Enhanced formation of flowers in salt-stressed Arabidopsis after genetic engineering of the synthesis of glycine betaine

Previously, we showed that transformation with the codA gene for choline oxidase allows plants to synthesize glycine betaine (GB) and enhances their ability to tolerate various kinds of stress during germination and vegetative growth. In this study, we examined the tolerance of transformed plants to salt stress at the reproductive stage, which is the stage at which plants are most sensitive to environmental stress. Salt-shock treatment of wild-type plants for 3 days resulted in the abortion of flower buds and decreased the number of seeds per silique. These deleterious effects were clearly visible 6 days after the termination of salt-shock treatment. Microscopic examination of floral structures revealed that salt stress inhibited the development of anthers, pistils, and petals. In particular, the production of pollen grains and ovules was dramatically inhibited. These effects of salt stress were significantly reduced by transformation with the codA gene, and our observations suggested that the enhanced tolerance of the transgenic plants was a result of the accumulation of GB in the reproductive organs. Indeed, levels of GB in flowers, siliques, and inflorescence apices were about five times higher than in leaves.