DNA methylation and histone acetylation: genotypic variations in hybrid poplars, impact of water deficit and relationships with productivity

? Several reports on annual plants have already shown the involvement of epigenetic modifiers such as DNA methylation in their adaptation to abiotic stresses.

? Nevertheless, the genotypic variations of epigenetic modifiers, their possible correlations with morphological traits and the impact of water deficit have not been described for perennial plants.

? Six genotypes of Populus deltoides × P. nigra were subjected or not to a moderate water deficit treatment. Various morphological traits such as the height of the plants, their biomass and the total leaf area were measured to characterize the productivity in both conditions. Levels of DNA methylation, histone acetylation and the activities and isoform accumulation of the corresponding enzymes were measured at the shoot apex, the site of morphogenesis. Genotypic variation was observed for the morphological traits and the epigenetic variables and correlations were established among them. Genotypic variation for DNA methylation was detected in hybrid poplars. A positive correlation was demonstrated between DNA methylation percentage and productivity under well watered conditions.

? While there was a general decrease of growth for all genotypes in response to a moderate water deficit, genotypic dependant variations of DNA methylation were found suggesting different strategies among hybrids.

     

Dynamics of acetylcholinesterase activity recovery in two earthworm species following exposure to ethyl-parathion

In order for cholinesterase (ChE) activity to be used as an effective biomarker in earthworms, the time course of enzyme activity inhibition and recovery must be fully characterized. A laboratory experiment was carried out using parathion as a model organophosphorus pesticide at the recommended dose (1 mg kg⁻¹) and a 10 fold higher dose (10 mg kg⁻¹), on two earthworm species (Allolobophora chlorotica and Aporrectodea caliginosa). ChE activity and weight were measured every week for a 14 day period of exposure to parathion and then for 8 weeks in uncontaminated soil. After 3 days of exposure, the weight of both earthworm species had decreased by 10–15% compared to the control, regardless of the dose used. During the remainder of the exposure period, no differences were observed between the two doses for A. chlorotica; but A. caliginosa showed rapid weight recuperation for the lowest dose applied. After 28 days and over, the control and both exposed species of worms lost similar amounts of weight. ChE inhibition was measured during and after the exposure period. ChE inhibition followed a different time course for the two species investigated. A. chlorotica appeared less sensitive to parathion than A. caliginosa. In this latter species, ChE inhibition was rapid at close to 70% of the control after 3 days, for either dose, and reached 80–90% after 7 days exposure. While A. chlorotica exhibited the same pattern of inhibition for 10 mg kg⁻¹ of parathion, the inhibition process was slower for the recommended dose with 50% inhibition after 7 days of exposure and 70% after 14 days. ChE activity recovery, after transfer to uncontaminated soil, also followed a different pattern for the two species. After exposure to 1 mg kg⁻¹ parathion, ChE activity from A. chlorotica underwent a slow but constant recovery process to regain the control value after 8 weeks in unpolluted conditions. On the other hand, the ChE activity from A. caliginosa remained strongly inhibited. The differential susceptibility to parathion found in this study could be related to differences in the specificity of the total ChE activities between those two species.     

A first insight into genotype × diet interactions in European sea bass (Dicentrarchus labrax L. 1756) in the context of plant‐based diet use

This preliminary study assessed genotype × diet interaction in late growth of European sea bass (Dicentrarchus labrax) fed with either a fish meal (FM)‐ or a fish oil (FO)‐based diet (M) or an all‐plant‐based (PB) diet. A total of 550 fish from 224 families were reared together and tagged. DNA was sampled and microsatellites were used to assign parentage. When fish weight was 192 ± 54 g, two tanks were fed with M (FM: 100%; FO: 100%) and two others with PB (FM: 0% and FO: 0%). Body weight (BW), fork length (FL) and fillet lipid content (CorrFat) were analysed with a linear model and with REML methodology. We observed no significant differences between groups, but a slightly lower (P=0.03) daily growth coefficient in sea bass fed PB than in those fed M. Heritability estimates of BW differed significantly from zero (PB: 0.37 ± 0.18; M: 0.47 ± 0.24). Sire × diet interactions were significant and genetic correlations ranged between 0.51 and 0.87, showing genotype × diet interaction for BW and CorrFat. For the first time, genetic parameters in the context of total replacement of marine fishery by‐products were estimated in European sea bass, showing re‐ranking of family performances with extremely contrasted diets.