Basel, Switzerland
November 27, 2007
By Tanuja Rohatgi,
Checkbiotech
Climate change is a major issue
these days that has awaken the concerns of the world as natural
catastrophes intensify. One of its most common catastrophes is
drought. However, now, a team of researchers is nearing a
solution.
Water is not only needed to drink, but to cultivate crops too.
In some parts of the world, occurrence of drought year after
year is having a disastrous effect on the agricultural
production.
To circumvent the problems caused by drought, a team comprising
of scientist from United States, Japan and Israel have
successfully generated drought-tolerant plants.
The ground-breaking study led by
Dr. Eduardo Blumwald’s
laboratory at the University of
California at Davis will be published on December 4 in the
scientific journal the Proceedings of the National Academy of
Science (PNAS).
Plants are receptive to the environment in which they grow and
have evolved ways to respond or adapt to the changes in their
surrounding. To counter the problem of water shortage due to
drought conditions, plants usually close the pores in their
leaves to avoid water loss.
In addition, during drought conditions, the plants will shed
leaves to help prevent the further loss of water. While the
leave shedding strategy helps them under drought conditions, it
results in reduce yield of crops, which is of no consolation for
farmers.
Dr. Blumwald and his team worked on the hypothesis that it
should be possible to delay the drought-induced shedding of
leaves. Senescence (shedding of leaves) is a built-in survival
mechanism, which is normally activated in plants during drought
conditions or change of season. Switching-on this signal helps
plants adapt internally and withstand the stress caused by the
drought conditions.
To generate drought tolerant transgenic plants, Dr. Blumwald and
his team introduced a gene for isopentenyltransferase (IPT)
enzyme. This was essential, because IPT leads to an increased
amount of a plant growth regulator called cytokinin, which helps
prevent plant senescence.
In an additional step, the IPT gene was coupled with another
gene, which is activated during late maturation and/or stress
and decreased during the onset of senescence. This strategy was
aimed to make sure that the growing plant has enough cytokinin
when it is about to enter the senescence stage.
Testing of transgenic plants
Once the transgenic tobacco plants were grown, the research
teams then assessed the health of the plants in comparison to
wild-type tobacco plants. The transgenic plants grown in
greenhouse showed no difference in their appearance when
compared with the wild-type tobacco plants. Also, they showed a
normal development cycle including flowering.
Next, the plants were tested for their drought tolerance. Unlike
the wild-type plants, which wilted and senesced progressively
under drought conditions, the transgenic plants were only
partially wilted, and showed no drought-induced senescence.
“While watering of wild-type plants could not recover them from
drought stress, transgenic plants recovered completely and
showed vigorous growth,” explained Dr. Blumwald. “Testing of
biomass, soil water potential and water content of the plants
clearly showed the superiority of transgenic plants over the
wild-types during drought conditions.”
Once the testing of basic growth characteristics verified their
hypothesis, the researchers then examined the expression of
certain proteins in different parts of the leaves during varying
experimental conditions. They found that indeed the production
of cytokinin is responsible for the enhanced drought tolerance
in the transgenic plants.
Further, Dr. Blumwald’s research looked at the mechanism behind
the cytokinin-enhanced drought tolerance. Gene expression
profiling is now used on a regular basis to check for change in
gene patterns under different conditions. The genetically
enhanced plants showed an increase in the expression of genes
associated with maintenance of cell integrity during stress. All
these factors confirm that the genetically engineered plants
generated by Dr. Blumwald and his team are fit for drought
conditions.
Equally important is the fact that transgenic plants can retain
their photosynthetic activity - albeit at a reduced level during
drought conditions - while also showing minimal yield loss.
Thus, the strategy of introducing a drought tolerant gene in
plants provides a big ray of hope to farmers who face severe
drought and limited water supply for irrigation.
When asked about the next stage of the project, Dr. Blumwald
told Checkbiotech, “We have developed a number of transgenic
lines of plants expressing our constructs in rice, wheat and
other important crops and are preparing material that will be
tested in the greenhouse and the field.”
Dr. Blumwald understands the reservations that some have towards
genetically modified crops, but adds, “Although this concern is
viable, it will be impossible to keep plants from crossing with
other species (if they are compatible in nature).”
However, he thinks this question is not of great concern where
his plants are concerned, “In general, wild-type species tend to
be much more stress-tolerant than the varieties that we have
developed by breeding in the last 10,000 years.”
Checkbiotech learned that the strategy developed by Dr. Blumwald
and his team can be applied to all crop plants, which is good
news for farmers all over the world and will benefit them all.
Meanwhile, the team is continuing their research to address the
questions concerning quality and taste of fruits and have
obtained interesting preliminary results indicating no major
shift in metabolite profiles of the transgenic fruit compared
with wild-type plants.
When asked if he is confident about the feasibility and economic
viability of growing transgenic crops on a large scale, Dr.
Blumwald emphatically replied, “Absolutely! That is what we are
working towards.”
Tanuja Rohatgi is a Science Writer for Chechbiotech at Basel,
Switzerland .
Source:
Delayed leaf senescence induces extreme drought tolerance in a
flowering plant.
Rosa M. Rivero, Mikiko Kojima, Amira Gepstein, Hitoshi
Sakakibara, Ron Mittler, Shimon Gepstein, and Eduardo Blumwald
PNAS. Dec 4, 2007. 104(49): 19631-19636.
ABSTRACT
Drought, the most prominent threat
to agricultural production worldwide, accelerates leaf
senescence, leading to a decrease in canopy size, loss in
photosynthesis and reduced yields. On the basis of the
assumption that senescence is a type of cell death program that
could be inappropriately activated during drought, we
hypothesized that it may be possible to enhance drought
tolerance by delaying drought-induced leaf senescence. We
generated transgenic plants expressing an isopentenyltransferase
gene driven by a stress- and maturation-induced promoter.
Remarkably, the suppression of drought-induced leaf senescence
resulted in outstanding drought tolerance as shown by, among
other responses, vigorous growth after a long drought period
that killed the control plants. The transgenic plants maintained
high water contents and retained photosynthetic activity (albeit
at a reduced level) during the drought. Moreover, the transgenic
plants displayed minimal yield loss when watered with only 30%
of the amount of water used under control conditions. The
production of drought-tolerant crops able to grow under
restricted water regimes without diminution of yield would
minimize drought-related losses and ensure food production in
water-limited lands.
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