Respuestas fisiológicas y metabólicas de macroalgas expuestas a estrés osmótico por hipersalinidadmecanismos de tolerancia y herramientas de biomonitoreo

Abstract

Hypersalinity can cause osmotic stress associated with dehydration and gradual accumulation of intracellular ions, which may induce damage and oxidative stress due to overproduction of reactive oxygen species. This can lead to a reduction of photosynthetic performance and induce synthesis of antioxidant molecules such as ascorbate (ASC) and glutathione (GSH), and genes encoding for antioxidant enzymes and for enzymes related to salinity tolerance. Naturally, evaporation and desiccation events produced during intertidal low tide periods increase the salinity in the marine environment. Also, excess of salts in the marine environment is generated by anthropic effects, such as desalination of seawater to obtain fresh water. This process carried out by desalination plants generates a residual effluent of brine, generally discarded to the subtidal medium, causing osmotic stress in marine benthic communities. The aim of this Thesis was to determine tolerance mechanisms at physiological and metabolic level of macroalgae to tolerate hypersalinity, as well as to evaluate their potential use as environmental biotechnology tools for monitoring desalination brines. First, this Thesis evaluated the exposition to hypersalinity of two populations of intertidal green macroalga Ulva compressa from a contaminated (Ventanas) and not contaminated (Cachagua) locality. The results showed that hypersalinity had an impact on both populations, but in the case of Ventanas population, it showed a depressed metabolism, which can be observed through a lower photosynthetic activity and a higher oxidative stress and damage, with a higher expression of antioxidant enzyme genes, which is a consequence of continuous exposure to different pollutants, interfering in the responses to interpopulation tolerance saline XVI stress of macroalgal species. Second, the exposure to the brine discharge of the brown macroalgae Ectocarpus was analyzed through transplanting experiments in sites nearby the discharge pipe (10 and 30 m) of a seawater desalination plant in Antofagasta, Chile. The results showed a decrease in photosynthetic activity, increase of oxidative stress and damage, accumulation of ASC, and a decrease of GSH. It also was promoted the up-regulation of enzymes related to salinity tolerance and antioxidant enzymes. This study provided information to understand the tolerance mechanisms against salt stress and identified cellular biomarkers to monitor desalination brine. Third, through laboratory experiments with the brown macroalgae Dyctiota kunthii from the North Pacific of Chile, in Antofagasta, and another experiment with Dictyota dichotoma from the Mediterranean Sea of Spain, in Alicante, the responses of exposition to hypersalinities with similar values of a bine discharge were compared in both species. The results showed an increase in primary productivity in both species under hypersalinity conditions, despite a high accumulation of H2O2 in D. kunthii, and a decrease in the photosynthetic efficiency of D. dichotoma. This suggested that both species would have different cellular strategies, which would be activated under hypersalinity conditions. The responses would probably be linked to the local adaptation history of the species. Fourth, the effect of brine was determined through two transplanting experiments nearby the discharge pipe, the first one exposing D. kunthii species to the brine from the Antofagasta desalination plant and the another one exposing D. dichotoma to the brine from the desalination plant in Alicante. The results showed that exposure to brine at the impacted sites caused in D. kunthii a decrease in primary productivity and light requirements, and an increase in photosynthetic XVII efficiency and dissipation through heat. In D. dichotoma it was observed a decrease in maximum fluorescence, photosynthetic efficiency and maximal no photochemical quenching in impacted sites, while decrease of primary production and saturation irradiance was only observed at the site closest to the brine discharge. Oxidative stress increased in both species at the impacted sites, but in the case of D. kunthii it was observed only at the first time, while in D. dichotoma at the end of the experiment. This study is a practical approach that could be considered to evaluate the potential impact of desalination brine. In conclusion, this Thesis demonstrated that all macroalgae species used in this work had different cellular tolerance strategies to face the condition of hypersalinity, and also that these responses would be linked to the type of experimentation, the species-specificity and the history of local adaptation of each species. The relevance of this doctoral Thesis is to demonstrate that the interdisciplinary perspective favors the understanding of tolerance mechanisms to hypersalinity and, for this purpose, there are cross-sectional methodological tools from physiology, biochemistry, and molecular that can be applied internationally and are feasible to incorporate into the brine impact environmental monitoring system