The Effects of Chilling Stress on Antioxidant Enzymes Activities and Proline, Malondialdehyde, Soluble Sugar Contents in Three Paphiopedilum Species

The genus Paphiopedilum with high ornamental and financial values is sensitive to the chilling temperature, but the underlying physiological and biochemistry mechanism(s) are not clear. The maximum quantum yield of photosystem II (PSII) (F-v/F-m), activities of antioxidant enzymes (SOD, POD, and CAT), malondialdehyde (MDA) content, proline and soluble sugar content were studied in P. purpuratum (Lindl.) Stein, P. dianthum Tang & F.T. Wang and P. armeniacum S.C. Chen & F.Y. Liu during chilling treatment. These three Paphiopedilum species displayed significant decreases in F-v/F-m during chilling treatment, especially in P. purpuratum. MDA content was decreased in P. armeniacum and P. dianthum, but significantly increased in P. purpuratum. Proline content was significantly higher in P. armeniacum than in P. dianthum and P. purpuratum, and significantly increased after chilling treatment. The soluble sugar content significantly decreased in P. purpuratum but significantly increased in the other species. SOD activity significantly increased while CAT activity significantly decreased in three species after treatment. POD activity significantly increased in P. purpuratum but significantly decreased in the other species. In addition, principal component analysis (PCA) was performed and three principal components were extracted with a cumulative contribution rate of 83%. PCA suggested that the effects of chilling stress on the physiological parameters were greatest in P. purpuratum and smallest in P. armeniacum. These results indicated that P. purpuratum was the least cold-tolerant and P. armeniacum was the most cold-tolerant among three species of Paphiopedilum. Our findings can provide valuable information for the conservation, cultivation, especially for the breeding of cold resistant varieties of Paphiopedilum.