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High Tech Harvest
Understanding Genetically Modified Food Plants
By Paul Lurquin
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Modified Food Plants
Paul F. Lurquin
All rights reserved. Printed in the United States of America. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher.
Copyright © 2002 by Westview Press, A Member of the Perseus Books Group
Westview Press books are available at special discounts for bulk purchases in the United States by corporations, institutions, and other organizations. For more information, please contact the Special Markets Department at the Perseus Books Group, 11 Cambridge Center, Cambridge MA 02142, or call (617) 252-5298 or (800) 255-1514, or e-mail firstname.lastname@example.org.
Published in 2002 in the United States of America by Westview Press, 5500 Central Avenue, Boulder, Colorado 80301-2877, and in the United Kingdom by Westview Press, 12 Hid’s Copse Road, Cumnor Hill, Oxford OX2 9JJ
Find us on the World Wide Web at www.westviewpress.com
Library of Congress has catalogued the hardcover edition as follows:
Lurquin, Paul F.
High tech harvest : understanding genetically modified food plants / Paul F. Lurquin.
Includes bibliographical references (p. ).
ISBN 0-8133-3946-4 (hc.)
eBook ISBN: 9780465009923
1. Transgenic plants. 2. Plant genetic engineering. 3. Plant biotechnology. I. Title.
SB123.57 .L88 2002
ISBN 0-8133-4175-2 (pbk.)
The paper used in this publication meets the requirements of the American National Standard for Permanence of Paper for Printed Library Materials Z39.48-1984.
First paperback printing, April 2004
10 9 8 7 6 5 4 3 2 1
To Antigone, Jean-Paul,
Lev, and Louis-Ferdinand,
for general inspiration and attitudes in life.
List of Illustrations
2.1 The mechanism of DNA replication
2.2 A simplified summary of the flow of information from DNA to protein
3.1 The first Boyer/Cohen DNA cloning experiment
3.2 Chimeric plasmid SLJ2011 containing the plant-expressible, herbicide resistance bacterial bar gene
4.1 Crown gall tumor (white, elongated, somewhat fuzzy mass) growing on the stem of a tobacco plant inoculated with A. tumefaciens
4.2 Experiment demonstrating Agrobacterium-mediated antibiotic resistance gene transfer into plant cells
4.3 Structures of a normal, virulent pTi molecule and its nonvirulent, engineered counterpart
4.4 Simplified representation of gene transfer between A. tumefaciens and a plant cell
4.5 Regeneration of plants from protoplasts
5.1 How genetically engineered plants become resistant to herbicides. Case 1: Roundup® Case 2: Liberty®
5.2 Control (top) and transgenic (bottom) rice plants of the “Kitaake” (japonica) variety
Members of the Ledoux laboratory in 1974
Photo of Mary-Dell Chilton
Photo of Ingo Potrykus
GENETICALLY ENGINEERED PLANT PRODUCTS line the shelves of our grocery stores but we do not know which ones they are because no labels identify them. Should we be concerned? Should we—figuratively speaking—be up in arms against biotechnology as are the Europeans, the Japanese, and the Canadians? What are genetic engineering and biotechnology anyway? How does one genetically engineer plants? Is it true that some plants have been engineered with a gene extracted from a fish? Biotechnology companies are saying that engineered corn and canola are safe. Are they telling us the truth? I have written this book to answer all these questions and more.
I believe the public has the right to know and understand how its food is being manipulated at the most intimate level, that of the DNA itself. My goal is to inform, not to take a stand in favor or against genetically modified organisms (GMOs). I am, however, critical of the way biotech companies have introduced (or rather, failed to introduce) their plant products to the public. I am equally critical of those who show their disapproval of GMOs through acts of vandalism rather than with open discussion. This being said, I add that I have never received grant money from any biotech company, nor have I ever consulted for monetary gains for one. I do know plant genetic engineering quite well, however. I have been involved since 1973 in the basic research that led to its development, always in an academic environment. I have met most of the scientists who made plant genetic engineering possible, and as far as I know the vast majority of them are not only still alive but also still actively involved with their work. This good news does not attest to their longevity or mine, it simply shows that biotechnology is an extremely young science. We should keep this fact in mind when we think about its implications.
Biotechnology is an innovation that requires some explanation. It involves a type of genetic manipulation that is entirely new, but it relies squarely on fundamental scientific discoveries made in decades past. Many of these discoveries are complex even though their applications may seem deceptively simple. Therefore, one must understand genetic engineering before one can formulate an informed opinion about it. To become an informed person, one must do more than gloss over difficult concepts and then declare that one is for or against genetically modified foods. For this reason, parts of this book will require attentive reading, in particular Chapter 3, which explains the basics of gene cloning. The reader will then understand that biotechnology is an offshoot of the basic science of genetics, not a technology that was developed for the specific purpose of making genetically modified organisms. I hope also to demonstrate that in the end acceptance or rejection of genetically modified food plants must rely on science and science alone. Politics, economics, or other societal factors cannot replace the objective tools of the scientific method, whose validity has never been refuted successfully since its inception about 400 years ago.
This book originated with another book project I undertook with Columbia University Press in 1999. That book, The Green Phoenix: A History of Genetically Modified Plants, published in 2001, is a scholarly work intended mostly for academics and university students. Holly Hodder (former publisher for the sciences at Columbia University Press and now vice president and publisher at Westview Press) then suggested that a general audience trade book on the history and applications of plant genetic engineering would serve a purpose—that of informing the public of what is happening in this field. Hence, this book. Basic genetic principles and elements of gene cloning are presented before plant genetic engineering proper and its implications. My philosophy here is simply that the cart should not precede the horse. Too many reports have assumed that readers already know genetics, and this assumption has resulted in the hideously wrong—but fairly common—misconception that anything that contains genes is, by definition, bad. All living creatures have genes, and we have learned to manipulate these with ultimate precision. That is a great and perhaps frightening novelty. After reading this book, the reader will understand how this knowledge and power evolved.
Hundreds of scientific articles dealing with plant genetic engineering have been published. Some are listed in the references at the end of this book. This bibliography presents articles that do not require any particular scientific knowledge in order to understand them, such as Scientific American articles, along with some primary sources that do require deeper knowledge of biology. This book, however, does not require any advanced understanding of biological science. In addition to literature references, relevant web sites, both for and against plant biotechnology, are also provided.
I am grateful to Jerry Swensen, Lászlo Márton, Charlotte Omoto, and Diter von Wettstein for reading drafts of this work and pointing out places where clarifications were needed. I also thank them for expressing their own viewpoints regarding plant biotechnology in general. I am particularly indebted to my wife, Linda Stone, for her careful multiple readings of the manuscript. Last but not least, my deepest gratitude goes to Holly Hodder, my editor, and Catherine Hope, my copy editor, for their meticulous editing of the manuscript and excellent stylistic suggestions. As usual, all errors, interpretations, and omissions are mine. Finally, I hope readers find this book a useful tool. Public opinion of plant biotechnology has become an emotional morass. I offer this book as a way for people to inform themselves and make up their minds in an objective way. This end is, perhaps, the best a scientist can hope to achieve.
Pullman, Washington and
Cannon Beach, Oregon
Chronology of Events
Described in This Book
Technical terms are defined in the glossary and in the main text.
1865 Gregor Mendel discovers and the laws of heredity.
1907 E. F. Smith and C. O. Townsend discover that crown gall tumors in plants are induced by the bacterium Agrobacterium tumefaciens.
1910 Thomas Morgan demonstrates that genes are on chromosomes.
1944 Oswald Avery and collaborators demonstrate that DNA is the material of which genes are made and discover transformation through DNA uptake.
1953 James Watson, Francis Crick, Rosalind Franklin, and Maurice Wilkins determine the double helical structure of DNA.
1953 L. Luca Cavalli-Sforza, Joshua and Esther Lederberg, and William Hayes establish the concept of plasmid DNA.
1962 Werner Arber and his group discover bacterial restriction endonucleases.
1966 Marshall Nierenberg and Gobind Khorana finish deciphering the genetic code.
1967 Jerome Vinograd and collaborators invent a technique to isolate and purify plasmid DNA.
1968 First experiments aimed at investigating DNA uptake in plants are conducted.
1970 M. Mandel and A. Higa develop transformation of the bacterium Escherichia coli.
1970 Georges Morel proposes that crown gall tumors appear on plants as the result of genetic information transfer from Agrobacterium tumefaciens to plant cells.
1972 Herbert Boyer and Stanley Cohen perform the first cloning experiment with plasmids.
1972 First attempts to produce genetic effects in plants with externally supplied foreign DNA are undertaken.
1974 Jef Schell, Marc Van Montagu, and others discover large plasmids in virulent Agrobacterium tumefaciens.
1976 Mary-Dell Chilton, Eugene Nester, Milton Gordon, and others discover gene transfer from Agrobacterium tumefaciens to plants.
1977 Walter Gilbert and Frederick Sanger develop techniques to determine the base sequence of DNA.
1982 Cell electroporation in the presence of DNA is invented.
1983 Jef Schell, Mary-Dell Chilton, Marc Van Montagu, Robert Fraley, Robert Horsch, and others transform plants with foreign genes via Agrobacterium-mediated gene transfer.
1984 Ingo Potrykus’s group demonstrates plant transformation with naked recombinant DNA.
1987 The “gene gun” is invented.
1987 First demonstration that transgenic plants containing the Bacillus thuringiensis (Bt) toxin gene are resistant to certain insects takes place.
1987 Plant Genetic Systems generates plants resistant to the herbicide Liberty®.
1988 The first commercially available genetically engineered fruit, the FlavrSavr® tomato, is produced by Calgene.
1988 Monsanto generates soybean plants resistant to the herbicide Roundup®.
1995 First laboratory production of “plantigens” is under way.
1996 Massive transgenic crop sales begin.
1998 Prince Charles of Wales publicly declares his opposition to biotechnology.
1999 Of the total 72 million acres planted with soybeans in the United States, half were planted with Roundup®-resistant seeds.
1999 Protest against the use of genetically modified plants in foods is in full swing in the United States and Europe and leads to street demonstrations.
2000 Provitamin A-producing “golden rice” variety is created. Genetic engineering techniques now exist for just about every conceivable cultivated plant species, from apple trees to coffee, from bananas to asparagus, to eggplant, to lettuce, to wheat.
2002 The complete DNA sequence of rice is published by two independent groups.
2003 “Golden rice” undergoes field trials.
2003 British scientists discover that insect populations are significantly depleted in fields planted with herbicide-resistant canola and sugarbeet. This does not happen in fields planted with herbicide-resistant corn. Their study strongly reinforces the idea that the ecological impact of genetically modified plants needs to be carefully evaluated.
The Old and the New
IN A SENSE, HUMANS DO LIVE by bread alone. Practically all life on Earth, animal and human, ultimately depends on the ability of plants to capture the photons of light released by our star, the Sun. The only well-documented exceptions are some microbial and worm communities that dwell in complete darkness near hydrothermal vents located deep under water on the ocean floor. These communities are sustained by chemical reactions taking place in the superheated water spewing out of these vents. Yet, even some of these creatures depend on oxygen dissolved in sea water; and their oxygen, like ours, is produced by plant life.
Plants, from microscopic marine phytoplankton to majestic sequoias as well as humble domesticated species, use sunlight to split water molecules into breathable oxygen and hydrogen ions (protons) and electrons. Oxygen is released into the atmosphere, and protons and electrons are used to power the reactions that reduce atmospheric carbon dioxide into sugars. These sugars are in turn metabolized through mechanisms that result in plant cell growth and development. Freed oxygen is used further by plants themselves and all animal species for crucial metabolic processes, survival, and proliferation.
Photosynthesis, as this light-harvesting mechanism is known, appeared approximately 3.5 billion years ago, roughly 1 billion years after the Earth formed. Microscopic bacterial cells (cyanobacteria), not land plants, first developed photosynthesis based on chlorophyll. Cyanobacteria still exist today and are everywhere. The first land plants appeared a little over 400 million years ago during the Silurian period of the Paleozoic era and were accompanied or closely followed by the first land animals. Much, much later, about 5 million years ago, our earliest-known bipedal ancestor, Australopithecus, roamed the African savanna in search of edible plants. Thus, for about 400 million years, plant life was left undisturbed except by natural events such as mutations, fires, and changing climate patterns that drove the slow process of evolution and led to great diversity of form. Evolution is driven by natural selection: Naturally occurring mutations can be favored or not by certain ecological conditions. This process can lead to the proliferation or extinction of species, both perfectly natural occurrences.
Then, about 10,000 years ago, Homo sapiens, ourselves, completely changed plant evolution by replacing natural selection with artificial, directed selection in some plant species. Today we call this agriculture. Therefore, genetic manipulation of plants is not new. The beginnings were modest; progenitors of modern wheat were first domesticated from wild relatives in the Middle East, whereas ancestors of modern corn appeared later in Mesoamerica. In this way, humans created the first engineered plants, possibly to free themselves from the vagaries of hunting and gathering in some ecological settings. (Another theory states that plant domestication was innovative but not caused by a need for more food. For the purpose of this book, regardless of which theory is more accurate, the result is the same.) Agriculture was soon followed by the establishment of cities, social classes, taxation, and writing, and it remains vital today.
The first experiments in plant breeding (along with animal husbandry) must have been performed purely by trial and error until a desirable result was obtained. It was not until the second half of the nineteenth century that plant breeding was put on a scientific basis by Gregor Mendel, the father of genetics. In the decades since that time, humans have learned how to alter the hereditary fabric of plants at the deepest level, that of the DNA molecule. We call this plant biotechnology, and the results of this technology are genetically modified (also called transgenic) plants.
It took a mere 10,000 years or so for humans to take control over the most intimate mechanisms of plant life and reproduction. What took evolution by natural selection millions of years to achieve, we can now alter in just a few weeks. Moreover, biotechnology can now do what nature could not; it can blend genes from totally different species, genera, and kingdoms of life. Biotechnology can defeat sexual barriers.
As just noted, humans had learned to manipulate plant genes in a crude manner well before the invention of biotechnology. How did this come about? Surely, cultivated crop plants look very different from their wild relatives. A classic example is that of teosinte, the ancestor of corn, that has very small, spiky ears and tiny seeds. Mesoamerican people, perhaps as early as 7,000 years ago, domesticated teosinte by finding spontaneous variants, or mutants, devoid of these undesirable characteristics and then propagated them. Wheat first appeared in the Fertile Crescent of the Middle East and resulted from accidental or deliberate hybridization between two related grass species that by themselves were far less convenient to harvest and process.
Ancient and not-so-ancient examples of stable plant hybrids and mutants created or propagated by humans are numerous and include cotton, chrysanthemum, potatoes, bananas, seedless grapes and watermelons, tiger lilies, some apple varieties (Winesap and McIntosh, for example), coffee, alfalfa, peanuts, triticale, strawberries, and some petunia varieties. In all these cases, either the progenitors of these new varieties are sexually compatible (they can fertilize one another) or their chromosome number has changed, which often happens accidentally and naturally. Nevertheless, without human intervention in the form of selection for useful traits and massive propagation, these plant varieties would be rarities. In that sense, humans have manipulated plant genomes (the genome is the suite of all genes contained in an organism) for thousands of years without any knowledge of genes or DNA. Some have called this primitive biotechnology.
Yet modern biotechnology is different. Here, theoretically, any plant species can be modified with genes from any source: bacterial, animal, fungal, or another plant. This technology no longer relies on natural hybrid formation or accidental changes in chromosome numbers. Rather, it hinges on our ability to isolate and clone genes from any species and introduce these cloned genes into plant cells through a variety of techniques. In other words, plants genetically modified by cloned foreign genes cannot be produced by nature. Scientists have now created plants that produce human proteins, express bacterial or fish genes, make plastics, and are able to detoxify toxic wastes. Genetically modified plants can do essentially whatever scientists force them to do. To use an old phrase, we can indeed play God.
This book tells the story of plant genetic manipulation by humans. It starts with the discoveries of Mendel and other early pioneers, which were followed many years later by the recombinant DNA revolution and demonstration that the genetic engineering of plants is possible. This story is not simple, and, in my opinion, it is impossible to have a good grasp of biotechnology without understanding genetics. In turn, it is impossible to understand genetics without comprehension of the gene as Mendel defined it well over 100 years ago. His discoveries are not obsolete, and it would be a mistake to believe that the modern DNA gene is somehow more real than the old Mendelian gene. Both are different facets of the same reality. Just as rocket scientists use Newton’s laws of gravitation, published in 1687, to launch spacecraft that can reach the outer planets and beyond, so do biotechnologists use Mendel’s laws of inheritance, published in 1865, to verify that their genetically modified plants do what they are supposed to do. After discussing Mendelian genetics, I will explain what genes are made of, how they work, and how this knowledge was acquired. This material constitutes Chapters 1 and 2. Current DNA cloning techniques will then be covered in Chapter 3. This overview of classical (Mendelian) and molecular (DNA-based) genetics will thus set the stage for the study of plant biotechnology proper, beginning with Chapter 4.
We will then see what commercial and basic applications were derived from the new technology and discuss the societal and economic consequences of these applications (Chapters 5 through 7). These are emotion-laden issues that have triggered street demonstrations, inflammatory declarations by celebrities, and commercial negotiations at the international level. It goes without saying that this clamor is not just political hype; some of the concerns about plant biotechnology are definitely valid. Unfortunately, the science behind this technology as well as its positive applications have not been cogently communicated to the public. A main goal of this book is to redress this situation and help the reader distinguish fact from fiction.
OUR PRESENT-DAY ABILITY TO MANIPULATE genes did not come overnight, as a great flash of creativity striking a single savant. This capability is the result of work done by thousands of scientists who have assembled knowledge on a foundation of a few landmark discoveries. These discoveries will be explained in this chapter and in the next two chapters. It should be realized first that biotechnology is a very young science, itself a part of the young science of genetics. In fact, my own grandparents were little children when Gregor Mendel, the inventor of genetics as we know it today, was still alive. The nature of the genetic material DNA was discovered when I was two years old, and I was in elementary school when the DNA double helix was revealed by James Watson and Francis Crick. The first cloned DNA molecules were produced in the early 1970s, shortly after I received my Ph.D., and the first genetically engineered plants were created in 1983, in other words, yesterday. Commercial exploitation of genetically modified plants started only a few years before the end of the last millennium. Biotechnology is baby-boomers’ science: Its story is ours.
- On Sale
- Oct 15, 2007
- Page Count
- 236 pages
- Basic Books