Description: As part of an ongoing research program aiming at monitoring molecular changes in the tissues and metabolite trafficking in the hydrosphere of algae subjected to chemical stresses, we are discussing the various analytical techniques that have been employed to characterize, and sometimes to quantity these metabolites. High-field multinuclear and solid-state nuclear magnetic resonance (NMR) spectroscopies are powerful tools for metabolite characterization from extracts and in vivo, but quantification and kinetic aspects show some limitations. Modern MS (mass spectrometry) is extremely useful for fingerprinting samples against databases and when dealing with very low concentrations of metabolites, the limitations being set by the type of chromatographic separation and mode of detection coupled with the mass spectrometer. Regarding chemical communication, optimization in terms of resolution and efficiency of hydrosphere chemical analysis can theoretically be achieved in a system which integrates (i) a multiparametric incubation chamber, (ii) a gasphase or a liquid-phase separation system and (iii) mass spectrometer(s) equipped with one or two detectors responding to the analytical and quantitative needs. This text reviews some of the techniques that have been employed in various types of plant metabolic studies, which may serve as a basis towards an integrative analytical strategy directly applicable to the metabolomics of selected marine macrophytes.

Description: A review is presented of ongoing research on the oligosaccharide signals involved in cell-cell recognition in the Chondrus crispus-Acrochaete operculata host-pathogen association. In this pathosystem, the host gametophytes are resistant to the pathogen, whereas the sporophytic generation is susceptible to infection. The virulence of the green algal pathogen is mediated by the recognition of carrageenan oligosaccharides released from its red algal host: kappa-carrageenan oligosaccharides inhibit A. operculata virulence while lambda carrageenan oligosaccharides enhance its pathogenicity. It appears that the recognition of A. operculata by C. crispus also involves an oligosaccharidic signal. This signal is present in the non-virulent form of the pathogen whereas it is absent from the virulent form. Altogether this pathosystem offers a unique model to investigate the recognition of oligosaccharide signals in plant-pathogen interactions. The possible applications of this research to develop new strategies for disease control in maricultured algal crops are discussed.

Description: Elicitation of Gracilaria conferta (Schousboe ex Montagne) J. ct G. Feldmann with oligoagars resulted in a defense response that was strong enough to kill epiphytic bacteria associated with the alga. Up to 60% of the resident bacterial flora of healthy plants was eliminated within 60 min after addition of neoagarohexaose to the algal medium. Single isolates of agar-degrading bacteria that had been isolated previously from healthy or decaying algal tissues proved to be more sensitive, Some of them were generally unable to survive on healthy G, conferta. Others survived on unelicited plants. Approximately 90% of these more resistant agar degraders were eliminated within 15 min after elicitation. The bacterial degradation of dead tissue of G, conferta resulted in a release of elicitors. The elicitors accumulated in the medium and reached high enough concentrations within 24 h to induce a hypersensitive response in healthy algae, The eliciting agent could be destroyed with beta -agarase and was thus probably oligoagar, Application of antibiotics prevented the accumulation of the elicitor, which indicated that bacteria were responsible for its release from the algal biomass, The hypersensitive response of G. conferta after contact with oligoagars is thus a true defense response, because it enables the plant to protect itself efficiently from enzymatic attacks on its cell wall.

Description: The responses of Gracilaria lemaneiformis, an easily epiphytized host, and the relatively resistant G. cornea mutant, to the green alga Ulva lactuca were studied using biculture experiments with and without antibiotics. Both Gracilaria species grown with and without U. lactuca showed different levels of growth rate, release of hydrogen peroxide and of halogenated hydrocarbons. These quantitative differences led to a successful response against Ulva lactuca in the case of G. cornea mutant and to a failure in response in the case of G. lemaneiformis. The response of each Gracilaria species to U. lactuca was qualitatively similar to its response to bacteria. This suggests the involvement of oligosaccharide elicitors produced in the presence of epiphytes and bacteria. A clear Gracilaria inhibition was demonstrated with extracts of the culture medium. It appears that hydrogen peroxide, halogenated hydrocarbons and oligosaccharides may be components of the inhibitory activity of the extracts. The responses of Gracilaria species to the presence of U. lactuca suggest the characterization of a defence response.

Description: A backfiring weapon: The release of H2O2 by an amino acid oxidase is the early defensive reaction of the red alga Chondrus crispus against the endophytic green algal pathogen Acrochaete operculata (see scheme). This reaction can be induced by L-asparagine, which is released by the attacker when it recognises host cell-wall κ-carrageenan oligosaccharides. The induced signal of the attacker thus serves directly as the substrate for the production of the defensive metabolite.

Description: Certain forms of oligocellulose and certainbacterially excreted peptides were identified asendogenous and exogenous elicitors, respectively, ofa tip bleaching response in Gracilaria conferta(Schousboe ex Montagne) J. et G. Feldmann. Thehalf-maximal tip bleaching response was observed when31.1 μM cellobiose or 11.6 μM cellotetraosewere present in the growth medium. In contrast, noresponse was detected after exposure to glucose,cellotriose, cellopentaose or maltooligosaccharides.The response was thus strongly dependent on themolecular size of the oligocellulose and onlysaccharides that consisted of an even number ofglucose residues were elicitor-active. Three bacterialspecies that had earlier been identified as potentialinducers of the tip bleaching symptom excretedelicitor-active compounds into the growth medium.These compounds were protease-sensitive and thuspeptides or proteins. The tip bleaching-inducingcompound that was excreted by one Cytophaga-likeorganism was partially purified. It could be extractedfrom culture supernatants with chloroform and itsmolecular size was between 700 and 1500 Da,corresponding with a structure of 4–20 amino acids.Various endogenous and exogenous elicitors are thusrecognized by G. conferta and allow this alga torespond hypersensitively to the maceration of its cellwall skeleton or just to the presence of certainepiphytic organisms

Description: Agar oligosaccharides in the neoagarobiose series were prepared by partial enzyme hydrolysis, separated on Biogel P2 and P4, and analyzed by high-performance anion exchange chromatography with pulsed amperometric detection, yielding neoagarosaccharide fractions with a disaccharide repetition degree ranging from 1 (neoagarobiose) to more than 8 (neoagarohexadecaose). These fractions were analyzed for their biological activity toward the marine red alga Gracilaria conferta (Schousboe ex Montagne) J. et G. Feldmann in terms of increase of oxygen consumption, release of hydrogen peroxide, elimination of epiphytic bacteria, and induction of thallus tip bleaching. The structure–activity and dose–response relationships of neoagarosaccharides were very similar in the respiratory and oxidative burst responses and in their bactericidal properties, with neoagarosaccharides consisting of 6 to 8 disaccharide repeating units being the most active. All these responses were competitively inhibited by the reduced form of neoagarohexaose, neoagarohexaitol. In contrast, the tip-bleaching response was light dependent, required much higher concentrations of neoagarosaccharides, and was not inhibited by neoagarohexaitol, suggesting that it is an unspecific oxidative stress reaction. Putative structural effects on the recognition of endogenous agar-oligosaccharide elicitors by G. conferta are discussed.

Description: The transit of RV SONNE from Las Palmas (departure: 11.12.2021) to Guayaquil, Ecuador (arrival: 11.01.2022) is directly related to the international collaborative project SO287-CONNECT of GEOMAR in cooperation with Hereon and the University of Bremen, supported by the German Federal Ministry of Education and Research (BMBF) between October 15 2021 and January 15 2024. The research expedition was conducted to decipher the coupling of biogeochemical and ecological processes and their influence on atmospheric chemistry along the transport pathway of water from the upwelling zones off Africa into the Sargasso Sea and further to the Caribbean and the equatorial Pacific. Nutrient-rich water rises from the deep and promotes the growth of plant and animal microorganisms, and fish at the ocean surface off West Africa. The North Equatorial Current water carries the water from the upwelling, which contains large amounts of organic material across the Atlantic to the Caribbean, supporting bacterial activity along the way. But how the nutritious remnants of algae and other substances are processed on their long journey, biochemically transformed, decomposed into nutrients and respired to carbon dioxide, has so far only been partially investigated. Air, seawater and particles were sampled in order to provide new details about the large cycles of carbon and nitrogen, but also of many other elements such as oxygen, iodine, bromine and sulfur. Inorganic and organic bromine and iodine compounds are generally emitted naturally from the ocean into the atmosphere, promote cloud formation and affect climate, and some even reach the stratosphere where they contribute to ozone depletion. We measured how much of these compounds are released from the ocean, and at what locations and how they are transformed in the ocean and in the atmosphere. Sargassum algae, which have become a nuisance on beaches in the western and eastern Atlantic, support life and contribute to carbon cycling in the middle of the Atlantic, the Sargasso Sea and in the Caribbean, while their contribution to halogen cycling and marine bromine and iodine emissions was previously unknown. We investigated the influence of various natural parameters such as temperature and solar radiation on the biogeochemical transformation processes in order to understand the influence of climate change on these processes in incubation experiments with seawater and algae. We investigated how anthropogenic signals such as shipping traffic influence the nitrogen and sulphur cycle in the ocean, as well as the impact of nitrogen oxides from ship exhaust and sulphurous, acidic and dirty water from purification systems on organisms and biochemical processes. Plastic debris was sampled from the surface waters to investigate its contribution to global biogeochemical transformation processes. The working hypotheses of the research program were:  Bioavailability of dissolved organic carbon in surface waters decreases along the productivity gradient and transport pathway from the Eastern to the Western Tropical North Atlantic.  Nutrient gradients from East to West constrain the microbial utilization of organic matter- contributing to an accumulation of C-rich organic matter due to a) limited mineralization and b) enhanced exudation- also leading to gel-like particles accumulation in the western tropical North Atlantic and Sargasso Sea.  Tropospheric and stratospheric ozone are strongly impacted by biogeochemical and ecological processes occurring around and in the NA gyre system related to marine iodine and bromine cycles.  The long-range transport of natural and anthropogenic organic matter in water and of gases and aerosols in the air impact carbon-export, biogeochemical cycles in the water column, and the release of gases and particles from the ocean significantly. 4 SONNE -Berichte, SO287, Las Palmas - Guayaquil, 11.12.2021 - 11.01.202 The data and samples obtained specifically target carbon, nutrient and halogen cycling, the composition of phytoplankton, bacteria, the transport and sequestration of macro algae and the air-sea exchange processes of climate relevant gases and aerosols. The influence of ecological and transport processes, as well as anthropogenic impacts on the North Atlantic gyre system, specifically in the Sargasso Sea and the influence of ship emissions throughout the Atlantic towards the west and into the Pacific will be investigated with the data.