Effects of Microcystis aeruginosa on the life history traits and SOD activity of Daphnia similoides sinensis

β-cyclocitral, a novel AChE inhibitor, contributes to the defense of Microcystis aeruginosa against Daphnia grazing

β-cyclocitral is one of the major compounds in cyanobacterial volatile organic compound (VOCs) and can poison other aquatic organisms. To investigate the effect of β-cyclocitral on cyanobacterial-grazer interactions, Daphnia sinensis was fed Microcystis aeruginosa and exposed to β-cyclocitral. Our present study demonstrated that M. aeruginosa could significantly inhibit D. sinensis grazing. And the grazing inhibition by Microcystis aeruginosa results from the suppression of feeding rate, heart rate, thoracic limb activity and swimming speed of D. sinensis. In addition, M. aeruginosa could also induce intestinal peristalsis and emptying in D. sinensis. Interestingly, our present study found that the exposure to β-cyclocitral could mimic a range of phenotypes induced by M. aeruginosa in D. sinensis. These results suggested that M. aeruginosa could release β-cyclocitral to inhibit Daphnia grazing. To further examine the toxic mechanism of β-cyclocitral in Daphnia, several in vivo and in vitro experiments displayed that β-cyclocitral was a novel inhibitor of acetylcholinesterase (AChE). It could induce the accumulation of acetylcholine (ACh) by inhibiting AchE activity in D. sinensis. High level of endogenous Ach could inhibit feeding rate and induce intestinal peristalsis and emptying in D. sinensis.

Effects of toxic Microcystis aeruginosa on the expression of Hox genes in Daphnia similoides sinensis

Lake eutrophication and cyanobacterial blooms have become worldwide environmental issues. Under cyanobacterial blooms (especially Microcystis), Daphnia spp. can transfer beneficial information to their offspring in order to improve adaptability. Hox genes are important regulatory factors of transcription in metazoans, and are involved in the growth and development of organisms. However, the mechanisms of Microcystis on the expression of Hox genes in Daphnia are unclear. In this study, the effects of Microcystis aeruginosa on Hox gene expression in the mothers and offspring (F1) of two Daphnia similoides sinensis clones were investigated using a mixed diet of M. aeruginosa and Scenedesmus obliquus. Compared with the 100%S food treatment, the survival rates at the end of the experiment of clone 1‐F1 in the food treatments containing M. aeruginosa were significantly lower, but it was significantly higher for clone 2‐F1 in the 20%M + 80%S food treatment. Moreover, the survival rates at the end of the experiment of clone 1‐F1 in the food treatments containing M. aeruginosa were significantly higher than those of their mother. Based on previous transcriptome data, 14 Hox genes of D. similoides sinensis were identified, including Abd‐B, CDX‐1, Dll, HOX‐1, HOX‐2, HOXA1, HOXA2, HOXB3, HOXB3‐2, HOXB7, HOXC4, HOXC7, HOXC8, and HOXD10. The expressions of Abd‐B, HOX‐2, HOXA1, HOXC7, and HOXD10 of clone 2‐mothers in the 40%M + 60%S food treatment were 2.9–22.5 times as high as in the 100%S food treatment, whereas the expressions of CDX‐1, HOX‐1, HOXB3, and HOXD10 of clone 1‐mothers were 4.8–13.1 times at same food level. The expression of HOXA2, HOXC7, HOXC8, and HOXD10 of clone 1‐F1 in the 40%M + 60%S food treatment was 8.2–21.1 times as high as in the 100%S food treatment. However, compared with the 100%S food treatment, the expressions of CDX‐1 in the mothers and F1 of clone 2 and HOXB7 in the mothers of clone 1 in the food treatments containing M. aeruginosa were significantly lower (p < .05). Our results suggest that the offspring (F1) produced by D. similoides sinensis mother pre‐exposed to toxic M. aeruginosa had stronger adaptability to M. aeruginosa than their mothers. Moreover, Hox gene expressions of D. similoides sinensis had obvious differences between clones under stress of toxic M. aeruginosa.

Transgenerational plasticity in the eye size of Daphnia

It is well established that environmental signals can induce phenotypic responses that persist for multiple generations. The induction of such 'transgenerational plasticity' (TGP) depends upon the ability of organisms to accurately receive and process information from environmental signals. Thus, sensory systems are likely intertwined with TGP. Here we tested the link between an environmental stressor and transgenerational responses in a component of the sensory system (eye size) that is linked to enhanced vision and ecologically relevant behaviours. We reared 45 clones of Daphnia pulicaria in the presence and absence of a low-quality resource (cyanobacteria) and evaluated shifts in relative eye size in offspring. Our results revealed divergent shifts in relative eye size within- and across-generations. Parental Daphnia that were fed cyanobacteria produced a smaller eye than Daphnia fed high-quality algae. Such differences were then reversed in the offspring generation; Daphnia whose mothers were fed cyanobacteria produced larger eyes than Daphnia that were continually fed green algae. We discuss the extent to which this maternal effect on eye size is an adaptive response linked to improved foraging.

Transcriptional and metabolite analysis reveal a shift in fruit quality in response to calcium chloride treatment on "Kyoho" grapevine

'Kyoho' grapevine (Vitis vinifera) treated by calcium ions solution has been proved as an effective treatment to extend grape quality during storage to reduce disease, but its molecular mechanism was not clear yet. In the current work, grape berries were treated with different concentration of Calcium chloride (CaCl₂) solution, and their effects on antioxidant enzyme activity and transcriptome and metabolome in fruit were investigated. CaCl₂ treatments reduced weight loss and inhibited the decrement of flesh firmness. 80 mM CaCl₂ significantly increased the activity of antioxidant enzymes POD, SOD and CAT, which was the optimum experimental concentration. The study showed that the expression level of heat shock transcription factor and UBX which involved in endoplasmic reticulum stress and degradation pathway increased significantly. Moreover, the corresponding metabolites, such as heat shock protein and organic acid, also increased significantly. The misfolded proteins are transported to the cytosol for degradation, so that the preservation ability of grape is improved.

Cell free Microcystis aeruginosa spent medium affects Daphnia magna survival and stress response

Primary consumers in freshwater ecosystems, such as the zooplankton organism Daphnia magna, are highly affected by cyanobacteria, both as they may use it as a food source but also by cyanobacterial metabolites present in the water. Here, we investigate the impacts of cyanobacterial metabolites focussing on the environmental realistic scenario of the naturally released mixture without crushing cyanobacterial cells or their uptake as food. Therefore, D. magna were exposed to two concentrations of cell free cyanobacterial spent medium from Microcystis aeruginosa PCC 7806 to represent higher and lower ecologically-relevant concentrations of cyanobacterial metabolites. Including microcystin-LR, 11 metabolites have been detected of which 5 were quantified. Hypothesising concentration and time dependent negative impact, survival, gene expression marking digestion and metabolism, oxidative stress response, cell cycle and molting as well as activities of detoxification and antioxidant enzymes were followed for 7 days. D. magna suffered from oxidative stress as both catalase and glutathione S-transferase enzyme activities significantly decreased, suggesting enzyme exhaustibility after 3 and 7 days. Moreover, gene-expressions of the 4 stress markers (glutathione S-transferase, glutathione peroxidase, catalase and thioredoxin) were merely downregulated after 7 days of exposure. Energy allocation (expression of glyceraldehyde-3-phosphate dehydrogenase) was increased after 3 days but decreased as well after 7 days exposure. Cell cycle was impacted time dependently but differently by the two concentrations, along with an increasing downregulation of myosin heavy chain responsible for cell arrangement and muscular movements. Deregulation of nuclear hormone receptor genes indicate that D. magna hormonal steering including molting seemed impaired despite no detection of microviridin J in the extracts. As a consequence of all those responses and presumably of more than investigated molecular and physiological changes, D. magna survival was impaired over time, in a concentration dependent manner. Our results confirm that besides microcystin-LR, other secondary metabolites contribute to negative impact on D. magna survival and stress response.

Robust natural ultraviolet filters from marine ecosystems for the formulation of environmental friendlier bio-sunscreens

Ultraviolet radiation (UVR) has detrimental effects on human health. It induces oxidative stress, deregulates signaling mechanisms, and produces DNA mutations, factors that ultimately can lead to the development of skin cancer. Therefore, reducing exposure to UVR is of major importance. Among available measures to diminish exposure is the use of sunscreens. However, recent studies indicate that several of the currently used filters have adverse effects on marine ecosystems and human health. This situation leads to the search for new photoprotective compounds that, apart from offering protection, are environmentally friendly. The answer may lie in the same marine ecosystems since molecules such as mycosporine-like amino acids (MAAs) and scytonemin can serve as the defense system of some marine organisms against UVR. This review will discuss the harmful effects of UVR and the mechanisms that microalgae have developed to cope with it. Then it will focus on the biological distribution, characteristics, extraction, and purification methods of MAAs and scytonemin molecules to finally assess its potential as new filters for sunscreen formulation.