Effect of change in light quality on physiological transformation of in vitro Phalaenopsis 'Fortune Saltzman' seedlings during the growth period

Changes in light quality strongly affect several plant anatomical, physiological, morphological, and biochemical parameters of orchid tissue culture seedling growth. In this experiment, ways in which light quality influence plant photosynthesis, growth parameters, and carbon dioxide rhythms of different sizes (stage I, II, and III) of Phalaenopsis tissue culture seedlings were examined. Stage I (Seedlings of 1-2 cm in height with 1-2 leaves and 1-2 roots) tissue culture seedlings were grown under six different light qualities under a T5 fluorescent lamp: White, Red (610 nm), Red (658 nm), Blue (440 nm), Red (610 nm) + Blue (440 nm), and Red (658 nm) + Blue (440 nm). After 5 months, cultured seedlings exposed to the Blue (440 nm) treatment showed significantly higher responses in terms of leaf quantities and chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid content. On the other hand, seedlings subjected to the Red (658 nm) treatment grew more stems and presented with higher fresh weight and leaf lengths compared to the results of other treatments. The number of roots increased under the Red (658 nm), Blue (440 nm) + Red (610 nm), and Blue (440 nm) + Red (658 nm) treatments. Moreover, seedlings subjected to Red light (658 nm) showed significantly higher levels of Rubisco enzyme activity than those subjected to the other treatments. Phosphoenolpyruvate carboxylase activities recorded during the nighttime in seedlings subjected to Red light (658 nm) were also significantly greater. The results showed that during stage I, the concentration of carbon dioxide rhythm ranged from 1500-1800 ppm and reflected a C3 photosynthesis system. As the seedlings matured, the carbon dioxide rhythm decreased to 400-800 ppm at night and reached stage III (CAM plant). After 5 months of culturing, the carbon dioxide rhythm of the Red (658 nm) treatment seedlings changed from C3 to CAM, while seedlings subjected to the other treatments were still in the intermediate stage (stage II). From these results, we conclude that to enhance seedling growth through commercial production, Red (658 nm) should be applied.