Đào Anh Phúc
Senior Member
Nguồn nước ?cung cấp cho nông nghiệp càng ngày càng khan hiếm ! việc tìm hiểu cơ ?chế chống hạn rất quan trọng trong việc canh tác cây trồng trên những vùng đất thiếu nước, giải quyết vấn đề lương thực cho con người .
?Có nhiều xu hướng nghiên cứu sự chống hạn của thực vật và người ta phát hiện thấy vai trò của aa proline cao khi cây bị hạn, nhưng theo những nghiên cứu mới nhất người ta phát hiện ra nhân tố thúc đẩy qua trình ?oxi hóa gây hai cho tế bào . Hướng nghiên cứu đó đi đến việc chuyển gen vào thực vật ?nhằm hạn chế sự tác động của enzim oxi hóa đó ( oxidative enzymes ) ?Vậy:
?
? ? ?Chúng ta hãy đi vào giải quyết vấn đề đó !
Friday, December 9, 2005
Abscisic acid is a plant hormone that regulates growth, and transcription factors associated with a plant’s response to it play a key role in allowing plants to survive under drought stress. ? ? ?
?One such transcription factor is AREB1, and Yasunari Fujita and colleagues from Tsukuba, Japan find, from their research, that “AREB1 Is a Transcription Activator of Novel ABRE-Dependent ABA Signaling That Enhances Drought Stress Tolerance in Arabidopsis.”
In their paper, which appears in the latest issue of Plant Cell, researchers report that under normal growth conditions, the intact AREB1 gene is insufficient to induce the expression of genes. They thus created an activated form of the gene, called AREB1 QT, and over expressed it in Arabidopsis in the laboratory. Researchers found that the plants were hypersensitive to abscisic acid, and showed enhanced tolerance to drought. Plants without the gene were insensitive to abscisic acid, and displayed reduced survival under dehydration.
Subscribers to Plant Cell may read the complete article at:
http://www.plantcell.org/cgi/content/full/17/12/3470
Wednesday, March 8, 2006
By Tawanda Zidenga
Dehydration stress is one of the most serious yield-reducing stresses in agriculture. Drought stress is especially important in countries where crop agriculture is essentially rain-fed.
? ?
?In sub-Saharan Africa, drought years have a devastating effect on regional food security. While irrigation is the method of choice in averting drought stress in many areas of the world, alternative low-input approaches are being explored, and biotechnology offers a promising array of tools that may be useful in achieving drought tolerance in plants. One such tool is the low input approach to crop production by which crops are modified to suit the environment in which they are growing, rather than modifying the environment to meet the needs of the crop. This approach is advantageous in areas where water supplementation by irrigation is either difficult or unaffordable.
What happens to plants during drought?
Drought stress causes an increase in solute concentration in the environment, leading to an osmotic flow of water out of plant cells. This in turn causes the solute concentration inside plant cells to increase, thus lowering water potential and disrupting membranes along with essential processes like photosynthesis. These drought-stressed plants consequently exhibit poor growth and yield. In worst case scenarios, the plants completely die. Certain plants have devised mechanisms to survive under low water conditions. These mechanisms have been classified as tolerance, avoidance, or escape.
ROSes may be bad
Central to signal transduction pathways related to drought and other stresses are reactive oxygen species (ROS), which are molecules formed by the incomplete one-electron reduction of oxygen. Under stress, ROS formation is usually exacerbated. Drought stress leads to the disruption of electron transport systems; therefore, under water deficit conditions, the main sites of ROS production in the plant cell are organelles with highly oxidizing metabolic activities or with sustained electron flows: chloroplasts, mitochondria, and microbodies.1 ROS are generally damaging to essential cellular components, and plants have evolved various ROS scavenging mechanisms. These include the enzymes superoxide dismutase (SOD), catalase, and peroxidases, as well as oxidized and reduced glutathione.1
Researchers have focused on expressing genes for enzymes involved in ROS scavenging to enhance plant protection against oxidative stress. Transgenic alfalfa (Medicago sativa) expressing Mn-superoxide dismutase cDNA tended to have reduced injury from water-deficit stress, and this improvement was also seen in field trials in yield and survival.5
Secrets of resurrection
4 What does it take to rise from the dead? This is a question scientists working on resurrection plants have been exploring recently. Resurrection plants can tolerate almost complete water loss in their vegetative parts.2 At the University of Cape Town in South Africa, researchers are trying to unlock the secrets of the resurrection plant Xerophyta viscosa in an attempt to achieve drought tolerance in crops.1 These plants can be a source of drought tolerance genes for transgenic crop improvement. To withstand periods of drought, resurrection plants practically "die" (by losing all their vegetative parts) and then "rise again" when water becomes available. Their vegetative tissues lose all free water and then rehydrate once water becomes available again. Resurrection plants minimize ROS formation and also upregulate various antioxidant protectants during drying and rehydration.1 The group has identified a novel stress-inducible antioxidant enzyme, XvPer1, by differential screening of a cDNA library of X. viscose.
Osmoprotectants
Osmolytes are involved in signaling/regulating plant responses to multiple stresses, including reduced growth that may be part of the plant’s adaptation against stress. In plants, the common osmolytes are proline, trehalose, fructan, mannitol and glycinebetaine.6 The protection mechanisms are not yet fully understood, but they are thought to work via osmotic adjustment, stabilizing macromolecules, and scavenging ROS. One proposed transgenic strategy has been to overproduce osmolytes. However, transgenic plants overproducing osmolytes often exhibit impaired growth.
Trehalose, a non-reducing disaccharide, protects biological molecules in response to different stress conditions in many microorganisms.7 Plant biologists are interested in channeling trehalose metabolism to enhance stress tolerance in plants. Trehalose is made from UDP-glucose and glucose-6-phosphate via a two step process.
The conversion of UDP-glucose and glucose-6-phosphate to trehalose-6-phosphate is catalyzed by trehalose-6-phosphate synthase, encoded by the bacterial otsA gene. In the second step, glucose-6-phosphate is converted to trehalose by a phosphatase encoded by the bacterial otsB gene. Tobacco plants transformed with bacterial otsA have a greater ability to retain water and a greater ability to photosynthesize under water stress.8
Protection only when needed
Genes imparting protection from drought stress can be expressed in plants in two ways: they can be expressed all the time, whether or not the plant is under stress; or they can be engineered to express only when there is drought stress. The second method is more favored, as it limits the side effects of the manipulations. One of the challenges biologists face in trying to engineer for drought tolerance is that drought tolerance and/or resistance traits are often negatively correlated with productivity. To achieve protection only when needed, scientists use promoters that are stress-inducible, typically abscisic acid (ABA) inducible promoters.
References
1. Mundree SG et al. (2002) Physiological and molecular insights into drought tolerance. African Journal of Biotechnology 1(2), 28–38.
2. Scott P (2000). Resurrection plants and the secrets of eternal leaf. Annals of Botany 85, 159-166
3. Drought tolerance in Agriculture at University of Toronto. http://dragon.zoo.utoronto.ca/~B03T0301D/
4. Peters S (2003) Resurrecting hope: Drought tolerant crop plants. Science in Africa, http://www.scienceinafrica.co.za/2003/october/drought.htm
5. McKersie BD et al. (1996) Water-deficit tolerance and field performance of transgenic alfalfa overexpressing superoxide dismutase. Plant Physiol. 111(4), 1177-1181
6. Zhang J et al. (2000) Genetic engineering for abiotic stress resistance in crop plants. In Vitro Cell. Dev. Biol. – Plant 36,108–114
7. Penna S. (2003) Building stress tolerance through overproducing trehalose in transgenic plants. Trends in Plant Science 8, 355-357
8. Pilon-Smits A et al. (1998) Trehalose-producing transgenic tobacco plants show improved growth performance under drought stress. J. Plant Physiol. 152, 525–532
Tawanda Zidenga
Department of Plant Cellular and Molecular Biology
Ohio State University
zidenga.1@osu.edu
Copyright ISB
?Có nhiều xu hướng nghiên cứu sự chống hạn của thực vật và người ta phát hiện thấy vai trò của aa proline cao khi cây bị hạn, nhưng theo những nghiên cứu mới nhất người ta phát hiện ra nhân tố thúc đẩy qua trình ?oxi hóa gây hai cho tế bào . Hướng nghiên cứu đó đi đến việc chuyển gen vào thực vật ?nhằm hạn chế sự tác động của enzim oxi hóa đó ( oxidative enzymes ) ?Vậy:
?
? ? ?Chúng ta hãy đi vào giải quyết vấn đề đó !
Friday, December 9, 2005
Abscisic acid is a plant hormone that regulates growth, and transcription factors associated with a plant’s response to it play a key role in allowing plants to survive under drought stress. ? ? ?
?One such transcription factor is AREB1, and Yasunari Fujita and colleagues from Tsukuba, Japan find, from their research, that “AREB1 Is a Transcription Activator of Novel ABRE-Dependent ABA Signaling That Enhances Drought Stress Tolerance in Arabidopsis.”
In their paper, which appears in the latest issue of Plant Cell, researchers report that under normal growth conditions, the intact AREB1 gene is insufficient to induce the expression of genes. They thus created an activated form of the gene, called AREB1 QT, and over expressed it in Arabidopsis in the laboratory. Researchers found that the plants were hypersensitive to abscisic acid, and showed enhanced tolerance to drought. Plants without the gene were insensitive to abscisic acid, and displayed reduced survival under dehydration.
Subscribers to Plant Cell may read the complete article at:
http://www.plantcell.org/cgi/content/full/17/12/3470
Wednesday, March 8, 2006
By Tawanda Zidenga
Dehydration stress is one of the most serious yield-reducing stresses in agriculture. Drought stress is especially important in countries where crop agriculture is essentially rain-fed.
? ?
?In sub-Saharan Africa, drought years have a devastating effect on regional food security. While irrigation is the method of choice in averting drought stress in many areas of the world, alternative low-input approaches are being explored, and biotechnology offers a promising array of tools that may be useful in achieving drought tolerance in plants. One such tool is the low input approach to crop production by which crops are modified to suit the environment in which they are growing, rather than modifying the environment to meet the needs of the crop. This approach is advantageous in areas where water supplementation by irrigation is either difficult or unaffordable.
What happens to plants during drought?
Drought stress causes an increase in solute concentration in the environment, leading to an osmotic flow of water out of plant cells. This in turn causes the solute concentration inside plant cells to increase, thus lowering water potential and disrupting membranes along with essential processes like photosynthesis. These drought-stressed plants consequently exhibit poor growth and yield. In worst case scenarios, the plants completely die. Certain plants have devised mechanisms to survive under low water conditions. These mechanisms have been classified as tolerance, avoidance, or escape.
ROSes may be bad
Central to signal transduction pathways related to drought and other stresses are reactive oxygen species (ROS), which are molecules formed by the incomplete one-electron reduction of oxygen. Under stress, ROS formation is usually exacerbated. Drought stress leads to the disruption of electron transport systems; therefore, under water deficit conditions, the main sites of ROS production in the plant cell are organelles with highly oxidizing metabolic activities or with sustained electron flows: chloroplasts, mitochondria, and microbodies.1 ROS are generally damaging to essential cellular components, and plants have evolved various ROS scavenging mechanisms. These include the enzymes superoxide dismutase (SOD), catalase, and peroxidases, as well as oxidized and reduced glutathione.1
Researchers have focused on expressing genes for enzymes involved in ROS scavenging to enhance plant protection against oxidative stress. Transgenic alfalfa (Medicago sativa) expressing Mn-superoxide dismutase cDNA tended to have reduced injury from water-deficit stress, and this improvement was also seen in field trials in yield and survival.5
Secrets of resurrection
4 What does it take to rise from the dead? This is a question scientists working on resurrection plants have been exploring recently. Resurrection plants can tolerate almost complete water loss in their vegetative parts.2 At the University of Cape Town in South Africa, researchers are trying to unlock the secrets of the resurrection plant Xerophyta viscosa in an attempt to achieve drought tolerance in crops.1 These plants can be a source of drought tolerance genes for transgenic crop improvement. To withstand periods of drought, resurrection plants practically "die" (by losing all their vegetative parts) and then "rise again" when water becomes available. Their vegetative tissues lose all free water and then rehydrate once water becomes available again. Resurrection plants minimize ROS formation and also upregulate various antioxidant protectants during drying and rehydration.1 The group has identified a novel stress-inducible antioxidant enzyme, XvPer1, by differential screening of a cDNA library of X. viscose.
Osmoprotectants
Osmolytes are involved in signaling/regulating plant responses to multiple stresses, including reduced growth that may be part of the plant’s adaptation against stress. In plants, the common osmolytes are proline, trehalose, fructan, mannitol and glycinebetaine.6 The protection mechanisms are not yet fully understood, but they are thought to work via osmotic adjustment, stabilizing macromolecules, and scavenging ROS. One proposed transgenic strategy has been to overproduce osmolytes. However, transgenic plants overproducing osmolytes often exhibit impaired growth.
Trehalose, a non-reducing disaccharide, protects biological molecules in response to different stress conditions in many microorganisms.7 Plant biologists are interested in channeling trehalose metabolism to enhance stress tolerance in plants. Trehalose is made from UDP-glucose and glucose-6-phosphate via a two step process.
The conversion of UDP-glucose and glucose-6-phosphate to trehalose-6-phosphate is catalyzed by trehalose-6-phosphate synthase, encoded by the bacterial otsA gene. In the second step, glucose-6-phosphate is converted to trehalose by a phosphatase encoded by the bacterial otsB gene. Tobacco plants transformed with bacterial otsA have a greater ability to retain water and a greater ability to photosynthesize under water stress.8
Protection only when needed
Genes imparting protection from drought stress can be expressed in plants in two ways: they can be expressed all the time, whether or not the plant is under stress; or they can be engineered to express only when there is drought stress. The second method is more favored, as it limits the side effects of the manipulations. One of the challenges biologists face in trying to engineer for drought tolerance is that drought tolerance and/or resistance traits are often negatively correlated with productivity. To achieve protection only when needed, scientists use promoters that are stress-inducible, typically abscisic acid (ABA) inducible promoters.
References
1. Mundree SG et al. (2002) Physiological and molecular insights into drought tolerance. African Journal of Biotechnology 1(2), 28–38.
2. Scott P (2000). Resurrection plants and the secrets of eternal leaf. Annals of Botany 85, 159-166
3. Drought tolerance in Agriculture at University of Toronto. http://dragon.zoo.utoronto.ca/~B03T0301D/
4. Peters S (2003) Resurrecting hope: Drought tolerant crop plants. Science in Africa, http://www.scienceinafrica.co.za/2003/october/drought.htm
5. McKersie BD et al. (1996) Water-deficit tolerance and field performance of transgenic alfalfa overexpressing superoxide dismutase. Plant Physiol. 111(4), 1177-1181
6. Zhang J et al. (2000) Genetic engineering for abiotic stress resistance in crop plants. In Vitro Cell. Dev. Biol. – Plant 36,108–114
7. Penna S. (2003) Building stress tolerance through overproducing trehalose in transgenic plants. Trends in Plant Science 8, 355-357
8. Pilon-Smits A et al. (1998) Trehalose-producing transgenic tobacco plants show improved growth performance under drought stress. J. Plant Physiol. 152, 525–532
Tawanda Zidenga
Department of Plant Cellular and Molecular Biology
Ohio State University
zidenga.1@osu.edu
Copyright ISB
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