Role of gibberellins in the development of floral organs of the gibberellin-deficient mutant, ga1-1, of Arabidopsis thaliana

The gibberellin-deficient mutant, ga1-1 (NG5) of Arabidopsis thaliana, when induced by 16-h-long days, will form floral buds. However, the flower stalk is very short and floral organs within the flowers remain undeveloped; petal growth is arrested, with the petals being scaly and translucent, the stamens are abortive, the filaments do not elongate, and the pollen does not mature. Sepals and pistils are also underdeveloped. All of the above defects of this mutant can be completely eliminated if certain gibberellins (GAs) are applied to the young floral buds. That is, the applied GA acts to normalize not only plant height but also development of floral organs, thereby yielding good seed set from self-pollination. There were appreciable differences in the efficacy of different GA structures in normalizing the various floral organs. For seed production, the order of efficacy was 2,2-dimethyl GA(4) > GA(7) > GA(3) = GA(4) > GA(1) > GA(5) = GA(9). When 2,2-dimethyl GA(4) was used to determine an optimal GA dose, the following pattern emerged: filament elongation and pollen development, 1-10 ng; petal and pistil growth, 1 ng; sepal growth, 0.1 ng; papilla elongation, 0.01 ng. However, one application at these doses was insufficient to normalize the flowers, which were formed one after another, and a continuing supply of GA at the optimal dose was required for normal flower development and seed set. We conclude from this work that GAs play an essential role in the development of floral organs of Arabidopsis and that petals and stamens (filaments and pollen) in particular develop normally only when GAs are present at the optimal level.