rolC-transgenic carnation plants: Adventitious organogenesis and levels of endogenous auxin and cytokinins

Overexpression of the rolC gene of Agrobacterium rhizogenes in plants alters growth and development. We studied whether the cytokinin (CK)-like and auxin-like effect of rolC on enhanced shoot and root regeneration in explants of three lines of rolC-transgenic carnation plants (Dianthus caryophyllus L. cv. White Sim) was related to altered levels of the endogenous auxin indole-3-acetic acid (IAA) or isoprenoid-CKs. rolC led to improved shoot and root organogenesis in transgenic petal and leaf explants and differences were observed between the lines. Total CKs and the CK/auxin ratio were not correlated with the organogenesis of these lines. However, zeatin riboside levels were up to 3-fold higher in rolC leaves and N⁶-isopentenyladenine levels up to 7-fold higher in transgenic petals. Immunolocalization of the latter showed cytoplasmic but mainly nuclear labelling in rolC and non-transgenic petals. The enhanced adventitious shoot organogenesis could be correlated with higher specific CK levels, although they might be an indirect effect of rolC on hormone metabolism. Since levels of IAA remained unaffected in transgenic explants, we propose that an increase in the auxin sensitivity in rolC carnation tissues is responsible for improved rhizogenesis. However, more studies are needed for clarification of the precise function of the RolC protein in transgenic plants.