In vitro control of de novo flower differentiation from tobacco thin cell layers cultured on a liquid medium

Thin cell layers of tobacco (three to six layers of epidermal and subepidermal cells) were allowed to float on the surface of a liquid medium. Whereas the control on an identical medium solidified by agar gave 100% of explant-forming flowers, no flowers formed in the absence of agar (100% of the explants formed buds). In order to initiate flower formation, various modifications of the liquid medium were tried: different ratios of indolyl-3-butyric acid (IBA) to kinetin (Kin) from 1 to 100, a range of pH from 4.0 to 7.0, and glass beads of different diameters (in an attempt to change the physico-chemical characteristics of the culture substrate itself). On a liquid medium with glass beads, four types of morphogenesis (flowers, buds, a mixed programme of flowers and buds, and a non-morphogenetic programme – i.e. the explants remained unchanged) were separately induced by changing one of the three factors: pH, IBA and Kin in equimolar concentrations, and diameter of the glass beads. Changing only the IBA/Kin ratio failed to provoke flower differentiation. pH of the medium was found to change after autoclaving and the effect of glass beads on morphogenesis was partly related to modification of pH.