Physiological Action of Ethylene in Crop Plants : VI. Effect of hydrocarbons especially ethylene on the root growth of soybean and rice seedlings

Abstract

Effects of hydrocarbons, such as methane, ethane, ethylene, propane and propylene, on the root growth of soybean (Glycine max Merr. cv. Enrei) and rice (Oryza sativa L. cv. Nihonbare) seedlings were examined. The results obtained are summarized as follows: 1. When roots of soybean were exposed to 1, 000 ppm of hydrocarbons, ethylene was most effective to inhibit the root growth with promortion of root-hair formation and increase of stem-diameter. The activity was decreased in the order of propyelene, propane, ethan and methane. Inhibitory activity of propylene on root growth was one hundredth of ethylene, and 50% inhibition of soybean root growth was obtained with 1 ppm ethylene. 2. In rice seedling, seminal root growth was stimulated with both of 1, 000 ppm ethylene and propylene, whereas the growth of first crown roots was inhibited greatly as well as the soybean roots. 3. Effect of ethylene on the growth of seminal root of rice seedling was examined in the range of concentrations from 0.1 to 10, 000 ppm. The most effectivc promotion was obtained at 0.1 to 1 ppm. On the other hand, the growth of first crown roots was promoted with 0.1 ppm ethylene, whereas concentrations higher than 10 ppm inhibited the growth greatly. 4. Effect of ethylene on rooting of rice seedlings was examined and promotion of new roots elongation was observed at 0.1 ppm of ethylene, whereas increase in number of new roots was observed at 10 ppm of ethylene. These results strongly suggest the view that ethylene in the rhizosphere may have direct effect on the growth and development of roots.