Comparative study on photosynthetic and antioxidant activities of Haematococcus pluvialis vegetative and resting cells: UVA light-induced stimulation.

AIM: This study aims to determine how photosynthetic and antioxidant activities vary in vegetative and dormant cells of Haematococcus pluvialis subjected to stresses in conditions representative of industrial productions of microalgae under solar light. METHODS AND RESULTS: The effects of short-term oxidative treatments were examined on photosynthetic and antioxidant activities of Haematococcus pluvialis vegetative and resting cells. The vegetative cells have 1.6 times higher levels of phenolic compounds, but 1.7 times less catalase, ascorbate peroxidase and superoxide dismutase activities than the astaxanthin-enriched resting cells. Mainly, a UVA dose of 4 J cm-2 induced increases in photosystem II electron transport rates (ETRmax) (+15%), phenolic compounds (+15%), astaxanthin (+48%), catalase (+45%) and superoxide dismutase (+30%) activities in vegetative cells. CONCLUSION: The UVA dose strongly stimulates the photosynthetic and antioxidant activities of vegetative cells, but only the accumulation of astaxanthin in resting cells. SIGNIFICANCE AND IMPACT OF THE STUDY: These preliminary results show that oxidative stresses at sub-lethal levels can stimulate the activities of microalgae. Further investigations are needed to estimate the real influence on metabolite productivities in industrial production conditions.

Reproductive performance in successive generations of the brine shrimp Artemia salina (Crustacea: Anostraca) from the Sebkha of Sidi El Hani (Tunisia).

Artemia salina cysts collected from the Sebkha of Sidi El Hani hatched and cultivated in the laboratory were investigated. Nauplii were acclimated to laboratory conditions until reproductively mature (Generation 1; G1). Reproductive performance in terms of total cysts and nauplii offspring, days between brood production, and cyst and nauplii numbers was evaluated. Nauplii produced by specimens in the G1 were defined as those of G2 with there also being third (G3) and fourth (G4) generations. The aims were to evaluate Artemia salina in aquaculture conditions with the long-term aim of developing a system for "artemiculture". There was a larger number of cysts or nauplii per brood between G1 (60.7 ±â€¯10.9 nauplii or cysts/female) and subsequent generations, notably G2 (122 nauplii or cysts/female, P <  0.05). The mean number of cysts and nauplii per female increased from the first and last brood. Number of cysts produced per female increased markedly (P <  0.05) from G1 (54.5 ± 14.2) to G3 (128.9 ± 39.2). Percentage of females producing nauplii increased from G1 (20 %) to G4 (100 %). There was, therefore, an increase in percentage of ovoviviparous offspring (nauplii) per female (P <  0.05) from G1 (7%) to G4 (71 %). There were no differences, however, between mean numbers of broods per female, and numbers of days between broods. The results indicate there are variations in reproduction from oviparity to ovoviviparity as consecutive generations of Artemia salina are cultivated. In summary, there was a rapid adaptation of Artemia salina of Sidi El Hani to laboratory conditions.

Osmoregulatory performance and immunolocalization of Na+/K+-ATPase in the branchiopod Artemia salina from the Sebkha of Sidi El Hani (Tunisia).

Artemia salina is an extremophile species that tolerates a wide range of salinity, especially hypertonic media considered lethal for the majority of other aquatic species. In this study, A. salina cysts were hatched in the laboratory and nauplii were acclimated at three different salinities (60, 139 and 212 ppt). Once in the adult phase, their hemolymph osmolality was measured. The animals were strong hypo-osmoregulators in the entire range of tested salinities, with up to 10 fold lower hemolymph osmolalities than their surrounding environment. Immunostaining of Na+/K+-ATPase was done on sections and on whole body mounts of adults in order to localize the ionocytes in different organs. An intense Na+/K+-ATPase immunostaining throughout the cells was observed in the epithelium of the ten pairs of metepipodites. A positive immunoreactivity for Na+/K+-ATPase was also detected in the maxillary glands, in the epithelium of the efferent tubule and of the excretory canal, as well as in the anterior digestive tract. This study confirms the strong hypo-osmotic capacity of this species and affords an overview of the different organs involved in osmoregulation in A. salina adults.

Thyroid hormone-induced demineralisation of the vertebral skeleton of the eel, Anguilla anguilla.

The role of thyroid hormones (TH) in bone remodelling is controversial. Indeed, in humans, while they are necessary for normal growth and development, their overproduction can induce important mineral bone loss and osteoporosis. Intense bone resorption is a natural phenomenon also observed in some teleosts, during reproductive migration and fasting. Our work aimed at investigating the effects of chronic treatments with TH (thyroxin, T4 or triiodothyronine, T3) on bone resorption in a migratory fish, the European eel (Anguilla anguilla), a representative species of an ancient group of teleosts (Elopomorphs). The incineration method showed that TH induced a significant mineral loss in eel vertebral skeleton. Histology and histophysical (qualitative and quantitative microradiographs) methods were then applied to vertebral sections to determine which types of resorption were induced by TH. Quantitative image analysis of microradiographs showed that TH significantly increased the porosity of the vertebrae, demonstrating the induction of a severe bone loss. Histology revealed the appearance of large osteoclastic lacunae, indicating a stimulation of osteoclastic resorption. Quantitative image analysis of ultrathin microradiographs showed a significant increase of the size of osteocytic lacunae, indicating a stimulation of periosteocytic osteolysis. Finally, quantitative microradiographs indicated a significant fall of mineralisation degree. TH treatments did not stimulate the production of the calcium-bonded lipo-phospho-protein vitellogenin, indicating that TH-induced bone demineralisation was not mediated by any indirect effect on vitellogenesis. Our study demonstrates that TH may participate in the mobilisation of bone mineral stores in the eel, by inducing different types of vertebral bone resorption, such as osteoclastic resorption and periosteocytic osteolysis. These data suggest that the stimulatory action of TH on bone resorption may be an ancient regulatory mechanism in vertebrates.