Outline

  • Abstract
  • Keywords
  • 1. Introduction
  • 2. Transgenic Plants for Environmental Remediation
  • 3. Degradation Pathways in Plants
  • 4. Cytochrome P450s: Environmental Perspectives
  • 5. Insertion of Cyp450 in Higher Plants for Enhanced Xenobiotic Metabolism
  • 5.1. Transgenic Plants Expressing Human P450s for Herbicide Metabolism
  • 5.1.1. Transgenic Rice
  • 5.1.2. Transgenic Tobacco and Potato Plants
  • 5.2. Transgenic Plants Expressing Human P450s for Halogenated Hydrocarbon Metabolism
  • 5.2.1. Transgenic Poplars
  • 5.3. Plant Cell Suspension Cultures As Expression System for Human P450 Isoenzymes
  • 6. Glutathione S-Transferases (gsts): Environmental Perspectives
  • 7. Transgenic Plants Overexpressing Gsts for Enhanced Degradation/conjugation of Organic Xenobiotics
  • 8. Transgenic Plants for the Enhanced Remediation of Explosives
  • 9. Transgenic Plants for the Rhizoremediation of Organic Xenobiotics
  • 10. Transgenic Plants to Be Developed for the Phytoremediation of Some Other Priority Pollutants
  • 11. Conclusions and Future Directions
  • Acknowledgements
  • References

رئوس مطالب

  • 1. مقدمه
  • کلیدواژه ها
  • 2. گیاهان ترانس ژنیک برای ترمیم محیطی
  • 3. راه های تجزیه در گیاهان
  • 4. سیتوکروم P450S: چشم اندازهای محیطی
  • 5. جاسازی CY450 در گیاهان بالاتر برای متابولیسم زنوبیوتیک ارتقا یافته
  • 5.1 گیاهان ترانس ژنیک استخراج کننده P450S انسانی برای متابولیسم آفت کش
  • 5.1.1 برنج ترانس ژنیک
  • 5.1.2 تنباکو و گیاهان سیب زمینی ترانس ژنیک
  • 5.2 گیاهان ترانس ژنیک استخراج کننده متابولیسم هیدروکربن هالوژنه
  • 5.2.1 درختان صنوبر ترانس ژنیک
  • 5.3 کشت های معلق سلول گیاهی به صورت سیستم استخراج برای ایزو آنزیمهای P450 انسانی
  • 6. گلوتاتیون S-ترانسفرازها (GSTs): چشم اندازهای محیطی
  • 7. گیاهان ترانس ژنیک بیش از حد استخراج کننده GSTها برای تجزیه ارتقا یافته/ ترکیب زنوبیوتیک های آلی
  • 8. گیاهان ترانس ژنیک برای ترمیم بهتر مواد منفجره
  • 9. گیاهان ترانس ژنیک برای ترمیم ریشه زنوبیوتیک های آلی
  • 10. گیاهان ترانس ژنیکی که برای ترمیم گیاهی برخی از آلاینده های دارای اولویت دیگر توسعه یافته اند
  • 11. نتیجه گیریها و رهنمودهای آینده
  • تقدیرنامه ها

Abstract

Phytoremediation — the use of plants to clean up polluted soil and water resources — has received much attention in the last few years. Although plants have the inherent ability to detoxify xenobiotics, they generally lack the catabolic pathway for the complete degradation of these compounds compared to microorganisms. There are also concerns over the potential for the introduction of contaminants into the food chain. The question of how to dispose of plants that accumulate xenobiotics is also a serious concern. Hence the feasibility of phytoremediation as an approach to remediate environmental contamination is still somewhat in question. For these reasons, researchers have endeavored to engineer plants with genes that can bestow superior degradation abilities. A direct method for enhancing the efficacy of phytoremediation is to overexpress in plants the genes involved in metabolism, uptake, or transport of specific pollutants. Furthermore, the expression of suitable genes in root system enhances the rhizodegradation of highly recalcitrant compounds like PAHs, PCBs etc. Hence, the idea to amplify plant biodegradation of xenobiotics by genetic manipulation was developed, following a strategy similar to that used to develop transgenic crops. Genes from human, microbes, plants, and animals are being used successfully for this venture. The introduction of these genes can be readily achieved for many plant species using Agrobacterium tumefaciens-mediated plant transformation or direct DNA methods of gene transfer. One of the promising developments in transgenic technology is the insertion of multiple genes (for phase 1 metabolism (cytochrome P450s) and phase 2 metabolism (GSH, GT etc.) for the complete degradation of the xenobiotics within the plant system. In addition to the use of transgenic plants overexpressed with P450 and GST genes, various transgenic plants expressing bacterial genes can be used for the enhanced degradation and remediation of herbicides, explosives, PCBs etc. Another approach to enhancing phytoremediation ability is the construction of plants that secrete chemical degrading enzymes into the rhizosphere. Recent studies revealed that accelerated ethylene production in response to stress induced by contaminants is known to inhibit root growth and is considered as major limitation in improving phytoremediation efficiency. However, this can be overcome by the selective expression of bacterial ACC deaminase (which regulates ethylene levels in plants) in plants together with multiple genes for the different phases of xenobiotic degradation. This review examines the recent developments in use of transgenic-plants for the enhanced metabolism, degradation and phytoremediation of organic xenobiotics and its future directions.

Keywords: - - - - - -

11. Conclusions and future directions

Although effectual under controlled conditions, the majority of the transgenic plants developed in different countries in the last decade never have been used in a real contaminated site. Furthermore, although less hindered by regulatory framework than transgenic microbial-based remediation, onsite introduction of transgenic plants are possible only with a considerable amount of bureaucracy. Major concerns over field release of such genetically manipulated plants include increased invasiveness and decreased genetic variability of native plants due to interbreeding. Dearth of knowledge with regard to detoxification mechanisms used by plants to cope up with xenobiotics is a major procedural constriction for focused engineering approach. Such enzymological knowledge for xenobiotics provides informed decisions on which genes to engineer. It has been suggested that increased understanding of the enzymatic process involved in plant tolerance and detoxification of xenobiotics will provide new directions for manipulating plant with superior remediation potential.

Further, some of the engineered plants are unsuitable for field application because of its small biomass and growth rates. However, in spite of these scruples, researchers continued to trail the development of transgenic plants bestowed with finer qualities (enhanced growth rate and biomass, deep root system, increased metabolism etc.). The uses of sterile clones have been suggested as a solution to invasiveness and interbreeding. However, as this new technology develops, the limitations accountable for the delay in its successful application will be overcome. The ecological paybacks offered by phytoremediation provide the impetus for pursuing its extensive execution.

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