Reduction of hyperhydricity in the culture of Lepidium meyenii shoots by the addition of rare earth elements

Adventitious shoots induced from maca calli on induction media without rare earth elements (REE) had higher water content and lower soluble protein concentration when compared with shoots sprouted from maca seeds. Due to lower activities of antioxidative enzymes, there were higher concentrations of H2O2 and malonyldialdehyde (MDA) in adventitious shoots than those in seed shoots. When La3+, Ce3+ and Nd3+ (0.04 mM to 0.1 mM) were added to induction media, induction rates of the adventitious shoots were only affected slightly, but hyperhydricity rates were significantly reduced. La3+, Ce3+ or Nd3+ enhanced the activities of antioxidative enzymes in adventitious shoots, e.g. peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). When the concentrations of La3+, Ce3+ and Nd3+ were 0.1 mM, the oxygen stress in adventitious shoots was decreased to levels similar to seed shoots, where most adventitious shoots grew normally.