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- Legrand, Catherine, et al.
(författare)
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Allelopathy in phytoplankton – biochemical, ecological and evolutionary aspects
- 2003
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Ingår i: Phycologia. - : Informa UK Limited. - 0031-8884 .- 2330-2968. ; 42:4, s. 406-419
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Tidskriftsartikel (refereegranskat)abstract
- It is considered self-evident that chemical interactions are a component of competition in terrestrial systems, but they are largely unknown in aquatic systems. In this review, we propose that chemical interactions, specifically allelopathy, are an important part of phytoplankton competition. Allelopathy, as defined here, applies only to the inhibitory effects of secondary metabolites produced by one species on the growth or physiological function of another phytoplankton species. A number of approaches are used to study allelopathy, but there is no standard methodology available. One of the methods used is cross-culturing, in which the cell-free filtrate of a donor alga is added to the medium of the target species. Another is to study the effect of cell extracts of unknown constituents, isolated exudates or purified allelochemicals on the growth of other algal species. There is a clear lack of controlled field experiments because few allelochemicals have been identified. Molecular methods will be important in future to study the expression and regulation of allelochemicals. Most of the identified allelochemicals have been described for cyanobacteria but some known toxins of marine dinoflagellates and freshwater cyanobacteria also have an allelochemical effect. The mode of action of allelochemicals spans a wide range. The most common effect is to cause cell lysis, blistering, or growth inhibition. The factors that affect allelochemical production have not been studied much, although nutrient limitation, pH, and temperature appear to have an effect. The evolutionary aspects of allelopathy remain largely unknown, but we hypothesize that the producers of allelochemicals should gain a competitive advantage over other phytoplankton. Finally, we discuss the possibility of using allelochemicals to combat harmful algal blooms (HABs). Allelopathic agents are used for biological control in agriculture, e.g. green manures to control soil diseases in Australia, but they have not yet been applied in the context of HABs. We suggest that phytoplankton allelochemicals have the potential for management of HABs in localized areas.
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| 2. |
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| 3. |
- Pavia, Henrik, 1964, et al.
(författare)
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Intraspecific variation in the phlorotannin content of the brown alga Ascophyllum nodosum
- 2003
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Ingår i: Phycologia. - 0031-8884. ; 42:4, s. 378-383
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Tidskriftsartikel (refereegranskat)abstract
- Many brown macroalgae contain substantial concentrations of polyphenolic compounds, known as phlorotannins. Previous studies have shown that much of the variation in phlorotannin concentration is correlated with taxonomy and biogeography, but little is known about patterns of variation within species and populations. In this study, we examined intraspecific variation in the phlorotannin content of the intertidal seaweed Ascophyllum nodosum, by testing for differences within as well as between genetic individuals (genets) and populations, and between algal tissues of similar age from juveniles and adults. The results show that variation in the phlorotannin content of annual shoots within primary shoots and genets contributes substantially to the total intraspecific variation. This pattern probably indicates that the phlorotannin content is a highly plastic trait that can be significantly influenced by small-scale variation in extrinsic factors. There were also significant differences in mean phlorotannin content among study sites, and these differences varied significantly between the two study years. The extensive variation within and among genetic individuals and populations shows that it is crucial to use proper sampling designs in field studies comparing phlorotannin levels between different populations, taxa, or experimental treatments, in order to avoid false conclusions. Phlorotannin levels were significantly higher in adult annual tissue than in juveniles in five of six sites, with an overall mean phlorotannin content of 7.8% of dry mass for adult tissue and 5.9% of dry mass for juveniles. This result may be explained by a trade-off between growth and phlorotannin production and a lower mortality risk for larger individuals, leading to a strategy where it is more advantageous for a juvenile to invest in growth than to allocate resources to chemical defence.
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| 4. |
- Rehnstam-Holm, Ann-Sofi, 1959, et al.
(författare)
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Molecular studies of Dinophysis (Dinophyceae) species from Sweden and North America
- 2002
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Ingår i: Phycologia. - 0031-8884. ; 41:4, s. 348-357
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Tidskriftsartikel (refereegranskat)abstract
- Diarrhoeic, shellfish poisoning has increasingly become 4 Problem throughout the world. Because the causative organisms Dinophysis spp. cannot be cultured in the laboratory, new approaches are needed to obtain ecological and physiological information. In this study, a acuminata, D. norvegica and D, acuta were collected directly from field samples and used in polymerase chain reactions. The D1-D2 region of the large-subunit ribosomal RNA gene was amplified, cloned and sequenced. Sequence analyses showed that D. acuminata and D, norvegica were nearly identical (> 99%), and that D. acuminata showed an intraspecies variation of 0.8% The D. acuta sequence was 98.7% similar to that of D. acuminata. The slight differences between D. norvegica and D. acuminata suggest that they may have evolved into separate species rather recently. Phylogenetic analyses show that species within the Dinophysiales order should be included in the 'GPP complex', a lineage associated with a diverse array of taxa within the orders Gymnodiniales, Prorocentrales and Peridiniales. The Prorocentrales and Dinophysiales would be sister groups within the GPP complex. Amplification of Swedish D, acuminata isolates always resulted in a single LSU rDNA fragment. In contrast, amplification of the North American D. acuminata always produced two distinct fragments, The longer (735 bp) fragment showed 99.3-100% homology among all sequenced clones of different D. acuminata field isolates. The shorter gene fragment had a 70 bp deletion, but it was otherwise highly homologous to the larger gene fragment, This fragment is possibly a pseudogene and might be an important genetic marker. A variable region that is suitable as a target for a probe to identify, Dinophysis was also identified, Dinopkysis g specificity was confirmed for the probe, in that hybridization to cultured representatives of dinoflagellates and environmental samples containing mixed phytoplankton assemblages resulted in specific labelling of D. acuminata, D. norvegica and D, acuta, but not other dinoflaggellates, No labelling of D. rotundata was observed.
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