## 4 Discussion
[66] showed that the genes _GolS1_, _GolS3_, and _stachyose synthase_ were significantly upregulated in the leaves of the _Phaseolus vulgaris_ cv. CIAP7247F under drought stress. Transcriptional analysis indicated that most _Citrus sinensis GolS_ (_CsGolS_) genes show a stress-inducible expression in response to drought and salt stress treatments, as well as to '_Candidatus_ Liberibacter asiaticus' infection [67]. The comprehensive analysis of _RS_ and _GolS_ gene families in kiwifruit (_Actinidia chinensis_ and _Actinidia eriantha_) revealed that abiotic stresses strongly induced _AcGolS1/2/4/8_ and _AcR52/4/8/11_ expression [68]. Similarly, the analysis conducted on potato (_Solanum tuberosum_ L.) showed that _StGolS4_ exhibited significantly high expression levels after PEG-6000, and abscisic acid (ABA) treatments, and under salt stress [69]. Furthermore, it was found that all four isoforms of _CsGolS_ in the cucumber genome were also upregulated by salt, drought, cold, and heat [70]. Transcriptome analysis carried out on rice reveals that Cd stress signalling controls the expression of genes in the drought stress signal pathway [63]. Exposure to Cd mediates gene expression by transcription factors such as DREB/CBS, WRKY, HSF, MYB, bHLH, bZIP, ERF, and NAC [63; 71]. Most of these transcription factors have been described as upstream regulators of genes that encode \(GolS\) and \(RS\)[72]. The presence of putative \(cis\)-regulatory elements recognised by some of these transcription factors has been noticed in promoter regions of \(PsGolS\) as well as \(PsRS\) genes [65]. Nonetheless, the knowledge of the Cd-induced signalling pathway that leads to an increase in galactinol and raffinose levels is still limited. Data show that ABA or reactive oxygen species (ROS) mediate the activity of GolS on an mRNA or protein basis [69; 73; 74; 75; 76]. The role of ABA in Cd response is not well-established [77]. ABA can induce or reduce the accumulation of Cd and mitigate its toxicity, which can vary among species [61; 77]. On the other hand, Cd induces oxidative stress in plants, including ROS production [78]. The role of galactinol and raffinose due to ROS-scavenging ability has been discussed [79; 80]. Recently, [PERSON] et al. [81] also showed that Arabidopsis \(CaGolS\) transgenic lines, with increasing levels of galactinol and raffinose, accumulate less ROS and are more resistant against various abiotic stresses. Moreover, it has been shown that raffinose could prevent cellular leakage during dehydration by membrane stabilisation and fusion after rehydration [82]. Additionally, the location of raffinose in chloroplast allows it to protect thylakoids and stabilise photosystem II [83; 84]. It is important to note that galactinol synthase (GolS) catalyses the first step in the biosynthetic pathway of the raffinose family of oligosaccharides (RFOs), producing galactinol from UDP-galactose and _myo_-inositol. Galactinol plays a crucial role as a major donor of galactosyl residues moieties in the synthesis of raffinose (from sucrose and galactinol) and later on stachvose (from raffinose) and vervascose (from stachvose). RFOs are believed to play a pivotal role in the tolerance to seed desiccation [85]. They are also the predominant transport carbohydrates in some plant families (i.e., Cucurbitaceae), act as signalling molecules after pathogen attack and wounding, and accumulate in vegetative tissues in response to a variety of abiotic stresses [85]. It has been shown that stress-inducible GolS plays a key role in the accumulation of galactinol and raffinose, which may function as osmoprotectants in drought, osmotic, a salt stress tolerance of plants [86; 87]. The root and epicotyl of the winter vetch seedlings accumulated elevated amounts of galactinol and raffinose as the osmotic potential was lowered [88]. The elevated levels of galactinol and raffinose could also be the result of the dehydration that often accompanies the Cd stress response in plants [22; 62; 89].