## 4 Discussion
### CK Treatments Caused Qualitative and Quantitative Changes in BC Profiles  
BC profiles showed qualitative and quantitative (Figure 3) variations depending on the type and concentration of CK used. For example, Figure 3 shows that _trans_-geraniol (geraniol, RT = 12.20) appears only in some BC profiles of acclimatized plants (Figure S3(Ab,Bc)). The pattern of EO terpen also varied quantitatively between MS-N and MS-S culture media (Figure 3). The content of these terpen was similar to or higher than the terpene contents reported by [PERSON] et al. [53] and [PERSON] et al. [54] extracted by hydrodistillation and by [PERSON] et al. [40] adsorbed by SPME. According to quantitative variations, different concentrations of BAP and tZ induced quantitative changes in the production of the main volatile compounds of in vitro shoots of _Thymus vulgaris_ L. [34]. In general, terpene content (%) differed between EO profiles of MS-N (3% sucrose) and MS-S (5% sucrose) (Figure 4). For instance, in MS-N, the highest content of \(\alpha\)-citral (64.96%) was induced by KIN, while in MS-S, the highest content of \(\alpha\)-citral (80%) was induced by BAP (Figure 4). In addition, the content of \(\beta\)-citral ranged from 27.52% (2 iP) to \(-\)42.99% (tZ) in MS-S, while the content of \(\alpha\)-citral ranged higher, from 25.62 (2 iP) to \(-\)64.96% (KIN). Likewise, the content of \(\beta\)-citral ranged lower (14.89-36.28%) in MS-S than in MS-N, but the content of \(\alpha\)-citral ranged higher (59.48-80.04%) in MS-S than in MS-N. Overall, the content of \(\beta\)-citral decreased by 31.1% from MS-N to MS-S, whereas \(\alpha\)-citral increased by 30.82%. Furthermore, when the effect of each CK was analyzed concerning \(\alpha\)-citral, it was found that the content of \(\alpha\)-citral was relatively increased in established plants derived from MS-S medium. The increments were 56.8% (2 iP), 24.5%(IZ), 38% (BAP), and 7.54% (KIN) in relation to MS-N. This increase was also consistent with the result that different concentrations of sucrose in culture media significantly affected the composition of the volatile profile in _C. pulegium_[43] (Figure 4). Besides the contents of \(\beta\)- and \(\alpha\)-citral, high limpence content (41%) was reached in plants derived from MS-N. Additionally, the content of \(\beta\)-caryophyllene (12.3%) was higher in established plants derived from MS-S with BAP (Table 2, Figure 4). Moreover, it has been reported that terpen accumulate in _Artemisia amnu_ concomitantly with a high expression of HMGR. The rate-limiting enzyme of MVA (mevalonic acid pathway/terpenoid biosynthesis pathways) increases under water stress as an adaptive response [20]. Variations in BC Profiles Related to Shoot Number and Shoot Branching Morphology Could Be Explained Because Plants Sense Distinct CK Types Differently  
Structurally distinct CKs are sensed differentially in Arabidopsis by different histidine kinase (AHK) receptors [55; 56]. Also, CK catabolism differs between isoprenoid and aromatic CKs [57; 58; 59; 60; 61; 62]. These differences may explain why in various reports, including this work, the use of a different type of CK has influenced the plant EO content and composition, such as in _Catharanthus roseus_[63], spearmint [17], _Mentha arvensis_[64], _Mentha piperita_[23],_Thymus vulgaris_[34], and _Artemisia alba_[65,66]. In addition, as we mentioned before, the highest content of \(\alpha\)-citral (80%) was detected in micropropagated plants grown on BAP (Figures 3 and 4). Therefore, we suggest that BAP could also be involved in regulating HMGR activity during citral biosynthesis. In support of this trial, the activity of HMGR was upregulated by the effect of the CK zeatin and other plant growth regulators [22]. Because BAP also produced the highest number of shoots per flask in MS-S (Table 1, Figure 2), it also might be involved in controlling axillary meristem growth and development.