Triacontanol: A New Naturally Occurring Plant Growth Regulator

Growth Enhancement of Plants by Femtomole Doses of Colloidally Dispersed Triacontanol

Colloidal dispersions of crystalline 1-triacontanol in water, upon foliar application to corn (Zea mays L.) seedlings, resulted in growth increases at femtomole dosages (spray concentrations as low as 1 nanogram per cubic decimeter). The maximum growth increase occurred at 100 nanograms per cubic decimeter; at both higher and lower concentrations lessened growth increase was observed. The dispersions were prepared by sonication, with control of temperature and composition. Selected surfactants, which facilitate the dispersion process, are effective at 1 percent of the 1-triacontanol composition and are nontoxic.

Comparative analyses of the effect of triacontanol on photosynthesis, photorespiration and growth of tomato (C3-plant) and maize (C 4-plant)

Tomato (C3-plants) and maize (C4-plants) were grown in a nutrient solution to which triacontanol was added twice a week. After about 4 weeks the triacontanol treatment caused a significant increase in the dry weight of the tomato plants. Leaf area and dry weight measurements of tomato leaves at different stages of development showed that the largest increase in growth was obtained when triacontanol treatment was initiated before bud formation. In maize, no effect of the triacontanol treatment on dry wieght was observed. Photosynthesis was inhibited by 27% in young leaves from triacontanol-treated tomato plants and 39% in the controls, when the oxygen concentration was raised from 2% to 21%. In maize no change in photosynthesis could be observed, neither after altered oxygen concentration nor after triacontanol treatment. The difference in the response of C3- and C4-plants to triacontanol indicates that it regulates processes related to photosynthesis.

Specificity of 1-triacontanol as a plant growth stimulator and inhibition of its effect by other long-chain compounds

The effect of several analogs of 1-triacontanol (TRIA), differing in C-chain length (16-32), the position of the hydroxyl group and the terminal functional group, were tested alone and in combination with TRIA on the growth of rice (Oryza sativa L.), maize (Zea mays L.) and tomato (Lycopersicon esculentum Mill.) seedlings. Applied alone, none of the compounds caused an increase in growth; thus, chain length (30 C) and presence and position (terminal) of the hydroxyl group appear to be specific for the growth-promoting activity of TRIA. When applied simultaneously with TRIA, all analogs inhibited the response to the latter in all three test plants, whether applied in the nutrient solution, as foliar spray or by seed soaking. 1-Octacosanol inhibited the response of rice seedlings to 2.3 x 10(-8) M TRIA at concentrations as low as 2.4 x 10(-12) M. Thus preparations of TRIA and application equipment must be free from trace amounts of other long-chain compounds if they are to be used to increase plant growth.

Growth responses of rice seedlings to triacontanol in light and dark

Triacontanol, a 30-carbon primary alcohol, applied in nutrient culture solutions to rice (Oryza sativa L.) seedlings at 2.3×10(-8) M (10 μg/l), caused an increase in dry weight and leaf area of the whole plants. The response could be observed as early as 3 h of treatment. It was observed at relatively high and low light intensities as well as in the dark where control plants lost but triacontanol-treated plants gained in dry weight. The dry weight gain in the dark was, however, eliminated by removing CO2 from the atmosphere. Triacontanol-treated plants also increased their content of Kjeldahl-N and contained 30% more total N per plant than controls after 6 h in the dark.