A method for producing a transformed plant cell, the method comprising the step: (i) transforming the plant cell with a genetic construct, wherein the genetic construct comprises first and second homologous recombination elements flanking a Transformation Cassette, wherein the nucleotide sequences of the first and second homologous recombination elements are selected such that the Transformation Cassette is specifically targeted to one or more selected plastids and wherein the first and second homologous recombination elements direct the integration of the Transformation Cassette into the genome of the one or more selected plastids which are present in the plant cell, wherein the Transformation Cassette comprises: (a) a first promoter which is operable in said plant cell, (b) an Excision Cassette, (c) one or more transgenes, (d) a first terminator element, wherein the Excision Cassette comprises: a first site-specific recombination element, an optional second promoter a nucleotide sequence encoding a plant-hormone biosynthetic polypeptide, wherein the plant-hormone biosynthetic polypeptide is IPT (isopentenyl transferase), a second terminator element, a second site-specifc recombination element, wherein the first and second site-specific recombination elements are capable of being recognised by a recombinase, wherein the method additionally comprises the step: (ii) selecting for transformed plant cells on media which is lacking cytokinin. (i) transforming the plant cell with a genetic construct, wherein the genetic construct comprises first and second homologous recombination elements flanking a Transformation Cassette, wherein the nucleotide sequences of the first and second homologous recombination elements are selected such that the Transformation Cassette is specifically targeted to one or more selected plastids and wherein the first and second homologous recombination elements direct the integration of the Transformation Cassette into the genome of the one or more selected plastids which are present in the plant cell, wherein the Transformation Cassette comprises: (a) a first promoter which is operable in said plant cell, (b) an Excision Cassette, (c) one or more transgenes, (d) a first terminator element, wherein the Excision Cassette comprises: a first site-specific recombination element, an optional second promoter a nucleotide sequence encoding a plant-hormone biosynthetic polypeptide, wherein the plant-hormone biosynthetic polypeptide is IPT (isopentenyl transferase), a second terminator element, a second site-specifc recombination element, wherein the first and second site-specific recombination elements are capable of being recognised by a recombinase, wherein the method additionally comprises the step: (a) a first promoter which is operable in said plant cell, (b) an Excision Cassette, (c) one or more transgenes, (d) a first terminator element, a first site-specific recombination element, an optional second promoter a nucleotide sequence encoding a plant-hormone biosynthetic polypeptide, wherein the plant-hormone biosynthetic polypeptide is IPT (isopentenyl transferase), a second terminator element, a second site-specifc recombination element, (ii) selecting for transformed plant cells on media which is lacking cytokinin.