Comparison of Gibberellins in Normal and Slender Barley Seedlings

Abstract

Gibberellins A₁, A₃, A₈, A₁₉, A₂₀, and A₂₉ were identified by full scan gas chromatography-mass spectrometry in leaf sheath segments of 7-day-old barley (Hordeum vulgare L. cv Golden Promise) seedlings grown at 20°C under long days. In a segregating population of barley, cv Herta (Cb 3014), containing the recessive slender allele, (sln 1) the concentration of GA₁ and GA₃ was reduced by 10-fold and 6-fold, respectively, in rapidly growing homozygous slender, compared with normal, leaf sheath segments. However, the concentration of the C₂₀ precursor, GA₁₉, was nearly 2-fold greater in slender than in normal seedlings. There was little difference in the ABA content of sheath segments between the two genotypes. The gibberellin biosynthesis inhibitor, paclobutrazol, reduced the final sheath length of normal segregants (50% inhibition at 15 micromolar) but had no effect on the growth of slender seedlings at concentrations below 100 micromolar. There was a 15-fold and 4-fold reduction in GA₁ and GA₃, respectively, in sheath segments of 8-day-old normal seedlings following application of 10 micromolar paclobutrazol. The same treatment also reduced the already low concentrations of these gibberellins in slender segregants. The results show that the pool sizes of gibberellins A₁ and A₃ are small in slender barley and that leaf sheath extension in this genotype appears to be gibberellin-independent. The relationship between gibberellin status and tissue growth-rate in slender barley is contrasted with other gibberellin nonresponsive, but dwarf, mutants of wheat (Triticum aestivum) and maize (Zea mays).