Only few studies in the plant tissue culture literature have examined the impact of lanthanoids, or rare earth elements, on in vitro plant organogenesis. In this study, using a model plant, hybrid Cymbidium Twilight Moon ‘Day Light’, the impact of six lanthanoids (lanthanum (III) nitrate hexahydrate (La(NO3)3 · 6H2O), cerium (III) nitrate hexahydrate (Ce(NO3)3 · 6H2O), neodymium (III) nitrate hexahydrate (Nd(NO3)3 · 6H2O), praseodymium (III) nitrate hexahydrate (Pr(NO3)3 · 6H2O), samarium (III) nitrate hexahydrate (Sm(NO3)3 · 6H2O), gadolinium (III) nitrate hexahydrate (Gd(NO3)3 · 6H2O) on new protocorm-like body (neo-PLB) formation on Teixeira Cymbidium (TC) medium was examined. 0 (control), 1, 2, 4 and 8 mg·dm-3 of each lanthanoid was tested. All lanthanoids could produce more neo-PLBs and neo-PLB fresh weight than TC medium lacking plant growth regulators (PGRs), suggesting some PGR-like ability of lanthanoids, although PLB-related traits (percentage of half-PLBs forming neo-PLBs; number of neo-PLBs formed per half-PLB; fresh weight of half-PLB + neo-PLBs) was always significantly lower than TC medium containing PGRs. Except for Gd, all other lanthanoids had no negative impact on the number of new leaves from neo-PLB-derived shoots, but all lanthanoids showed a significantly lower plant height, shoot fresh weight and shoot dry weight and, in most cases, SPAD (chlorophyll content) value. In addition, using the same concentration of the six lanthanoids, the ability to fortify root formation of neo-PLB-derived plantlets was also assessed. Except for Sm, all other lanthanoids significantly increased the number of roots, root fresh and dry weight.
