampled for morphological analysis based on SEM micrographs. Morphological data is presented and then used in a multivariate discriminant analysis to determine the utility of each morphological character in distinguishing the six populations studied. Results suggest that some features of cyst morphology (i.e. cyst diameter) are invariant among the populations, while other features show distinctive variation. The density of spines covering the cyst body as well as the morphology of those spines appear correlated to the specific clones involved, and thus may represent useful phenotypic genetic markers. The length and definition of both the spines and the cyst collar, on the other hand, are markedly influenced by encystment temperature. The implications of these findings for paleoecological studies is discusse

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00064.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTDunaliella tertiolecta(Butcher) was grown in chemostat culture over a wide range of ammonium limited growth rates. The addition of ammonium caused a rapid temporary suppression of photosynthetic carbon fixation. The magnitude of ammonium induced photosynthetic suppression increased with the severity of ammonium limitation. Cells growing at rates greater than ca. 80%μmaxexhibited no photosynthetic suppression in response to additions of the limiting nutrient. The duration of photosynthetic suppression was related to the concentration of added ammonium. Immediately following the suppression, photosynthesis was enhanced with respect to the controls. The eventual degree of enhancement increased with the concentration of added ammonium. Steady‐state cellular chlorophyll concentrations, photosynthetic rates, and assimilation numbers are report

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1983.00070.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY