Genotypic variation and water deficit effect on traits related to histone acetylation in six Populus deltoides × P. nigra hybrids growing in glasshouse in well-watered (white bar) or in water deficit (black bar) conditions. Studied traits encompassed: (A) histone H₃ acetylation ratio (AcH₃). (B) histone H₄ acetylation ratio (AcH₄). (C) HDAC activity. For each graph, G indicates the genotype effect, T the treatment effect and (GxT) genotype by treatment effect. Means are accompanied by their standard errors SE (n = 6). Significant differences between well-watered and water deficit conditions are indicated by asterisk: * P ≤ 0.05, ** P ≤ 0.01 and *** P ≤ 0.001. (D) immunodetection of the three classes of HDAC using anti-HD1A antibody, truncated anti-HD1A antibody (HD1A-Nterminal part of the protein), anti-HD1B1 antibody and anti-HD2 antibody. C (Control) represents plants in well-watered condition and S (Stressed) plants in water deficit condition. Sizes of the different isoforms are indicated in kiloDalton. Two arrows indicate specific bands mentioned in the result section.