Different Dynamics: Meta-Topolin Induces Faster and More Pronounced Upregulation of Selected Shoot Development-Related Genes in Arabidopsis thaliana Compared to Trans-Zeatin and Thidiazuron.

Cytokinins (CKs) are a class of phytohormones that regulate a wide range of developmental processes in plants. Different structural forms of these phytohormones have been widely used in plant tissue culture, although comparative studies on their temporal effects on gene expression remain limited. In this study, we compared the effects of trans-zeatin (tZ), meta-topolin (mT), and thidiazuron (TDZ) on the expression dynamics of ten CK-responsive genes associated with shoot growth and development in Arabidopsis thaliana. Ten-day-old Arabidopsis seedlings were exposed to liquid nutrient media containing 5 μM tZ, mT, or TDZ, or a control medium, for 15 min and 1, 2, 4, 8, and 24 h. Gene expression was analyzed by RT-qPCR using three independent biological replicates. All tested genes were strongly upregulated at 4 h following mT treatment, whereas most genes showed the highest expression at 8 h in response to TDZ. In contrast, tZ generally induced weaker and slower transcriptional responses. Expression levels of all analyzed genes returned to control-like or lower levels within 24 h. Overall, the three structurally distinct cytokinins induced markedly different temporal transcriptional responses, with mT producing the fastest and most pronounced effects on the expression of the tested genes under the applied experimental conditions. These findings improve our understanding of CK-dependent transcriptional dynamics during shoot development and provide a basis for future studies on CK-regulated morphogenesis and plant regeneration.