Processing of defensive pigment in Aplysia californica: acquisition, modification and mobilization of the red algal pigment, r-phycoerythrin by the digestive gland

The red alga Tsunamia transpacifica (Stylonematophyceae) from plastic drift shows adaptation to its uncommon habitat in ultrastructure and soluble low molecular weight carbohydrate composition

The recently described red alga Tsunamia transpacifica (Stylonematophyceae) was previously isolated from plastic drift found at the pacific coast, but the natural habitat remains unknown. Here, we investigate ultrastructural details and the low molecular weight soluble carbohydrate composition to get further insight into the adaptation to this uncommon habitat. By means of high pressure freeze fixation, followed by freeze substitution, we could detect an up to 2-µm-thick cell wall surrounded by a distinct layer of extracellular polymeric substances (EPS), likely responsible for the adhering capacities of Tsunamia. The central position of the nucleus and multilobed parietal chloroplast, already observed by light microscopy, could be confirmed. The ultrastructure revealed large electron-dense bodies (EB) in the central cytoplasm, likely resembling degradation products of the chloroplast. Interestingly, these structures contained phosphorous and cobalt, and iron was found in smaller rounded electron-dense bodies by electron energy loss spectroscopy (EELS). Accumulation of these elements suggests a high biosorption activity of Tsunamia. Liquid chromatography-mass spectrometry (LC-MS) data showed the presence of two heterosides (floridoside and digeneaside) together with the polyol sorbitol, which are known as organic osmolytes and compatible solutes. Taken together, these are the first observations on ultrastructural details, element storage and accumulation of protective compounds are contributing to our understanding of the ultrastructural and osmotic solute basis for the ability of Tsunamia to thrive on plastic surfaces.

The potential role of spherocrystals in the detoxification of essential trace metals following exposure to Cu and Zn in the fighting conch Strombus (Lobatus) pugilis

Crypt cells-one of the three cell types composing Strombidae digestive tubules-are characterized by the presence of numerous metal-containing phosphate granules termed spherocrystals. We explored the bioaccumulation and detoxification of metals in Strombidae by exposing wild fighting conch Strombus pugilis for 9 days to waterborne CuSO₄ and ZnSO₄. The total amount of Cu and Zn was determined in the digestive gland and in the rest of the body by Inductively Coupled Plasma (ICP) analyses. The digestive gland spherocrystal metal content was investigated based on the semi-quantitative energy dispersive X-ray (EDX) elemental analysis. ICP analyses of unexposed individuals revealed that 87.0 ± 5.9% of the Zn is contained in the digestive gland, where its concentration is 36 times higher than in the rest of the body. Regarding Cu, 25.8 ± 16.4% of the metal was located in the digestive gland of the control individuals, increasing to 61.5 ± 16.4% in exposed individuals. Both Cu and Zn concentrations in the digestive gland increased after exposures, pointing to a potential role of this organ in the detoxification of these metals. EDX analysis of spherocrystals revealed the presence of Ca, Cl, Fe, K, Mg, P, and Zn in unexposed individuals. No difference was found in the relative proportion of Zn in spherocrystals of exposed versus control individuals. Contrastingly, copper was never detected in the spherocrystals from controls and Zn-exposed individuals, but the relative proportion of Cu in spherocrystals of Cu-exposed individuals varied from 0.3 to 5.7%. Our results show the direct role of spherocrystals in Cu detoxification.

Use of the sea hare (Aplysia fasciata) in marine pollution biomonitoring of harbors and bays

Our study evaluated heavy metal concentrations in soft tissues of sea hare, Aplysia fasciata, from the Lower Laguna Madre, Texas. Heavy metals in tissues followed Se>As>Pb>Cd. Concentrations ranged As (BDL-28.08), Cd (BDL-5.50), Pb (BDL-12.85) and Se (4.25-93.43ppm). Median As, Cd, Pb, and Se tissue levels exceeded exposure levels. Significant relationships occurred in metal-metal (AsCd, AsPb, CdPb, CdSe, and PbSe), metal-tissue (significant Se uptake by inhalant and exhalant siphons and As in the hepatopancreas), and metal-metal within tissue (AsPb in the hepatopancreas and CdPb in the digestive cecum) analyses (p<0.05). Bioaccumulation factors (BAF) suggested the inhalant siphon, hepatopancreas, and digestive cecum function as macroconcentrators of Cd, hepatopancreas and digestive cecum as macroconcentrators of Pb, and all tissues were deconcentrators for As and Se. As a bioaccumulator of heavy metals, Aplysia was evaluated as a bioindicator of marine pollution in harbors and bays.

Cytochemical investigation of the digestive gland of two strombidae species (Strombus gigas and Strombus pugilis) in relation to the nutrition

Strombus gigas and Strombus pugilis are threatened species and aquaculture represents a good alternative solution to the fishing. In this study, we highlighted the intracellular digestion process in the digestive gland of two Strombidae species, S. gigas and Strombuspugilis, by the cytochemical characterization of two lysosomal enzymes: acid phosphatase and arylsulfatase. In order to check the efficiency of artificial food digestion, we conducted the characterization on freshly collected, starved and artificially fed individuals of S. pugilis. TEM observations of digestive gland sections from freshly collected individuals of both species revealed the presence of acid phosphatase and arylsulfatase activity mostly located in the apical third of digestive cells. Both enzymes were also detected in artificially fed individuals. In response to the starvation, acid phosphatase is not produced anymore by digestive cells, while arylsulfatase is still present. To our knowledge, this is the first cytochemical validation of intracellular digestion of artificial food in Strombidae. This study highlights the intracellular digestion of artificial food developed for Strombidae aquaculture. Moreover, we have shown that the lysosomal activity could be used as a feed index.

Oesophageal chemoreceptors of blue crabs, Callinectes sapidus, sense chemical deterrents and can block ingestion of food

Decapod crustaceans such as blue crabs possess a variety of chemoreceptors that control different stages of the feeding process. All these chemoreceptors are putative targets for feeding deterrents that cause animals to avoid or reject otherwise palatable food. As a first step towards characterizing the chemoreceptors that mediate the effect of deterrents, we used a behavioral approach to investigate their precise location. Data presented here demonstrate that chemoreceptors located on the antennules, pereiopods and mouthparts do not mediate the food-rejection effects of a variety of deterrents, both natural and artificial to crabs. Crabs always searched for deterrent-laced food and took it to their oral region. The deterrent effect was manifested as either rejection or extensive manipulation, but in both cases crabs bit the food. The biting behavior is relevant because the introduction of food into the oral cavity ensured that the deterrents gained access to the oesophageal taste receptors, and so we conclude that they are the ones mediating rejection. Additional support comes from the fact that a variety of deterrent compounds evoked oesophageal dilatation, which is mediated by oesophageal receptors and has been linked to food rejection. Further, there is a positive correlation between a compound’s ability to elicit rejection and its ability to evoke oesophageal dilatation. The fact that deterrents do not act at a distance is in accordance with the limited solubility of most known feeding deterrents, and likely influences predator–prey interactions and their outcome: prey organisms will be attacked and bitten before deterrents become relevant.

Antiproliferative activity and induction of apoptosis in human colon cancer cells treated in vitro with constituents of a product derived from Pistacia lentiscus L. var. chia

In this report, we demonstrate that a 50% ethanol extract of the plant-derived product, Chios mastic gum (CMG), contains compounds which inhibit proliferation and induce death of HCT116 human colon cancer cells in vitro. CMG-treatment induces cell arrest at G(1), detachment of the cells from the substrate, activation of pro-caspases-8, -9 and -3, and causes several morphological changes typical of apoptosis in cell organelles. These events, furthermore, are time- and dose-dependent, but p53- and p21-independent. Apoptosis induction by CMG is not inhibited in HCT116 cell clones expressing high levels of the anti-apoptotic protein, Bcl-2, or dominant-negative FADD, thereby indicating that CMG induces cell death via a yet-to-be identified pathway, unrelated to the death receptor- and mitochondrion-dependent pathways. The findings presented here suggest that CMG (a) induces an anoikis form of cell death in HCT116 colon cancer cells that includes events associated with caspase-dependent pathways; and (b) might be developed into a chemotherapeutic agent for the treatment of human colon and other cancers.

Packaging of chemicals in the defensive secretory glands of the sea hare Aplysia californica

Sea hares protect themselves from predatory attacks with several modes of chemical defenses. One of these is inking, which is an active release of a protective fluid upon predatory attack. In many sea hares including Aplysia californica and A. dactylomela, this fluid is a mixture of two secretions from two separate glands, usually co-released: ink, a purple fluid from the ink gland; and opaline, a white viscous secretion from the opaline gland. These two secretions are mixed in the mantle cavity and directed toward the attacking predator. Some of the chemicals in these secretions and their mechanism of action have been identified. In our study, we used western blots, immunocytochemistry, amino acid analysis, and bioassays to examine the distribution of these components: (1) an L-amino acid oxidase called escapin for A. californica and dactylomelin-P for A. dactylomela, which has antimicrobial activity but we believe its main function is in defending sea hares against predators that evoke its release; and (2) escapin's major amino acid substrates--L-lysine and L-arginine. Escapin is exclusively produced in the ink gland and is not present in any other tissues or secretions. Furthermore, escapin is only sequestered in the amber vesicles of the ink glandand not in the red-purple vesicles, which contain algal-derived chromophores that give ink its distinctive purple color. The concentration of escapin and dactylomelin-P in ink, both in the gland and after its release, is as high as 2 mg ml(-1), or 30 micromol ml(-1), which is well above its antimicrobial threshold. Lysine and arginine (and other amino acids) are packaged into vesicles in the ink and opaline glands, but arginine is present in ink and opaline at <1 mmol l(-1) and lysine is present in ink at <1 mmol l(-1) but in opaline at 65 mmol l(-1). Our previous results showed that both lysine and arginine mediate escapin's bacteriostatic effects, but only lysine mediates its bactericidal effects. Given that escapin's antimicrobial effects require concentrations of lysine and/or arginine >1 mmol l(-1), our data lead us to conclude that lysine in opaline is the primary natural substrate for escapin in ink. Furthermore, packaging of the enzyme escapin and its substrate lysine into two separate glands and their co-release and mixing at the time of predatory attack allows for the generation of bioactive defensive compounds from innocuous precursors at the precise time they are needed. Whether lysine and/or arginine are substrates for escapin's antipredatory functions remains to be determined.

Integrative biology: sea hares saved by a delicious distraction

When threatened, sea hares secrete ink and opaline. This mixture has now been shown to act on peripheral chemosensory neurons of spiny lobsters, stimulating feeding-related behaviours as a deceptive method of avoiding predation.

Defensive inking in Aplysia spp: multiple episodes of ink secretion and the adaptive use of a limited chemical resource

The seahare Aplysia spp. extracts many of its defensive chemicals from its red seaweed diet, including its purple ink, which is an effective deterrent against predators such as anemones and crabs. It is believed that the inking behavior is a high-threshold, all-or-none fixed act that nearly completely depletes the seahare of its ink supply. If a seahare depletes its gland of ink, it must seek out a source of red seaweed and then feed for at least 2 days to replenish its ink supply. This suggests that the animal would not be able to deploy ink more than once in rapid succession in response to successive attacks from one or more predators. However, we found that Aplysia spp. can secrete ink in response to three or more successive stimulations with (i) anemone tentacles, (ii) a mechanical stimulus, consisting of grabbing and lifting the animal from the substratum, or (iii) a noxious electric shock. A spectro-photometric measure of ink secretion showed that only approximately 48 % of the gland's releasable ink reserves are deployed initially. Thus, deployment of this defensive chemical is not strictly all-or-nothing, although the trigger mechanism is. Moreover, the animal tends to secrete a relatively fixed proportion (30–50 %) of its available ink reserves even after its gland has been depleted to approximately half its initial content. Since an animal need only use a proportion of its ink reserves to deter an attacker effectively, the inking behavior is adaptive in its economical use of a limited resource.