Dianthus caryophyllus (carnation) is a globally important ornamental plant. Tissue culture techniques have been used for the commercial production of carnation; however, the micropropagation of carnation has been impeded due to the occurrence of hyperhydricity during the shoot multiplication process or micropropagation stage 2. In the present study, the effects of different concentrations of rare earth elements on the reduction of hyperhydricity in micropropagated carnation were investigated. Nodal explants of D. caryophyllus ‘13827’ were cultured on Murashige and Skoog medium containing 1.0 mg·L-1 6-benzyladenine and 0.5 mg·L-1 indole-3-acetic acid with 3.0% (w/v) sucrose and 0.8% (w/v) agar (control medium). The medium was supplemented with lanthanum nitrate, La(NO3)3, cerium nitrate, Ce(NO3)3, or neodymium chloride, NdCl3 at a concentration of 0.05, 0.1, or 0.15 mM. Hyperhydricity was observed in 68.9% of the cultures produced on the control medium. The lowest percentage (42.2%) of hyperhydricity was observed in plants propagated on the medium supplemented with 0.05 mM Ce(NO3)3. Furthermore, the soluble protein concentration was higher in both the non-hyperhydric and hyperhydric plants produced on the medium supplemented with 0.05 mM Ce(NO3)3, whereas the activity of catalase, guaiacol peroxidase, and ascorbate peroxidase was lower in comparison with the media lacking Ce3+. The results of this study suggest that supplementation of the culture medium with 0.05 mM Ce(NO3)3 alleviates oxidative stress and reduces hyperhydricity in carnation during the adventitious shoot multiplication stage.

Abstract
 Introduction
 Materials and Methods
  Medium preparation and culture conditions
  Malondialdehyde (MDA) concentrations
  Enzyme extraction and assay
  SOD activity
  CAT activity
  GPX activity
  APX activity
  Superoxide radical (O2-) staining
 Results
  Effect of REEs on the hyperhydricity ratio and induction rates of carnation
  Effect of REEs on soluble protein concentration
  Effect of REE on MDA concentrations
  Effect of REE on activities of antioxidative enzymes
 Discussion
  REE supplementation results in reduced hyperhydricity rate during the tissue culture
  Regulation of antioxidant enzymes by REEs in response to the oxidative stress
 References

• Bo Ling Liu(College of Life Sciences, Qufu Normal University, Institute of Agriculture and Life Science, Gyeongsang National University)
• Hao Wei(Department of Horticulture, Division of Applied Life Science (BK21 Plus Program), Graduate School of Gyeongsang National University)
• Ji Eun Park(Department of Horticulture, Division of Applied Life Science (BK21 Plus Program), Graduate School of Gyeongsang National University)
• Byoung Ryong Jeong(Department of Horticulture, Division of Applied Life Science (BK21 Plus Program), Graduate School of Gyeongsang National University, Institute of Agriculture and Life Science, Gyeongsang National University, Research Institute of Life Science, Gyeongsang National University) Corresponding author