Effects of Glyphosate-Based Herbicide on Primary Production and Physiological Fitness of the Macroalgae Ulva lactuca

Abstract

The use of glyphosate-based herbicides (GBHs) worldwide has increased exponentially over the last two decades increasing the environmental risk to marine and coastal habitats. The present study investigated the effects of GBHs at environmentally relevant concentrations (0, 10, 50, 100, 250, and 500 μg L−1) on the physiology and biochemistry (photosynthesis, pigment, and lipid composition, antioxidative systems and energy balance) of Ulva lactuca, a cosmopolitan marine macroalgae species. Although GBHs cause deleterious effects such as the inhibition of photosynthetic activity, particularly at 250 μg L−1, due to the impairment of the electron transport in the chloroplasts, these changes are almost completely reverted at the highest concentration (500 μg L−1). This could be related to the induction of tolerance mechanisms at a certain threshold or tipping point. While no changes occurred in the energy balance, an increase in the pigment antheraxanthin is observed jointly with an increase in ascorbate peroxidase activity. These mechanisms might have contributed to protecting thylakoids against excess radiation and the increase in reactive oxygen species, associated with stress conditions, as no increase in lipid peroxidation products was observed. Furthermore, changes in the fatty acids profile, usually attributed to the induction of plant stress response mechanisms, demonstrated the high resilience of this macroalgae. Notably, the application of bio-optical tools in ecotoxicology, such as pulse amplitude modulated (PAM) fluorometry and laser-induced fluorescence (LIF), allowed separation of the control samples and those treated by GBHs in different concentrations with a high degree of accuracy, with PAM more accurate in identifying the different treatments.

Ecotoxicological Effects of the Anionic Surfactant Sodium Dodecyl Sulfate (SDS) in Two Marine Primary Producers: Phaeodactylum tricornutum and Ulva lactuca

“…In addition, previous work showed that growth variations in P. tricornutum in response to a stressor are generally associated with impaired photosynthesis, and altered fatty acid content [27,28,47,48], often leading to reactive oxygen species (ROS) formation, which are the cellular response to stress signalling metabolites par excellence, responsible for opening and activating defence pathways. On the other hand, in U. lactuca, the negative effects of stress are not so visible, with the macroalgae showing tolerance to contamination and even the potential for remediation [40,93,94].…”

“…Photobiological assessments were performed through chlorophyll fluorescence analysis (PAM fluorometry) with a FluoroPen FP100 (Photo System Instruments, Drásov, Czech Republic), on a 1 mL cuvette (for P. tricornutum) or with leaf clips (for U. lactuca), in darkadapted samples. The OJIP test was used to determine the chlorophyll transient light curves [40,47,48,54], from which the photochemical parameters (Table 1) were obtained according to this method and the equations provided in [55][56][57].…”

“…Pigment extraction was carried out in sample pellets from P. tricornutum, and freezedried (48 h) U. lactuca disks, according to previous works [40,47]. Pigment analysis was performed according to [61], allowing the detection of chlorophyll a (Chl a) and c (Chl c), pheophytin a (Pheo a), β-carotene (b-carot), fucoxanthin (Fx), diadinoxanthin (DD), and diatoxanthin (DT) in P. tricornutum, and chlorophyll a (Chl a) and b (Chl b), pheophytin a (Pheo a), lutein, β-carotene (b-carot), zeaxanthin (Zea), antheraxanthin (Anthera), violaxanthin (Viola), and auroxanthin (Auro) in U. lactuca.…”

“…Antioxidant enzyme extraction was performed as described in previous works [40,47]. Protein content was determined according to the Bradford method [62].…”

“…The macroalgae Ulva lactuca (Ulvaceae, Chlorophyta), commonly known as sea lettuce, is ubiquitous in coastal benthic communities around the world, in marine and estuarine environments [31,32], having a highly charged cell wall composed of the mucopolysaccharide ulvan, which allows the adsorption of pollutants [33]. Since this species responds directly to environmental pollution, it has been used in ecotoxicology bioassays (e.g., Ul-vaTox) for metals (e.g., silver, arsenic, cadmium, cobalt, chromium, copper, iron, mercury, manganese, nickel, lead, and zinc); disinfectants (e.g., formalin); fossil fuels (e.g., diesel); medicines (e.g., thiazolidinediones); fungicides (e.g., tributyltin oxide); and herbicides (e.g., glyphosate) [34][35][36][37][38][39][40].…”