Allelopathic effects of volatile cineoles on two weedy plant species

The volatile monoterpene analogs, 1,4-cineole and 1,8-cineole, have been identified as components of many plant essential oils, but relatively little is known about their biological activities. We compared the effects of 1,4- and 1,8-cineole on two weedy plant species by monitoring germination, mitosis, root and shoot growth, chlorophyll content, and photosynthetic efficiency. 1,4-Cineole severely inhibited growth of roots and shoots, causing cork-screw shaped morphological distortion, whereas 1,8-cineole caused a decrease in root growth and germination rates. Chlorophyll fluorescence data (yield and F-v/F-m) indicated that 1,4-cineole caused significantly higher stress (P less than or equal to 0.001) to photosynthesis when compared to controls. Mitotic index data showed that 1,8-cineole severely decreased (P less than or equal to 0.001) all stages of mitosis when compared with controls, while 1,4-cineole only caused a decrease in the prophase stage (P less than or equal to 0.05). Although superficially similar in structure, these two cineoles appear to have different modes of action.