Indole-3-acetic acid and rice coleoptile elongation under anoxia

To investigate the presence of a possible synergistic effect of IAA and anaerobiosis on rice coleoptile elongation, excised coleoptiles grown in aerobic and anaerobic conditions were tested and compared with intact seedling aerial parts for response to exogenous IAA and for levels of endogenous IAA. Excised coleoptiles were fed with³H-IAA to study aerobic and anaerobic IAA metabolism. Our results can be summarized as follows. (1) IAA and anaerobiosis have no synergistic effect on rice coleoptile elongation. (2) This behavior is due not to an inhibition of IAA uptake but probably to a reduced and different IAA metabolism in coleoptile grown in the absence of oxygen. (3) In anaerobic rice coleoptiles, the conversion to inactive conjugate (IAA-Asp) could be adopted as means of detoxification in the case of abnormally high and unutilized IAA levels. (4) The increase in IAA level found in coleoptiles of intact seedlings during anaerobic treatment could be due, as in the roots, to a translocation from the endosperm, in which the hormone is contained in a great quantity.