Abstract
In this study, the elongation of plumules grown from seeds which were pre-treated at high temperature through soils after germination was examined. Materials used were two paddy rice cultivars in japonica type and two rice varieties in indica type. High temperature pre-treatment of seeds before sowing was conducted as follows: After immersion at 25°C for 20 hours, the seeds were treated at 40°C for 8 days. Seeding depth was 6cm, soil moisture content about 20% and cultural temperature about 20°C. The following results were obtained. 1. In paddy rice plants injaponica type, the numbers of days from seeding to emergence time of plumules was shorter in the lot of high temperature pre-treatment of seeds than the untreated lot. However, no significant difference between the lots of high temperature pre-treatment of seeds and immersing seeds (25°C for 20 hours) was observed. 2. Though the mesocotyl of plumules grown from seeds pre-treated at high temperature in japonica type was as same long as that of untreated plumules in indica type, the growth of the plumules of the former was less slow than those in the latter. This was due to the difference of the speed of mesocotyl elongation between the plumules of the japonica and indica types. Moreover, multiplication of the parenchyma cells in mesocotyl was more active in the latter than in the former.
