Cell walls (CWs) represent a hallmark of plant cells. The plant CW determines cell shape and function, and plays an important role in responding to the environment. The CW is a complex mixture of polysaccharides, proteins and aromatic substances, which are secreted outside the cell. Three structural CW layers can be distinguished: the middle lamella, the primary cell wall (PCW) and the secondary cell wall (SCW). While almost all plant cells contain the primary CW, only specialized cell types form a SCW as innermost layer. Many proteins are involved in synthesis, arrangement and modification of SCWs. The expression of these proteins and therefore the process of SCW formation is controlled by a regulatory cascade consisting of several cross-regulated transcription factors (TFs). The whole cascade is under control of NAM, ATAF1/2, CUC2 (NAC) TFs, which represent the master switches for SCW formation. In Arabidopsis thaliana, two groups of NAC TFs, characterized by certain spatial constraints of their action can be distinguished: i) VASCULAR NAC-DOMAIN 1-7 (VND1-7) TFs mediate SCW formation in xylem vessels and ii) NAC SECONDARY WALL THICKENING PROMOTING FACTOR 1-3 (NST1-3) mediate SCW formation in xylary fibers, interfascicular fibers, anthers and siliques Our preliminary unpublished data indicate an involvement of cytokinin signaling in the regulation of NST expression and SCW formation. E.g. an impairment of cytokinin sensing in ahk2ahk3 mutants leads to upregulation of NST3 expression and premature SCW formation in fibers. Interestingly, differences in SCW thickness in this mutant are not only evident in fibers, but also in vessels where NST3 is not supposed be active. In this bachelor thesis, the quadruple mutant ahk2ahk3nst1nst3 will be generated to analyze the impact of NST expression on phenotypes observed in ahk2ahk3.