The Rapid Stimulation of Monoterpenes in Response to UV-B- Induced Oxidative Stress in Hou????uynia cordata

Houttuynia cordata Thunb. is an edible and medicinal wild herb rich in monoterpenes. This study was conducted to investigate the stress physiology and monoterpene accumulation of H. cordata after exposure to elevated ultraviolet-B (UV-B) radiation in order to better understand the physiology and optimize commercial cultivation of H. cordata. The findings showed that the shock of UV-B-induced oxidative stress as a result of an increase of hydrogen peroxide (H2O2), malondialdehyde (MDA) and antioxidant enzymes (catalase, superoxide dismutase, and peroxidase). However, the downward trend of both H2O2 and MDA was found after 2 d of UV-B shock, and the plants recovered from the oxidative damage to normal based on the normal photosynthesis standard after 6 d. Monoterpenes, known as antioxidants, showed rapid accumulation after UV-B exposure. One of them, 4-terpineol, was quickly induced to its peak at 24 h; β-ocimene, γ-terpinene and D-limonene reached the maximum at 48 h, and four terpenes including α-pinene, β-phellandrene, β-pinene and β-myrcene showed a continuous increase. These results clearly suggest that not only antioxidant enzymes but also monoterpenes play important roles in rapid defense responses to UV-B-induced oxidative stress, and that UV-B shock can be used as a strategy to increase the yield of monoterpenes in H. cordata.