Effects on Growth and Metabolism of Difference between Day and Night Temperatures (DIF) and Supplementation with Rare Earth Elements (REE) in Micropropagated Dendrobium aphyllum (Roxb.) C. E. Fischer

Abstract

Dendrobium aphyllum (Roxb.) C. E. Fischer is an ornamental plant with certain medicinal values from the Orchidaceae family. Currently, micropropagation is the main means through which it is propagated. In this research, the effects of different daytime and nighttime temperatures (DIF) and medium supplementation with rare earth elements (REE) on the growth and metabolism of D. aphyllum during a micropropagation period were investigated. Three kinds of REE nitrates, La(NO₃)₃, Ce(NO₃)₃ and Nd(NO₃)₃, at four concentrations, 50, 100, 150, and 200 μM, were added to the culture medium. Three DIFs, 0, 6 and 12 °C, with an identical mean daily temperature of 20 °C, were used with photoperiod/dark period temperatures of 20/20 °C, 23/17 °C and 26/14 °C, respectively. After four weeks of culture, both supplemental REE and DIF treatments promoted growth of the plant compared with the control group. With increased REE concentration and DIF, the growth of the plants was suppressed and symptoms of stress response occurred. At the same concentration, Ce(NO₃)₃ had a more significant promotional effect on plant growth. In general, the medium supplemented with 100 μM Ce(NO₃)₃ combined with a 6 °C DIF was the most optimal for the vegetative growth of the plant. A 12 °C DIF promoted synthesis of more primary metabolites such as total proteins and polysaccharides. From the perspective of improving the medicinal values of this plant, increasing the DIF for an optimal growth environment is a valuable reference. This study can provide a technical basis for the propagation and production of Dendrobium aphyllum in the future.