ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00001.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00003.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY

ISSN:0022-3646    

DOI:10.1111/j.1529-8817.1989.tb02566.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTAbundances of the erect, blade phase ofEndarachne binghamiaeJ. Ag. (Scytosiphonales, Phaeophyta) varied seasonally at a southern California rocky intertidal site. Blade cover and density were much greater in the fall through early spring; blades were mostly absent from quadrats during the summer. Blade abundances were negatively correlated with both seasonal variations in seawater temperature and photoperiod. Laboratory culture studies failed to provide evidence for sexual reproduction. The life history appears to be of the “direct” type with plurangia‐produced zooids germinating into crustose disks. Most disks developed erect blade clusters under spring/fall (17° C) and winter (13° C) temperatures over the range of natural photoperiods employed (14:10, 12:12, 10:14 h LD). In contrast, cultures held under the summer temperature (21° C) produced almost entirely crustose growths regardless of photoperiod. Similar results were obtained for cultures grown at 100 and 200 μE · m−2· s−1.E. binghamiaeblades were fertile throughout the year and produced viable zooids indicating that reproductive seasonality did not influence the seasonal pattern of blade abundance. Culture and field studies suggest that the initiation of new erect blade clusters from crustose disks is confined to the cooler months of the year (winter and spring). The summer reduction or absence ofE. binghamiaeblades appears to be due to increased mortality rates and temperature constraints on the development of new erect bladed thalli. Hypothetical causes of mortality are desiccation stress, sand burial, increased grazing activity and a genetically‐base

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00006.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThis paper describes the perizonium and initial valve formation inNavicula cuspidataKütz., based on light microscope (LM) and scanning electron microscope (SEM) observations. The perizonium consists of concentric over‐lapping bands, laid down sequentially at the tips of the expanding biconical auxospore during its elongation. The central perizonial band has fimbriate edges and is considerably more rigid than the more distal bands. During auxospore elongation and the band secretion, the chloroplasts continuously oscillate between the two ends of the cell; this oscillation ceases once the elongation is complete. The initial valves, formed within the perizonium, are molded into the basically biconical shape of the perizonium except for a central flattening of each valve face. In contrast to the raphes in gametangial and vegetative valves which are surrounded by a smooth axial area, the raphes in initial valves lie within a raised ridge running along the apical axis of the valve. The regular pattern of apically oriented ridges on the outer surface of vegetative valves is also lacking on initial valves. Comparison of pore–pore spacing within striae of gametangial valves, initial values and post‐initial valves (first division and vegetative cells) reveals that the pore–pore distance within striae is conserved at all sexual stages. However, the distance between striae is considerably larger in initial valves than in gametangial and post‐initial valves. Vegetative interstriae spacing as well as the planar morphology of the valve face is regained at the first division of the initial cell. This suggests that the spacing between striae is dependent on the sexual stage of the cell during valve formation (i.e. not directly dependent on the cell size) and can be altered independently of the pore–

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00015.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThe three‐dimensional structure of the flagellar apparatus inWoloszynskiasp. was determined. This recently discovered dinoflagellate possesses two basal bodies that are offset from one another and lie at an angle of approximately 110°. The transverse basal body is associated with a striated fibrous root assemblage that consists of two differently staining fibrous portions with identical striation periodicity. Unlike the transverse striated fibrous roots reported in other dinoflagellates, this assemblage extends to the cell's right beyond the proximal end of the transverse basal body. The striated fibrous root complex is attached to the anterior end of the longitudinal microtubular root by a broad striated fibrous connective. The longitudinal basal body is also associated with the longitudinal microtubular root. The flagellar opening of each emerging axoneme is surrounded by a striated collar. The striated collars are linked to one another by a striated fibrous, striated collar connective. The variations and similarities of the flagellar apparatus and the ventral ridge/striated collar connective inWoloszynskiasp. are compared to similar components in other dinoflagellat

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00026.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTMethylammonium, an ammonium analog, was used to study the short‐term kinetics of ammonium uptake in a diatom,Phaeodactylum tricornutumBohlin, and a green alga,Dunaliella tertiolectaButcher. Time courses of methylammonium disappearance were measured over a wide range of initial substrate concentrations for the two species. It was shown that feedback inhibition, described mathematically by a reversible enzyme kinetic model, can be used to explain the data. For the two species, there was good agreement between the kinetic parameters obtained from the analysis of the uptake versus substrate curve and those from the fit of the reversible kinetic model to the time‐course data. All time courses of CH3NH3+disappearance could be described by constants Vmand ks. Ammonium time‐course data show some similarities to its analog, methylammonium. Our study suggests that the apparent change in Vmand kswith time measured after the addition of saturating ammonium concentrations reflects an uncoupling between transport and assimilation of the substrate rather than a real change in the kinetic parameters of the transport mech

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00036.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTNitrate‐grown cells ofStichococcus bacillarisNaeg. (UTEX 314) contained much higher activities of glutamine synthetase (GS) and NADPH‐glutamate dehydrogenase (GDH) than ammonium‐grown cells. Methylamine, a non‐metabolizable ammonium analog, caused a decrease in GS activity in nitrate‐grown cells suggesting that GS is regulated by the size of the endogenous ammonium pool. The decrease in GS observed in methylammonium‐loaded nitrate‐grown cells was accompanied by an increase in NADPH‐GDH activity.Stichococcus bacillariscan be grown in the presence of methionine sulfoximine (MSX), a potent inhibitor of GS. However, only a fraction of a control cell population showed a requirement for glutamine or arginine for growth following MSX addition. Fully adapted MSX‐grown cells were indistinguishable from control cells in their ability to photosynthesize and utilize amino acids as nitrogen sources. Alanine, arginine, asparagine, glutamine, glycine and proline were good nitrogen sources, and maximum capacity for amino acid transport was developed in cells grown on these amino acids. Compared to nitrate‐grown cells the activity of GS in ammo acid‐grown cells was low, whereas NADPH‐GDH was very active. The activity of NADH‐GDH in amino acid‐grown cells was highest und

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00048.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTEpiphyte communities in a phosphorus‐limited hard‐water lake were compared over a 14‐week period from Potamogeton illinoensis and structurally similar artificial plants of different leaf ages. Artificial plants were serially incubated in the lake to simulate the age of natural leaves. The physiognomy of loosely attached epiphytes appeared similar on the two substrata. Algal cell number and biovolume were 15‐fold and 17‐fold higher, respectively, on artificial leaves early in the growing season, but total algal density gradually became similar on natural and artificial plants. In contrast, the taxonomic composition of loosely attached algae became increasingly distinct, and mean cell biovolume on natural leaves was twice that on artificial leaves. Adnate epiphytes on both substrata developed from sparse populations of bacteria on new leaves to a community of diatoms, blue‐green algae and numerous bacteria on mature and senescent leaves. Adnate community succession on natural leaves in late senescence/death differed from that on artificial leaves colonized for comparable periods in having (1) a marked increase in filamentous blue‐green algae, (2) a subsequent decrease in all algae, and (3) a final fungi‐dominated stage. The trends in colonization indicate that macrophytes in this oligotrophic lake provided a distinct habitat from that of artificial substrata for epiphytes throughout the

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00055.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThe UTEX 2193 strain ofScenedesmus armatus(Chod.) Chod, when cultured in any of several media (whether natural or artificial, concentrated or dilute) produced a variety of colonial morphologies as well as a unicell population. Morphological expression was related to culture ape. When the initial cell density was just a feu1 hundred cells per mL. the culture first produced a unicell population, then spiny colonies, and as stationary phase was approached, spine‐less colonies.Two classes of spiny colonies were detected. Type I colonies had elongate cells with the terminal cells shorter than median cells. Spines were longer than cell length. The wider, oval, grainy cells of Type II colonies were uniform m length. Spines were shorter and thicker than those on Type I colonies. Only Type I colonies produced unicells: the latter appeared as two morphs. The smaller unicell was obovoid with four delicate spines: the larger had ovate cells bearing four thicker spines.Control of unicell development in all media was achieved by carefully monitoring colony type and cell number used for the inoculum. A unicellular population developed in batch culture in defined media, both concentrated and dilute, when the initial cell density (either Type I or Type II colonies) was low (below 1000 cells‐mL−1), as well as in synchronous cultures. With higher initial cell densities, e.g. 2 × 104cells·mL−1, the inoculum had to contain Type I colonies to produce unicells. Unicells were also produced in water from Agronomy Pond, where the strain originated. We discuss the role of unicell populations in the distribution ofSc

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1989.00065.x

出版商:Blackwell Science Inc    

年代:1989

数据来源: WILEY