Cerium and lanthanum promote floral initiation and reproductive growth of Arabidopsis thaliana

The effects of cerium and lanthanum on the vegetative growth, floral initia tion and reproductive growth of Arabidopsis thaliana were studied. Addition of cerium nitrate (0.5-10 mu M) or lanthanum nitrate (0.5-50 mu M) to the culture medium significantly increased the lengths of primary roots, but ha d no significant effects on the number of rosette leaves produced per plant , plant heights and dry weights during the vegetative growth stage (17 days after seed germination). The percentage of plants bolted was significantly increased with the addition of 0.5-10.0 mu M cerium nitrate or lanthanum n itrate. The combination of 0.5 mu M cerium nitrate and 0.5 mu M lanthanum n itrate was found to be most effective on the induction of floral initiation . The height, dry weight and average number of flower numbers of 35-day-old plants growing in media containing cerium nitrate or/and lanthanum nitrate (0.5-10.0 mu M) were found to be significantly higher than those in the co ntrol medium. The endogenous levels of cytokinins (zeatin riboside, dihydro zeatin riboside and isopentenyl adenosine) and carbohydrates (sucrose, gluc ose and fructose) in leaf and root tissues of plants growing in the medium supplemented with 0.5 mu M cerium nitrate and 0.5 mu M lanthanum nitrate we re not significantly different from those of plants in the control medium. Application of 0.5 mu M cerium nitrate and 0.5 mu M lanthanum nitrate enhan ced the effects of 10(-6) M IPA on root growth, plant height and flowering. The role of cerium and lanthanum in promoting floral initiation and reprod uctive growth and the possibility of developing non-hormonal flowering prom oting agents are discussed. (C) 2000 Elsevier Science Ireland Ltd. All righ ts reserved.