After being harvested, carnation flowers have a defined 'vase life', or time for which the flowers will stay fresh prior to beginning to shrink, dry<br>out and die. This senescence process is triggered by production of a gaseous hormone (ethylene) by the flower. Flower death can also be<br>triggered by exposure of flowers to external sources of ethylene, such as fruit and exhaust fumes. Flowers treated with chemicals which either<br>inhibit ethylene biosynthesis by the flower, or prevent the flower responding to ethylene, last longer. At present, the most widely used of these<br>chemicals is silver thiosulphate, a polluting metal salt. <br>Florigene has generated carnation plants which produce flowers that do not synthesise ethylene. As a result, the flowers last much longer<br>without the need to use preservative chemicals. The genetic modification has entailed the addition of a second copy of one of the carnation's<br>own genes, encoding ACC synthase, which, by a process called TranswitchR, acts to suppress the production of the ACC synthase enzyme.<br>The enzyme ACC synthase is a key enzyme in the pathway to ethylene biosynthesis and plants lacking the enzyme do not produce ethylene. As<br>well as the additional copy of the ACC synthase gene, a gene for herbicide resistance has been inserted into the carnation. This gene, which<br>confers resistance to sulfonylurea type herbicides, is only to allow selection of transgenic plants in tissue culture. Such herbicides are not, and<br>will not be, used in the carnation industry. <br>The genetically modified carnation has been trialled under previous planned release proposals in Australia (PR-19, PR-29, and an extension to<br>PR-29). As well, some lines have been trialled in the USA and by Florigene in Holland. Florigene now intends to transport, grow and retail the<br>genetically modified carnation flowers throughout Australia.