Abstract

Salicylic acid (SA) plays important roles in plant defense responses. However, little is available about its effects on monoterpene responses. Therefore, monoterpene contents and antioxidant systems were measured three days after foliar application of SA with different concentrations in Houttuynia cordata. SA at low concentrations (≤ 1 mM) suitably enhanced the efficiency of antioxidant system, however, at high concentrations (10 and/or 100 mM), a strong accumulation of peroxidase, catalase and malondialdehyde suggested the induction of oxidative stress. High concentrations of SA resulted in a marked accumulation of total monoterpenes, which might be attributed to the oxidative burst. A significant increase in total monoterpene contents was also observed at 0.01 mM SA, which might be favorable for the induction of monoterpenes because of less oxidative damage to the plants. Total monoterpene contents showed a decline in the treatments of 0.1 and 1 mM SA. However, not all of monoterpene individuals were significantly induced and/or suppressed in the corresponding treatments. This implied that different monoterpenes might be differentially mediated at different concentrations of SA.

Key words: Houttuynia cordata, monoterpenes, oxidative stress, salicylic acid.

Abbreviation

CAT, Catalase; H₂O₂, hydrogen peroxide; MDA, malondialdehyde;NBT, nitroblue tetrazolium; ^.O₂^–, superoxide radicals; POD, peroxidase; SA, salicylic acid; SAR, systemic acquired resistance; SOD, superoxide dismutase; ROS,reactive oxygen species; EDTA, ethylene diamine tetraacetic acid; UV-Vis,ultraviolet/visible; FW, fresh weight; TCA, trichloroacetic acid; GC-MS, gas chromatography-mass spectrometry; SE, standard errors.