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Adapted by: Khang Pham, OCT
C4 Photosynthesis
Plants fix carbon dioxide (CO2) into sugar using sunlight as the source of energy. This fixed carbon makes up the bulk of the plant itself – roots, stems, leaves, flowers - and the sugars or starches that are stored in the seeds or fruits that we harvest for food.
In the majority of plants, including rice, CO2 is first fixed into a compound with three carbons (C3) by the photosynthetic enzyme ribulose bisphosphate carboxylase oxygenase (Rubisco)—this is known as C3 photosynthesis. Rubisco is inherently inefficient because it can also catalyze a reaction with oxygen from the air, in a wasteful process known as photorespiration (rather than photosynthesis). At temperatures above 20°C, there is increasing competition by oxygen (O2), with a dramatic reduction in CO2 fixation and photosynthetic efficiency. While all this is happening, water is escaping from the leaves while the CO2 is diffusing in. Thus, in the hot tropics where most rice is grown, photosynthesis becomes very inefficient.
C4 plants are more efficient in carbon dioxide concentration that results in increased efficiency in water and nitrogen use and improved adaptation to hotter and dryer environments.
In nature, this has occurred more than 50 times in a wide range of flowering plants, indicating that, despite being complex, it is a relatively easy pathway to evolve.
Kranz (C4) anatomy arose before the C4 biochemistry within the bundle sheath cell, in response to photorespiration. Therefore, strategies to engineer C4 photosynthesis should first address the introduction of Kranz anatomy into C3 plants.
Improvement on existing crops
Our calculations show that the cost-benefit ratio of C4 rice is likely to be of the same order as the “dwarf-cultivars” produced in the first Green Revolution bringing benefits to hundreds of millions of people in the poorer parts of the world. Inserting the C4 photosynthetic pathway into rice should increase rice yield by 50%, double water-use efficiency, and use less fertilizer to achieve those improvements. No other evolutionary mechanism exists that could be added to C3 rice that could deliver that superior combination of benefits.
Poverty alleviation would be further magnified if the C4 syndrome were added to other C3 crops, such as wheat, growing in the hot countries of the developing world.
Value proposition:
- Increased water use efficiency. C4 rice would need less water because water loss will be reduced and the water used more efficiently. C4 plants would have the pores in the leaves (stomata) partially closed during the hottest part of the day. Also C4 plants absorb more CO2 per unit of water lost. C4 plants are able to do this because of the compartmentalization and concentration of CO2 that occurs in the bundle sheath cells.
- Increased nitrogen use efficiency. C4 rice would increase nitrogen-use efficiency by 30% because the plant will need lower amounts of Rubisco, an abundant enzyme that fixes CO2 into sugars. By requiring less Rubisco for the same amount of CO2 fixed, C4 rice can achieve the same productivity with fewer enzymes, which means less nitrogen. (enzymes and proteins contain 15% nitrogen).
- Yield benefits. Models show that increased water and nitrogen use efficiencies and other characteristics would support yield increases of 30% to 50% based on comparative studies between rice and maize.
What is C4 Rice
Background
Agriculture is the indispensable base of human society and the nature and productivity of agriculture is determined by land, water, climate, management and agricultural research. Only 29% of the earth’s surface is land and only a little over a third of that is suitable for agriculture; the rest is ice, desert, forest or mountain and is unsuitable for farming. More simply stated, only 10% of the surface of the earth has topographical and climatic conditions suitable for producing the food requirements of human beings. Today, 75% of the world’s 6.6 billion people live in the developing world where most of the world’s existing poverty is concentrated.
Currently, about a billion people live on less than a dollar a day and spend half their income on food; 854 million people are hungry and each day about 25,000 people die from hunger-related causes. Sixty percent of the world’s population lives in Asia, where each hectare of land used for rice production currently provides food for 27 people, but by 2050 that land will have to support at least 43 people. Nonetheless, the area for rice cultivation is continually being reduced by expansion of cities and industries, to say nothing of soil degradation. Climate change will likely result in more extreme variations in weather and cause adverse shifts in the world’s existing climatic patterns. Water scarcity will grow; the increasing demand for biofuels will result in competition between grain for fuel and grain for food resulting in price increases. Furthermore, more than 75% of the world's people will live in cities, the populations of which will need to be largely supported by a continuous chain of intensive food production and delivery.
All of these adverse factors are growing now, at a time when the growth in rice production has slowed as efficient farmers have approached yield limits. Research shows that current maximum rice yields are close to a fundamental yield barrier shaped by the efficiency of solar energy conversion.
How will the required increases in yield be achieved? Solar energy captured in photosynthesis over the duration of a crop gives it the capacity to grow. There is now a growing body of scientific opinion, that the only way to achieve the rice harvests needed for the future is to change the biophysical structure of the rice plant, making it a much more efficient user of energy from the sun. Plants use solar radiation to grow—to develop leaves, roots, stems, flowers, and seeds in a process known as photosynthesis. Rice has what is known as a C3 photosynthetic pathway, less efficient than that of maize, which has a C4 pathway. Taking a lesson from evolution and converting a plant from C3 to C4 would involve a rearrangement of cellular structures within the leaves and more efficient expression of various enzymes related to the photosynthetic process. However, all the components for C4 photosynthesis already exist in the rice plant, but they are distributed differently and are not as active.
Roadmap
Why C4 Rice
Problem and Urgency
Currently, a billion people live on less than a dollar a day and spend half their income on food, 854 million people are hungry and each day about 25000 people die from hunger-related causes.
Sixty percent of the world’s population lives in Asia where each hectare of land used for rice production currently provides food for 27 people, but by 2050 that land will have to support at least 43 people. Climate change will likely result in more extreme variations in weather and cause adverse shifts in the world’s existing climatic patterns. Water scarcity will grow. The increasing demand for biofuels will result in competition between grain for fuel and grain for food, resulting in price increases. Furthermore, more than 75% of the world’s people will live in cities, whose populations will need to be largely supported by a continuous chain of intensive food production and delivery. However, growth in production is slowing. The elite rice cultivars, which dominate the food supplies of the millions of poor people in Asia, have approached a yield barrier, plant breeding seems to have exploited all of the intrinsic high yield-linked genes Ultimately insufficient yields of rice produce food insecurity, unsustainable agricultural practices, environmental degradation and social unrest This vicious cycle must be replaced by a virtuous cycle where raised productivity improves food security so that investments in sustainable agriculture are attractive; then the environment is protected.
The Solution
What technology could simultaneously solve those problems and prevent the bleak future outlined above from becoming a reality? Innovative research at IRRI suggested that the solution to the challenges ahead for rice would require solar energy to be used more efficiently in photosynthesis. Fortunately, there is one example from evolution of a supercharged photosynthetic mechanism; the C4 system.
Converting the photosynthetic system in rice to the more efficient, supercharged C4 one used by maize would increase rice yields while using scarce resources (land, water, fertilizer) more effectively. However a technological innovation of this magnitude requires the skills and technologies of a global alliance of multidisciplinary partners from advanced institutions. In 2008, IRRI formed the International C4 Rice Consortium.
International Rice Research Institute
Philippines
rice TODAY
Science of C4 Rice
Science of C4 Rice
C4 Photosynthesis
Plants fix carbon dioxide (CO2) into sugar using sunlight as the source of energy. This fixed carbon makes up the bulk of the plant itself – roots, stems, leaves, flowers - and the sugars or starches that are stored in the seeds or fruits that we harvest for food.
In the majority of plants, including rice, CO2 is first fixed into a compound with three carbons (C3) by the photosynthetic enzyme ribulose bisphosphate carboxylase oxygenase (Rubisco)—this is known as C3 photosynthesis. Rubisco is inherently inefficient because it can also catalyze a reaction with oxygen from the air, in a wasteful process known as photorespiration (rather than photosynthesis). At temperatures above 20°C, there is increasing competition by oxygen (O2), with a dramatic reduction in CO2 fixation and photosynthetic efficiency. While all this is happening, water is escaping from the leaves while the CO2 is diffusing in. Thus, in the hot tropics where most rice is grown, photosynthesis becomes very inefficient.
C3 Photosynthesis: Rubisco
(Click vao hinh)
C4 Photosynthesis: PEP Carboxylase then Rubisco
(Click vao hinh)
C4 Photosynthesis: PEP Carboxylase then Rubisco
C4 plants are more efficient in carbon dioxide concentration that results in increased efficiency in water and nitrogen use and improved adaptation to hotter and dryer environments.
In nature, this has occurred more than 50 times in a wide range of flowering plants, indicating that, despite being complex, it is a relatively easy pathway to evolve.
Kranz (C4) anatomy arose before the C4 biochemistry within the bundle sheath cell, in response to photorespiration. Therefore, strategies to engineer C4 photosynthesis should first address the introduction of Kranz anatomy into C3 plants.
Improvement on existing crops
Our calculations show that the cost-benefit ratio of C4 rice is likely to be of the same order as the “dwarf-cultivars” produced in the first Green Revolution bringing benefits to hundreds of millions of people in the poorer parts of the world. Inserting the C4 photosynthetic pathway into rice should increase rice yield by 50%, double water-use efficiency, and use less fertilizer to achieve those improvements. No other evolutionary mechanism exists that could be added to C3 rice that could deliver that superior combination of benefits.
Poverty alleviation would be further magnified if the C4 syndrome were added to other C3 crops, such as wheat, growing in the hot countries of the developing world.
Value proposition:
- Increased water use efficiency. C4 rice would need less water because water loss will be reduced and the water used more efficiently. C4 plants would have the pores in the leaves (stomata) partially closed during the hottest part of the day. Also C4 plants absorb more CO2 per unit of water lost. C4 plants are able to do this because of the compartmentalization and concentration of CO2 that occurs in the bundle sheath cells.
- Increased nitrogen use efficiency. C4 rice would increase nitrogen-use efficiency by 30% because the plant will need lower amounts of Rubisco, an abundant enzyme that fixes CO2 into sugars. By requiring less Rubisco for the same amount of CO2 fixed, C4 rice can achieve the same productivity with fewer enzymes, which means less nitrogen. (enzymes and proteins contain 15% nitrogen).
- Yield benefits. Models show that increased water and nitrogen use efficiencies and other characteristics would support yield increases of 30% to 50% based on comparative studies between rice and maize.
What is C4 Rice
Background
Agriculture is the indispensable base of human society and the nature and productivity of agriculture is determined by land, water, climate, management and agricultural research. Only 29% of the earth’s surface is land and only a little over a third of that is suitable for agriculture; the rest is ice, desert, forest or mountain and is unsuitable for farming. More simply stated, only 10% of the surface of the earth has topographical and climatic conditions suitable for producing the food requirements of human beings. Today, 75% of the world’s 6.6 billion people live in the developing world where most of the world’s existing poverty is concentrated.
Currently, about a billion people live on less than a dollar a day and spend half their income on food; 854 million people are hungry and each day about 25,000 people die from hunger-related causes. Sixty percent of the world’s population lives in Asia, where each hectare of land used for rice production currently provides food for 27 people, but by 2050 that land will have to support at least 43 people. Nonetheless, the area for rice cultivation is continually being reduced by expansion of cities and industries, to say nothing of soil degradation. Climate change will likely result in more extreme variations in weather and cause adverse shifts in the world’s existing climatic patterns. Water scarcity will grow; the increasing demand for biofuels will result in competition between grain for fuel and grain for food resulting in price increases. Furthermore, more than 75% of the world's people will live in cities, the populations of which will need to be largely supported by a continuous chain of intensive food production and delivery.
All of these adverse factors are growing now, at a time when the growth in rice production has slowed as efficient farmers have approached yield limits. Research shows that current maximum rice yields are close to a fundamental yield barrier shaped by the efficiency of solar energy conversion.
How will the required increases in yield be achieved? Solar energy captured in photosynthesis over the duration of a crop gives it the capacity to grow. There is now a growing body of scientific opinion, that the only way to achieve the rice harvests needed for the future is to change the biophysical structure of the rice plant, making it a much more efficient user of energy from the sun. Plants use solar radiation to grow—to develop leaves, roots, stems, flowers, and seeds in a process known as photosynthesis. Rice has what is known as a C3 photosynthetic pathway, less efficient than that of maize, which has a C4 pathway. Taking a lesson from evolution and converting a plant from C3 to C4 would involve a rearrangement of cellular structures within the leaves and more efficient expression of various enzymes related to the photosynthetic process. However, all the components for C4 photosynthesis already exist in the rice plant, but they are distributed differently and are not as active.
Roadmap
Why C4 Rice
Problem and Urgency
Currently, a billion people live on less than a dollar a day and spend half their income on food, 854 million people are hungry and each day about 25000 people die from hunger-related causes.
Sixty percent of the world’s population lives in Asia where each hectare of land used for rice production currently provides food for 27 people, but by 2050 that land will have to support at least 43 people. Climate change will likely result in more extreme variations in weather and cause adverse shifts in the world’s existing climatic patterns. Water scarcity will grow. The increasing demand for biofuels will result in competition between grain for fuel and grain for food, resulting in price increases. Furthermore, more than 75% of the world’s people will live in cities, whose populations will need to be largely supported by a continuous chain of intensive food production and delivery. However, growth in production is slowing. The elite rice cultivars, which dominate the food supplies of the millions of poor people in Asia, have approached a yield barrier, plant breeding seems to have exploited all of the intrinsic high yield-linked genes Ultimately insufficient yields of rice produce food insecurity, unsustainable agricultural practices, environmental degradation and social unrest This vicious cycle must be replaced by a virtuous cycle where raised productivity improves food security so that investments in sustainable agriculture are attractive; then the environment is protected.
The Solution
What technology could simultaneously solve those problems and prevent the bleak future outlined above from becoming a reality? Innovative research at IRRI suggested that the solution to the challenges ahead for rice would require solar energy to be used more efficiently in photosynthesis. Fortunately, there is one example from evolution of a supercharged photosynthetic mechanism; the C4 system.
Converting the photosynthetic system in rice to the more efficient, supercharged C4 one used by maize would increase rice yields while using scarce resources (land, water, fertilizer) more effectively. However a technological innovation of this magnitude requires the skills and technologies of a global alliance of multidisciplinary partners from advanced institutions. In 2008, IRRI formed the International C4 Rice Consortium.
International Rice Research Institute
Philippines
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