摘要:

ABSTRACTIntertidal seaweeds are periodically exposed to air where they experience a variety of potentially stressful environmental conditions, including nutrient limitation, high light, high and low temperature, desiccation, and osmotic stress. This paper considers the current understanding of stress tolerance in intertidal seaweeds and discusses ways in which future research could increase our understanding of the role of environmental factors in the ecology and physiology of these algae. We believe research is required in at least three areas. 1) Laboratory physiological studies have established that correlations exist between stress tolerance and the vertical distribution of species. However, little information is available on the importance of stress in determining community structure in nature. Field experiments are essential to relate the impact of single or multiple stresses on the survival, growth, and reproductive output of macroalgae. In paticular, it is necessary to clarify the role of sublethal stress in determining the outcome of competitive interactions. 2) With the exception of obvious lethal effects or damage associated with extreme environmental conditions, such as unusually hot and dry weather, it is difficult to evaluate the occurrence and severity of stress in natural populations of seaweeds. There is a need to develop molecular and biochemical markers specific for individual stresses or groups of stresses to allow the unambiguous and direct determination of stressin situ.3) Despite the apparent importance of stress in intertidal seaweeds, we are largely ignorant of the mechanistic basis of tolerance. The application of currently available tools of molecular and cell biology to the investigation of stress‐induced transcriptional and translational changes could enormously increase our understanding of both the sites of, and pathways involved in, stress tolerance. In summary, there are numerous unanswered fundamental questions about the stress tolerance of intertidal seaweeds, providing opportunities for research ranging from field ecology to molecular biology and biochemistr

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00197.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWind direction and fresh water runoff determine the circulation pattern of the Ría de Vigo (NW Spain), which in turn influence the selection and distribution of its phytoplankton populations. Coastal winds with a south–southwesterly component reverse the positive estuarine circulation in the Ría, causing an off‐shore to in‐shore flow of surface waters and, consequently, the outflow of inner waters via deeper layers. We found that this reversal imposed a selective force on the phytoplankton population: diatoms, which could not counteract the sinking movement of the surface waters, were diminished, while dinoflagellates remained in the water column. From the end of September to the beginning of October 1993, an accumulation ofGymnodimium catenatumGraham was observed coinciding with an intrusion of coastal water induced by westerly winds which provoked a reversal in the circulation of the Ría. The slow reestablishment of the positive estuarine circulation pattern, which was due to a weak coastal upwelling and considerable fresh water runoff, allowed the population ofG. catenatumto

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00212.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTDiatom and water chemistry data from 35 wetland sites in western Kentucky were used to assess diatoms as indicators of ecological conditions in wetlands. The wetlands were affected by different degrees of acid mine drainage and agriculture. Canonical correspondence analysis indicated that the distribution of diatoms was highly correlated with conductivity and total phosphorus (TP), two variables commonly associated with acidic mine drainage and agriculture, respectively.Diatom‐based inference models were developed for use as quantitative indicators of two important environmental variables in wetlands: conductivity and TP. Diatom‐inferred conductivity and TP values were highly correlated with measured values. Cross‐validation with jackknifing procedures suggested that high apparentr2between inferred and measured conductivity was overly optimistic and should be treated with caution. Jackknifing‐derived TP inference models performed poorly in predicting TP toward the ends of low and high TP concentrations. In general, the conductivity inference models based on plankton had better predictability than those based on epiphyton. Epiphyton‐based inference models can predict TP better than plankton. Therefore, diatoms in planktonic and epiphytic assemblages could provide complementary information on ecological conditions.Our data suggest that diatoms can reflect major regional environmental gradients and therefore can be used as indicators of the ecological conditions in wetlands. Quantitative inference models with known predictive power can aid the development of realistic and ecologically sound biotic indices for th

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00222.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTFertilization (phosphorus and nitrogen) of Kootenay Lake, British Columbia, was begun in 1992 in an attempt to increase food resources for declining stocks of kokanee salmon. In 1992 and 1993, significant changes in diatom abundance, species composition, diversity, and morphology of individual species were observed in the fertilized North Arm in comparison to the unfertilized South Arm. Effects of fertilization were most obvious during the spring. During summer stratification, fertilization did not result in significant changes in total abundance, but changes in species composition were observed. In 1993, with continued fertilization of the North Arm, diatom abundance in both spring and summer was significantly higher than at the same sites in 1992. No significant differences were observed in the unfertilized South Arm. Diatom abundance was significantly correlated with dissolved inorganic nitrogen (positive) and dissolved reactive silica (negative). Diatom assemblages in the fertilized North Arm in both the spring and summer of 1993 were dominated byAsterionella formosaandFragilaria crotonensis, taxa considered mesotrophic. Abundance of the oligotrophic taxaRhizosolenia eriensisandCyclotella michiganianawas higher in the South Arm than in the North Arm. Differences in diatom assemblages between the two arms in both years were further summarized by multivariate statistical analyses. Morphological variations in two smallCyclotellaspecies(C. comensisandC.cf.pseudostelligera)were observed between the fertilized and “control” stations. Populations of both species from fertilized stations exhibited stronger silicification with coarser striations and a smaller mean s

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00232.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe measured maximum ammonium uptake rates of the green algaScenedesmus quadricauda(Turpin) Brébisson and the blue‐green algaMicrocystis novacekii(Kom.) Comp. grown in nitrogen (ammonium)–limited chemostats. Maximum uptake rates per cellular carbon were larger inS. quadricaudathan inM. novacekii.These rates increased with increased specific growth rates. Maximum uptake rates per cellular nitrogen were also larger inS. quadricaudathan inM. novacekii.The maximum uptake rates per cellular nitrogen were nearly constant against increased cellular N:C ratios under nitrogen‐limited conditions. The higher maximum uptake rates indicate thatS. quadricaudahad higher uptake abilities for ammonium thanM. novacekiiwhen grown under nitrogen limitation. We examined the competition between both species under two distinct nutrient supply modes, using measured maximum uptake values and computer simulations.Microcystis novacekiiprevailed in the small‐pulse, high‐frequency nutrient supply mode, whereasS. quadricaudabecame competitively superior in the large‐pulse, low‐frequency nutrient supply mode. These results indicate that we could control nuisance blooms of blue‐green algae in lakes and reservoirs by changing the nutri

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00243.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTGenetic differentiation among geographic isolates of the pantropical to warm‐temperate red algaDigenea simplex(Wulfen) C. Agardh was investigated using random amplified polymorphic DNA (RAPD) markers, crossing studies, and temperature tolerances experiments. Eleven isolates representing populations from the Caribbean, eastern Atlantic, and Indo‐West Pacific were compared. RAPD analysis clearly revealed an Indo‐West Pacific group, a Caribbean/Cape Verde Islands group, and a Canary Islands group. Crossing studies showed different levels of inter fertility. In most crosses between Western Australian and Atlantic isolates, no hybrid tetrasporophytes were formed. In crosses between Caribbean and Cape Verde Islands isolates, tetrasporophytes developed, but the viability of tetraspores was reduced. Full sexual compatibility was observed among Cape Verde Islands isolates and among isolates from Bonaire. Temperature tolerance studies indicate that Pacific isolates have a broader temperature survival range than Atlantic isolates, which may be correlated to local temperature extremes. Despite the reduced level of sexual compatibility between Caribbean and Cape Verde Islands isolates, their shared position in the RAPD analysis and similar temperature responses suggest trans‐Atlantic dispersal in the near geological past. In addition to their discrete position in the RAPD distance analysis, the Canary Islands isolates were significantly more cold‐tolerant than the other Atlantic isolates. This finding is consistent with the hypothesis that the Canary Islands were recolonized from cold‐adapted eastern Mediterranean populations after the last Pleistocene

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00250.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTIn the non‐N2‐fixing cyanobacteriumPhormidium laminosum(Agardh) Gomont (strain OH‐I‐pCl1), N starvation induced an increase in the rate of respiration and a decrease in the rate of O2evolution. When NO3−was added to illuminated N‐starved cells, O2evolution immediately increased to levels shown by NO3−grown cells, even though N‐starved cells had lost most of theirin vitrophotosynthetic activities. Stimulation of noncyclic electron flow was maximal under light‐saturating conditions and after 2–3 days of N starvation. The respiratory rate of N‐starved cells was stimulated by the addition of NO3−or NH4+and partially inhibited at very low irradiances, even in the presence of DCMU (3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea). Results indicate that N‐starved cells obtain the energy supply for N assimilation through a process different from that used by N‐sufficient cells. N‐starved cells were able to take up NO3−in the dark and when illuminated in the presence of DCMU under anaerobiosis. Following NO3−addition, the photosynthetic yield of thein vivononcyclic electron transport slightly increased, whereas it decreased after NH4+addition. Addition of NO3−or NH4+favored photoinhibition of photosystem II,

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00258.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe studied the synthesis and binding of phycoerythrin and its associated linkers to the phycobilisome (PBS) inRhodella violacea(Kornmann) Wehrmeyer and compared the effects of high light and translation inhibitors on these processes.Rhodella violaceahas a simple hemidiscoidal PBS structure with a well‐known composition. The number of PBSs per cell decreases when irradiance is increased, and at higher irradiances the rods are shortened with a specific loss of the terminal hexamer of phycoerythrin (PE) and its associated linker. To test whether or not the observed variations were due to a coordination between the expression of the chloroplast‐encoded PE and the nuclear‐encoded linkers, we inhibited the expression of the chloroplast genes by the translation inhibitor chloramphenicol. In the few PBSs synthesized, the linker associated to the terminal PE hexamer was missing while that associated with the intermediate PE hexamer was still present. The inhibition by cycloheximide of the translation of the nuclear‐encoded linkers did not influence the synthesis of the chloroplast‐encoded phycobiliproteins. The absence of linkers prevented the formation of PE hexamers and their binding to the PBSs.We therefore propose the existence of two levels of regulation for PE and associated linkers: the intermediate PE hexamer and associated linker are always present even though their amount is reduced when irradiance is increased. In contrast, the terminal hexamer of PE and its associated linker are no longer present under high light. Their absence can be due to a feedback control between the level of PE and the synthesis of the linker: when the level of PE is lowered below a given value by the action of light on the chloroplast, a signal coming from the chloroplast reaches the nucleus and the synthesis of the linker is repressed. There is no sign of nuclear regulation of the synthesis of PE, but the nuclear‐encoded linkers have a structural role in the formation of

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00265.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTDunaliella bardawilBen‐Amotz&Avron, a β‐carotene‐accumulating halotolerant alga, was analyzed for the effect of growth temperatures on its pigment content and on the stereoisomeric composition of β‐carotene by the use of advanced liquid chromatography and photodiode array detection. Decreasing culture temperature from 30° to 10°C increased the β‐carotene content twofold and the ratio of 9‐cis to all‐trans β‐carotene fourfold, with no significant changes in the other cell pigments. The variation of total β‐carotene content by temperature was correlated with the integral irradiance received by the algal culture during a cell division cycle, whereas the9‐cisstereoisomer increased over the amount expected by that integration. The massive accumulation of9‐cisβ‐carotene within the β‐carotene globules is interpreted as indicating that the oily9‐cisstereoisomer protects against the crystallization of all

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00272.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTA psychrophilic green alga belonging to theChloromonasgenus and here named ANT1 was collected in Antarctica. The activities of two enzymes, nitrate reductase and argininosuccinate lyase, were measured at various temperatures and compared to the corresponding enzyme activities in the mesophilic speciesChlamydomonas reinhardtiiDangeard. For both enzymes, the temperature for apparent optimal activity was about 20°C lower in ANT1 than inC. reinhardtii.The enzymes were also submitted to various heat treatments before measuring their activities. Both psychrophilic enzymes were more sensitive to heat than the corresponding mesophilic enzymes. It is worth stressing, however, that in both species nitrate reductase was much more sensitive to heat than argininosuccinate lyase, which probably indicates that the peculiar structure of each protein primarily determines its dependence to temperature. Secondary adaptations to low temperatures should then occur to confer the psychrophilic character

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00276.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY