The effects of chilling-light stress on photosystems I and II in three Paphiopedilum species.

BACKGROUND

Low temperatures pose a critical limitation to the physiology and survival of chilling-sensitive plants. One example is the genus Paphiopedilum (Orchidaceae), which is mainly native to tropical and subtropical areas from Asia to the Pacific islands. However, little is known about the physiological mechanism(s) underlying its sensitivity to chilling temperature. We examined how chilling-light stress influences the activities of photosystem I (PSI) and photosystem II (PSII) in three species: P. armeniacum, P. micranthum, and P. purpuratum. All originate from different distribution zones that cover a range of temperatures.

RESULTS

Photosystem II of three Paphiopedilum species was remarkable sensitivity to chilling stress. After 8 h chilling stress, the maximum quantum yield of PSII of three species of Paphiopedilum was significantly decreased, especially in P. purpuratum. The quantity of efficient PSI complex (P ) value did not significantly differ after 8 h chilling treatment compared to the original value in three species. The stronger PSII photoinhibition and significantly less capacity for cyclic electron flow (CEF) were observed in P. purpuratum.

CONCLUSIONS

In conclusion, the three species of Paphiopedilum showed significant PSII photoinhibition when exposed to 4 °C chilling treatment. However, their PSI activities were not susceptible to chilling-light stress during 8 h. The CEF was important for the photoprotection of PSI and PSII in P. armeniacum and P. micranthum under chilling conditions. Our findings suggested that the photosynthetic characteristics of Paphiopedilum were well adapted to their habitat.