Abstract: The present invention relates to methods for the cryopreservation of transformed and non-transformed cells. Also provided by the subject invention are methods of recovering cells that have been cryopreserved. Cultures of cells that have been successfully recovered from cryopreservation are also provided.

Abstract: The subject invention provides totipotent, chlorophyllous, cell cultures of maize. In addition, the methods of producing such cultures are applicable to other related species, including cereals such as rice, oats, barley, and heat. The subject cultures are valuable for herbicide studies, studies for enhancing photosynthesis, and genetic manipulation, such as plastid transformation. The methods of the subject invention are capable of providing high percentages of totipotent cells. These cells are capable of sustained cell division and are competent for regeneration over long periods; they provide high-quality target tissue for nuclear and organelle transformation. The invention also describes methods for the introduction of heterologous DNA into the chloroplast genome. The present invention also provides methods, vectors, and gene constructs for enhancing expression of a recombinant nucleic acid sequence in transgenic plants and plant tissues.