Auxins and Auxin Precursors in Acid and Nonacidic Fractions of Plant Extracts. Contributions from the Hull Botanical Laboratory 641

Abstract

1. A marked increase in the rate of production of nonacidic growth substance (presumably indoleacetaldehyde) by the internodes of etiolated pea seedlings over the rate during the first hour occurs between the first and fourth hours of extraction with ether at 22⚬ C. 2. The production rate of acid growth substance (presumably indoleacetic acid) falls during the same period. 3. The decrease in the production rate of nonacidic growth substance at 22⚬ C. after the fourth hour to about the rate during the first hour of extraction is not accompanied by an increase in the production rate of acid growth substance to the rate during the first hour of extraction. 4. No nonacidic growth substance can be extracted from the internodes at 0⚬ C. during 24 hours, and thus it does not seem to be present in large quantities in etiolated pea seedlings but is formed during extraction. 5. The rate of production of acid growth substance at 0⚬ C. is only approximately half that at 22⚬ C. during the first hour. The rate of production falls after the first hour of extraction (removal of free auxin) and remains low at both 0⚬ and 22⚬ C. 6. The presence of a nonacidic auxin precursor is indicated in nonacidic fractions of ether extracts of etiolated peaseedling internodes and in nonacidic fractions of juice of such tissue and of etiolated cabbage leaves. This precursor can be converted into active auxin by Avena coleoptile juice. 7. The presence of an acid auxin precursor is indicated in acid ether fractions of the juice of etiolated pea-stem internodes and of etiolated cabbage leaves. This acid precursor can also be converted into active auxin by Avena coleoptile juice. 8. A nonacidic growth substance is formed from the inactive nonacidic fraction of juice of pea stems and from the inactive acid fraction of juice of cabbage leaves.