Fuente: WIPO "biotechnology" The present invention provides means and methods of transforming bacteria, fungi including yeast, animal and plant cells, seeds, tissues and whole plants in order to yield transformants capable of expressing β-carotene 15, 15′ dioxygenase and accumulating vitamin A aldehyde. The present invention further provides means and methods to biotechnically produce retinoids using cells, tissues, organs or whole organisms which natively or after transformation accumulate β-carotene or which take up β-carotene from the medium. The present invention also provides DNA molecules encoding β-carotene 15, 15′ dioxygenases derived from different sources and taxonomic groups of living organisms designed to be suitable for carrying out the method of the invention, and plasmids or vector systems comprising said molecules. Furthermore, the present invention provides transgenic bacteria, fungi including yeast, animal and plant cells, seeds, tissues and whole plants that display an improved nutritional quality or physiological condition and contain such DNA molecules and/or that have been generated by use of the methods of the present invention.