## 3 Discussion  
Plant growth parameters are frequently reduced in response to salt stress conditions [53]. However, some studies have reported that mVOCs can induce tolerance against abiotic stress [25; 54; 55; 56]. In the present study, we observed that the growth parameters were reduced in peppermint plants subjected to saline stress, but this negative effect was reversed for plants grown under 75 mM NaCl when exposed to SJ46 VOCs, and also for those grown under 100 mM NaCl when exposed to either SJ04 or SJ46 mVOCs. In these cases, the number of leaves and the shoot weight and length were increased, as well as the root development, with a corresponding gain in root dry weight. An enhanced root system increases the ability of plants to uptake water from the surroundings [57]. Moreover, increasing root development may have the ecological consequence of increasing colonization of roots by beneficial rhizobacteria [58]. Some related effects were previously observed in _M. piperita_ exposed to _Bacillus amyloidefaciens_ GB03 VOCs and grown under 75 and 100 mM, with six compounds being identified in the GB03 mVOCs, of which acetoin (3-hydroxybutanone) was the main compound present in the GB03 blend [54]. In agreement, [PERSON] et al. [59] showed that VOCs emitted by _Praburburbfoldeira phytofilirmus_ mitigated salt stress effects in _Arabidopsis thaliana_, increasing the primary root length, rosette area and total fresh weight under 150 mM NaCl salt stress. Related to this, it has been shown by transcriptional analysis that gene expression is modified in the presence of salinity in _A. thaliana_ in the case of the transporter of K\({}^{+}\) (HKT1), which is responsible for the adjustment of the Na\({}^{+}\) and K\({}^{+}\) levels. Moreover, the expression of the HKT1 gene is decreased, thereby reducing the Na\({}^{+}\) influx through the root. Transcriptional analysis has also shown that VOCs produced by GB03 [60; 61], such as 2,3-butanediol [25], decreased the expression of HKT1 in the root, but increased it in the aerial part, thus maintaining the balance in Na\({}^{+}\) levels throughout the plant [62]. In addition, GB03 VOCs positively affected _A. thaliana_ under salt stress by promoting the accumulation of the osmoprotectants of choline and glycine betaine [63]. A similar observation was made in soybean plants grown under salt stress, where VOCs emitted by _Pseudomonas simiae_ decreased Na\({}^{+}\) concentrations and increased phosphorus and potassium [64]. This study showed that proline and other vegetative storage proteins that confer salt tolerance increased in the roots of plants exposed to VOCs. Additionally, _P. simiae_ VOCs in combination with sodium nitroprusside enhanced salt tolerance [65], revealing an up-regulation \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \multirow{2}{*}{**RT** **(min)**} & \multirow{2}{*}{**Compound**} & \multicolumn{4}{c}{**Non-Exposed**} & \multicolumn{4}{c}{**DH05**} & \multicolumn{4}{c}{**SJ04**} & \multicolumn{4}{c}{**SI46**} \\ \cline{3-14}  & & **0 mM** & **75 mM** & **100 mM** & **0 mM** & **75 mM** & **100 mM** & **0 mM** & **75 mM** & **100 mM** & **0 mM** & **75 mM** & **100 mM** \\ \hline
1.56 & Nitrogen oxide & x & x & x & x & x & x & x & x & x & x & x & x \\ \hline
2.74 & Tridhoromethane & x & x & x & x & x & x & x & x & x & x & x \\ \hline \multirow{2}{*}{5.05} & Propane, & & & & & & & & & & & & & \\  & 2-chloro-2-nitro- & & x & x & x & x & x & x & x & x & x & x & x \\ \hline \multirow{3}{*}{10.44} & 1-(N-) & & & & & & & & & & & & & \\  & 2 morpholino & & & & & & & & & & & & & \\  & cyclohexene & & & & & & & & & & & & & \\ \hline
10.95 & Tridecane & & & & & & & & x & x & & & & \\ \hline
11.49 & n-Octanol & & & & & & & & x & x & x & x & x \\ \hline
11.62 & Decane & & & & & & & & x & x & x & x & x \\ \hline \multirow{2}{*}{13.15} & Butane, & & & & & & & & x & x & x & x & x \\  & 2-methyl- & & x & x & x & x & x & x & x & x & x \\ \hline
15.92 & Tetradecane & & & & & & & x & x & x & x & x \\ \hline \end{tabular}
\end{table}