Effect of in vitro Culture Period on the Photosynthesis of Phalaenopsis amabilis Plantlets

Phalaenopsis amabilis with facultative CAM photosynthetic mechanism is one of the most valuable ornamental plants in the world. This plant's most common method of propagation is through its in vitro culture. In tissue culture plants, photosynthesis is strongly affected by many factors. The role of photosynthesis of in vitro plantlets in their performance and acclimation is still unknown. In the present study, photosynthetic performance was investigated based on gas exchange and fluorometry in Phalaenopsis under in vitro conditions for two periods, including short-term (2 weeks) and long-term (8 weeks), and four times of recording during the day. The aim was to investigate the stomatal and photosynthetic behavior of Phalaenopsis plantlets under these conditions. According to the obtained results based on the gas exchanges and chlorophyll fluorometry, the rate of photosynthesis and the quantum yield of plantlets in vitro significantly affected the ability of plantlets to regenerate and create relative adaptation in plant cells under high humidity conditions. Photosynthetic and quantum performances in the long-term culture period were better than their performance in the short-term, while non-photochemical quenching (NPQ) and heat loss were decreased in the plantlets grown in the long-term culture period. The total chlorophyll and carotenoid content were also higher in the long-term than in the short-term. The performance of the stomata was disturbed due to high humidity for a long-term period. So, the effect of the stomata on photosynthesis in the plantlets was almost ineffective under in vitro conditions. Therefore, the finding showed flexibility, better photosynthetic and physiological performance for Phalaenopsis plantlets under in vitro conditions, and better adaptation to stress.