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Why a natural rose could not have the true blue colour?
The rose is the world's most popular flower. However, despite sustained efforts made by rose breeders, amateurs and professionals, the rose displays so many beautiful colours except blue!
The colours of flowers are due to their capabilities of biosynthesizing
the pigments.
There are majorly two types of flower pigment:
Flavonoids - contribute to a range of colours from yellow to red to blue.
These flavonoid molecules are anthocyanins which are glycosylated derivatives of cyanidin
(red), pelargonidin (brick red), delphinidin (blue), petunidin and malvidin. They are
localised in the vacuole.
Carotenoids - commonly the pigmant for yellow to orange flowers.
Flower colour is also influenced by co-pigmantation with colourless flavonoids, metal complexation, glycosylation, acylation, methylation and vacuolar pH.
The biosynthetic pathway of the flavonoid pigmants is well established.
"Flavonoid 3', 5'- hydroxylase"
is one of the key enzymes involved in this pathway.
Unfortunately the rose is deficient of this key enzyme and incapable to
synthesize the major blue pigment delphinidin.
This is an example of the approaches of the classical breeding techniques have been limited by the constraints of a particular species gene pool. That's the natural reason of rarely to have a single species displaying a full spectrum of coloured varieties.
Another important factor that we should not forget is: delphinidin is
located in the vocuole of the petal epidermal cells in an alkaline
pH 6 -7. But the vacular pH of rose is generally pH 4.5 - 5.5
"Blue gene"
To develop blue varieties of the major cutflower species like rose,
chrysanthemum, carnation and gerbera
by new biotechnology is an active research area in the flower industry.
They called those genes which may lead to the synthesis of the blue
pigment in flowers as "blue genes".
To overcome the natural gene pool limitation and develop the true blue rose, a rational solution is to isolate the "blue gene" from other beautiful blue flowers and put it into rose to help the biosynthesis of blue pigment. Hopefully this new strategy wil turn the "blue rose" from a dream into reality.
The genes of "flavonoid 3', 5'- hydroxylase" have been
identified and cloned from a number of plants.
Scientists have been using the one from the petunia to make a blue rose.
How to put the petunia "blue gene" into the rose? Genetic engineering provides the facilities for the gene transfer in plants.
Plant gene transfer methods
To introduce foreign genes into a plant using two types of transformation method:
(A) Agrobacterium - mediated :
Agrobacterium tumefaciens and Agrobacterium rhizogenes
are soil-borne, bacterial plant pathogens. These soil bacterium infect the plant and
transfer several of its genes to the infected plant cells, resulting in high rate of plant
cell division and the gall formation. This naturally occuring genetransfer system have
been exploited by scientists who have disarmed the Agrobacterium by
delete their tumorigenic genes and engineered them. These Agrobacterium
become widelt used safe vectors for plant transformation.
(B) Uptake of naked DNA : Including electroporation, PEG-meduated and
particle gun methods.
The petunia "blue gene" was cloned into a binary plasmid
vector, then introduced into the Agrobacterium tumefaciens strain.
The co-cultivation of the "blue gene" containing Agrobacterium
strain with a rose explant bringing the "blue gene" into the rose
genome.
The regenerating explants were cultured in the presence of a selectable
marker (the select marker gene can be an antibiotic or herbicide resistance gene
which was co-transferred with the "blue gene". The transgenic cells, shoots and
rooted-shoots are selected.
The transgenic rose is screened for the expression of the new "blue
gene".
Growing progeny of the transgenic rose and determine the inheritance of
the introduced "blue gene".
"Transgenic blue rose"
The scientists in Florigene (Calgene Pacific) have been working on the development of the transgenic blue rose for several years. They transferred the "flavonoid 3', 5'- hydroxylase" gene from petunia to the hybrid tea rose (Rosa x hybrida) to help the rose synthesize delphinidin. A selectable marker gene of antibiotic kanamycin or herbicide chlorsulfuron resistance was transferred together with the "blue gene".
The Genetic Manipulation Advisory Committee (GMAC, Australia) had
announced a Planned Release
of approximately 1200 "transgenic blue roses" from Florigene
(PR-35, GMAC). The expected date of release was; "Summer of 1994/1995 - end of 1997.
This glasshouse trial was aimed to test the growth and productivity of the
transgenic roses under the conditions of commercial rose flower production. Some of the
transgenic plants will also be used as a pollen source to fertilise non-transgenic plants,
in attempts to introduce the "blue gene" into other cultivars.
To develop the stable species of true blue roses will take a long period of time. However the genetic engineering technology might open a new avenue of adding a million beautiful blue roses into our gardens in the next century.
Long vase life flowers
Our knowledge of the genes controlling flower development is expanding fast.
Since 1995, Florigene have already marketed two types of transgenic carnation (Dianthus caryophyllus):
The white carnation lacks delphinidin sysnthesis, after it accepts two of the anthocyanin biosynthesis genes ("flavonoid 3'5' hydroxylase" and "dihtdroflavonol reductase"), the transgenic carnation produces delphinidin and shows a unique violet/mauve colour.
Another transgenic carnation has long vase-life.
After being harvested, flower death is triggered by production of a
gaseous hormone, ethylene.
By transfering a second copy of ACC synthase gene, the production of ACC
synthase in the transgenic carnation was suppressed. And the plants do not synthesize
ethylene.
Hence this new type of long vase-life carnation flowers will stay fresh in
your home for much a longer time.
Who knows, perhaps the long vase life roses are on the way.
Finally I have heard good news: Dr. Steve Chandler
of Florigene said recently that they expect a prototype of true blue rose to be developed
in 1998 or 1999.
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