Growth activity, diterpenoids with

Figure 8. Diterpenoids with growth-regulating activity...

There are a number of allelochemicals among the mono-, sesqui-, and diterpenoids. In particular, plants in arid and semiarid regions produce diverse volatile terpenoids with allelopathic activity.5 Among the volatile monoterpenes, 1,8-cineole (4) and camphor (5) exhibit strong growth inhibitory effects on plants and are considered to be involved in plant competition. 1,4-Cineole (6), a minor isomer of 1,8-cineole, is a potent inhibitor of asparagine synthetase.6 -Menthane-3,8-diols (fir 7 and frw .r8), -menth-2-en-l-ols (cis 9 and trans 10), thymol (11), carvacrol (12), 1,8-cineole, cr-pinene (13), and /3-pinene (14) were isolated as allelopathic monoterpenes from Eucalyptus species.7 Eucalyptus trees also produce allelopathic sesquiterpenes including spathulenol (15), and a-, (3-, and 7-eudesmols (16-18).7... 

In Japan, R.japonica and R. trichocarpa have been used as bitter stomachics and anthelminthics, while in China R. ternifolia has been used as an antiphlogistic, germicide, antipyretic, and toxicide and R, rubescens is used in cancer of the esophagus. Initial studies to track down the compounds responsible for the activity of Rabdosia species were carried out in 1954. Subsequent studies dealt with cytotoxicity, antitumor activity, inhibition of oxidative phosphorylation, anti-feeding activity, growth inhibitory activity, and bitterness. All of the foregoing activities have been attributed to the diterpenoid constituents. 

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