Effects of Scopoletin on Growth, CO 2 Exchange Rates, and Concentration of Scopoletin, Scopolin, and Chlorogenic Acids in Tobacco, Sunflower, and Pigweed

In an attempt to establish the effects of scopoletin on growth of tobacco, sunflower, and pigweed, seedlings were treated with scopoletin through a nutrient culture. A threshold level of inhibition was found in all cases between 10-4M and 10-3M concentrations of scopoletin with the former showing no major growth effects, whereas the 10-3M solutions were greatly inhibitory to all three species. All 5 x 10-4M treatments had an intermediate effect on growth. Analyses of scopoletin, scopolin, and chlorogenic acid concentrations of tobacco and sunflower treated with 10-4M and 5 x 10-4M scopoletin concentrations showed that at both of these levels, scopoletin and scopolin increased significantly in the tissue when compared with the control. The plants treated with the 5 x 10-4M solution had the largest increase in these compounds. The great increase in scopolin suggested a direct conversion of scopoletin to its glycoside, scopolin, within the plant. Chlorogenic acid levels were not different from controls and the variations in isomers (band 510 and neochlorogenic acid) were indefinite. A reduced shoot:root ratio coincided with a greater build up of scopoletin and scopolin in the shoots than in the roots of inhibited tobacco seedlings. Respiration rates in treated plants remained unchanged, but CO2 exchange analyses indicated that a reduced net photosynthetic rate was a contributing factor to reduced growth. Net photosynthesis in 10-3M scopoletin treated tobacco plants was depressed to as low as 34% of that of the controls by the fourth day after treatment. In sunflowers, which normally have very small amounts of scopoletin and scopolin in the tissue, growth retardation was not as pronounced and the lowest photosynthetic rate resulting from treatment was 74% of controls. Reduced growth in leaf area over a 12 day experiment correlated well with the significant reduction in the rate of net photosynthesis in tobacco and a fairly good correlation was found also in sunflower. Amounts of CO2 fixed/illumination hour in treated plants compared with controls reinforced the conclusion that a reduction in net photosynthesis contributed to plant inhibition in tobacco and sunflower plants. Limited experiments with pigweed also indicated significantly reduced photosynthesis in the 10-3M scopoletin treated seedlings. Scopoletin could contribute to a cooperative effect causing plant inhibition in the natural environment and therefore be a factor of ecological significance