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NatureInterface > No.07 > P013-017 [Japanese]

Plant Growth: Agricultural Biotechnology Opens Up Our Future -- Satoshi Mori




Plant Growth: Agricultural Biotechnology Opens Up Our Future

SATOSHI MORI

Professor of Graduate School of Agricultural and Life Sciences, The University of Tokyo

Interviewer: KIYOSHI ITAO

General Editor of Nature Interface


Technological development in new fields of study is progressing on the basis of frontier sciences such as life science, nanoscience and information science. Especially, by applying to agriculture microsystem technology in which microbiotechnology and information technology is merged is creating a new industry: It is agricultural biotechnology. Agricultural biotechnology boosts productivity of crops and helps develop functional foods for health. Agricultural biotechnology is a technology of the 21st century that may utterly transform the agricultural production system. What has agricultural biotechnology attained, and how will such achievements change future agriculture? In this article, we will consider the potential of agribusiness in the near future.

(This story has been compiled based on °»Frontier Science Forum- Pioneering New Spheres°… organized by Kiyoshi Itao, General Editor of Nature Interface and held by Graduate School of Frontier Sciences, The University of Tokyo, in September 2001.)

Growth Control in Plants

Itao: Nonprofit Organization the Advanced Institute of Wearable Environmental Information Networks, or WIN, launched a research project on IT in agriculture in January 2002. Today, I°«d like to interview you on plant growth control. First, what is crucial in plant growth?

Mori: Plant growth comprises cell division and expansion. Apical cells called growing points in roots and stems divide and expand. While these growing points are new tissues, other parts of the plant body already completed cell division and expansion. From this viewpoint, plant tissues contain their histories in themselves. In other words, the plant body has new and developed cells built in it together.

By the way, higher plants have vessels and sieve tubes. Vessels transport water and nutrients absorbed by roots to aboveground organs, while sieve tubes transport nutrients synthesized in aboveground organs by photosynthesis to underground organs. Smooth functioning of these two conducting tissues realizes efficient circulation of substances in the plant body, thereby growing the plant.

Itao: Can you tell me how these tissues work as transportation pumps?

Mori: Leaf stomata generate driving power for absorbing water and nutrients from roots and moving them upward in vessels. When leaves are exposed to the sunlight, stomata open and water evaporates. Vapor pressure difference between the atmosphere and leaves produces difference in water potential among the rhizosphere, the plant body and the atmosphere, thereby generating enough force to pull up water by some 100 m. Meanwhile, membrane proteins called transporters conduct intertissue and intercellular nutrient movement through cell membranes. Membrane proteins can be regarded as highly functional pores implanted in cell membranes, and various substances such as ions, saccharides, organic acids, amino acids and water pass through these proteins. Each kind of transporters is specific to each substance, and controls its movement through cell membranes.

Itao: Do transporters have any other functions?

Mori: They collect varying environmental information on light, temperature, water, nutrients, and substance concentrations. For example, when transporters detect deficit of ammonium nitrogen available around the roots, ammonium transporters in roots become active. In addition, the number of ammonium transporters in cell membranes increases. The plant tries to absorb ammonium of quite low concentration as much as possible. In this way, plants adapt to the environment.

Itao: Plants have sophisticated environmental sensors.

Mori: Plants cannot move around, so they employ various environmental sensors. For example, some plants alter their metabolic systems under drastic environmental changes in order to produce seeds, which are their offspring, as many as possible. For instance, even in a desert with its annual precipitation of about 50 mm, it has sudden downpour. At that time, dormant seeds wake up perceiving water, germinate all at once, and flower in four weeks or so. These plants complete vegetative and reproductive growth in a short period when soil contains water. Many plants have adapted to deserts in this way.

Itao: Well, in contrast to plants adapted to severe environments, hothouse crops require minimum energy for survival because their environment is well managed. Then, what do these plants spend their energy on?

Mori: Quantitative growth of such cultivated crops is vigorous because they have less stress. However, their quality as foods is not always fine. For instance, hothouse tomatoes are less delicious than tomatoes grown outdoors. Living things in nature undergo variable and severe stresses and express genes to tolerate them. On the other hand, hothouse crops grow in an ideal environment, so they do not need to highly express these genes. Thus, in order to enhance expression of genes for increasing stress resistance, farmers put seawater onto the field, for example. When soil has a high salt concentration, water potential outside root cells becomes very low, so the plant may die because of dehydration. Thus, the plant tries hard to synthesize substances with high osmotic pressure to make the water potential in the plant body lower than that of soil, because water moves from high to low water potential.

Itao: Plants change their systems.

Mori: Exactly. For instance, when we put seawater on tomatoes, they synthesize substances that taste sweet for people. Actually, sugar concentration in tomato fruits rises. There are agricultural methods for making delicious crops by imposing stresses on them in this way.

When crops are cultivated outside, they need to consume much of the energy generated by photosynthesis and stored in their bodies in order to tolerate environmental stresses. Consequently, their yields decrease. On the other hand, crops cultivated in a hothouse or a climate chamber can express many genes for reproduction because their environment is controlled artificially with outside energy invested.

Itao: Tomatoes growing in an ideal environment are not always delicious, so what should we do?

Mori: We can employ breed improvement or genetic engineering to overcome this hurdle. For example, we may introduce into the plant a gene for synthesizing and accumulating sugar in cells in high concentration.

Itao: Have such genes been discovered already?

Mori: We have plenty kinds of these genes. Yet, even if we don°«t employ genetic engineering, a conventional method of breeding such as crossing of wild types of tomatoes is useful. We can increase sugar concentration of a tomato even up to 10%, while its general concentration is 5%.

If you want to increase the sugar concentration further to about 20%, you may introduce a gene helping sugar accumulation into the plant, making good use of genetic engineering. When we employ this method, we clearly know which gene we have introduced into the plant. In contrast, in conventional breeding, we exchange chromosomes at random by crossing, so we generate plenty of unnecessary varieties. Thus, much time is required to select desired varieties. FLAVOR SAVER is the first genetically engineered variety of tomatoes, which stays green and is not damaged even in transit. In other words, this variety can be easily handled. Flavor Saver tomatoes hold their shapes even at the store.

Genetically Modified Foods

Itao: By the way, what has been achieved in development of Genetically Modified foods (GM foods) in Japan?

Mori: Researchers have discovered genes helping farmers to enhance labor productivity or to generate fruits and vegetables that can be easily handled upon distribution, and have introduced them into crops. Herbicide-resistant and pest-resistant varieties are examples of such GM crops.

Recently, however, the world agribusiness, as well as the Ministry of Agriculture, Forestry and Fisheries of Japan, has been promoting development of tasty and advantageous foods from the viewpoint of consumers. This trend is called the third era of plant biotechnology. We are thinking about incorporating components with medical effects, such as enhancing health or immunity, or lowering blood pressure, into rice and vegetables. For example, we may increase iron content in salad to treat young people°«s anemia. If we can maintain our health by daily ingestion of such foods, we will rarely need to go to hospital, our medical expenses will decrease, and medical expenditure by the government will be lowered, too. I hope we can make such a favorable cycle.

Itao: I remember that when I interviewed with Prof. Isao Karube in Vol. 1, No. 5 of Nature Interface, he also talked about generating medical foods.

Mori: I think business in GM foods in Japan will obtain public acceptance through herbal medicinal foods that are good for health or have high nutritive values. Actually, we take GM foods daily from processed foods containing GM soybeans or maize. Yet, no damages have been reported around the world.

I have a good example. When black tea and coffee became popular among young people three decades ago, Japanese green tea makers suffered from declining sales. Kiosks sold coffee and black tea, but not green tea. Green tea makers exerted themselves to sell green tea at kiosks. They added vitamin C into green tea and developed a method to improve transparency of the tea. Recently, research on green tea has progressed markedly and revealed that teanine, an amino acid in green tea that a Japanese discovered 50 years ago, is effective in nourishing and calming the brain. In addition, it has been proved that a substance called catechin helps prevent brain aging. Furthermore, mass media has publicized such added values.

Itao: Effects of green tea served as its added values.

Mori: Many young people today carry plastic bottles of green tea with them and green tea sales have skyrocketed. People who researched green tea two or three decades ago are amazed by such enormous sales.

Public Acceptance

Itao: Obtainment of public acceptance of GM foods is still lying as a hurdle, isn°«t it?

Mori: As understood from the example of Japanese green tea, it is crucial that the public recognize the advantages of GM foods through their added values. I think when a GM food obtains public acceptance, science and feelings of the public interface with each other. This is exactly the nature interface, and we need to incorporate such interface into the sphere of science little by little.

Itao: What can we do to achieve it?

Mori: Newspapers, radio and television play an important role in obtaining public acceptance of new technologies, because they educate the public intellectively. In addition, thorough science education is necessary at junior high schools, elementary schools and kindergartens. Genetic engineering kits are sold in the U.S., so I am proposing educators to employ such materials in class. Some U.S. elementary and junior high schools already use these genetic engineering kits. If people get used to the word °»gene recombination°… from their childhood, they come to feel no fear about it. We need to °»imprint°… on people from their childhood the fact that gene recombination is general science and technology.

Itao: Mass media sometimes criticize gene recombination as mere play of scientists and blasphemy against God.

Mori: I hate to say this, but I think mass media survive by keeping people°«s awareness at a lower level and intensifying people°«s fear.

Itao: In this sense, we need to bring the interface between intellect, or science, and feeling to the side of intellect. Our magazine, Nature Interface, will try hard to achieve such a goal.

Influence on the Ecosystem

Itao: Now, can you talk about influence of GM plants?

Mori: We have not clarified impacts of GM plants on ecosystems. We cannot control their effects completely, although we can investigate where their pollens are carried. We always encounter this problem whenever we introduce cultivated plants into agriculture.

Itao: When exotics enter a certain place, they damage the ecosystem there. Do you think a similar phenomenon may occur when GM plants are applied?

Mori: There is a possibility of it.

Itao: Scientists say we just need to completely manage new varieties generated by gene recombination. However, is it actually difficult?

Mori: Opponents of gene recombination bring up this question. When a variety of animal feed corn called StarLink containing allergenic proteins was mixed in imported corn for human consumption, a serious social problem arose. Trading firms of corn say they handle GM and non-GM corn separately upon transporting seeds and don°«t import the corn if they cannot divide it completely. Yet, GM corn was mixed into non-GM corn. Their thorough selection is quite difficult so far. Though Japan has sophisticated quality control technology in industrial production, perfect quality control in farmwork is still impossible.

Itao: There is a possibility that an error may occur.

Mori: Thus, we must develop technology taking such possibilities into consideration.

Itao: In that sense, gene recombination encounters a serious obstacle.

Mori: Meanwhile, no matter how we improve quality management, the problem of pollen dispersion from the fields will still remain. A non-GM variety in a remote field may cross with a GM variety through its pollens dispersed.

However, as in naturalized plants, I think crossing between a GM plant and a wild plant is inevitable. Cultivated plants are varieties that are advantageous for people and have survived after natural and artificial selection. Though people say, °»Nature is the best,°… we have no virgin nature around us in fact. We must remember that nature continues to change.

I think it is essential to develop GM varieties benefiting not only producers and distributors but also consumers.

Technology for Dealing with Environmental Change

Mori: Now, I°«d like to talk about technological development with respect to global warming. While atmospheric carbon dioxide concentration was 100 ppm in ancient times, it is more than 330 ppm now. There was nothing wrong when the concentration increased little by little long ago. However, the problem is that the concentration jumped in these 100 years. Annual climate fluctuations are becoming greater. Moreover, fluctuations in world grain yields are becoming far wilder. Therefore, we must exert ourselves to establish technology for dealing with radical change in the environment.

For example, in agriculture, there developed a variety of rice that is not damaged from cold weather even at the northernmost tip of Hokkaido. If global warming worsens, we may be able to harvest rice in Sakhalin and Russia. Meanwhile, in the south of Japan, it will become hotter, and tropical crop pests may move northward and propagate there. As a consequence, even people in Japan may develop malaria. Thus, we need to improve medical technology to tackle such problems. I oppose such poetic justice deeming any kind of carbon dioxide emission as evil. Of course, it is important to improve energy conservation technology and efficiency of environmentally friendly energy. Yet, I think it is more essential to comprehensively develop technology helping to tolerate environmental change taking into consideration what will happen several decades later. When we look back the history, we realize that only people who could develop such technology have survived.

Though people criticize gene recombination, it is in fact an ordinary and beneficial technology in the 21st century.

Itao: Even locomotives were denounced for their smoke, though they are recognized today as an epoch-making invention.

Mori: Also, Luddites broke down machines during the Industrial Revolution.

I°«m afraid that if people judge whether a certain technology is acceptable only with their scientific knowledge obtained from mass media, they will not be able to use the technology when it is really necessary in the future. I think every right-minded scientist or engineer feels this anxiety.

Itao: Today, I could hear interesting stories about IT in agriculture. Now, I°«d like to summarize your remarks. While plants consume much energy for growth and survival under a severe environment, they bear many fruits in a favorable environment such as a hothouse. However, the fruits are not always sweet, as in tomatoes. Accordingly, we may employ gene recombination in order to increase sweetness of the fruits. Moreover, with gene recombination, we can generate highly functional foods. Control of hothouse environment is crucial anyway. Thus, environmental control and gene recombination will play an important role in industrial development of agricultural biotechnology.

Thank you very much.

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