Veränderungen des Wuchsstoffes Indolyl-3-essigsäure bei der Keimung von Avena sativa L.

Abstract

Summary The procedures for extracting free and bound indoleacetic acid (IAA) from plant material were re-investigated. Reproducible results (free IAA) without degradiation of either the free or bound IAA were obtained by extractions with methanol at 0° and 64° or by extractions with buffer solutions. The IAA was liberated from it's bound form by hydrolysing the plant material for 48 hrs with 1 n NaOH in the dark at 22°. The contents of total, free and bound IAA were determined in etiolated oat seedlings from the onset of germination until 96 hrs after germination had begun. The total amounts of free and bound IAA did not change during this period. IAA contents in the entire plant, per 100 g seeds, were determined to be: total IAA 1754 ± 50 μg, bound IAA 1642 ± 50 μg and free IAA 115 ± 10 μg. The distribution of the endogenous IAA in a 96 hrs old seedling was: shoot : total IAA content 91.8 ± 6 μg, bound IAA 82.6 ± 6.9 μg, free IAA 8.1 ± 0.4 μg; radical : total IAA content 98.8 ± 6.5 μg, bound IAA 94.6 ± 5.0 μg, free IAA 2.1 ± 0.1 μg; rest seed : total IAA content 1553 ± 55 μg, bound IAA 1441 ± 63 μg, free IAA 100 ± 9.0 μg. Preliminary characterizations of the water soluble fraction of the bound IAA from the dry seed yielded a protein with a molecular weight of 36,000 daltons, whereas the water soluble fraction of the bound IAA from the shoot is a substance with a low molecular weight. From these data it was concluded that no biosynthesis of IAA takes place in etiolated seedlings and that the bound IAA of the dry seed is transformed to the bound IAA of the shoot, perhaps with free IAA as intermediate. This newly formed bound IAA is probably transported to the coleoptile tip, where the physiologically active free IAA is liberated.