Transgenic Flowers. 

When your tomato or banana fruits turn mushy or if those carnation flowers in the vase droop quickly, blame it on ethylene. This gaseous hormone elicits a cascade of developmental responses in plants resulting in fruit ripening and flower senescence. Biotechnologists have sought to extend the shelf life of fruits and flowers by silencing the genes involved in ethylene biosynthesis. However, such transgenic fruits and flowers still respond to ethylene produced by other plants and begin to decay just like non-transgenic plants. 

Ethylene plays an important role in the senescence of flowers, such as carnation and sweet pea. Ethylene production often increases during the senescence of flowers, and the treatment of flowers with ethylene promotes senescence. Inhibition of ethylene synthesis or action delays the onset of senescence symptoms and increases vase life of cut flowers, thus being of economical importance. Currently, antisenescent preservatives are widely used to lengthen the vase life of cut flowers. There is another option for extending flower longevity, that is, the production of transgenic flowers with reduced ethylene production or ethylene sensitivity. The generation of transgenic carnations showing decreased ethylene production and increa sed flower longevity has recently been reported. However, the source of ethylene is frequently external, and control of ethylene synthesis would not be sufficient to improve vase life. The generation of transgenic plants with reduced ethylene sensitivity has the potential to greatly extend the vase life of the flowers. In this respect, it is desirable to find genes controlling ethylene perception pathways in given plant species. 

A recent report describes a new solution to this problem that entails the use of a hormone receptor gene from Arabidopsis which confers ethylene insensitivity. Tomato fruits ripened very slowly on plants engineered with this gene, while petunia flowers from transgenic plants remained fresh longer than their nontransgenic counterparts. The dominant mutant etr1-1 gene, cloned from Arabidopsis, encodes a protein that alters the perception of ethylene by plant cells and thus makes the plant unresponsive to the hormone. 

University of Florida, introduced this gene into tomato and petunia using Agrobacterium vectors. Transgenic tomato plants exposed to ethylene exhibited a dramatically delayed fruit ripening and senescence compared with those on untransformed plants. Harvested tomato fruits retained their original golden yellow color even when stored for 100 days while the regular tomato fruits soon "turned red, became soft and started to rot". Similarly, petunia flowers with the 'ethylene- insensitive' gene senesced slowly and remained longer on the plant. When exposed to ethylene, the transgenic flowers stayed fresh for nine days in the vase while the untransformed flowers wilted within just three days. 

According to the researchers, the ethylene insensitive gene from Arabidopsis may have to be weakened by molecular alterations to ensure its broad application, because fruits and vegetables eventually must respond to ethylene for ripening to proceed. The use of appropriate promoters may also permit targeted ripening. Industry scientists anticipate that the immediate beneficiary of their finding will be the floriculture business, a multibillion dollar industry worldwide. 

Many chemicals that affect ethylene synthesis or its action, which are currently in use to extend the shelf life of flowers, are being banned because of environmental concerns. The floriculture industry thus may gain substantially from the use of the 'ethylene-insensitive' gene by making their colorful blooms last longer either on plants or in vases. Arabidopsis may never be considered pretty enough to be taken seriously by nurserymen but the Nature Biotechnology study clearly underscores one of the potential pay-offs to agriculture from the investment in research on this humble weed.