Absorption and Metabolism of Radioactive Auxins in the Induced Rice Callus

[摘要] During callus induction, auxin uptake and metabolism in rice seeds were investigated with 14C-carboxyl-labelled 2, 4-D and IAA. The uptake and metabolism in rice callus were compared with tobacco and barnyardgrass callus cultures. Radioactivity of 2, 4-D absorbed in the callus cultures and rice seeds was high in the 80% ethanol fraction and low in the residual fraction but scarce in the gas phase, expected to contain CO2 owing to the decarboxylation. Two kinds of 2, 4-D metabolites were present in the 80% ethanol fraction extracted from rice seedlings, rice callus and barnyardgrass callus. Inhibitory activities of them were lower than that of 2, 4-D in the growth test with rice seedlings. It seems that they are different from 2, 4-D-aspartic acid on the base of Rf value of chromatogram. From the quantitative research on 2, 4-D and 2, 4-D metabolites, it was shown that the tissues inducing callus contained higher level of 2, 4-D than those which had not induced callus. The barnyardgrass, which had required high concentrations of 2, 4-D for callus induction, contained high level of 2, 4-D metabolites but low level of 2, 4-D, when compared with rice callus. Therefore, it is assumcd that 2, 4-D level plays an important role in callus induction on the tissues. In ricc callus, most of IAA was converted to IAA-aspartic acid or degraded into CO2. Requirement of high concentration of IAA in rice callus for callus induction and subculture seems to be caused by faster degradation and inactivation of IAA than those of 2, 4-D. It is probable that 2, 4-D directly acts to the callus induction but not via IAA production by 2, 4-D, because the level of IAA, which would be required for callus induction, was not found in the 2, 4-D treated rice tissues. And also, selectivity of 2, 4-D as a herbicide is dis-cussed here in the relation to 2, 4-D metabolism in plants.

[学科分类] 农业科学（综合）