A DNA encoding a neoxanthin cleavage enzyme used for improving stress tolerance in a plant, a method for increasing stress tolerance in a plant by introducing the DNA into the plant, and a transgenic plant into which a neoxanthin cleavage enzyme gene is introduced, are provided. A DNA used for reducing stress tolerance in a plant, a method for decreasing stress tolerance in a plant by introducing the DNA into the plant, and a transgenic plant into which the DNA is introduced, are also provided. The present invention enables creating a plant in which stress tolerance has been increased or decreased.