## 4 Discussion
The reduction in chlorophyll content can be explained by the accumulation of intracellular Na+ that blocks the uptake of K+ from the medium. Therefore, the plants suffer from deficiency of K+, leading to leaf chlorosis [43]. Phenolic compounds, including flavonoids, are the most widely distributed secondary metabolites present in the plant kingdom. These compounds play numerous biochemical and molecular roles in plants, such as signaling molecules, plant defense, mediating auxin transport, antioxidant activity, and free radical scavenging [44]. Phenolic compounds are highly produced by the Lamiaceae family [45], particularly in basil. Our results showed that in SSM, the TPC and TFC decreased when the salt concentration was 6 g/L or more, but DPPH increased. In contrast, in SETIS, salt concentration did not affect the TPC, but decreased the TFC and DPPH. The latter showed a remarkable increase at 3 g/L NaCl. This trend was also reported in pot experiments. Salt stress decreased the TPC and TFC for _Schizonepeta tenifolia_, except at the lowest concentration (1.5 g/L NaCl) where the TPC and TFC increased [46]. Salt stress not only affected the TPC, but also the profile to phenolic compounds in basil leaves [47]. In both the SSM and the SETIS bioreactor, VOCs of _S. indica_ significantly improved plant growth under salt stress, expressed as an increase in shoot length and number and biomass. There was also an overall positive effect on root length, even without salt stress. The growth-promoting effects of VOCs produced by _S. indica were_ only recently discovered. The shoot biomass of in vitro seedlings of _Arabidopsis_ increased up to nine-fold in the presence of VOCs from _S. indica_ compared to control [22]. The most abundant volatile compound produced by _S. indica_ was methyl benzoate, but its single application did not affect plant growth [22]. The beneficial effect of this fungus on seed germination, growth, and biomass was further reported only under field conditions in numerous horticultural and medical plant species [48; 49; 50; 51; 52; 53; 54; 55]. A positive effect of _S. indica_ was also reported on the growth of _Ocinum sanctum_[56]. Root colonization by _S. indica_ has also been found to improve crop tolerance to a number of abiotic stressors, including low temperatures, heavy metals, and salt [57; 58; 59; 60]. Regarding the positive effect of VOCs, reference should also be made to _Trichoderma_ and other fungi. In arabidopsis, beneficial effects of _Trichoderma_ VOCs on growth were reported [61; 62]. Physically separated _Trichoderma_ spp. and _A. thaliana_ enhanced both shoot and root biomass, root production, and chlorophyll content [63]. Stimulation of salt stress tolerance by _Trichoderma_ VOCs was likewise reported [64]. VOCs emitted by _T. viride_ showed a growth promotion of tomato plants [61]. _Streptomyces_ VOCs were found to promote growth of tomato seedlings irrigated with 12 g/L NaCl, with an increase in fresh weight, shoot length, and number of fibrous roots [65]. The volatiles emitted by _Cladosporium cladosporoides_ promote tobacco growth [66]. In addition, VOCs from rhizosphere bacteria were reported to promote plant growth [11; 67]. In both examined systems, salt stress led to chlorosis. But the _S. indica_ VOCs counteracted this effect, which was reflected in a significant increase in chlorophyll content. In a pot experiment, _S. indica_ was found to significantly increase the chlorophyll content of rice plants under salt conditions compared to non-inoculated plants [16], which helped the plants to survive the stress conditions. Several _Trichoderma_ strains also significantly in creased the chlorophyll content of _A. thaliana_, in control plants or plants with salt stress [64]. Similarly, volatiles emitted by _Fusarium oxysporum_ and _Verticillium dahliae were reported to affect the response of _A. thaliana_ to salt stress by promoting growth and increasing chlorophyll content [68].