Gibberellin Biosynthesis Mutations and Root Development in Pea

Dwarf mutants of pea (Pisum sativum), with impaired gibberellin (GA) biosynthesis in the shoot, were studied to determine whether the roots of these genotypes had altered elongation and GA levels. Mutations na, lh-2, and ls-1 reduced GA levels in root tips and taproot elongation, although in lh-2 and ls-1 roots the reduction in elongation was small (less than 15%). The na mutation reduced taproot length by about 50%. The roots of na plants elongated in response to applied GA1 and recombining na with mutation sln (which blocks GA catabolism) increased GA1 levels in root tips and completely restored normal root development. In shoots, Mendel's le-1 mutation impairs the 3β-hydroxylation of GA20 to the bioactive GA1, resulting in dwarfism. However, GA1 and GA20 levels were normal in le-1 roots, as was root development. The null mutation le-2 also did not reduce root GA levels or elongation. The results support the theory that GAs are important for normal root elongation in pea, and indicate that a 3β-hydroxylase gene other than LE operates in pea roots.