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284 Abiotic Stress in Plants Mechanisms and Adaptations. Stress Consequences Plant Responses,High temperature lead to high. Efficient protein repair systems and,evaporation and water deficit. general protein stability support,Heat stress The consequent increased. survival temperature can lead to,turnover of enzymes leads to. acclimation,plant death,Biochemical reactions proceed.
at slower rate photosyntesis,Cessation of growth in adaptable. proceeds carbon dioxide,species may be overcome by changes in. Chilling and fixation lags leading to oxigen,metabolism Ice crystal formation can. cold stress radical damage Indeed,be prevent by osmolyte accumulation. freezing lead to ice crystal,and synthesis of hydrophilic proteins.
formation that can distrupt,cells membranes,Leaf rolling and other morphological. adaptations Stoma closure reduces,Inability to water transport to. evaporative transpiration induced by,Drought leaves leads to photosyntesis. ABA Accumulation of metabolities,consequently lower internal water. potential and water attracting, Generates anoxic or Development of cavities mostly in the.
Flooding and microaerobic conditions roots that facilitate the exchange of. submergence interfering with mitochondrial oxigen and ethylene between shoot and. respiration root aerenchyma, Heavy metal In excess detoxification Excess of metal ions may be countered. accumulation reactions may be insufficient by export or vacuolar deposition but. and metal or storage capacity may metal ions may also generate oxygen. stress exceeded radicals,Exposure of a plant to light exceeding. what is utilized in photochemistry leads,Excess light can lead to. to inactivation of photosynthetic,increased production of highly. functions and the production of reactive,High light reactive intermediates and by.
oxygen species ROS The effects of,stress products that can potentially. these ROS can be the oxidation of lipids,cause photo oxidative damage. proteins and enzymes necessary for the,and inhibit photosynthesis. proper functioning of the chloroplast,and the cell as a whole. Table 1 Consequences of abiotic stress and plant responses. Xiong et al 2002 Also accumulation of abscisic acid ABA plays an important role in. abiotic stress signalling and transduction pathways mediating many responses. Wasilewska et al 2008, It is well known that abiotic stresses in general through regulation of both gene expression.
and protein turnover alter the abundance of many transcripts and proteins Wong et al. 2006 Yan et al 2006 Jiang et al 2007 indicating that transcriptional and post. transcriptional regulation play an essential role in the adaptation of cellular functions to the. environmental changes,www intechopen com,Plant Genes for Abiotic Stress 285. Recent advances in molecular biology genomics proteomics and metabolomics have. provided insight into plant gene regulatory network system which is mainly composed of. inducible genes environmental factors and developmental cues expression programming. and regulatory elements cis element and trans element corresponding biochemical. pathways and diverse signal factors Tang et al 2003 Wang et al 2003 Zhu 2003 Munns. 2005 Genetic studies revealed that stress tolerance traits are mainly quantitative trait loci. QTLs which make genetic selection of traits difficult. Responses to abiotic stress require the production of important metabolic proteins such as. those involved in synthesis of osmoprotectants and of regulatory proteins operating in the. signal transduction pathways such as kinases or transcriptional factors TFs In addition. new transcripts are made and within a few hours a steady level of stress adaptation has. been reached In general the transcriptional regulation of genes is directly controlled by a. network of TFs and transcription factor binding sites TFBS Chaves Oliveira 2004 TFs. are proteins with a DNA domain that binds to the cis acting elements present in the. promoter of a target gene They induce activators or repress repressors the activity of the. RNA polymerase thus regulating gene expression TFs can be grouped into families. according to their DNA binding domain Riechmann et al 2000 The presence or absence. of transcription factors activators and suppressors regulating transcription of target genes. often involves a whole cascade of signalling events determined by tissue type. developmental stage or environmental condition Wyrick Young 2002. Environmental stress inducible genes can be mainly divided into two groups in terms of. their protein products one type of genes whose coding products directly confer to plant. cells the resistence to environmental stress such as late embryogenesis abundant LEA. protein anti freezing protein osmotic regulatory protein enzymes for synthesizing. betaine proline and other osmoregulators the other groups of genes whose coding. products play an important role in regulating gene expression and signal transduction. such as the transcriptional elements At least four different regulons can be identified two. ABA independent 1 and 2 and two ABA dependent 3 and 4 1 the CBF DREB. regulon 2 the NAC NAM ATAF and CUC and ZF HD zinc finger homeodomain. regulon 3 the AREB ABF ABA responsive element binding protein ABA binding. factor regulon and 4 the MYC myelocytomatosis oncogene MYB myeloblastosis. oncogene regulon, Our knowledge of the molecular mechanisms underlying the responses of plants to such. environmental stresses is still rather limited but an increasing number of genes have been. identified in recent years that mediate these responses Some of these genes are induced by. stress stimuli and encode products that confer tolerance to adverse conditions whereas. others encode upstream regulators that function within signalling pathways controlling the. stress response, The aim of this book chapter is to describe the regulation of gene expression under abiotic. stresses and report recent advances in the stress response mechanisms. 2 Abiotic stress inducible genes, The complex plant response to abiotic stress involves many genes and biochemical. molecular mechanisms The analyze of the functions of stress inducible genes is an. important tool not only to understand the molecular mechanisms of stress tolerance and the. responses of higher plants but also to improve the stress tolerance of crops by gene. www intechopen com, 286 Abiotic Stress in Plants Mechanisms and Adaptations.
manipulation Hundreds of genes are thought to be involved in abiotic stress responses. Seki 2003 Avni ktem et al 2008, Many drought inducible genes are also induced by salt stress and cold which suggests the. existence of similar mechanisms of stress responses. These genes are classified into three major groups 1 those that encode products that. directly protect plant cells against stresses such as heat stress proteins HSPs or chaperones. LEA proteins osmoprotectants antifreeze proteins detoxification enzymes and free radical. scavengers Bray et al 2000 Wang et al 2000 2 those that are involved in signalling. cascades and in transcriptional control such as Mitogen activated protein kinase MAPK. Calcium dependent protein kinase CDPK Ludwig et al 2004 and SOS kinase Zhu et al. 2001 phospholipases Frank et al 2000 and transcriptional factors Cho et al 2000. Shinozaki et al 2000 3 those that are involved in water and ion uptake and transport. such as aquaporins and ion transporters Blumwald et al 2000. 3 Transcriptional factor genes involved in abiotic stress. Plant growth and productivity are under constant threat from environmental changes in the. form of various stress factors The most common abiotic stresses are drought flooding or. submergence salinity extreme temperatures heat and freezing and high light. Furthermore the continued modification of the atmosphere by human activities lead to. increase in the concentration of ozone in the troposphere and this can generate oxidative. stress which leads to the destruction of proteins and cells premature ageing and reduced. crop yields, Tolerance or susceptibility to these abiotic stresses is a very complex phenomenon both. because stress may occur at multiple stages of plant development and more than one stress. simultaneously affects the plant Therefore the perception of abiotic stresses and signal. transduction to switch on adaptive responses are critical steps in determining the survival. and reproduction of plants exposed to adverse environments Chinnusamy et al 2004. During the past few years transcriptome analysis has indicated that distinct environmental. stresses induce similar responses Overlap between stress responses can explain the. phenomenon known as cross tolerance a capability to limit collateral damage inflicted by. other stresses accompanying the primary stress, Responses to abiotic stresses require the production of important metabolic proteins such as. those involved in synthesis of osmoprotectants and regulatory proteins operating in signal. transduction pathways that are kinases or transcription factors TFs The regulation of. these responses requires proteins operating in the signal transduction pathways such as. transcriptional factors which regulate gene expression by binding to specific DNA. sequences in the promoters of respective target genes This type of transcriptional regulatory. system is called regulon At least four different regulons that are active in response to abiotic. stresses have been identified Dehydration responsive element binding protein 1. DREB1 C repeat binding factor CBF and DREB2 regulons function in abscisic acid. ABA independent gene expression whereas the ABA responsive element ABRE binding. protein AREB ABRE binding factor ABF regulon functions in ABA dependent gene. expression Saibo et al 2009 In addition to these major pathways other regulons. including the NAC or NAM No Apical Meristem and Myeloblastosis Myelocytomatosis. MYB MYC regulons are involved in abiotic stress responsive gene expression Fig 1. Particularly NAC type TF OsNAC6 is induced by abiotic stresses including cold drought. www intechopen com,Plant Genes for Abiotic Stress 287. Fig 1 Transcriptional network of abiotic stress responses. and high salinity Microarray analysis showed that many abiotic inducible genes were up. regulated in rice plants over expressing OsNAC6 Nakashima et al 2007. TFs are powerful targets for genetic engineering in abiotic stress resistance in crop plants. and many studies have been done in the last two decades on this topic. Transcription factors are shown in ovals Transcription factor modifying enzymes are. shown in circles The small triangles correspond to post translational modifications Green. squares with question marks represent putative MYC ICE1 like transcription factors that. may activate CBF1 DREB1B and CBF2 DREB1C The green boxes represent the cis. elements present in stress responsive genes The red dot corresponds to the sumoylation. modification by SIZ1 of the ICE1 transcription factor The dashed black line from SIZ1 to. HOS1 represents competition for binding places on the ICE1 transcription factor SIZ1. blocks the access of HOS1 to the ubiquitination sites on the ICE1 CBF4 DREB1D is a DRE. cis element binding factor that is ABA dependent,4 Drought stress transcriptional factors.
The genome controls the regulation of the response to water deficit as well as the. effectiveness of the response Microarrays largely performed using Arabidopsis thaliana as. model plant have been used to catalogue the many genes that are induced or repressed in. www intechopen com, 288 Abiotic Stress in Plants Mechanisms and Adaptations. response to conditions that may lead to cellular water deficit stress Seki et al 2002 These. genes can be placed in at least four different functional groups signal transduction. transcriptional regulation cellular metabolism and transport and protection of cellular. structures, There are at least six different classes of TFs that participate in gene induction or repression. in response to water deficit Homeobox domain and NAC domain containing TFs are. induced by multiple treatments that mimic water deficit stress Accumulation of proteins. which have metabolic or structural functions promote adaptation to stress One class of. genes that could play a role in protection is called the late embryogenesis abundant Lea. genes The Lea genes are also developmentally programmed for expression in desiccating. seeds These genes encode small hydrophilic proteins that are predicted to protect proteins. and membranes through chaperone like functions These proteins were thought to improve. the performance of rice plants by protecting cell membranes from injury under abiotic stress. Chandra et al 2004, 4 1 Gene regulation and transcriptional factors in water deficit. A recent review Shinozaki Yamaguchi Shinozaki 2007 on analysis of gene expression. during drought stress response in plants show and summarize the functions of some genes. in both stress response and tolerance Microarray analysis performed on wheat genome. showed that among 300 unique single expressed sequences tag ESTs the 30 of genes. were significantly up regulated and the 18 were down regulated under drought stress. Way et al 2005, Potential functions of approximatively 130 genes of A thaliana up regulated in water defic. those involved in synthesis of anti freezing protein osmotic regulatory protein enzymes for TFs are powerful targets for genetic engineering in abiotic

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