[Responses of Jatropha curcas L. seedlings to drought stress]

By adding different concentrations (5%-25%) of polyethylene glycol (PEG) into Hoagland solution to simulate a gradient of drought stress, the photosynthetic characteristics and drought resistance of Jatropha curcas L. seedlings were investigated. The results showed that when treated with lower concentrations (< or = 15%) of PEG, the photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular carbon dioxide concentration (Ci) of the seedlings decreased with increasing PEG concentration, while the chlorophyll fluorescence parameters optimal/maximal quantum yield of PS II (Fv/Fm) decreased slightly and minimal fluorescence (Fo) was almost unaltered. The certain reduction of actual photochemical efficiency of PS II in the light (Phi(PS II)), coefficient of photochemical quenching (qP), and apparent electron transport rate (ETR) was associated with a significant increase in non-photochemical quenching (NPQ), whereas as the PEG concentration was increased to higher than 15%, Ci increased remarkably, Pn, Gs, and WUE had a sustained decrease, while Fv/Fm, Phi(PS II), qP and ETR decreased more significantly, Fo increased rapidly, and NPQ decreased. The reduction of Pn under low concentration PEG was mainly due to stomatal limitation, while that under high PEG concentration was referred to the combination of non-stomatal and stomatal limitation. When the PEG concentration was lower than 20%, Pn decreased but photosynthetic structure was not damaged. The recovery of PS II activity and the survival of plant were found after the severe drought stress was removed 15 days later. It was concluded that Jatropha curcas had stronger tolerance to drought stress.