Benzyladenine-induced inhibition of flowering in Chenopodium rubrum in vitro is not related to the levels of isoprenoid cytokinins

The effect of 6-benzylaminopurine (BAP) on flowering and on endogenous leve ls of isoprenoid cytokinins was investigated in explanted terminal shoots o f Chenopodium rubrum cultivated in vitro. The mother plants were grown unde r continuous light and explants were cut off when the 6th leaf primordium o riginated at the shoot apex. The explants were exposed to one dark period o f 13 hours inductive for flowering or to continuous light on medium with or without BAP (0.05;0.2;0.4 mg.l(-1)). Under non-inductive conditions no flo wering was observed either in the control or after BAP treatment. After rec eiving one inductive dark period, the control explants flowered. However, B AP application either at the beginning of the inductive dark period and/or during the following light cultivation inhibited flowering and stimulated i nitiation and growth of leaf primordia. In the case of the most efficient B AP concentration (0.05 mg.l(-1)) flowering was inhibited by 80% and the num ber of leaf primordia was increased by 3. Explantation caused a significant increase in the total amount of endogenous cytokinins in the explants with in first 13 h, provided they were kept in light. When explants were kept in darkness, only a slight increase in cytokinin levels was observed. BAP tre atment had no influence on the levels of endogenous cytokinins either in li ght or in darkness. We may thus conclude, that BAP application inhibited fl owering of photoperiodically induced terminal shoot explants and stimulated leaf primordia formation with no significant effect on changes in levels o f endogenous isoprenoid cytokinins, This may suggest the direct ability of BAP to regulate morphogenesis.