Chapter
16
Developments
in Plant
Sciences
Learning Objectives
1. Explain the importance of DNAbased biotechnology in agriculture
Offical
TMG
Instructor
Copy
2. Explain the fundamental concepts
of genetic engineering in plants
3. Discuss economically important
plant traits that have been modified
or enhanced by biotechnology
4. Discuss the use of tools and
techniques used for the genetic
modification of plants
5. Discuss some of the social and
ethical issues related to the
genetic modification of plants
Developments in Plant Sciences
P
lant domestication was developed when
humans noticed desirable traits in wild
plants and began cultivating for those
specific traits. One of the earliest known examples of this was the cultivation of wheat and
barley in the Middle East in the eighth millennium BC. Another early example of this was
the domestication of rice in China and southeastern Asia in 5500 BC. Essentially, during
those times, and up until the relatively recent
past, people were selecting “good” genes and
dismissing “bad” genes without even knowing
that something called “genes” existed. With
this early form of “active” selection, agriculture
developed. Agriculture was thought to have
developed 10,000 to 12,000 years ago in the
regions of present day Syria, Turkey, Iraq, Iran
and northern Egypt.
The Beginning of Plant
Breeding
Present day agricultural methods have improved tremendously since the first days of
agriculture. Many advances in plant breeding
have come as a result of research performed
in the 19th century by a Czechoslovakian
monk named Johann Gregor Mendel. In 1866,
he published an important work on classical
genetics. Most people remember the “Mendel’s peas” lesson from school days past. In
this experiment, Mendel crossed plants with
contrasting traits, for example short versus tall.
He then hypothesized that “elements” were
Figure 1. Crop Research in Soybean
responsible for contrasting traits and that these
elements, now known as genes, do not blend
to form a mixed trait in the next generation.
Rather, the elements, or genes, act independently of one other. His experiments with
crossing pea plants and analyzing the physical
traits of offspring laid the foundation for our
present day understanding of how genes are
transmitted from one generation to the next.
For his contributions to the field, Mendel is
known as the “father of genetics.”
As stated above, Mendel’s research laid the
foundation for plant breeding. Plant breeding is when two different plant lines with
favorable characteristics are crossed and then
have their offspring screened for the desired
characteristics-thus the term hybrids. As plant
breeding continued to develop as a means to
change crop genetics, it laid the foundation for
modern day plant biotechnology.
Introduction to
Biotechnology
Biotechnology is the modification of living
organisms to create useful products. Plant
biotechnology involves the altering of genes
and plant cells for the purpose of modifying
and enriching economically important traits.
The term “biotechnology” is relatively new, but
humans have been applying the principles of
basic biotechnology for hundreds of years. The
utilization of microorganisms to make bread,
wine and beer is a simple form of biotechnol-
Hybrids
Many of the highest-yielding varieties
of crops in the world, such as corn, are
hybrids. Modern-day corn was generated through years of breeding from its
ancestor teosinte, which still grows in the
highlands of Mexico. While teosinte is a
different-looking plant than corn, they
are both members of the same biological species, Zea mays. In contrast to corn,
teosinte is a spindly grass plant without
ears.
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A Timeline of Biotechnology
▪▪ 10,000 BC: Yeast is used to make food items such as wine and bread
▪▪ 8,000 BC: Early farmers begin cultivating the land and saving seeds to grow for the next season
▪▪ 1866: Gregor Mendel publishes his work on the heredity of traits in plants
▪▪ 1908: The first corn hybrid is produced in the USA by G. H. Shull of the Carnegie Institute
▪▪ 1919: Hungarian engineer Karl Ereky coins the term “biotechnology”
▪▪ 1953: Watson and Crick propose the double helical structure of DNA
▪▪ 1982: The first transgenic plant is produced
▪▪ 1988: Cornell scientists invent the gene gun
▪▪ 1994: The first genetically modified food crop, the FlavSavrTM is approved by the FDA for human consumption
▪▪ 1995-1996: Biotechnology-derived soybean, corn and cotton are approved for sale and cultivation in the United States
▪▪ 2003: Over 38 trillion transgenic plants have been grown in the United States since 1988
▪▪ 2004: The National Center for Food and Agriculture Policy reports that the use of biotechnology in agriculture generated a 2.5 billion dollar increase in farm income, with 14 billion more
pounds of food produced and 163 million pounds less of pesticides applied in the fields
ogy. However, today there is the capacity
to practice biotechnology on a much more
controlled and precise scale. Many scientists
believe that in the future, biotechnology will
be necessary to feed the world’s growing
population without harmful effects on the
environment.
The Green Revolution
The Green Revolution of the 1960s and 1970s
was an effort by the Rockefeller and Ford
Foundations to boost crop production in developing countries. Dr. Norman Borlaug2, an
American scientist, played a pivotal role during
this time by developing high-yielding varieties
of dwarf wheat and other crops by conventional breeding. Simply, the result of his experiments was that millions of lives were saved
from starvation in India, Pakistan and other
countries that routinely suffered from terrible
food shortages. Dr. Borlaug was awarded the
Nobel Peace Prize in 1970 for this astonishing
achievement and service to humanity; the only
time a plant scientist has won this prize.
Since the Green Revolution, world population growth has increased exponentially, and
is expected to exceed 10 billion people by
20503. Unfortunately, agricultural production has grown at a much slower rate. Thus,
in the future, it will be a challenging task to
meet the dietary needs of the earth’s popula-
tion. Although conventional plant-breeding
methods have increased crop yields, there are
limitations. For example, it can take up to 10
years to breed out undesirable traits, a process
called backcrossing, to develop a desirable hybrid line. Additionally, there are limits to the
available genes resident in each crop that can
be manipulated for crop improvement.
The bright side is that science is progressing. DNA-based plant biotechnology can reduce the time it takes to create crops with new
or improved traits. In this approach, a gene
that controls a desired trait is taken from one
organism and transferred into a crop plant’s
genetic make-up, or genome. Because the
technique is precise, it takes less time to release
a crop with the desired traits. As did the first
revolution, DNA-based biotechnology is helping to revolutionize agriculture. Plant biotechnology uses well-understood lab techniques
to transfer a gene or genes from any organism
into plants. The new genes then essentially
become part of plant genome and are inherited
to offspring, just as if they were plant genes
all along. To summarize, while the Green
Revolution primarily addressed crop yield; the
biotechnological revolution has the potential to
improve food quality as well as yield.
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Difficulties of Plant Breeding
Traditional plant breeding is time-consuming and labor-intensive which is a
problem as the pressure mounts on agricultural producers to create more food
for more people in less time.
Trait Enhancement and
Modification of Plants
Plants are continually exposed to both biotic,
living, and abiotic, non-living, stresses. From
these stresses, plants have no option but to
adjust to the stress or die. Reports suggest
that there can be between 65-87 percent loss
in crop productivity due to biotic and abiotic
stresses. One of the goals of plant biotechnology has been to develop stress-tolerant plants.
Specifically, researchers are developing plants
that have increased tolerance to: drought, salt,
cold, insects, diseases and herbicides. They are
also developing plants that have: traits for human health, increased nutritional quality, the
ability to developed into a vaccine and modified flowers.
Figure 2.
Dr. Max Cheng, University of Tennessee Researcher,
genetically modifies plants that have invasive
characteristics to be sterile.
Drought and Salt Tolerance
Drought is one of the major problems responsible for damage to crops and loss of productivity. Fortunately, in some plants, scientists have
identified chemicals known as osmoprotectants
that help protect plants against drought stress.
Biosynthetic pathways of some of the osmoprotectants have been identified and plants
have been modified to produce osmoprotectants. However, drought tolerance has proven
to be a difficult modification because a plant
that is drought-tolerant in the lab might not be
tolerant in the field.
Cold Tolerance
Low temperatures may cause stress for plants
not tolerant to cold conditions. In an effort to
better understand the physiology behind the
effects of cold on plants, scientists have been
studying plants that thrive in cold climates.
They have discovered that some freeze-tolerant
plants form ice crystals surrounding the
outside of their cells. This layer of ice appears
to help protect the inside of the cells from
forming ice crystals that would cause death.
Scientists believe that cold-acclimated plants
sense low temperatures and turn on specific
genes like those responsible for ice barrier
formation. Efforts have been made to incorporate cold-protection genes into crops such
as canola, potato and flax. Recently, scientists
modified the plant cell membrane to improve
freeze-tolerance, indicating that an effective,
commercial, freeze-tolerant plant is feasible.
Insect Resistance
From biblical locust plagues to boll weevils,
farmers have experienced large economic losses
from crop-eating insects. To control insects,
farmers often resort to chemical insecticides.
Unfortunately, many insecticides are harmful
to human health. Additionally, the accumulation of insecticides in ecosystems can be problematic. As a result, there have been efforts
worldwide to produce genetically engineered
crops that are resistant to insects. In other
words, to produce plants that produce their
own insecticide. The most successful development so far has been the creation of Bt plants.
Bacillus thuringiensis, better known as “Bt,”
is a naturally occurring bacterium found in
the soil that produces a toxin lethal to certain
types of insects. Genes coding for Bt toxins are
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well characterized and have been transferred
into several types of plants.
The amazing characteristic of Bt toxins
is their ability to target specific pests. For
example, one type of Bt toxin kills only specified caterpillars and no others. Bt toxins do
not harm people, birds, fish or wildlife. Many
organic farmers and homeowners have used Bt
sprays to control insects for about a half a century. Thus, much is known about the effects,
and it is considered safe.
When the gene responsible for producing Bt toxin protein is incorporated into crop
plants through genetic engineering, the Bt
gene triggers production of a toxin. When the
insect larvae feed on transgenic Bt plants, the
toxin enters the gut of the insect, binds with
specific Bt receptors, causes gut leakage and
eventually death. This technology has been
very successful in protecting plants against insect damage. For example, more than half the
cotton and nearly one third of the corn grown
in the U.S. produce Bt. Bt technology has
successfully controlled European corn borer
and cotton boll worm, decreasing the need for
insecticidal sprays, especially in cotton.
Biotechnology vs. Insecticides
Millions of gallons of chemical insecticide spray have been replaced annually
in the United States due to biotechnology yielding an astounding environmental benefit.
Disease Resistance
Plants are continuously challenged by pathogens such as bacteria, viruses and fungi. To
survive these attacks, plants have developed
their own defense systems. However, many of
these are weak. Strong disease resistance does
exist in nature, but not always in the desired
plants. Therefore, farmers and gardeners must
apply chemical pesticides when desired plants
are infected with diseases and unable to defend
against them.
Despite advances, disease resistant modifications to crops have been slow to succeed.
Plants like rice, tobacco and canola have been
modified with plant genes to help protect
them against a type of soil-borne fungus
called Rhizoctonia solani. Additionally, some
tomato plants have been modified for resistance against tobacco mosaic virus (TMV) and
potato and rice were engineered for resistance
against nematodes. However, none of these
applications have made it to commercial
release for various reasons. The most successful
disease-resistant plant produced through biotechnology is a virus-resistant papaya, presently grown commercially in Hawaii. Produced by
a research team led by Dr. Dennis Gonsalves,
this virus-resistant variety is believed to have
saved the Hawaiian papaya industry.
Herbicide Resistance
Weeds rank highly as one of growers’ worst
enemies, and herbicide application is the most
popular method for their control. Herbicides
are applied either to the soil or sprayed onto
plant leaves, depending on the types of weeds
that need to be eradicated. The main problem with herbicide application is associated
with the residual effects on the soil. Residual
herbicide in the soil can damage other sensitive crops in the crop rotation system as well as
contribute to pollution.
Herbicide-tolerant crops are useful because
they allow farmers to control a wide range
of weeds with no damage to the crops themselves. Non-selective herbicides can be applied
to fields planted with transgenic herbicidetolerant crops without any damage to those
crops. Examples of herbicide tolerant crops are
Roundup Ready ® cotton and Roundup Ready ®
soybeans. Roundup Ready ® soybeans are
grown in more than two-thirds of the soybean
fields in the U.S.
Traits for Human Health
Stress tolerance is only one aspect of useful
crop modification being researched by scientists. There is also a growing interest in creating crops with enhanced nutritional qualities.
In addition, some researchers are finding ways
of providing edible vaccines.
Edible Vaccines
Vaccines are molecules that trigger the human
immune system to attack invading pathogens.
The development of vaccines has changed the
way people experience disease. Because of
vaccines, smallpox, polio and whooping cough
are virtually non-existent in the U.S. However,
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Trans Fats
Trans fat is monounsaturated or polyunsaturated fat that is altered
by partial hydrogenation. The process of partial hydrogenation
forces oils that are naturally liquid at room temperature to become
solid, thereby modifying the fat so that it is similar to saturated fat.
While trans fatty acids are considered unsaturated by chemical
definition, the transformation is so severe that trans fats cannot be
legally labeled as monounsaturated or polyunsaturated on packages. However, the FDA only requires that saturated fat be labeled on
food products and limits the extent to which items can be labeled
as low cholesterol. Trans fat does not need to be labeled. Therefore,
a company is able to label their product cholesterol free when in reality, the product may contain a substantial amount of cholesterol
by means of trans fat. In response to this, laws regarding labeling
for trans fats are being examined.
due to the lack of infrastructure and prohibitive costs in many parts of the world, vaccine
availability may be limited or completely
unavailable to some individuals. In developing countries, people face life-threatening
diarrheal diseases at a much higher frequency
than in the U.S. Therefore, there is great need
to develop vaccines against such diseases and
deliver them economically.
Perhaps food plants can help. Possibilities
exist to produce vaccines in plants by genetically modifying them with antigens that, when
ingested, deliver the vaccination. Antigens
in the plants would trigger the formation of
antibodies in human cells, like vaccines, providing immunity and thus eliminating costly
vaccination by injection. Currently, tobacco
and lettuce plants have been modified with a
hepatitis vaccine and vaccines against footand-mouth and diarrheal diseases are currently
in development.
Enhanced Nutritional
Quality
Nutritionally enhanced food crops may be particularly useful in developing countries where
the availability of nutritious foods is a serious
issue. As an illustration, night blindness is a
common condition found amongst children
who are deficient in vitamin A. Dr. Ingo
Potrykus, from the Swiss Federal Institute
of Technology, and his colleagues developed
a type of rice with high vitamin A content,
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popularly known as “golden rice.” This rice was
genetically modified to produce beta-carotene,
a precursor of vitamin A. The name “golden
rice” comes from the yellow-gold color of the
enhanced rice grain. The current goal is to incorporate golden rice into the local rice breeding lines of developing countries at no cost to
their farmers. If the effort to distribute and
cultivate golden rice in developing countries is
successful, it will be an outstanding example of
biotechnology’s application for humanitarian
purposes.
Other crops have also been genetically
modified for enhanced nutritional qualities.
Canola plants were engineered to contain no
trans fats-unsaturated fats. Trans fats are a
current topic of concern as medical studies
have shown them to be responsible for negatively affecting the “good” fat levels in humans.
Canola Oil: The Good the
Bad and the Ugly
Peanut oil comes from peanuts and
soybean oil comes from soybeans. However, there is no such thing as a canola.
Canola is a marketing name derived from
“Canadian-oil.” Canola oil comes from
the rapeseed plant (Brassica napus). It belongs to the mustard family, which also
includes turnips and broccoli.
As we know it today, canola oil is the
result of the hybridization and genetic
modification of the rapeseed plant to
breed out its undesirable taste and its
hazards to health. Because canola oil hydrogenates better than corn or soybean
oils, it is often the first choice of processors. However, when it is hardened
through hydrogenation, as it often is
when used in food processing, the trans
fat level can go as high as 40 percent.
This is desirable for the food industry because higher levels of trans fat translates
to longer self life for processed food, and
greater profits for the food industry. For
more information on this topic, please
visit the Natural News website. The link is
posted at the end of this chapter.
On the Lighter Side-Altered Flowers
Horticultural crops have also been engineered
for targeted trait enhancement and modification. An Australian company named Florigene
was able to clone a ‘blue gene’ and genetically
transform carnations to produce blue petals. According to Florigene, this was the first
case of any carnation flower expressing a blue
color hue. They credit themselves with having
produced the world’s first genetically modified
flower.
Regulating Transgenic
Plants
Either university or governmental officials
regulate all biotechnological manipulations.
In every university, there is an institutional
biosafety committee that oversees laboratory
work. This committee is comprised of experts
who ensure that experiments are done safely.
The University of Tennessee is no exception in
this regard. If researchers or companies wish to
test transgenic plants in the field or ship them
between states, the USDA Animal and Plant
Health Inspection Service (APHIS) becomes
involved, along with the Tennessee Department of Agriculture. Applications must be
filled out, and certain restrictions often apply.
Additionally, agriculture officers frequently
inspect field sites to assure that correct procedures and safeguards are in place. If Bt genes
or other pesticidal genes are put into plants,
then the EPA has regulatory authority as well.
The FDA and EPA make sure transgenic food
is safe to eat.
As indicated by the above information,
there is a long chain of procedures that must
take place before any transgenic plant is grown
commercially. In fact, it often takes several
years to gain approval, and sometimes certain
plants are not approved. It has been often
said that transgenic plants are the most tested
plants in the history of the world.
Figure 3. Regulating Transgenic Plants
Current and Potential Benefits
for Plant Biotechnology
Current and potential benefits of plant
biotechnology include:
▪▪ Edible vaccines
▪▪ Enhance nutrition
▪▪ Aesthetics
▪▪ Resist herbicides
▪▪ Resist diseases
▪▪ Resist drought
▪▪ Resist Insects
▪▪ Increase salt tolerance
▪▪ Increase cold tolerance
▪▪ Increase the genetic diversity of
species populations
▪▪ Increase to the efficiency of the
ecosystem services provided by
the other organisms. For example,
modifying trees to have hardier
root systems to withstand frequent
flooding
Public Perception of
Transgenic Plants
There is an ongoing debate regarding the development of genetically modified crops, their
consumption by humans and their potential
ecological effects. The major controversies
surrounding genetically engineered crops and
foods commonly focus on either: the longterm health effects for anyone eating them;
environmental safety; labeling and consumer
choice; intellectual property rights; ethics; food
security; poverty reduction; environmental
conservation; and potential disruption, or even
possible destruction, of the food chain. Some
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Figure 4.
Reasons People May Oppose
Plant Biotechnology:
Crop breeding of
Switchgrass for Biofuels
Production in Tennessee
▪▪ Lack of information
▪▪ Perceive it as “unnatural”
▪▪ Ethical reasons
▪▪ Environmental concerns
▪▪ Religious reasons
▪▪ Perceived potential for significant
unforeseen consequences
unease is due to a general lack of understanding of the science behind the technology. Most
information the public receives about genetically modified organisms (GMOs) is spun
by media frenzy and environmental activist
organizations that are opposed to GM plants.
Those opposed to plant biotechnology argue
that DNA-based genetic modification of plants
is abnormal, or going against nature. However,
virtually none of the plants we eat are genetically natural. Most of the cultivated crops we
consume today are the result of 10,000 years
of selection, domestication and breeding –in
other words “engineering.”
Corn’s ancestor, teosinte, has few similarities with modern-day cultivated corn. This
example proves how humans have manipulated
the genes of wild plants for thousands of years
to develop food crops with better qualities.
Another example is the tomato. The large,
red tomatoes we buy at the grocery store and
grow in our gardens exist nowhere in nature.
They are the result of years of breeding and
selection. Wild tomatoes are tiny greenishyellow things that most people would not care
to eat. Consider the many choices of fruits
and vegetables found in grocery stores today.
These foods could be considered “unnatural”
in the sense that they are also the results of
thousands of years of breeding, crossing and
moving genes from one population to another.
Some concerns about genetic modification
are legitimate. For example, there is a concern
that crops modified to resist herbicidal sprays
may pass the trait for herbicide resistance to
weedy relatives, resulting in new weed problems. Research is currently being performed
in this area to conclude how likely it would
be for this to occur. Indeed, transgene flow
from crops to wild relatives has been one of
the biggest concerns among scientists and
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environmentalists. Thus, it is doubtful that
crops with noxious weedy wild relatives will be
engineered. No one in biotechnology wants to
create new weed problems.
Summary
People eat products from genetically engineered foods every day. For example,
Americans have been consuming genetically
modified soybean oil and corn products for
some time now. To date, there have been no
scientific reports indicating that genetically
modified foods pose a threat to human health.
Additionally, the application of biotechnology
in agriculture promises sustainable production
with higher yields and less poisonous chemicals in the food and the environment.
However, despite its many current and
potential benefits to the earth and to humans,
biotechnology is not a cure-all. Also, it has not
been universally understood and accepted by
the general populace. There are social, political
and economic issues associated with the use
of any new technology. Everyone in the world
might someday enjoy the benefits of plant
biotechnology, but seeds produced via patented technology may be initially out of reach
for poor farmers in the developing countries.
As biotechnology progresses, however, it will
certainly enhance agricultural productivity and
sustainability around the world by providing
environmental and dietary benefits.
This chapter has taught you the importance
of DNA-based biotechnology in agriculture,
the fundamental concepts of genetic engineering in plants, the economically important plant
traits that have been modified or enhanced by
biotechnology, the use of tools and techniques
used for the genetic modification of plants, and
some of the social and ethical issues related to
the genetic modification of plants.
Terms to Know
Abiotic
Biotic
Biosafety
Biosynthetic pathways
DNA
Gene
Genome
Osmoprotectants
Transgene flow
Transgenic plants
Yield
Test Your Knowledge
1. Who was the “father of genetics” and
when did he publish his works on classic
genetics?
2. What is the precursor to plant biotechnology ? Give an example of a modern crop.
3. What is the amazing characteristic about
insect resistant Bt developed trangenially?
4. What is “golden rice”?
5. Name two reasons one may oppose plant
biotechnology.
Resources
America Society of Plant Biologists
aspb.org
Council for Biotechnology Information
whybiotech.com
Greenpeace
greenpeace.org
National Agricultural Library. Contains various
outside links for more information about
genetically modified crops
nal.usda.gov/bic
National Center for Food and Agriculture
Policy
ncfap.org:
Natural News
naturalnews.com/026365_canola_oil_
food_health.html
United States Department of Agriculture
usda.gov/agencies/biotech
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