Abstract: The invention relates to cassettes for the expression of storable gene products in leaves and specifically in seeds, especially single-chain antibody fragments in leaves and seeds of transgenic tobacco and pea plants. The fields of application of the invention are biotechnology, medicine (diagnosis and therapy), foodstuffs and plant control and agriculture. The expression cassette of the invention comprises constitutive or seed-specific promoters, the LeB4 signal peptide, a gene to be expressed and an ER retention signal. Preference is given to an expression cassette containing the CaMV 35S promoter as the constitutive promoter, the gene for a single-chain antibody fragment as the gene and the amino acid sequence KDEL as the ER retention signal.