The gibberellin (GA) content of barley (Hordeum vulgare L.) cv. Triumph was analysed by full scan gas chromatography-mass spectrometry. Developing grain contained several di-, tri-, and tetra-hydroxylated GAs, with the most abundant ones being hydroxylated at C-2, C-3, C-12-beta, and/or C-18. In contrast, the only GAs to be detected in shoots of 9-day old dark- and light-grown seedlings of Triumph were 13-hydroxylated C19-GAs, namely GA1, GA8, GA20 and GA29 (all of which are components of the early 13-hydroxylation GA biosynthetic pathway) and GA3. Feeds of [C-13, H-3(2)]GA20 confirmed that GA20 is a precursor of GA1, GA8, and GA29 in barley shoots. From these results it is suggested that stem growth of barley, in common with that of several other mono- and di-cotyledons, is controlled by GA1. Homozygous gal and gai lines were obtained after backcrossing to Triumph. These were then compared to Triumph with respect to their GA content and response to applied GAs and GA precursors. Shoots of the homozygous gal gal plants contained ca 6-fold less GA1 than Triumph. These plants responded to all ent-kaurenoids and 13-hydroxylated C20- and C19-GAs tested. It is concluded that the gal locus impairs the GA biosynthetic pathway prior to ent-kaurene, most probably at ent-kaurene synthetase. In contrast, shoots of homozygous gai gai line contained ca 10-fold higher levels of GA1 than Triumph, but failed to respond to applied GA1 or GA3. The gai locus therefore confers insensitivity to both exogenous and endogenous GAs, possibly by perturbing the reception or transduction of the GA1 signal.
