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
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
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.