Biogenesis of auxin in the coleptile of a semi-brachytic barley, uzu

The coleoptile of a semi-brachytic barley, uzu(Hordeum vulgare L. cv. Akashinriki), elongated ca 1/2 as much as the coleoptile of the contrasting normal form which is isogenic excepting the uz gene. This retarded growth of the uzu coleoptile, as compared to the normal coleoptile, is not due to changes in the rate of basipetal transport of auxin, neither to the destruction of auxin during transport, nor to sensitivity to auxin. Furthermore, less of the extractable and bound auxins were found in the uzu(uzuz) coleoptile than in the normal(UZUZ)coleoptile, suggesting that the retarded growth of uzu coleoptile may be due to less auxin production. Apical tips of the normal coleoptile grown under sterile conditions responded to both tryptophan and tryptamine, but uzu coleoptile tips responded only to tryptamine. Thus, growth retardation of the uzu coleoptile may be due to lower activity of the enzyme which converts tryptophan to tryptamine in the uzu coleoptile.