Effects of photosynthetic photon flux density and light period on growth and camptothecin accumulation of Ophiorrhiza pumila under controlled environments

Ophiorrhiza pumila is a medicinal plant distributed on the floors of humid inland forests in subtropical areas and accumulates camptothecin (CPT) in whole plant organs. To elucidate the proper light and air temperature conditions for plant growth and CPT yield, we conducted two experiments under controlled environments. In experiment 1, we measured the net photosynthetic rate (Pn) and transpiration rate (E) of the whole plant O. pumila using an open-type assimilation chamber under different photosynthetic photon flux densities (PPFDs) and air temperatures. The result showed that the combination of an air temperature of 28 °C and a PPFD of 100 μmol m s was a good condition for photosynthesis and transpiration. In experiment 2, O. pumila was cultivated for 35 days under three PPFDs and three light periods at an air temperature of 28 °C. At a PPFD of 100 μmol m s and a light period of 16 h, growth was accelerated by the generating the lateral shoots and branches, and total CPT content per plant was the highest among these treatments. The present study revealed that the proper PPFD and light period conditions could enhance growth and CPT accumulation of O. pumila.