Intracellular conversion of cytokinin bases into corresponding mononucleotides is related to cell death induction in tobacco BY-2 cells

The in vitro cell death induction by cytokinin bases, benzyladenine (BA) and isopentenyladenine (iP) was investigated in tobacco BY-2 cells. Both BA and iP induced cell death in micromolar concentrations. Results indicated that the above-mentioned effects of cytokinin bases were related to their intracellular conversion to corresponding mononucleotides via phosphoribosyl transferase pathway. The treatment with BA and iP led to a rapid depletion of intracellular adenosine 5′-triphosphate (ATP), extensive production of reactive oxygen species (ROS) and these events preceded cell death. Adenine, that prevented conversion of bases into corresponding mononucleotides restored ATP synthesis, inhibited ROS production, and abrogated cell death. Selective inhibition of ROS production without affecting formation of mononucleotides did not increase cell survival. This is the first evidence of direct relationship between intracellular conversion of bases into corresponding mononucleotides and cell death induction in BY-2 cells.