Algal Defenses Research Articles

Host-Parasite interaction between brown algae and eukaryote biotrophic pathogens

Brown algae belong to the class Phaeophyceae which are mainly multicellular, photosynthetic organisms, however they evolved independently from terrestrial plants, green and red algae. In the past years marine aquaculture involving brown algae has gained enormous momentum. In both natural environments and aquaculture, brown algae are susceptible to infection by various prokaryotic and eukaryotic parasites. While our understanding of host-parasite interactions in brown algae is gaining recognition, our understanding of how brown algae react to biotic stress remains incomplete. The objective of this review is to address research gaps in the field by providing a summary of what is already known about the response of brown algae to abiotic and biotic stress. The biology of eukaryotic zoosporic pathogens Maullinia ectocarpii, Eurychasma dicksonii, Anisolpidium ectocarpii is also discussed, as those parasites have been used in laboratory experiments to study diseases of brown algae. These studies often relied on parasites-infecting Ectocarpus siliculosus which has become a brown algal model organism to study host-pathogen interactions. Stress response in brown algae involves processes similar to hypersensitivity response, oxidative stress response and activation of peroxidases, but also the production of blue fluorescent metabolites and deposition of β-1,3-glucan in the cell wall. Cell wall modification, expression of several defence related proteins, and secondary metabolite production also holds a crucial role in brown algal defence mechanism. Understanding host-pathogen interactions and the associated mechanisms is vital to discover strategies to control pathogens in the growing aquaculture sector.

Oomycete pathogens, red algal defense mechanisms and control measures

Oomycete pathogens are one of the most serious threats to the rapidly growing global algae aquaculture industry but research into how they spread and how algae respond to infection is unresolved, let alone a proper classification of the pathogens. Even the taxonomy of the genera Pythium and Olpidiopsis, which contain the most economically damaging pathogens in red algal aquaculture, and are among the best studied, needs urgent clarification, as existing morphological classifications and molecular evidence are often inconsistent. Recent studies have reported a number of genes involved in defense responses against oomycete pathogens in red algae, including pattern-triggered immunity and effectortriggered immunity. Accumulating evidence also suggests that calcium-mediated reactive oxygen species signaling plays an important role in the response of red algae to oomycete pathogens. Current management strategies to control oomycete pathogens in aquaculture are based on the high resistance of red algae to abiotic stress, these have environmental consequences and are not fully effective. Here, we compile a revised list of oomycete pathogens known to infect marine red algae and outline the current taxonomic situation. We also review recent research on the molecular and cellular responses of red algae to oomycete infection that has only recently begun, and outline the methods currently used to control disease in the field.

Individual and combined toxicity of silver nanoparticles and triclosan or galaxolide in the freshwater algae Euglena sp.

With the widespread production and usage, silver nanoparticles (AgNPs) can be extensively found in the aquatic environment and co-exist with other pollutants for a prolonged time, leading to a more complex ecological risk in natural waters. In this work, the model freshwater algae Euglena sp. was selected to study the toxicity of AgNPs and explore their influences on the toxicity of two frequently detected personal care products, triclosan (TCS) and galaxolide (HHCB). The LC-MS targeted metabolomics was used to analyze the possible toxicity mechanism at the molecular level. Results showed that AgNPs was toxic to Euglena sp. upon 24 h exposure, but the toxicity decreased gradually as exposure times increased. AgNPs (<100 μg L−1) attenuated TCS and HHCB toxicity to Euglena sp., which could be attributed primarily to the decreased oxidative stress. Metabolomic analysis revealed that AgNPs induced a stress on algal defense system upon TCS exposure, but promoted the algal defense system upon HHCB exposure. Furthermore, DNA or RNA biosynthesis was accelerated in algae exposed to TCS or HHCB after the addition of AgNPs, implying that AgNPs may mitigate the genetic toxicity of TCS or HHCB in Euglena sp. These results emphasize the potential of metabolomics to reveal toxicity mechanism and provide new perspectives on the aquatic risk assessment of personal care products in the presence of AgNPs.

Salinization and heavy metal cadmium impair growth but have contrasting effects on defensive colony formation of Scenedesmus obliquus

Driven by anthropogenic activities, freshwater salinization has become an emerging global environmental issue. Recent studies indicate that salinization increases the mobility of heavy metals in soil and causes higher flux into surface waterbodies. The present study assessed the combined effects of salinization (0, 3, 6 PSU) and the heavy metal Cd2+ (0, 0.2, 0.4 mg L−1) on the anti-grazing colony formation and population growth of Scenedesmus obliquus, a common freshwater alga. The results showed that the increase in salinity promoted colony formation of S. obliquus with or without the presence of grazing cues and, in contrast, Cd2+ contamination depressed the defensive colony formation of S. obliquus to Daphnia filtrate. The increase in both salinity and Cd2+ concentration depressed the population growth of S. obliquus, including impaired photosynthesis and a decreased population growth rate. Salinization moderated the negative effects of Cd2+ on defensive colony formation of S. obliquus, suggesting increased absorption of Cd2+ ions by a thicker outer layer of the algal cell wall under saltier conditions. As a result, larger defensive colonies of S. obliquus under freshwater salinization may cause higher bioaccumulation of heavy metals by algal cells and heavier influence on zooplankton. This study provides evidence that freshwater salinization could interfere with plankton interactions by affecting algal defense and growth, which may lead to bottom-up cascading effects on freshwater food webs.

Functional diversity in herbivorous fishes on Caribbean reefs: The role of macroalgal traits in driving interspecific differences in feeding behavior

Understanding how functional traits drive plant-herbivore interactions often illuminates the mechanisms driving niche partitioning and functional diversity in this important guild of consumers. On coral reefs, a diverse suite of herbivorous fishes is key for controlling algal abundance and impacting benthic community dynamics. Here, we focus on how algal traits shape complementarity in feeding for a diverse suite of large herbivorous fishes on a coral reef in the wider Caribbean. We used feeding assays in the field to document feeding patterns of the different herbivorous fishes across 50 species of macroalgae. Then, we used a suite of macroalgal traits such as dry mass, nutrient content, calcification, and chemical defenses to assess how these traits influenced patterns of consumption. Algal defenses were the major traits determining the overall vulnerability of algae to herbivores, with uncalcified algae from undefended genera being consumed 40% more rapidly than algae that were either calcified or chemically defended. Nutrient content of algae explained little in patterns of overall herbivory. We found significant niche diversification in feeding both among and within genera with the three major genera having unique feeding patterns on different suites of algae (Acanthurus spp. - red macroalgae, Sparisoma spp. - brown and green macroalgae, and Scarus spp. - benthic filamentous algae). With respect to how algal traits influenced patterns of feeding in individual species, we found that: (1) some herbivore species were almost exclusively influenced by avoiding algal defenses, (2) some species showed strong interactions between algal defenses and nutrient content that determined their feeding, and (3) some species (Kyphosus spp., Pomacanthus arcuatus) targeted chemically-defended algae with high nutrient content. Our work highlights the role that algal traits play in influencing patterns in the diversity and redundancy of feeding in herbivorous fishes on coral reefs.

What’s new in marine botany of the Eastern Mediterranean?

Abstract This article provides a topical review of East Mediterranean phycology and seagrass biology, with a special focus on the outcomes of the multi-year project “Brown algal biodiversity and ecology in the Eastern Mediterranean Sea” supported by the TOTAL Foundation. Following a general overview of East Mediterranean seaweed biogeography and taxonomy, the review covers seagrasses, deep-water (circalittoral) macroalgal diversity, pathogens and algal defence, human impacts and biotic indices, alien species as well as the papers of this special issue.

The Role of Phytohormones in Enhancing Metal Remediation Capacity of Algae.

Heavy metal (HM) contamination of the environment is a major issue worldwide, creating an ever-increasing demand for remediation techniques. Remediation with algae offers an ecologically safe, cost-effective, and efficient option for HM removal. Similar to plants, growth and development of algae are controlled by the hormonal system, where phytohormones are involved in HM tolerance and thus can regulate remediation ability; however, the underlying mechanisms of phytohormone function remain elusive. This review aims to draw a comprehensive model of phytohormone contributions to algal performance under HM stress. We focus on the mechanisms of HM biosorption, uptake and intracellular storage, and on how phytohormones interact with algal defence systems under HM exposure. We provide examples of successful utilization of algae in remediation, and of post-processing of algal materials. Finally, we discuss the advantages and risks of using algae for remediation. An in-depth understanding of these processes can inform effective HM remediation techniques.

Gamma Radiation Induced Changes in the Biochemical Composition of Aquatic Primary Producers and Their Effect on Grazers

Changes in the biochemical composition of primary producers can alter their food quality, influencing their consumers and further propagating through the food web. Gamma (ɣ) radiation is an environmentally important type of ionising radiation as it can damage macromolecules such as DNA, proteins, and lipids due to its high frequency, short wave length, and high energy photons. Here, we investigate whether short-term ɣ-radiation changes the biochemical composition of primary producers and if radiation-induced changes affect higher trophic levels. Two phytoplankton species were exposed to two doses of ɣ-radiation and compared to a control. The metabolic profile and total protein content of the algae were measured at five time points within 24 hours. Additionally, we measured carbon incorporation rates of Daphnia magna fed with the exposed algae. Gamma radiation had a significant effect on phytoplankton biochemical composition, although these effects were species-specific. The changes in phytoplankton biochemical composition indicate that ɣ-radiation induced the production of reactive oxygen species (ROS). D. magna incorporated more carbon when fed with algae previously exposed to ɣ-radiation; this could be due to radiation-induced changes in nutritional quality, algal anti-grazing defences, or chemical feeding stimuli.

The chemical defences of the invasive alga Sargassum muticum (Yendo) Fensholt correlate to mesoherbivore diversity, but not to time-since-invasion

Populations of the invasive alga Sargassum muticum were sampled along a time-since-invasion (TSI) gradient to test the hypothesis that chemical defences would increase with TSI, and diversity of native mesoherbivores. Algal chemical defences, phlorotannins, were quantified as a proxy for top-down-pressure, and these were compared with both native enemy diversity and time-since-invasion at each of seven sites along the west coast of the UK. The defences in the annual fronds showed a strong positive correlation with the biodiversity of native mesoherbivores. The defences in the perennial holdfasts, whilst generally higher than those in the fronds, showed no relationship. In contrast, defences in neither the fronds nor the holdfasts showed any relationship with TSI. The majority of mesoherbivores found in this survey were small and probably juvenile. Many of these individuals are known to occupy the fronds of S. muticum for shelter or to feed on its epiphytes, and are probably less likely to feed directly on its tissues than adults. The low probability that any one species of grazer was feeding on S. muticum tissues may explain why the alga contained a greater level of phlorotannin when the diversity of potential enemies was high. This study highlights the importance of enemy diversity in invasion ecology.

Isolation and pathogenicity identification of bacterial pathogens in bleached disease and their physiological effects on the red macroalga Gracilaria lemaneiformis

Marine macroalga, Gracilaria lemaneiformis, is affected by bleached disease in recent years, but the bacterial pathogens for bleached disease in G. lemaneiformis are either known or unknown. In this study, we identified eight bacterial pathogens, of which Agarivorans albus, Aquimarina latercula (T) and Brachybacterium sp. had the strongest pathogenicity on healthy G. lemaneiformis. These pathogens had strong agarase activity, suggesting a possible infection mechanism through the degradation of algal-agar. Furthermore, analysis of the macroalgal defense against pathogens in terms of hydrogen peroxide and malondialdehyde content indicated that oxidative burst started at an early stage during the bacterial infection. On the other hand, the increasing activity of peroxidase and the occurrence of different peroxidases were to protect algae from the oxidative damage, by compensating for the decrease in catalase and total antioxidant capacity in bleached tissue. The photosynthetic pigment – phycobiliprotein was dramatically decreased after the bacterial infection, with the beta subunit but not the alpha subunit of phycoerythrin being degraded first as the disease progressed. The findings here provide very important fundamental information for future research on understanding the algae-bacteria interaction mechanism, the mechanism of algal defense against bacterial infection, which is important for the efficient and healthy cultivation of G. lemaneiformis.

Bacteria may induce the secretion of mucin-like proteins by the diatom Phaeodactylum tricornutum.

Benthic diatoms live in photoautotrophic/heterotrophic biofilm communities embedded in a matrix of secreted extracellular polymeric substances. Closely associated bacteria influence their growth, aggregation, and secretion of exopolymers. We have studied a diatom/bacteria model community, in which a marine Roseobacter strain is able to grow with secreted diatom exopolymers as a sole source of carbon. The strain influences the aggregation of Phaeodactylum tricornutum by inducing a morphotypic transition from planktonic, fusiform cells to benthic, oval cells. Analysis of the extracellular soluble proteome of P.tricornutum in the presence and absence of bacteria revealed constitutively expressed newly identified proteins with mucin-like domains that appear to be typical for extracellular diatom proteins. In contrast to mucins, the proline-, serine-, threonine-rich (PST) domains in these proteins were also found in combination with protease-, glucosidase- and leucine-rich repeat-domains. Bioinformatic functional predictions indicate that several of these newly identified diatom-specific proteins may be involved in algal defense, intercellular signaling, and aggregation.

Recognition- and defense-related gene expression at 3 resynthesis stages in lichen symbionts.

Recognition and defense responses are early events in plant-pathogen interactions and between lichen symbionts. The effect of elicitors on responses between lichen symbionts is not well understood. The objective of this study was to compare the difference in recognition- and defense-related gene expression as a result of culture extracts (containing secreted water-soluble elicitors) from compatible and incompatible interactions at each of 3 resynthesis stages in the symbionts of Cladonia rangiferina. This study investigated gene expression by quantitative PCR in cultures of C. rangiferina and its algal partner, Asterochloris glomerata/irregularis, after incubation with liquid extracts from cultures of compatible and incompatible interactions at 3 early resynthesis stages. Recognition-related genes were significantly upregulated only after physical contact, demonstrating symbiont recognition in later resynthesis stages than expected. One of 3 defense-related genes, chit, showed significant downregulation in early resynthesis stages and upregulation in the third resynthesis stage, demonstrating a need for the absence of chitinase early in thallus formation and a need for its presence in later stages as an algal defense reaction. This study revealed that recognition- and defense-related genes are triggered by components in culture extracts at 3 stages of resynthesis, and some defense-related genes may be induced throughout thallus growth. The parasitic nature of the interaction shows parallels between lichen symbionts and plant pathogenic systems.

Consumer diversity interacts with prey defenses to drive ecosystem function

Prey traits linking consumer diversity to ecosystem function remain poorly understood. On tropical coral reefs, herbivores promote coral dominance by suppressing competing macroalgae, but the roles of herbivore identity and diversity, macroalgal defenses, and their interactions in affecting reef resilience and function are unclear. We studied adjacent pairs of no-take marine reserves and fished areas on reefs in Fiji and found that protected reefs supported 7-17x greater biomass, 2-3x higher species richness of herbivorous fishes, and 3-11x more live coral cover than did fished reefs. In contrast, macroalgae were 27-61x more abundant and 3-4x more species-rich on fished reefs. When we transplanted seven common macroalgae from fished reefs into reserves they were rapidly consumed, suggesting that rates of herbivory (ecosystem functioning) differed inside vs. outside reserves. We then video-recorded feeding activity on the same seven macroalgae when transplanted into reserves, and assessed the functional redundancy vs. complementarity of herbivorous fishes consuming these macroalgae. Of 29 species of larger herbivorous fishes on these reefs, only four species accounted for 97% of macroalgal consumption. Two unicornfish consumed a range of brown macroalgae, a parrotfish consumed multiple red algae, and a rabbitfish consumed a green alga, with almost no diet overlap among these groups. The two most chemically rich, allelopathic algae were each consumed by a single, but different, fish species. This striking complementarity resulted from herbivore species differing in their tolerances to macroalgal chemical and structural defenses. A model of assemblage diet breadth based on our feeding observations predicted that high browser diversity would be required for effective control of macroalgae on Fijian reefs. In support of this model, we observed strong negative relationships between herbivore diversity and macroalgal abundance and diversity across the six study reefs. Our findings indicate that the total diet breadth of the herbivore community and the probability of all macroalgae being removed from reefs by herbivores increases with increasing herbivore diversity, but that a few critical species drive this relationship. Therefore, interactions between algal defenses and herbivore tolerances create an essential role for consumer diversity in the functioning and resilience of coral reefs.

Highly dynamic exon shuffling in candidate pathogen receptors ... what if brown algae were capable of adaptive immunity?

Pathogen recognition is the first step of immune reactions. In animals and plants, direct or indirect pathogen recognition is often mediated by a wealth of fast-evolving receptors, many of which contain ligand-binding and signal transduction domains, such as leucine-rich or tetratricopeptide repeat (LRR/TPR) and NB-ARC domains, respectively. In order to identify candidates potentially involved in algal defense, we mined the genome of the brown alga Ectocarpus siliculosus for homologues of these genes and assessed the evolutionary pressures acting upon them. We thus annotated all Ectocarpus LRR-containing genes, in particular an original group of LRR-containing GTPases of the ROCO family, and 24 NB-ARC–TPR proteins. They exhibit high birth and death rates, while a diversifying selection is acting on their LRR (respectively TPR) domain, probably affecting the ligand-binding specificities. Remarkably, each repeat is encoded by an exon, and the intense exon shuffling underpins the variability of LRR and TPR domains. We conclude that the Ectocarpus ROCO and NB-ARC–TPR families are excellent candidates for being involved in recognition/transduction events linked to immunity. We further hypothesize that brown algae may generate their immune repertoire via controlled somatic recombination, so far only known from the vertebrate adaptive immune systems.

Extract powder from the brown alga Ascophyllum nodosum (Linnaeus) Le Jolis (AMPEP): a “vaccine-like” effect on Kappaphycus alvarezii (Doty) Doty ex P.C. Silva

The benefits of using Acadian Marine Plant Extract Powder (AMPEP), obtained from the brown algae Ascophyllum nodosum, for improving growth of the red alga Kappaphycus alvarezii has been demonstrated by authors in the Philippines and Brazil, particularly for increasing daily growth rate and mitigation of epiphytes. However, the processes which occur have not been discussed. This study examined in vitro the relationship between those red algal defense mechanisms and K. alvarezii responses using AMPEP treatments. The administration of the extract reduced the effects of the oxidative burst (production of hydrogen peroxide) which may be extremely aggressive for an individual and its epiphyte. The bleaching of the non-corticated portions of Polysiphonia subtilissima thalli that were cultivated as simulated epiphytes with AMPEP samples confirmed that the reaction was evident in which AMPEP protected K. alvarezii from the hydrogen peroxide effects. It is proposed that the use of the brown seaweed powder AMPEP acts as a potential vaccine, eliciting activation of the red seaweed K. alvarezii natural defenses against pathogens and ameliorating the negative effects of long-term exposure to oxidative bursts.

The snail Potamopyrgus antipodarum grows faster and is more active in the shade, independent of food quality

Ecological stoichiometry has advanced food web ecology by emphasising the importance of food quality over food quantity for herbivores. Here, we focus on the effects of abiotic factors such as nutrients and light (known to influence food quality) on grazer growth rates. As model organism we used the mudsnail Potamopyrgus antipodarum that is native to New Zealand but invasive elsewhere. In a stream channel experiment in New Zealand, we manipulated light (two levels) and nutrients (four levels) to achieve a range of primary producer carbon: nutrient ratios and added mudsnails (3 densities + ungrazed control) to 128 periphyton covered stream channels in a 2 × 4 × 4 full factorial design. We measured snail growth rate and activity, food quality and nutritional imbalance, to test the predictions that (1) less light and more nutrients increase periphyton food quality and thus snail growth rates, and (2) less crowding leads to higher food availability and thus higher snail growth rates. We found that snail growth rates were higher under low light than under high light intensities and this difference increased with increasing nutrient addition. These changes in growth rate were not mediated by food quality in terms of periphyton nutrient ratios. Furthermore, experimental treatments strongly affected snail behaviour. Snails grazed more actively in the low light treatments, and thus it is more likely that snail growth rates were directly affected by light levels, maybe as a result of innate predator avoidance behaviour or as a reaction to high UV intensities. We conclude that in our stream channels snail growth rate was limited by factors other than food quality and quantity such as UV exposure, algal defences or the relatively low ambient water temperature.

Stressed, but not defenceless: no obvious influence of irradiation levels on antifeeding and antifouling defences of tropical macroalgae

The production of defence metabolites is assumed to be costly in metabolic terms. If this holds true, low-light stress should reduce the ability of seaweeds to defend themselves chemically against herbivory and fouling. We investigated the effect of energy limitation on the defensive status of seaweeds by assessing their attractiveness to mesograzers and their activity against a bivalve macrofouler in comparison with non-stressed conspecifics. The macroalgae Codium decorticatum (Woodw.) M. Howe, Osmundaria obtusiloba (C. Agardh) R. E. Norris, Pterocladiella capillacea (S. G. Gmel.) Santel. and Hommer., Sargassum vulgare C. Agardh and Stypopodium zonale (Lamour.) Papenf. collected at the southeastern Brazilian coast were exposed to six levels of irradiation (between 1 and 180 μmol photons m−2 s−1) for 10–14 days. After this period, algae from all treatment levels were: (a) processed as artificial food and offered to an amphipod community dominated by Elasmopus brasiliensis Dana and (b) extracted to test for differences in settlement rates of the fouling mussel Perna perna L. on filter paper loaded with the crude extracts. Generally, photosynthesis rates and growth were reduced under low light conditions. Attractiveness to herbivores and macrofoulers, however, was insensitive to energy limitation. We discuss possible explanations for the observed absence of a relationship between light availability and algal defence including the change in nutritional value of the algal tissue, the allocation of resources towards defence instead of growth and the absence of costs for defence.

Algal defenses, population stability, and the risk of herbivore extinctions: a chemostat model and experiment

AbstractThe effects of inducible defenses and constitutive defenses on population dynamics were investigated in a freshwater plankton system with rotifers as predators and different algal strains as prey. We made predictions for these systems using a chemostat predator–prey model and focused on population stability and predator persistence as a function of flow‐through rate. The model exhibits three major types of behavior at a high nutrient concentration: (1) at high dilution rates, only algae exist; (2) at intermediate dilution rates, algae and rotifers show stable coexistence; (3) at low dilution rates, large population fluctuations occur, with low minimum densities entailing a risk of stochastic rotifer extinctions. The size and location of the corresponding areas in parameter space critically depend on the type of algal defense strategy. In an 83‐day high‐nutrient chemostat experiment we changed the dilution rate every 3 weeks, from 0.7 to 0.5 to 0.3 to 0.1 per day. Within this range of dilution rates, rotifers and algae coexisted, and population fluctuations of algae clearly increased as dilution rates decreased. The CV of herbivore densities was highest at the end of the experiment, when the dilution rate was low. On day 80, herbivorous rotifers had become undetectable in all three chemostats with permanently defended algae (where rotifer densities had already been low) and in two out of three chemostats where rotifers had been feeding on algae with inducible defenses (that represented more edible food). We interpret our results in relation to the paradox of enrichment.

Metal accumulation and oxidative stress in Ulva sp. substantiated by response integration into a general stress index

In an attempt to correlate external levels of exposure, bioaccumulation markers and oxidative stress responses in the green macroalgae Ulva sp., an investigative biomonitoring study was performed in a Portuguese coastal lagoon with a complex contamination scenario (eutrophication and moderate metal levels). Ulva sp. was collected seasonally in three stations: BB (Barrosa branch) and BS (Bom-Sucesso branch) located in confined areas of the upper lagoon; LL (lower lagoon) closer to the lagoon inlet and selected as reference station. Water and sediment were both monitored for metals (Mn, Cu, Cr, Ni, Cd). Additionally, nutrients and organic matter were measured in water and sediment, respectively. Catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST), total glutathione (GSH t) and lipid peroxidation (LPO), as well as Mn, Cu, Cr, Ni and Cd were measured in the algae. Metal levels in Ulva sp. consistently reflected their occurrence in water. Ulva sp. from BB exhibited higher CAT activity (autumn and spring) in agreement with Cu and Ni increases in water and algae and supported by significant Pearson correlations. The involvement of GPx on algal defences was considered since a positive correlation was observed with accumulated Mn. At BB, a direct implication of accumulated metals on increases of GR (autumn) and GSH t (summer) was also assumed. The contribution of GST to algal defences seemed to be less prominent. Despite the enzymatic antioxidant activation at BB, Ulva sp. collected in autumn and spring did not show efficient coping with ROS overproduction as LPO occurred. Globally, the adopted multi-biomarker approach coupled with environmental chemical characterization, pointed out BB as a major impacted area. The integration of oxidative stress responses into a general stress index (IBR) substantiated the data interpretation, providing a more definitive identification of the level of pollution, and therefore contributing to the understanding of cause–effect relationships.

No evidence for the induction of brown algal chemical defense by the phytohormones jasmonic acid and methyl jasmonate.

Induced chemical defense reactions are widespread in marine brown algae. Despite the evidence that the biosynthesis of defense metabolites can be up-regulated upon herbivory, we do not know how this regulation of biosynthetic pathways to secondary metabolites is achieved in brown algae. In higher plants, the phytohormone jasmonic acid (JA) is crucial for the mediation of induced chemical defenses, and several findings of this metabolite from marine sources have been reported. We tested the hypothesis that JA or related metabolites play a role in induced brown algal defense. Quantification of oxylipins with a detection limit around 20 ng g(-1) algal tissue did not reveal the presence of JA in the seven examined brown algal species Dictyota dichotoma, Colpomenia peregrina, Ectocarpus fasciculatus, Fucus vesiculosus, Himanthalia elongata, Saccharina latissima (formerly Laminaria saccharina), and Sargassum muticum. Moreover, treatment with ecologically relevant concentrations of JA and methyl jasmonate did not lead to a significant change in the profile of medium- and non-polar metabolites of the tested algae. Only when high concentrations of > or =500 microg ml(-1) medium of the phytohormones were applied that a metabolic response which could be attributed to unspecific stress was observed. Bioassays with D. dichotoma that focused on medium- and non-polar compounds confirmed the lack of a biological role of JA and methyl jasmonate in the induction of algal induced chemical defenses. The phytohormone-treated samples did not exhibit any increased defense potential towards the amphipod Ampithoe longimana and the isopod Paracerceis caudata. JA and related phytohormones, known to be active in higher plants, thus appear to play no role in brown algae for induction of the defense chemicals studied here.