GIBBERELLINS AND PEA SEED DEVELOPMENT - EXPRESSION OF THE LH(I) LS AND LE(5839) MUTATIONS

The gibberellin (GA)-biosynthesis mutations, lh(i), ls and le(5839) ha ve been used to investigate the role(s) of the GAs in seed development of the garden pea (Pisum sativum L.). Seeds homozygous for lh(i) poss ess reduced GA levels, are more likely to abort during development, an d weigh less at harvest, compared with wild-type seeds due to expressi on of the lh(i) mutation in the embryo and/or endosperm. Compared with wild-type seeds, the lh(i) mutation reduces endogenous GA(1) and gibb erellic acid (GA(3)) levels in the embryo/endosperm a few days after a nthesis and fertilizing lh(i) plants with wild-type pollen dramaticall y increases GA(1) and GA(3) levels in the embryo/endosperm and restore s normal seed development. By contrast, the ls and le(5839) mutations do not appear to reduce GA levels in the embryo/endosperm of seeds a f ew days after anthesis, and do not affect embryo or endosperm developm ent. However, both the ls and lh(i) mutations substantially reduce end ogenous GA levels in embryos at contact point (the first day the liqui d endosperm disappears). Levels of GAs in seeds from crosses involving the Is and lh(i) mutations suggest that GAs are synthesised in both t he embryo/endosperm and testa and that the expression of Is depends on the tissue and developmental stage examined. These results suggest th at GAs (possibly GA(1) and/or GA(3)) play an important role early in p ea seed development by regulating the development of the embryo and/or endosperm. By contrast, the high GA levels found in wild-type seeds a t contact point (and beyond) do not appear to have a physiological rol e in seed development.