[Tannins and growth : III. Analysis of the IAA/Tannin-Antagonism in oat-coleoptile cylinders].

An analysis of the IAA/Tannin-Antagonism which occurs in oat-coleoptiles was carried out. The investigations were done with 10 mm coleoptile sections of 4-day-old seedlings of Avena sativa L. var. "Flämingsgold".First it was shown that the IAA/Tannin-antagonism which could be established with a tannin-preparation by "Fluka" resembled very much that caused by "Merck-Tannin". Whereas the antagonism which was demonstrated by "Merck-Tannin" seemed to be independent of the IAA concentration, the antagonism induced by "Fluka-Tannin", showed a strict correlation to the applied amount of IAA. An increase of the IAA concentration resulted in a decrease of the antagonistic tannin effect. A 5·10(-5) molar tannin solution reduced the activity of an IAA-oxydase preparation by 71-92%.Oat-coleoptile cylinders which were preincubated for 4 hours in a 10(-5) molar or a 10(-4) molar IAA solution and subsequently treated with tannin for 16 hours showed no growth inhibition at all.After a preincubation period with tannin solutions (5·10(-6) up to 5·10(-4) M) for 3 hours the uptake of IAA during 20 hours by oat-coleoptile cylinders was lowered by 12-45%. It seems to be clear that the IAA/Tannin-antagonism in buffered solutions is due to a remarkable drop in the IAA uptake by the coleoptile tissue.