Targeted exudates analysis
Figure 2 shows the compounds detected by the targeted metabolomics analysis. We were able to quantify aconitic acid, total phenols, flavonoids and flavonols, as well as glycine, threonine and alanine in all the samples (Figure 2). Formic and lactic acid were also detected, yet only in some random samples. Furthermore, we were able to detect, but not quantify serine, histidine, proline, tyrosine and phenylalanine.
Aconitic acid exudation rate was significantly affected by the treatments (Figure 2a). Plants exposed to T3 exuded 107% more aconitic acid than T2 plants, while T1 and T4 treatments exhibited intermediate values. Also, the root zones pointed out statistically significant difference of aconitic acid exudation: the apical zone exuded 151% more aconitic acid than the sub-apical one.
The total phenols (Figure 2b) were affected in the same way by the treatments and root zones: T3 vs T2 (+120%), and the other two treatments displayed intermediate exudation rates while the apical zone exuded more (+157%) than the sub-apical one (Figure 2b).
On the other hand, the release of total flavonoids was higher in T1 plants (Figure 2c), being nearly 4-fold higher when compared to T2. T3 showed intermediate values and in T4 no flavonoids were detected (<LOD). However, similar to the phenols and aconitic acid exudation, the apical zones exuded more total flavonoids than the sub-apical one (+295%).
Threonine exudation rate showed the same trend as the total flavonoids (Figure 2d). Indeed, T1 exuded significantly more threonine compared to T2 (+105%), while both T3 and T4 exhibited intermediate threonine exudation rates. Once again, the apical zone exudes more threonine than the sub-apical one (+246%, Figure 2d). Glycine and alanine exudation were significantly affected by root zone being the apical zone more responsive (+213% and +193%, respectively, respect the sub-apical zone) (Figure 2e and f).
Total flavonols exudation rate was not altered by any factor (Figure 2g).