Uptake of ¹⁴C-Acetic Acid by Rice Plant as Related to Root Function and Microbial Activity on the Root Surface

Experiments using rice plants (Oryza sativa L.) were conducted to examine uptake of ¹⁴C-acetic acid via the root and ¹⁴C behavior on the root surface. For hydroponics, three types of rice plants were cultured with ¹⁴C-acetic acid solution: complete plant, half-rooted plant, and non-rooted plant. Also, for the root incubation experiment, sterilized root and non-sterilized root were incubated with ¹⁴C-acetic acid solution. The ¹⁴C radioactivities in the plant parts and solution were measured. Non- and half-rooted plant had ¹⁴C radioactivity in their aerial part, but the complete plant did not. The trends of radioactivity levels in the solution were directly opposite to those of plant root biomass. A high level of ¹⁴C radioactivity was observed on the entire root surface of non-sterilized root in the incubation experiment, and ¹⁴C radioactivity in the solution also remarkably decreased from 7 h to 96 h after the ¹⁴C addition. These results suggest that the amount of ¹⁴C-acetic acid absorbed by the plant through the roots is very small. However, the plant absorbs ¹⁴C-acetic acid through breaks in the roots. Once ¹⁴C-acetic acid is inside the plant, it immediately transfers to the shoots. Degradation of ¹⁴C radioactivity in the solution and ¹⁴C fixation on the root surface arise from the context of microbial activities.