Growth and Physiological Responses of Adenophora triphylla (Thunb.) A.DC. Plug Seedlings to Day and Night Temperature Regimes

Abstract

Adenophora triphylla (Thunb.) A.DC., three-leaf lady bell, is an important medicinal plant used against cancers and obesity. It has been well-established that the temperature regime affects plant growth and development in many ways. However, there is no study available correlating the growth of A. triphylla seedlings with different day and night temperature regimes. In order to find an optimal temperature regime, growth and physiology were investigated in A. triphylla plug seedlings grown in environment-controlled chambers at different day and night temperatures: 20/20 °C (day/night) (TA), 25/15 °C (TB), and 20/15 °C (TC). The seedlings in plug trays were grown under a light intensity of 150 μmol·m−2·s−1 PPFD (photosynthetic photon flux density) provided by white LEDs, a 70% relative humidity, and a 16 h (day)/8 h (night) photoperiod for six weeks. The results showed that the stem diameter, number of roots, and biomass were significantly larger for seedlings in TB than those in TA or TC. Moreover, the contents of total flavonoid, total phenol, and soluble sugar in seedlings grown in TB were markedly higher than those in seedlings in the other two treatments. Soluble protein content was the lowest in seedlings in TC, while starch content was the lowest in seedlings grown in TA. Furthermore, seedlings grown in TB showed significantly lower activities of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase. Native PAGE (polyacrylamide gel electrophoresis) analysis further proved low activities of antioxidant isozymes in TB treatment. Meanwhile, the lowest content of hydrogen peroxide was observed in seedlings grown in TB. In conclusion, the results suggested that the 25/15 °C (day/night) temperature regime is the most suitable for the growth and physiological development of A. triphylla seedlings.