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 stal k is very short and floral organs within the flowers remain undeveloped; pe tal growth is arrested, with the petals being scaly and translucent, the st amens are abortive, the filaments do not elongate, and the pollen does not mature. Sepals and pistils are also underdeveloped. All of the above defect s 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 norm alize not only plant height but also development of floral organs, thereby yielding good seed set from self-pollination. There were appreciable differ ences 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 G A(4) was used to determine an optimal GA dose, the following pattern emerge d: filament elongation and pollen development, 1-10 ng; petal and pistil gr owth, 1 ng; sepal growth, 0.1 ng; papilla elongation, 0.01 ng. However, one application at these doses was insufficient to normalize the flowers, whic h were formed one after another, and a continuing supply of GA at the optim al dose was required for normal flower development and seed set. We conclud e from this work that GAs play an essential role in the development of flor al organs of Arabidopsis and that petals and stamens (filaments and pollen) in particular develop normally only when GAs are present at the optimal le vel.