Effects of drought simulated by PEG on plant growth，essential oil content and components of Foeniculum vulgare Mill

Using the method of hydroponics four treatments（0%，5%，12.5% and 20%） were designed to study the effects of different polyethylene glycol6000（PEG6000）concentrations on the growth，content and components of essential oil in fennel. The results showed that different concentrations of PEG inhibited the growth of fennel（plant height，leaf number，leaf length，leaf width，fresh weight，dry weight，root/shoot ratio and dry matter content）. However their effects on soluble sugar，protein，activities of SOD and POD，MDA content and the content and components of essential oil in fennel varied between the aboveground part and underground part of the plant. PEG concentration of 5% was beneficial to the accumulation of protein，soluble sugar，yield of essential oil and MDA content for both the aboveground part and the underground part. Concentration of 20% enhanced the activities of SOD and POD in the aboveground and underground parts of fennel，but improved the MDA content and yield of essential oil in the aboveground part. A total of 16 components were identified in the essential oil of aboveground part of fennel. The main components were（E）-anethole 46.30%-62.94% and limonene 17.28%-33.16%. Nine components were identified in the essential oil from underground part of the plant and their main components were dill apiol， 35.26%-58.77%；myristicin，7.55%-36.36% and γ-terpinene，11.0%–26.01%. The concentrations of（E）-anethole， myristicin and γ-terpinene decreased as the PEG concentration rose，but limonene and dill apiol showed the opposite tendency. The correlation analysis showed that essential oil yield was positively correlated with fresh weight，dry weight，soluble sugar，protein，（E）-anethole，γ-terpinene and myristicin. There was also a significant positive correlation with the fresh weight of the whole plant. The essential oil yield was negatively correlated with the activities of SOD and POD，MDA content，limonene and dill apiol，but significantly negatively correlated with SOD and POD activities