The uptake and metabolism of 3H-benzylaminopurine in tobacco (Nicotiana tabacum L.) and cucumber (Cucumis sativus L.) explants

The uptake and metabolism of H-3-benzylaminopurine (H-3-BAP) were studied in explanted stem pith and leaves of tobacco and in the hypocotyls and cotyledons of cucumber. The explants were kept for 2, 5, 8 and 20 h on MS medium with 0.8 mg.l(-1) 2,4-D, 0.5 mg.l(-1) BAP and 13.2 mg.l(-1) aspartic acid (induction medium) with or without H-3-BAP and C-14-sucrose. The highest uptake of H-3-BAP was observed in tobacco leaves and cucumber cotyledons. The major metabolite in both species was H-3-benzylaminopurine riboside (H-3-BAPR). The highest level was found in explanted cucumber cotyledons after 20 h in culture, the lowest in explanted tobacco stem pith. Intensive 7-glucosylation of H-3-BAP was observed in explanted tobacco leaves after 20 h in culture, where the levels of 7-glucoside of H-3-BAP and of free H-3-BAP were equal. To study the morphogenic effect of growth regulators (BAP and 2,4-D), the explants were subcultured after short-term induction (20 h) to MS medium without any growth regulators. In most cases, incubation of 20 h on induction medium was sufficient to induce the respective morphogenesis. Cucumber hypocotyl and tobacco stem pith explants formed a callus on their basal end. Root formation was observed on explanted cucumber cotyledons and shoot formation on tobacco leaves. Long-term culture (3 weeks) of tobacco leaves on induction medium led to the formation of callus and globules. The microscopic analysis of globules indicated the presence of meristematic and tracheidal cells.