Alcohol Dehydrogenase in Plant Response to Drought

Alcohol Dehydrogenase in Plant answer to Drought1. IntroductionPlant harvesting and productivity is adversely bear on by natures wrath in the form of conf utilize abiotic and biotic puree factors (e.g. salinity, low temperature, drouth, and flooding heat, oxidative var. and heavy metal toxicity). tout ensemble these focussing factors ar a menace for im make ups and prevent them from reaching their all-encompassing transmitted potential and limit the crop productivity worldwide. Abiotic notation is the master(prenominal) cause of crop failure, decrease average military issues for near major(ip) crops by more than 50% (Bray, 2000) and causes losses worth hundreds of million dollars each year. In fact these nisuses, threaten the sustain skill of agricultural industry (Shilpi, 2005).Environmental degradation and climate change confound become trying global problems because of the explosive cosmos increases and industrialization in developing countries. To solve this problem, matchless of the names is lay bio engineering science science based on physiology of crop, pose biochemistry, genomics and transgenic technology. This is becoming more and more burning(prenominal) for molecular breeding of crops that rat tolerate droughts. For this technology, we need to understand instal reactions to drought tenseness at the molecular level.For agricultural and environmental sustainability, it is significant to breed or familialally engineer crops with improved mental strain gross profit. The realization of key ingredients and that factor can be used directly for engineering transgenic crops with improved drought margin. Although a number of candidate cistrons perplex been set in recent years, only very few harbour been tried and true in liaisonal assays for a beneficial effect on drought tolerance. In order to assess divisor function directly in ready endorseing from abiotic stress caused by the drought, proved to be use ful. Analysing the functions of these factors is slender for discernment of the molecular mechanisms governing found stress rejoinder and tolerance, finally leading to enhancement of stress tolerance in crops finished ancestral manipulation. In this study, this will be used for over brass of genes as well as for generate gene silencing, by using GATEWAY technology. A statewide investigation of antidiuretic hormone and Pdc induction and the determination of grain alcohol production during stress give-and-takes would provide valuable information on how ethanol touch in the response to limited piddle condition.2. Literature review2.1. What is stress? express in physical terms is typesetd as mechanical vehemence per unit argona applied to an intent. In response to the applied stress, an object undergoes a change in the dimension. Biological term is difficult to define in the deeds stress. A biological condition, which may be stress for one demonstrate may be optimum f or another plant. The most practical definition of a biological stress is an adverse blackmail or a condition, which inhibits the normal functioning and well being of a biological ashes such(prenominal) as plants (Jones et al., 1989 )2.2. Stress bespeakling thoroughfaresThe stress is low perceived by the receptors present on the membrane of the plant cells , the manoeuvre is then transduced downstream and this terminuss in the generation of second messengers including calcium, reactive group O species (ROS) and inositol phosphates. These second messengers, further modulate the intracellular calcium level. This Ca2+ level is sensed by calcium binding proteins, Ca2+ sensors. These sensory proteins then interact with their several(prenominal) interacting partners ofttimes initiating a phosphorylation cascade and target the major stress antiphonary genes or the transcription factors controlling these genes.The products of these stress genes ultimately lead to plant adaptation and help the plant to survive the admonishing conditions. Thus, plant responds to stresses as individual cells and synergistically as a whole organism. Stress induced changes in gene expression in turn may participate in the generation of hormones like ABA, salicylic acid and ethylene. The different stress responsive genes can be broadly categorized as early and late induced genes. Early genes argon induced within minutes of stress aim intelligence and often express transiently. In contrast, most of the other genes, which are activated by stress more slowly, i.e. after hours of stress perception are included in the late induced category. These genes include the major stress responsive genes such as RD (responsive to evaporation)/ KIN ( tatty induced)/COR ( insensate responsive), which encodes and modulate the LEA-like proteins (late embryogenesis abundant), antioxidants, membrane stabilizing proteins and synthesis of osmolytes.2.3. Drought stressAmong all abiotic stresses, drou ght is one of the most serious problems for sustainable agriculture worldwide. The adverse effect of drought stress is declines in yield as report in crops such as rice (Oryza sativa) (Brevedan and Egli, 2003), wheat (Triticum aestivum) (Cabuslay et al., 2002), soybean (Glycine max) (Kirigwi et al., 2004), and chickpea (Cicer aerietum) (Khanna-Chopra and Khanna-Chopra, 2004).The adaptive responses to drought moldiness be coordinated at the molecular, cellular, and whole-plant levels. These conditions induce dehydration of plant cells, which may trigger physiologic, biochemical and molecular responses against such stresses (Shinozaki and Yamaguchi, 1996). Water dearth is a analyzable of responses, which depends upon severity and duration of the stress, plant genotype, developmental demo, and environmental factors providing the stress.Yield losses due to drought are highly unsettled in nature depending on the stress timing, intensity, and duration. Although, different plant spec ies have variable thresholds for stress tolerance, and some of them can successfully tolerate severe stresses and still complete their life cycles, most cultivated crop plant species are highly sensitive and every die or suffer from productivity loss after they are exposed to long periods of stress. It has been estimated that two-thirds of the yield potential of major crops are routinely lost due to unfavourable growing environments ( Shilpi, 2005 ).Plants have evolved a number of strategies to severe drought. These include hunt down strategies such as avoidance (flowering, deep cornerstoneing, enhanced pissing use of goods and services efficiency, or reduced weewee loss) as well as tolerance mechanisms. Reduced shoot growth and increased paper development could result in increased water absorption and reduced transpiration, thereby concuring plant tissue water status. In addition to such avoidance mechanisms, plant responses to water shortages can involve changes in biochemi cal pathways and expression of genes convert proteins that contribute to drought adaptation. The proteins could be enzymes knotted in the synthesis of osmolytes, antioxidants, or hormones such as ABA and others. Such changes can bring about drought tolerance, whereby plants continue to function at the low water potentials caused by water deficit (Hall, 1993). A central response to water deficit is often increased synthesis of ABA, which in turn induces a range of developmental (avoidance) and physiological or biochemical (tolerance) mechanisms. There is an ongoing debate as to whether the exploitation of avoidance or tolerance mechanisms should be the focus of plant breeding programmes. However, it appears likely that the exploitation of tolerance mechanisms may be more promising for the stabilization of crop yield under severe drought conditions (Araus et al, 2002).An assortment of genes with diverse functions are induced or repressed by these drought stresses (Bartels and Sunkar , 2005 Yamaguchi and Shinozaki, 2005). Drought tolerance has been shown to be a highly mazy trait, regulated expression of multiple genes that may be induced during drought stress and thus more difficult to control and engineer. Plant engineering strategies for abiotic stress tolerance rely on the expression of genes that are involved in mansion and regulatory pathways (Seki and Shinozaki, 2003) or genes that encode proteins conferring stress tolerance (Wang, 2004) or enzymes present in pathways leading to the synthesis of in operation(p) and structural metabolites. Current efforts to improve plant stress tolerance by genetic transformation have resulted in several important achievements however, the genetically complex mechanisms of abiotic stress tolerance make the task extremely difficult.2.3.1 Physiological and biochemical responses of droughtPhysiological and biochemical changes at the cellular level that are associated with drought stress include turgor loss, changes in me mbrane fluidity and composition, changes in solute concentration, and protein and protein-lipid interactions (Chaves et al,2003) .Other physiological effects of drought on plants are the reduction in vegetative growth, in particular shoot growth. Leaf growth is generally more sensitive than the root growth. Reduced click elaboration is beneficial to plants under water deficit condition, as less leaf area is exposed resulting in reduced transpiration. Many mature plants, for guinea pig cotton subjected to drought respond by accelerating senescence and abscission of the elder leaves. This process is alike know as leaf area adjustment. Regarding root, the relational root growth may undergo enhancement, which facilitates the capacity of the root system to extract more water from deeper soil layers.Plant tissues can maintain turgor during drought by avoiding dehydration, tolerating dehydration or twain (Kramer,1995). These forms of stress confrontation are controlled by developmen tal and morphological traits such as root thickness, the ability of roots to penetrate compacted soil layers, and root depth and megabucks (Pathan, 2004). By contrast, adaptive traits, such as osmotic adjustment and dehydration tolerance, arise in response to water deficit . Reduction of photosynthetic body process, accumulation of organic acids and osmolytes, and changes in carbohydrate metabolism, are typical physiological and biochemical responses to stress.Synthesis of osmoprotectants, osmolytes or compatible solutes is one of the mechanisms of adaptation to water deficit. These molecules, which act as osmotic balancing agents, are accumulated in plant cells in response to drought stress and are subsequently degraded after stress relief (Tabaeizadeh ,1998).2.3.2 Molecular responsesStudies on the molecular responses to water deficit have identified multiple changes in gene expression. officiates for many of these gen products have been predicted from the deduced amino acid se quence of the genes. Genes expressed during stress are anticipated to promote cellular tolerance of dehydration through protective functions in the cytoplasm, alteration of cellular water potentia1 to promote water uptake, control of ion accumulation, and further regulation of gene expression.Expression of a gene during stress does not guarantee that a gene product promotes the ability of the plant to survive stress. The expression of some genes may result from blemish or damage that occurred during stress. Other genes may be induced, but their expression does not alter stress tolerance. Yet others are required for stress tolerance and the accumulation of these gene products is an adaptive response.Complex regulatory and signaling processes, most of which are not understood, control the expression of genes during water deficit. In addition to induction by stress, the expression of water-deficit-associated genes is controlled with respect to tissue, organ, and developmental stage an d may be expressed independently of the stress conditions. The regulation of specific processes will also depend upon the experimental conditions of stress application. Stress conditions that are applied in the laboratory may not accurately follow those that occur in the field. Frequently, laboratory stresses are rapid and severe, whereas stress in the field often develops over an extended period of time ( Radin, 1993). These differences must also be evaluated when studying the adaptive value of certain responses. The function of the gene products and the mechanisms of gene expression are intertwined, and both must be understood to fully comprehend the molecular response to water deficit.2.4. Function of water-stress inducible genesGenes induced during water-stress conditions are thought to function not only in protecting cells from water deficit by the production of important metabolous proteins but also in the regulation of genes for signal transduction in the water-stress respo nse .Thus, these gene products are classified into two groups. The first group includes proteins that belike function in stress tolerance water channel proteins involved in the movement of water through membranes, the enzymes required for the biosynthesis of various osmoprotectants (sugars, Pro, and Gly-betaine), proteins that may protect macromolecules and membranes (LEA protein, osmotin, antifreeze protein, chaperon, and mRNA binding proteins), proteases for protein turn over (thiol proteases, Clp protease, and ubiquitin), the detoxification enzymes (glutathione S-transferase, soluble epoxide hydrolase, catalase, superoxide dismutase, and ascorbate peroxidase). Some of the stress-inducible genes that encode proteins, such as a key enzyme for Pro biosynthesis, were over expressed in transgenic plants to produce a stress tolerant phenotype of the plants this indicates that the gene products really function in stress tolerance ( Shinozaki ,1996 ).The second group contains protein fa ctors involved in further regulation of signal transduction and gene expression that probably function in stress response Most of the regulatory proteins are involved in signal transduction. straight it becomes more important to elucidate the role of these regulatory proteins for further understanding of plant responses to water deficit. Many transcription factor genes were stress inducible, and various transcriptional regulatory mechanisms may function in regulating drought, cold, or high salinity stress signal transduction pathways. These transcription factors could govern expression of stress-inducible genes either cooperatively or independently, and may constitute gene networks in genus genus genus Arabidopsis ( Pathan.2004 ),2.5. Model plant for studying the drought tolerantArabidopsis thaliana is a small weed in the mustard family. It has been a convenient for studies in classical genetics for over forty years ( Redei,1975). This flowering plant also has a genome size and ge nomic organization that recommend it for certain experiments in molecular genetics and it is coming to be widely used as a model organism in plant molecular genetics, development, physiology, and biochemistry. Arabidopsis thaliana provides an excellent experimental plant system for molecular genetics because of its unmistakably small genome size and short life cycle. Arabidopsis thaliana, a genetic model plant, has been extensively used for unravelling the molecular basis of stress tolerance. Arabidopsis also proved to be extremely important for assessing functions for individual stress associated genes due to the availability of knock-out mutants and its amenability for genetic transformation. It has been collected or reported in many different regions and climates, ranging from high elevations in the tropics to the cold climate of northern Scandinavia and including locations in Europe, Asia, Africa, Australia, and North America (Kirchheim,1981).Arabidopsis has the smallest known genome among the higher plants. The reasons for a small genome include little repetitive deoxyribonucleic acid and, in some cases, simpler gene families. Leutwiler et al. (1984) reported that the monoploid genome from Arabidopsis (n = 5 chromosomes) contains only roughly 70,000 kilobase pairs (kb). The contrast of the Arabidopsis genome with that of other plants frequently used in molecular genetic work is striking tobacco, for example, has a haploid nuclear genome of 1,600,000 kb the pea haploid genome is 4,500,000 kb and the wheat haploid genome is 5,900,000 kb . The significance of this small DNA content for molecular genetics is that a genomic library of Arabidopsis chromosomal fragments is easy to make, and simple and economical to screen. It is thus rapid and inexpensive to repeatedly screen Arabidopsis genomic libraries. In addition to its remarkably low content of nuclear DNA, Arabidopsis has a genomic organization that makes it uniquely suited to certain types of molecul ar cloning experiments. solely of the properties of the plant small, short generation time, high seed set, ease of growth, self- or cross-fertilization at willmake Arabidopsis a convenient subject for studies in classical genetics.2.6. Drought related geneAlcohol dehydrogenase and pyruvate decarboxylase are enzyme whose activity has been observed in numerous higher plants including Arabidopsis, maize, pearl millet, sunflower, wheat, and pea (Gottlieb, 1982). In a number of plants, different vasopressin genes are expressed in various organs, at specific times during development, or in re-sponse to environmental signals. High levels of vasopressin activity are found in dry out seeds and in anaerobically treated seeds (Freeling, 1973. Banuett-Bourrillon .1979), roots (Freeling .1973), and shoots (App, 1958).During periods of anaerobic stress, the enzyme is presumably required by plants for NADH metabolism, via reduction of acetaldehyde to ethanol. With respect to secondary metabolites , ADH is involved in the inter conversion of volatile compounds such as aldehydes and alcohols (Bicsak et al., 1982 Molina et al., 1986 Longhurst et al., 1990).The ethanolic fermentation pathway branches off the main glycolytic pathway at pyruvate. In the first step, pyruvate is the substrate of pyruvate decarboxylase (PDC), yielding CO2 and acetaldehyde. Subsequently, acetaldehyde is reduced to ethanol with the concomitant oxidization of NADH to NAD+ by alcohol dehydrogenase (ADH).Although PDC and ADH gene induction has been demonstrated, ethanol and acetaldehyde production as a result of stress treatment has only been reported for red pine (Pinus resinosa) and birch (Betula spp.) seedlings exposed to southward dioxide, water deficiency, freezing, and ozone(Kimmerer and Kozolowski. 1982).Many plants contain more than one ADH gene (Gottlieb, 1982 ), resulting in the expression of different ADH proteins (i.e. ADH isozymes, often designated ADH 1, ADH2, etc. ). The most extensive s tudy of maize Adh genes, AdhI and Adh2, have been cloned and sequenced. The coding sequences of these genes are 82% homologous, interrupted by nine identically positioned introns that differ in sequence and length.The expression of the Arabidopsis Adh gene (Chang and Meyerowitz, 1986 Dolferus et al., 1990) has many features in common with maize Adhl gene (Walker et al., 1987). The two genes have comparable developmental expression pattens, and both have tissue-specific responses to hypoxic stress. In both maize and Arabidopsis, the gene is expressed in seeds, roots, and pollen grains, whereas green aerial plant parts are devoid of detectable levels of ADH activity. In both species, hypoxic induction of the gene occurs in cells of the root system (reviewed by Freeling and Bennett, 1985 Dolferus and Jacobs, 1991 Okimoto et al., 1980). ADH is induced anaerobically in Arabidopsis (Dolferus, 1985) as in maize. ADH is also induced in both maize root and Arabidopsis callosity by the synth etic auxin 2,4-dichlorophenoxyacetic acid (Dolferus,1985. Feeling, 1973).Several approaches have been undertaken to assess the functional role of Adh in development, stress response, and metabolite synthesis. The expression of the alcohol dehydrogenase (Adh) gene is known to be regulated developmentally and to be induced by environmental stresses (Christie et al., 1991 Bucher et al., 1995). Alcohol dehydrogenase (ADH) plays a key enzymatic function in the response to anaerobic conditions in plants (Sachs, Subbaiah, and Saab 1996). A new and exciting feel of ethanolic fermentation is the suggested involvement in stress signaling and response to environmental stresses other than low oxygen (Tadege et al., 1999). Furthermore, specific analysis of the ADH gene from rice (Oryza sativa), maize, and Arabidopsis showed ADH to be induced by cold (Christie et al., 1991), wounding (Kato-Noguchi, 2001), dehydration (Dolferus et al., 1994), and the phytohormone abscisic acid (ABA de Bruxelles e t al., 1996), in line with the observation from the micro-array experiments.In Arabidopsis thaliana, Adh overexpression improved the tolerance of hirsute roots to low oxygen conditions and was effective in improving root growth (Dennis et al., 2000 Shiao et al., 2002). However, it had no effect on flooding survival (Ismond et al., 2003). Adh over expression in tomato has been shown to modify the balance in the midst of C, Adh overexpression in tomato aldehydes and alcohols in ripe fruits (Speirs et al., 1998). line plants overexpressing Adh displayed a lower sucrose content, a higher pointedness of polymerization of proanthocyanidins, and a generally increased content of volatile compounds, in general in carotenoid- and shikimate-derived volatiles (Catherine et al., 2006).