Figure 4.

Metabolomics pattern of leaves when roots of the same plant are under control (normoxia) or waterlogging (hypoxia) (grey and blue shades, respectively). (a) Heat map showing significant metabolites (p < 0.01; two-way ANOVA) with a hierarchical clustering on left (Pearson correlation). The two main groups are framed and numbered (group 1 framed in blue: metabolites decreasing under hypoxia; group 2 framed in red: metabolites increasing under hypoxia). (b) Score plot of the multivariate analysis by O2PLS demonstrating the very good sample discrimination. (c) Volcano plot showing best discriminating metabolites (waterlogging vs. control) with the p-value (y-axis) and the loading in the O2PLS (x-axis). The horizontal dash-dotted line represents the Bonferroni threshold (0.0005). The two best discriminating features under waterlogging are an increase in tyrosine and a decrease in urea. (d) Relative metabolic ratio succinate-to-fumarate (left) and percentage (%) of photorespiratory intermediates (serine + glycine + glycolate + glycerate) in total metabolites (right). For both, the difference between waterlogging and control is significant (p < 0.01, Welch). (e) Metabolites that have a significant waterlogging × time interaction effect (arginine, glutamine, threonolactone). Conditions under which the difference between control and waterlogging is significant is labelled with an asterisk (*).