Extent of ipt gene expression and resulting amount of cytokinins affect activities of carboxylation enzymes in transgenic plants

Transgenic plants of Solanum tuberosum cvs. Kamyk and Oreb, and Nicotiana tabacum cvs. Maryland Mammoth and Trapezond were selected according to the intensity of introduced ipt gene expression and resulting amount of synthesised cytokinins (CKs). In comparison with controls, transgenic tobacco plants showed an increase of CK concentrations by 379%, potatoes by 159% (MAS). Potato grown in soil from tubers of transgenic plants demonstrated a moderate increase (44%) of CK conc. (MOD). Transgenic tobacco grown from seeds in vitro did not show any significant change in CK concentrations. In MOD plants, ribulose-1,5-bisphosphate carboxylase/oxygenase activities were stimulated by up to 34%, whereas the activity of phosphoenolpyruvate carboxylase decreased by 17%. Leaf area, fresh and dry masses, chlorophyll and soluble protein conc. also decreased with increasing CK amounts. Endogenous CK conc. became a stress factor for MAS plants.