Biosynthesis of Indole-3-Acetic Acid from L-Tryptophan in Coleoptile Tips of Maize (Zea mays L.) : GROWTH AND DEVEROPMENT

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Coleoptile tips (about 2.5 mm in length) were excised from 3-day-old dark-adapted maize (Zea mays L.) seedlings and incubated in darkness in potassium phosphate buffer that contained ^<14>C-L-tryptophan (Trp). Subsequent analysis by gas chromatography-mass spectrometry indicated that a significant portion of endogenous indole-3-acetic acid (IAA) had been labeled with ^<14>C. About 8% of the IAA that diffused from the tissue into the medium during incubation from 0.5 to 2 h was labeled, and 12% of the IAA extracted from the tissue after a 2-h incubation was labeled. On the other hand, 30% of the Trp extracted from the tissue after a 2-h incubation was ^<14>C-Trp, which was more than those determined for IAA. Since the experiments were carried out under the non-steady-state conditions in which the tissue content of ^<14>C_Trp increased with time, and since the extracted Trp included the ^<14>C-Trp in the apoplastic space, it seemed that synthesis de novo from Trp was the major means by which IAA was produced in the coleoptile tip. The con-version of Trp to IAA was not detected in sub-apical segments (5-7.5 mm from the top) that were incubated similarly, an indication that synthesis of IAA occurs specifically in the tip region. When intact seedlings were irradiated with a pulse of red light 2 h before excision of tips and the application of ^<14>C-Trp, the amounts of extractable and diffusible IAA were reduced by 40-60% without a change in the rate of ^<14>C incorporation. This result indicated that the production of IAA from Trp is controlled by a red-light signal.
日本植物生理学会の論文

Biosynthesis of Indole-3-Acetic Acid from L-Tryptophan in Coleoptile Tips of Maize (Zea mays L.) : GROWTH AND DEVEROPMENT

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