Cytokinin-induced abnormal shoot organogenesis is associated with elevated Knotted1-type homeobox gene expression in tobacco

Abstract

The molecular mechanisms that regulate the transcription of key developmental genes involved in shoot organogenesis have yet to be fully elucidated. However, it is clear that plant growth regulators, such as cytokinin, play a critical role in the differentiation of adventitious shoots. In Nicotiana tabacum zz100 leaf discs, high frequency shoot formation could be induced with 5 microM of the cytokinin N6-benzyladenine (BA). Increasing the exogenous BA concentration to greater than 20 microM resulted in stunted explants with abnormal shoot morphology and altered mineral composition. Explants with abnormal shoots did not appear to be hyperhydric. Abnormalities were, however, associated with an increase in the expression of a knotted1-type homeobox gene (TobH1) isolated from normal shoot-forming cultures. The results suggest that the development of cytokinin-induced abnormal shoot morphology possibly involves changes in TobH1 gene expression.

A simple plant regeneration-ability assay in a range of Lycopersicon species

“…In other words, this type of acute defect is a terminal one because the regenerant will not complete a life cycle. Impaired in vitro organogenesis has been attributed to detrimental influences of PGRs, and a pivotal role for cytokinins specifically in the differentiation of normal or abnormal shoot meristems has been suggested (Toponyanon et al, 1999;Howell et al, 2003;Ramage and Williams, 2004). We show here for the first time that stemdeficiency appears also in cultures not treated with PGRs (Table 1).…”

High frequency plant regeneration following abnormal shoot organogenesis in the medicinal tree Hovenia dulcis

“…Previously, it has been reported that elevated levels of exogenous cytokinin could lead to the initiation of abnormal shoots (Ramage and Williams 2004). In this study, the presence of various cytokinins lead to abnormal morphology of regenerated shoots.…”

“…Plant regeneration through organogenesis induced abnormal morphology in Nicotiana tabaccum and Camellia sinensis (Mondal et al 2004;Ramage and Williams 2004). In earlier reports, indirect organogenesis of H. dulcis resulted in abnormal morphology when shoots are grown on MS medium supplemented with GA 3 and kinetin (Park et al 2006).…”

Brassinolide influences the regeneration of adventitious shoots from cultured leaf discs of tobacco

“…Through its interaction with auxin, cytokinin is involved in adventitious root and shoot formation (Miller et al, 1955), leaf senescence, vascular development, and lateral bud formation (Mok and Mok, 1994). The determination times associated with the process of shoot or root differentiation and related phenomena have been investigated by pretreating tissues with auxin and cytokinin, then transferring them to hormone-free media (Ramage and Williams, 2004;Christianson and Warnick, 1983). This 'time', defined as when organ formation is observed in plant segments, can differ among individuals within the same species (Ramage and Williams, 2004).…”

“…The determination times associated with the process of shoot or root differentiation and related phenomena have been investigated by pretreating tissues with auxin and cytokinin, then transferring them to hormone-free media (Ramage and Williams, 2004;Christianson and Warnick, 1983). This 'time', defined as when organ formation is observed in plant segments, can differ among individuals within the same species (Ramage and Williams, 2004). In addition, no plant growth-regulating substance is needed after that determination occurs (Komamine et al, 1992).…”