The composition, in accordance with the present invention, for producing a plant body having an improved sugar content includes glutathione, a polynucleotide encoding γ-glutamylcysteine synthetase, or a polynucleotide encoding glutathione-binding plastid type fructose-1,6-bisphosphate aldolase. The composition preferably includes oxidized glutathione. This allows provision of a composition for easily producing a plant body having an improved sugar content.
