Evaluation of linear growth differed more among test species than did overall fresh weight. Even the most sensitive assay, root extension in lettuce required a psilotin concentration of 0.3 mM. Levels of this magnitude are not indicative of a particularly potent regulator. However, the reported psilotin contents of 0.6-1.22% (fr. wt) [1,2] corresponds to ca 4-37 mmol/kg of tissues hence fall easily within the range of inhibitory concentrations. The concept of psilotin as part of a regulatory system is reinforced by the demonstration that its inhibitory effects are reversed by glutathione, other thio-compounds and gibberellin A3 (Table 2). Glutathione, thiourea and thioproline at 1 mM restore nearly full germination to seeds near the ID50 level in 5 mM psilotin. Hydroxyproline, lacking the reducing group, is inactive, but gibberellin A3 is ca 10-100-fold more active than the thiols. These responses underscore the coumarin-like character of psilotin [4,6] as well as its potential role in growth regulation. Virola multinervia Ducke (Myristicaceae), trivial name "ucuuba grande", occurs in the western part of Amazonas State. Previous work identified N,N-dimethyltryptamine and 5-methoxy-N,N-dimethyltryptamine in roots, and sitosterol, stigmasterol, 1-(2'-hydroxy-4'-methoxyphenyl)-3-(3",4"-methylenedioxyphenyl)-propane (virolane) and 2-hydroxy-1-(2'-hydroxy-4'-methoxyphenyl)-3-(3",4"-methylenedioxyphenyl)-propane (virolanol) in trunk wood. Present work on the ethanol extract of trunk wood isolated a new dihydroxy-dimethoxy-1,3-diarylpropane (C17H20O4), identified as 1-(4'-hydroxy-2'-methoxyphenyl)-3-(3"-hydroxy-4"-methoxyphenyl)-propane using 1H NMR, mass spectrometry, IR spectroscopy, and chemical methods (acetylation, Gibbs test). This compound is an isomer of the Gibbs test negative metabolite 1b of Virola coriacea Ducke for which very similar 1H NMR and MS were reported [5]. Since their discovery by Lester [1] and Morton [2], ubiquinones have received much attention from many workers in various fields of research. In the case of cultured plant cells, Threlfall and Goodwin [3] reported the occurrence of ubiquinone-10 in Paul's scarlet rose while Thomas and Stobart examined the time-course of ubiquinone and α-tocopherol formation in Kalanchöe daigremontiana callus [4]. According to our investigations [5], tobacco cells in suspension culture appear to contain much more ubiquinone-10 than the parent plants and so might be a suitable source for the large scale production of this compound. In order to obtain basic information on the synthesis of ubiquinone-10 by cultured plant cells, some observations on the variation in the ubiquinone content during the growth of the cultured cells have been made and are detailed in this paper. The time-course of ubiquinone formation during cell growth was examined using three kinds of cultured cells which have a high growth rate in suspension culture. The clone BY-2 reached a maximum dry weight 6 days after inoculation, while their ubiquinone content decreased during the early period of the logarithmic phase of growth and then increased reaching the highest level (360 μg per g-dry weight) on the 10th day. Changes in the ubiquinone content of Xanthi cells were also observed.