Changes in cytokinin levels and metabolism in tobacco (Nicotiana tabacum L.) explants during in vitro shoot organogenesis induced by trans-zeatin and dihydrozeatin

The uptake and metabolism of trans-zeatin and/or dihydrozeatin, in correlation with cytokinin oxidase/dehydrogenase (CKX) and β-glucosidase activity, were studied in leaf segments derived from wild-type (WT) and transgenic (T) tobacco (Nicotiana tabacum L. cv. Petit Havana SR1) during in vitro induction of shoot organogenesis. T explants harbored the maize gene Zm-p60.1β-glucosidase. Higher levels of shoot regeneration were observed on T explants in the early stages of cultivation. In WT explants, the content of cytokinin (CK)-O- and N-glucosides increased. In T explants, a higher content of Z-9-riboside and Z-9-riboside-5′-monophosphate and higher CKX activity during the early stage of cultures were found. A positive correlation was obtained for bioactive CK content and the organogenic response in T explants. Our results indicate a connection between the organogenic capacity of tobacco explants, metabolism of endogenous CKs and uptake of exogenous CKs from the cultivation medium.