Gibberellins in dark- and red-light-grown shoots of dwarf and tall cultivars of Pisum sativum: The quantification, metabolism and biological activity of gibberellins in Progress no. 9 and Alaska.

The stem growth in darkness or in continuous red light of two pea cultivars, Alaska (Le Le, tall) and Progress No. 9 (le le, dwarf), was measured for 13 d. The lengths of the first three internodes in dark-grown seedlings of the two cultivars were similar, substantiating previous literature reports that Progress No. 9 has a tall phenotype in the dark. The biological activity of gibberellin A20 (GA20), which is normally inactive in le le geno-types, was compared in darkness and in red light. Alaska seedlings, regardless of growing conditions, responded to GA20. Dark-grown seedlings of Progress No. 9 also responded to GA20, although red-light-grown seedlings did not. Gibberellin A1 was active in both cultivars, in both darkness and red light. The metabolism of [(13)C(3)H]GA20 has also been studied. In dark-grown shoots of Alaska and Progress No. 9 [(13)C(3)H]GA20 is converted to [(13)C(3)H]GA1, [(13)C(3)H]GA8, [(13)C]GA29, its 2α-epimer, and [(13)C(3)H]GA29-catabolite. [(13)C(3)H] Gibberellin A1 was a minor product which appeared to be rapidly turned over, so that in some feeds only its metabolite, [(13)C(3)H]GA8, was detected. However results do indicate that the tall growth habit of Progress No. 9 in the dark, and its ability to respond to GA20 in the dark may be related to its capacity to 3β-hydroxylate GA20 to give GA1. In red light the overall metabolism of [(13)C(3)H]GA20 was reduced in both cultivars. There is some evidence that 3β-hydroxylation of [(13)C(3)H]GA20 can occur in red light-grown Alaska seedlings, but no 3β-hydroxylated metabolites of [(13)C(3)H]GA20 were observed in red light-grown Progress. Thus the dwarf habit of Progress No. 9 in red light and its inability to respond to GA20 may be related, as in other dwarf genotypes, to its inability to 3β-hydroxylate GA20 to GA1. However identification and quantification of native GAs in both cultivars showed that red-light-grown Progress does contain native GA1. Thus the inability of red light-grown Progress No. 9 seedlings to respond to, and to 3β-hydroxylate, applied GA20 may be due to an effect of red light on uptake and compartmentation of GAs.