Studies on the Emergence of Rice Seedlings in the Direct-Sowing Culture : VI. Varietal difference in stimulation of mesocotyl elongation by high temperature treatment of seeds before sowing

Abstract

Using thirty-four varieties of paddy rice in japonica type, effect of high temperature treatment of seeds (40°C for 10 days) before sowing on the mesocotyl elongation was examined at the cultural temperatures of 20 and 25°C in darkness. The following results were obtained. 1. Mesocotyl elongation was stimulated in the all varieties by the high temperature treatment of seeds before sowing at the both cultural temperatures. The stimulation ratio of treated mesocotyl to control one was from 6 to 31 at 20°C and from 6 to 55 at 25°C. 2. At 20°C, number of parencyma cells per one cell layer in longitudinal sections of treated mesocotyls was from 5 to 12 times that of control ones, On the other hand, parenchyma cell length of the former was from 0.8 to 1.6 times that of the latter. Moreover, parenchyma cell width was almost all the same in treated and control plants. 3. Coleoptile elongation was stimulated also in the all varieties by the high temperature treatment of seeds before sowing at 20°C. At 25°C, coleoptile elongation of one variety was inhibited slightly by the high temperature pre-treatment, while coleoptile elongation of thirty-three varieties were stimulated. In these thirty-three varieties, the stimulation ratio of treated coleoptile to control one was from 1.1 to 1.8. 4. Partial correlations were obtained between mesocotyl length in treated plants and mesocotyl length (r=0.518) or the number of parenchyma cells per one cell layer in longitudinal sections of the mesocotyl (r=0.543) in control plants at 20°C. 5. No positive correlations between mesocotyl length in treated plants and culm length (r=0.026 at 20°C, r=0.216 at 25°C) or the number of days from sowing to heading (r=0.199 at 20°C, r=0.188 at 25°C) were obtained.