User:Phebehl/sandbox

Nov 26, Monday - today I did the following:


 * I picked page drought tolerance: initial impression is that:


 * 1) There is a focus on xerophytes and needs additional sections about other relevant plants that have mechanisms drought tolerance, such as crop varieties(ie. corn, wheat, rice) and/or model organisms (ie. arabidopsis)
 * 2) The drought tolerance definition may want to be refined to expand to reflect the current definitions in reviews.
 * 3) There should be a section explaining the drought tolerance mechanism
 * 4) In the "importance to agriculture" section, genetic manipulation of plants should be elaborated on, and some companies can be mentioned.
 * 5) The "importance to horticulure" section can also be elaborated on.
 * 6) More pictures displaying drought/drought tolerance/drought tolerance pathways can be inserted into the article.


 * I clicked on every reference to confirm that they all work
 * The reference for 4 carbon fixation/CAM no longer works and should be updated.
 * The reference for the ARS project via the USDA no longer works and should be updated.
 * All other links to articles within Wikipedia work.


 * I found relevant reviews and websites to use for this article- will read over them since they are a bit lengthy
 * Biotechnology for the Development of Drought Tolerant Crops from ISAAA
 * The Physiological Basis of Drought Tolerance in Crop Plants: A Scenario-Dependent Probabilistic Approach
 * Progress in understanding drought tolerance: from alleles to cropping systems [Instructor HWB says: - this is a good article for 1st sentence as a review]
 * Genetic Engineering and Breeding of Drought-Resistant Crops
 * Inducing drought tolerance in plants: Recent advances
 * Drought Tolerance In Plants: A Review
 * Toward the Genetic Improvement of Drought Tolerance in Crops

Article is below

= Drought tolerance = From Wikipedia, the free encyclopedia Jump to navigationJump to searchSedum is a drought tolerant plant whose specific adaptations include succulence and a waxy surface on its leaves and stems.

Drought tolerance is the degree to which a plant is adapted to arid or drought conditions. Desiccation tolerance is an extreme degree of drought tolerance. Plants naturally adapted to dry conditions are called xerophytes.

Contents

 * 1Adaptations to dry conditions
 * 2Importance for agriculture
 * 3Importance in horticulture
 * 4See also
 * 5References

Adaptations to dry conditions[edit]
Main article: Xerophyte

Drought tolerant plants typically make use of either C4 carbon fixation or crassulacean acid metabolism (CAM) to fix carbon during photosynthesis. Both are improvements over the more common but more basal C3 pathway in that they are more energy efficient. CAM is particularly good for arid conditions because carbon dioxide can be taken up at night, allowing the stomata to stay closed during the heat of the day and thus reducing water loss.

Many adaptations for dry conditions are structural, including the following:


 * Adaptations of the stomata to reduce water loss, such as reduced numbers or waxy surfaces.
 * Water storage in succulent above-ground parts or water-filled tubers.
 * Adaptations in the root system to increase water absorption.
 * Trichomes (small hairs) on the leaves to absorb atmospheric water.

Importance for agriculture[edit]
Arid conditions can lower the yield of many crops. Plant breeding programs for improved yield during drought conditions have great economic importance, and these programs may be broad in scope. For example, one study on soybeans currently being conducted by the United States Department of Agriculture is scheduled to span several years, with research taking place across that country, and has among its goals the identification of specific mechanism by which soybeans resist wilting and of the specific genes for drought tolerance.

Importance in horticulture[edit]
In landscapes in arid or drought-prone regions, drought tolerance is an important consideration in plant selection. Xeriscaping is an approach to landscaping first developed in Denver, Colorado, a region with hot, dry summers. The use of drought tolerant plants is essential to a successful xeriscape, which ideally requires no supplemental irrigation

Editing article below

= Drought tolerance = From Wikipedia, the free encyclopedia Jump to navigationJump to searchSedum is a drought tolerant plant whose specific adaptations include succulence and a waxy surface on its leaves and stems.

Drought tolerance is the ability to which a plant maintains its biomass production during arid or drought conditions. Some plants are naturally adapted to dry conditions and are called xerophytes, surviving with protection mechanisms such as desiccation tolerance, detoxification, or repair of xylem embolism. Other plants, specifically some crop varieties like corn, wheat, and rice, have become more tolerant to drought via conventional breeding methods. More recently, methods of genetically engineering drought tolerant plants have been proposed.

The mechanisms behind drought tolerance are complex and involve many pathways which allows plants to respond to specific sets of conditions at any given time. Some of these interactions include stomatal conductance, carotenoid degradation and anthocyanin accumulation, the intervention of osmoprotectants (such as sucrose, glycine, and proline), ROS-scavenging enzymes. The molecular control of drought tolerance is also very complex and is influenced other factors such as environment and the developmental stage of the plant. This control is mainly comprised of transcriptional factors, such as dehydration-responsive element-binding protein (DREB), abscisic acid (ABA)- responsive element-binding factor (AREB), and NAM (no apical meristem).

Contents

 * 1Adaptations to dry conditions
 * 2Importance for agriculture
 * 3Importance in horticulture
 * 4See also
 * 5References

Physiology of drought tolerance [edit]
Plants can be subjected to slowly developing water shortages (ie, taking days, weeks, or months), or they may face short-term deficits of water) (ie, hours to days). In these situations, plants adapt by responding accordingly, minimizing water loss and maximizing water uptake. Plants are more susceptible to drought stress during the reproductive stages of growth, flowering and seed development. Therefore, the combination of short-term plus long-term responses allow for plants to produce a few viable seeds. Some examples of short-term and long-term physiological responses include:

=== Short-term responses ===


 * In the leaf: root-signal recognition, stomatal closure, decreased carbon assimilation
 * In the stem: inhibition of growth
 * In the xylem: hydraulic changes, signal transport, assimilation of transport
 * In the root: cell-drought signalling, osmotic adjustment

Long-term responses

 * In the above-ground portion of the plant: inhibition of shoot growth, reduced transpiration area, grain abortion, senescence, metabolic acclimation, osmotic adjustment
 * In the below-ground portion of the plant: turgor maintenance, sustained root growth, increased root/shoot, increased absorption area

Regulatory network of drought tolerance [edit]
In response to drought conditions, there is an alteration of gene expression, induced by or activated by transcription factors (TFs). These TFs bind to specific cis-elements to induce the expression of targeted stress-inducible genes, allowing for products to be transcribed that help with stress response and tolerance. Some of these include dehydration-responsive element-binding protein (DREB), ABA-responsive element-binding factor (AREB), no apical meristem (NAM), Arabidopsis transcription activation factor (ATAF), and cup-shaped cotyledon (CUC).

DREB1/CBF TFs
DREB1A, DREB 1B, and DREB 1C are plant specific TFs which bind to drought responsive elements (DREs) in promoters responsive to drought, high salinity and low temperature in Arabidopsis. Overexpression of these genes enhance the tolerance of drought, high salinity, and low temperature in transgenic lines from Arabidopsis, rice, and tobacco.

DREB2 TFs
DREB proteins are involved in a variety of functions related to drought tolerance. For example, DREB proteins including DREB2A cooperate with AREB/ABF proteins in gene expression, specifically in the DREB2A gene under osmotic stress conditions. DREB2 also induces the expression of heat-related genes, such as heat shock protein. Overexpression of DREB2Aca enhances drought and heat stress tolerance levles in Arabidopsis.

AREB/ABF TFs
AREB/ABFs are ABA-responsive bZIP-type TFs which bind to ABA-responsive elements (ABREs) in stress-responsive promoters and activate gene expression. AREB1, AREB2, ABF3, and ABF1 have important roles in ABA signalling in the vegetative stage, as ABA controls the expression of genes associated with drought response and tolerance. The native form of AREB1 cannot target drought stress genes like RD29B in Arabidopsis, so modification is necessary for transcriptional activation. AREB/ABFs are positively regulated by SnRK2s, controlling the activity of target proteins via phosphorylation. This regulation also functions in the control of drought tolerance in the vegetative stage as well as the seed maturation and germination.

Other TFs
TFs like NAC (comprised of NAM, ATAF, and CUC), are also related to drought response in Arabidopsis and rice. Overexpression in the aforementioned plants improves stress and drought tolerance. They also may be related to root growth and senescence, two physiological traits related to drought tolerance.

Natural adaptations to drought [edit]
Plants in naturally arid conditions retain large amounts of biomass due to drought tolerance and can be classified into 4 categories of adaptation :


 * 1) Drought-escaping plants: annuals that germinate and grow only during times of sufficient times of moisture to complete their life cycle.
 * 2) Drought-evading plants: non-succulent perennials which restrict their growth only to periods of moisture availability.
 * 3) Drought-enduring plants: also known as xerophytes, these evergreen shrubs have extensive root systems along with morphological and physiological adaptations which enable them to maintain growth even in times of extreme drought conditions.
 * 4) Drought-resisting plants: also known as succulent perennials, they have water stored in their leaves and stems to sparing uses.

Structural adaptations
Many adaptations for dry conditions are structural, including the following :


 * Adaptations of the stomata to reduce water loss, such as reduced numbers, sunken pits, waxy surfaces.
 * Reduced number of leaves and their surface area.
 * Water storage in succulent above-ground parts or water-filled tubers.
 * Crassulacean acid metabolism (CAM metabolism) allows plants to get carbon dioxide at night and store malic acid during the day, allowing photosynthesis to take place with minimized water loss.
 * Adaptations in the root system to increase water absorption.
 * Trichomes (small hairs) on the leaves to absorb atmospheric water.

Importance for agriculture[edit]
With the frequency and severity of droughts increasing in recent years, damage to crops has become more serious, lowering the overall yield. However, research into the molecular pathways involving stress tolerance have revealed that overexpression of such genes can enhance drought tolerance, leading to projects focused on the development of transgenic crop varieties.

Collaborations to improve drought tolerance in crop-variety plants
International research projects to improve drought tolerance have been introduced, such as the Consultative Group on International Agricultural Research (CGIAR). One such project from CGIAR involves introducing genes such as DREB1 into lowland rice, upland rice, and wheat to evaluate drought tolerance in fields. This project aims to select at least 10 lines for agricultural use. Another similar project in collaboration with CGIAR, Embrapa, RIKEN, and the University of Tokyo have introduced AREB and DREB stress-tolerant genes into soybeans, finding several transgenic soybean lines with drought tolerance. Both projects have found improved grain yield and will be used to help develop future varieties that can be used commercially.

Examples of current commercial drought tolerant plants
Performance Plants Inc, a Canadian plant biotechnology campany, is developing technology called Yield Protection Technology™ (YPT™). YPT™ protects plants against seed yield losses under suboptimal water levels by downregulating α or β subunits of protein farnesyl transferase, which is involved in the ABA signaling pathway, enhancing drought tolerance. In field trials, canola with YPT™ had 26% more seed yield with moderate drought stress than control canola. YPT™ has been demonstrated in corn and petunia, and is currently being developed in soybean, rice, sorghum, cotton and turf grass.

Impediments to the agricultural commercialization of drought tolerant plants
The development of genetically modified crops includes multiple patents for genes and promoters, such as the marker genes in a vector, as well as transformation techniques. Therefore, freedom-to-operate (FTO) surveys should be implemented in collaborations for developing drought tolerant crops. Large amounts of money are also needed for the development of genetically modified groups. To bring a new genetically modified crop into the commercial market, it has been estimated to cost USD 136 million over 13 years. This poses a problem for development, as only a small number of companies can afford to develop drought-tolerant crops, and it is difficult for research institutions to sustain funding for this period of time. Therefore, a multinational framework with more collaboration among multiple disciples is needed to sustain projects of this size.

Importance in horticulture[edit]
Plant transformation has been used to develop multiple drought resistant crop varieties, but only limited varieties of ornamental plants. This significant lag in development is due to the fact that more transgenic ornamental plants are being developed for other reasons than drought tolerance. However, abiotic stress resistance is being explored in ornamental plants by Ornamental Biosciences. Transgenic Petunias, Poinsettias, New Guinea Impatiens, and Geraniums are being evaluated for frost, drought, and disease resistance. This will allow for a wider range of environments in which these plants can grow.

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