Abstract
Effects of gibberellic acid (GA3) on Culm internodes were observed in the rice dwarf mutant, Fukei 71, and its original cultivar, Fujiminori. Although plant heights in the vegetative growth period, panicle number and elongated internode number of culm were greatly affectecd by GA3 repeated treatments at 3 to 4 days intervals in Fukei 71 and Fujiminori, no significant difference was detected in the responses of these characters to GA3 between both cultivars. On the contrary, a marked difference was observed in the response of culm elongation to GA3 between two lines. Under the greenhouse or high temperature (30°C-25°C) condition, the culm elongation of Fujiminori was strongly promoted, while Fukei 71 did not respond as strognly to GA3 as Fujirninori. Especially, it is noteworthy that Fukei 71 showed the similar responses at three levels of GA3 concentration. However, it was observed that under low temperature (23°C-18°C) condition the response of culm elongation to GA3 in Fukei 71 restored very nearly to that of Fujiminori. The parenchyma cells in the elongated internodes caused by GA3 treatments in Fukei 71 had an abnormal form compared with those of Fujiminori, and the form resembled to that of parenchyma cells in the upper internodes of Fukei 71 as shown in the previous work (KITANO and FUTSUHARA 1982). Gibberellin-like substances were ascertainecl by the bioassay with Tangin-bozu and Waito-C in the acidic ethyl acetate fraction of 70 percent aceton extracts from the culm, panicle and leaves of Fukei 71 and Fujiminori at various growth stages. The similar level of GA activities was cletected in Fukei 71 only Tangin-bozu assay, compared with Fujiminori. No GA activity was detected in both culitivars with Waito-C assay
