Studies in Plant Growth Hormones

An examination has been made of the hormones present in extracts of excised roots and intact seedling roots of tomato. Acid and neutral ether-soluble fractions and the ether-insoluble aqueous fraction were chromatographed, and the chromatograms assayed using oat coleoptile sections. 2. The pattern of hormone activity in excised roots differed little from that in seedling roots. 3. On chromatograms of the aqueous fraction developed in iso propanol/ ammonia, growth promotion occurred at the position of 3-indolylacetic acid (IAA, Rf 0·5) and sometimes at the position of 3-indolylacetonitrile (IAN, Rf 0·8). When the IAA zone was eluted off the paper and rechromatographed, it formed the IAN zone and another zone of promotion at Rf 0·1–0·2. 4. When the aqueous fraction was developed in n -butanol/ammonia, promotion occurred at the position of IAA (Rf 0·15), at Rf 0·5, and at the position of IAN (Rf 0-85). These zones have been called X, Y, and Z respectively. They were also formed when the IAA zone in wopropanol/ammonia was rechromatographed in ammoniacal n-butanol. It is shown that X and Y are interconvertible, and that each can form Z on rechromatography; also, there is some evidence that Z can form X and Y. When Z was separated into ether-soluble (acid and neutral) and ether-insoluble fractions with sodium bicarbonate solution and chromatographed in iiopropanol/ammonia, growth resulted at the position of Z in the neutral and aqueous fractions, but in the acid fraction it occurred at Rf 0·24–O·35. Comparison with other chromatograms indicates that this last zone does not occur in the aqueous fraction but has been formed as a result of extraction with sodium bicarbonate solution. 5. The zones found in the aqueous fraction also occurred in small quantities in acid and neutral ethereal fractions in a number of experiments. 6. The ethereal fractions gave no chromogenic reactions with ferric chloride/ perchloric acid, nitrous/nitric acid, or p -dimethylaminobenzaldehyde (MeAB). In the aqueous fraction only MeAB gave a reaction (yellow) which showed any consistent correlation with biological activity. A yellow colour with this reagent is not a characteristic chromogenic reaction of indole compounds. It is suggested that a non-indole hormone system may be operating in tomato roots.