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

Abstract

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 [¹³C³H]GA₂₀ has also been studied. In dark-grown shoots of Alaska and Progress No. 9 [¹³C³H]GA₂₀ is converted to [¹³C³H]GA₁, [¹³C³H]GA₈, [¹³C]GA₂₉, its 2α-epimer, and [¹³C³H]GA₂₉-catabolite. [¹³C³H] Gibberellin A₁ was a minor product which appeared to be rapidly turned over, so that in some feeds only its metabolite, [¹³C³H]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 [¹³C³H]GA₂₀ was reduced in both cultivars. There is some evidence that 3β-hydroxylation of [¹³C³H]GA₂₀ can occur in red light-grown Alaska seedlings, but no 3β-hydroxylated metabolites of [¹³C³H]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.