Possible processes of each mechanism have been indicated in the boxes. Plants and how they react to water deficit can be summarised in three ways i. Since, drought tolerance is characterized by the capability of plants to grow satisfactorily under water deficit condition Turner Escaping the drought is shortening the life cycle mainly in reproductive phase and desiccation tolerance can be performed in both reproductive and vegetative phases of some specific plants.
Tolerance to an environmental factor could be defined as the fitness response of a plant to a diverse concentration of that element. Accordingly, water stress tolerance means the ability to retain the fitness under the water deficit condition Simms Hence, a more tolerant genotype minimizes fitness losses in water deficit conditions from that attained in benign water conditions with respect to less tolerant or sensitive genotypes. Desiccation tolerance is observed in a specific category of the plant kingdom called resurrection plants.
Even though certain plants have evolved specific adaptive mechanisms to alleviate adverse effects of water deficit stress, there are some common metabolic adaptations observed in diverse economical plants. It seems these results regarding key metabolites and identified mechanisms could be used in plant breeding programs particularly for improving stress tolerance in economical plants.
Given the importance of shortening the plant breeding procedures to release new improved varieties, such compounds can serve as biomarker. In this way, selection of superior individuals in segregation generations could be facilitated. Therefore, it is necessary to recognise plant adaptive mechanisms and differentiate avoidance and tolerance strategies with the aim to understand the tolerance mechanisms at the metabolite level.
Drought escape. Basically the plant shortens the life cycle in this way; two outstanding examples are converting to flowering phase when water is limited at late season and also germination at early season growth. Dehydration avoidance. As the direction of water movement is from higher to lower water potential, in dehydrated soil, roots will lose water. The first strategy of the plant is dehydration avoidance by keeping the balance between water loss from the roots and water uptake. Several morphological developments have been demonstrated previously to be correlated with avoidance mechanisms through minimizing the water loss.
Root structure is associated with dehydration avoidance mechanisms. For instance, long roots with plentiful branches allow the plant to absorb more water sustainably and access larger soil volume Passioura , Arndt Dehydration tolerance.
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When low water potential persists, dehydration tolerance mechanisms contribute to prevent cellular damage by water loss Verslues et al. Moreover, under severe drought stress conditions, dehydration tolerance is the final strategy that plants can employ to survive under drought stress conditions Connor Early responses are including stress perception and signalling to provide initial protection.
Stress perception is the first stage of drought stress response, to sense water deficit in the soil. While, Cre1 cytokininresponse 1 as a two-component histidine kinase receptor act through phosphorilation pathway. When drought stress condition persists, late responses initiate, which is expression of set of genes responsible for osmolyte synthesis, LEA Late Embryogenesis Abundant proteins, aquaporins, signalling molecules and transcription factors TFs Yang et al.
Osmotic adjustment. This mechanism is called osmotic adjustment, and these solutes are known as compatible solutes, because with their increase, plant metabolism is not disturbed and they are not toxic even in higher concentrations Yancey et al. When osmotic potential decreases due to osmolyte accumulation, water potential will decrease Zhang et al. Osmotic pressure rises by increasing accumulating the solutes. Therefore, when solute concentration increases, osmotic pressure will increase while osmotic potential will decrease.
This mechanism is shown in Figure 3. Water always flows from higher water potential to lower water potential. Under normal conditions, water moves into the cell due to the difference in water potential of outside -1Bar from inside -3 Bar. Under drought condition, two possible responses of cell are presented. Without osmotic adjustment, plasmolysis will be happened. If cell activates osmotic adjustment mechanism, both turgor pressure and osmotic potential will decrease. Therefore still water moves into the cell because of lower water potential.
In general, these metabolites stabilize enzymes, protect membranes and produce osmotic adjustments to keep the turgor pressure Chaves et al. Activation of antioxidant systems against oxidative stress damage. ROS or free radicals O 2. These toxic molecules damage cells by oxidation of vital macromolecules such as proteins, membrane lipids, DNA, pigments and nucleic acids Dat et al. Various studies have established the enhancement of ROS under osmotic stress conditions Serrato et al. In accordance, plants are equipped with complex defence mechanisms using enzymatic and non-enzymatic antioxidants to mitigate oxidative damages caused by ROS Dat et al.
Non-enzymatic antioxidants are ascorbate AsA , glutathione GSH , carotenoids, tocopherols, and phenolics Sharma et al. Strong correlation has been reported between stress tolerance and higher concentrations of antioxidants Zaefyzadeh et al. Many studies on crop plants including sorghum, rice and rapeseed confirmed that tolerant cultivars as compared to sensitive ones, exhibited up-regulation of antioxidant gene network products, to protect the plant subjected to drought stress.
ABA and its physiological role in drought stress response. In response to unfavourable environments such as drought, plants employ ABA abscisic acid to activate adaptive metabolic responses Kusaka et al. In addition, ABA serves as a plant development optimizer Cheng et al. Obviously water status is a stimulus of ABA formation Petropoulos et al.
In general, ABA enhances dehydration tolerance through induction of genes encoding tolerance proteins in most of the cells Kusaka et al. ABA-dependent pathways are activated following the accumulation of ABA, and leading to expression of two kinds of stress related genes namely functional and regulatory.
But ABA-independent pathways are not related to each other and seem there is some cross-talk between them Chaves et al. Other mechanisms of dehydration tolerance. Membrane proteins such as aquaporins AQP can transport water, solutes and gases through membranes or even throughout the plant Bray et al. The XIPs were found in some plant species more recently. Under water limitation condition, AQPs modulate the water balance for the whole plant by passive water transport through membrane Maurel et al.
These membrane proteins form channels to pass water easily through the plasma Kammerloher et al. Therefore, under dehydration conditions, these membrane-associated transporters may serve as water movement facilitators Bray et al. Key plant products involved in water deficit response. Many compounds contribute to adaptive response to drought stress acclimation process.
These compounds belong to three groups: the first group is all major compounds with a key role in adaptive response such as osmolytes Slama et al. Third group are signalling molecules which regulate adaptive responses such as salicylic acid Mittler , Mittler et al. However, to explain the role of adaptive compounds we had to classify them into major classes such as lipids, compatible solutes, proteins and secondary metabolites. Likewise, function and structure of membranes as well as enzyme activity and transport capacity are affected by the physical state and composition of lipids Gronewald et al.
Main lipids of membranes are phospholipids PL mostly in mitochondrial and plasma membrane and glycolipids GL mostly in chloroplast membrane. In general, studies demonstrated that long water deficit causes decreasing PLs and GLs and linoleic acid contents but increasing tricylglycerols in leaf tissue. Likewise, previous investigations showed that water deficit inhibits biosynthesis of polyunsaturated fatty acids which leads to reduced fatty acid unsaturation Anh et al.
These modifications include decreasing polar lipid contents and also polyunsaturated fatty acids, but particularly the major leaf glycolipid MGDG or MonoGalactosyl DiacylGlycerol Chetal et al. These alterations are likely due to increased lipolytic performance, lipid biosynthesis inhibition Anh et al.
Previous studies established that the extent of these modifications in drought tolerant plants is less than sensitive ones because their cell membrane is more stable Pham Thi et al. Compatible solutes. As described in previous sections, compatible solutes contribute to the well-known tolerance mechanism called osmotic adjustment.
Nevertheless, enhanced accumulation of mentioned osmolytes has been reported in various plants exposed to abiotic stresses, but threshold level and diversity of the osmolytes depend on the species and environmental condition Szabados et al. In the other hand, some species accumulate only some specific kinds of osmolytes, not all the kinds. For instance, sugar accumulation has been observed in monocots rather than dicots. Likewise, glycine betain is less accumulated in grasses Slama et al. Dehydrins were observed in response to various abiotic stresses including drought, but its detailed function is not well understood Cellier et al.
LEAs have multiple tasks ranging from maturity in seeds to protection of membrane structure, stabilizing enzymes and promoting ion sequestration in vegetative organs Close , Garay-Arroyo et al. Another class of proteins known as molecular chaperones or originally known as HSP: Heat Shock proteins has been reported under abiotic stress conditions such as drought Alamillo et al. Much evidence confirms that HSPs act in protein refolding, stabilizing proteins and membranes under stress conditions Wang et al.
In this way, HSPs protects other proteins from denaturation during drought stress Gorantla et al. Some sHSPs gene expression and protein synthesis up-regulated with stress in sunflower Coca et al. Role of HSPs in tolerance mechanism been confirmed while up-regulation of a specific HSP observed in tolerant varieties of wheat compare to down regulation in sensitive varieties under drought stress conditions Hajheidari et al.
Secondary metabolites. To date, , diverse compounds have been identified as secondary metabolites Schwab which are classified into three major groups namely alkaloids, isoprenoids and phenylpropanoids Frey et al. According to definition, secondary metabolites are produced from primary metabolites and certain secondary metabolites SMs are synthesized in specific genera or species. Secondary metabolites can serve as protective agent or antioxidants under unfavourable environments such as drought.
For example, in bean and tobacco under diverse abiotic stress conditions, high concentrations of polyamines and phenyl amides have been observed Jenks et al. Moreover, they act as regulatory element in developmental, physiological and biochemical events including biotic and abiotic stress response Malmberg et al. Nevertheless the exact mechanism of PAs incorporation into stress response is less known to date Pathak et al. In general, several reports consistently confirmed an increase in Spd and Spm for tolerant cultivar compared with sensitive cultivars of wheat Liu et al.
While, in these experiments, sensitive cultivars exhibited elevation in Put level under stress condition. Correspondently, transgenic plants with increasing accumulation of Put, Spd and Spm enhanced tolerance to drought stress Capell et al. Jasmonates consisting of methyl jasmonate and jasmonic acid are correlated to the accumulation of defence systems, i. Recently, the contribution of various secondary metabolites in enhancing abiotic stress tolerance through functioning as antioxidants has been proved.
These compound are saponin Chan et al. Tolerant plants accumulate or maintain high levels of particular metabolites to cope with unfavourable conditions. Reviewed compounds could be used as biochemical indicators in breeding programs to improve drought stress tolerance. Exogenous application of compounds involved in adaptive responses to drought stress might alleviate adverse effects of stress.
Whereas previous works support the enhancement of water deficit stress tolerance by foliar application of major compounds such as glycine betaine, kinetin, nitric oxide and salicylic acid Rao et al. Foliar applying spraying or fumigating of the selected metabolites in the form of available commercial products might be an alternative method to enhance sensitive plants productivity under drought stress conditions.
The author is very grateful to Dr. Jeremy Pritchard, Dr. Youness Saidi, Dr. Juliet coats and Prof. Brian Ford-Lloyd for their helpful comments. Plant Physiology Abedi T, Pakniyat H. Antioxidant enzyme changes in response to drought stress in ten cultivars of oilseed rape Brassica napus L. Czech Journal of Genetics and Plant Breeding Physiological responses to water stress by Cucumis sativus L. Plant Water-Stress Response Mechanisms. Water Stress , Croatia: intechweb. Constitutive expression of small heat shock proteins in vegetative tissues of the resurrection plant Craterostigma plantagineum.
Plant Molecular Biology Polyamines: molecules with regulatory functions in plant abiotic stress tolerance. Planta Alpert P, Oliver MJ. Drying Without Dying. In: Black M, Pritchard H,eds. Alpert P. The limits and frontiers of desiccation-tolerant life. Integrative and Comparative Biology Constraints of tolerance: why are desiccation-tolerant organisms so small or rare? Journal of Experimental Biology Effects of water stress on lipid metabolism in cotton leaves.
Phytochemistry Growth characteristics and antioxidant metabolism of moongbean genotypes differing in photosynthetic capacity subjected to water deficit stress. Journal of Plant Interactions Arndt SK. Sclerophylly and leaf anatomical traits of five field-grown olive cultivars growing under drought conditions.
Tree physiology Bartels D, Sunkar R. Drought and salt tolerance in plants. Critical Reviews in Plant Sciences Transgenic wheat plants expressing an oat arginine decarboxylase cDNA exhibit increases in polyamine content in vegetative tissue and seeds. Molecular Breeding Bhargava S, Sawant K. Drought stress adaptation: metabolic adjustment and regulation of gene expression.
Plant Breeding Blokhina O, Fagerstedt KV. Reactive oxygen species and nitric oxide in plant mitochondria: origin and redundant regulatory systems. Physiologia Plantarum Photosynthesis of olive leaves: effect of light flux density, leaf age, temperature, peltates, and H2O vapor pressure deficit on gas exchange.
Journal of the American Society for Horticultural Science Cell Responses to abiotic stresses. In: Gruissem, W. Bray EA. Plant Response to Water-deficit Stress. Modulation of the polyamine biosynthetic pathway in transgenic rice confers tolerance to drought stress. Journal of experimental Botany Diverse transcriptional programs associated with environmental stress and hormones in the Arabidopsis receptor-like kinase gene family. Molecular Plant Effects of abiotic stress on biomass and anthocyanin production in cell cultures of Melastoma malabathricum. Biological Researchs Chaves MM.
Effects of water deficits on carbon assimilation. Understanding plant responses to drought from genes to the whole plant. Functional Plant Biology Effect of salt on malondialdehyde and antioxidant enzymes in seedling roots of Jerusalem artichoke Helianthus tuberosus L. Acta Physiologiae Plantarum Enhancement of tolerance of abiotic stress by metabolic engineering of betaines and other compatible solutes. Current opinion in plant biology The Plant Cell Glycolipid changes in wheat and barley chloroplast under water stress.
Plant Science Letters Close TJ. Dehydrins: A commonality in the response of plants to dehydration and low temperature. Differential regulation of small heat-shock genes in plants: analysis of a water-stress-inducible and developmentally activated sunflower promoter. Connor DJ. Adaptation of olive Olea europaea L. Crop and Pasture Science Dual action of the active oxygen species during plant stress responses. Cellular and Molecular Life Sciences Proline Biosynthesis and Osmoregulation in Plants. Plant Journal Reactive oxygen species and reactive nitrogen species in peroxisomes.
Production, scavenging, and role in cell signaling. Douglas TJ, Paleg Lg. Lipid composition of Zea mays seedlings and water stress-induced changes. Fang Y, Xiong L. General mechanisms of drought response and their application in drought resistance improvement in plants. Plant drought stress: effects, mechanisms and management. Agronomy for Sustainable Development Effect of water stress on the lipid and fatty acid composition of cotton Gossypium hirsutum chloroplasts.
Physiologia Plantarium Oxygen metabolism and the regulation of photosynthetic electron transport. Foyer CH. Oxygen metabolism and electron transport in photosynthesis. Cold Spring Harbor Monograph Archive Engineering seed dormancy by the modification of zeaxanthin epoxidase gene expression. Highly hydrophilic proteins in prokaryotes and eukaryotes are common during conditions of water deficit. Journal of Biological Chemistry Identification of stress-responsive genes in an indica rice Oryza sativa L.
Proteome analysis of sugar beet leaves under drought stress. Proteomics Hendrick J, Hartl FU. The role of molecular chaperones in protein folding. Oxygen activation at the plasma membrane: relation between superoxide and hydroxyl radical production by isolated membranes. Hirt H, Shinozaki K Eds. Plant responses to abiotic stress.
Berlin Heidelberg: Springer-Verlag. Mechanisms of plant desiccation tolerance. Trends in Plant Science Vegetative and seed-specific isoforms of a putative solute transporter in the tonoplast of Arabidopsis thaliana. Hong S-W, Vierling E. Oils, lipid-based and related chemicals D1 - Technical reports: non-confidential. Hughes, K. Oils, lipid-based and related chemicals. Silsoe Research Institute, Silsoe. Salicylic acid-induced accumulation of glucosinolates in oilseed rape Brassica napus L.
Journal of Experimental Botany. Biosynthesis of glucosinolates in oilseed rape leaves C2 - Non-edited contributions to conferences. Biosynthesis of glucosinolates in oilseed rape leaves. Problems and limitations in studying plant primary metabolism C2 - Non-edited contributions to conferences. Problems and limitations in studying plant primary metabolism. Baron, A. The kinetics of azaserine and phosphinothricin inhibition of glutamate synthase cycle enzymes from barley leaves A - Papers appearing in refereed journals.
The kinetics of azaserine and phosphinothricin inhibition of glutamate synthase cycle enzymes from barley leaves. Avila, C. Synthesis of glucosinolate precursors and investigations into the biosynthesis of phenylalkyl- and methylthioalkylglucosinolates A - Papers appearing in refereed journals. Dawson, G. Synthesis of glucosinolate precursors and investigations into the biosynthesis of phenylalkyl- and methylthioalkylglucosinolates.
Journal of Biological Chemistry. Cloning and sequence analysis of a cDNA for barley ferredoxin-dependent glutamate synthase and molecular analysis of photorespiratory mutants deficient in the enzyme A - Papers appearing in refereed journals. Cloning and sequence analysis of a cDNA for barley ferredoxin-dependent glutamate synthase and molecular analysis of photorespiratory mutants deficient in the enzyme.
Using plant secondary metabolites to engineer enhanced crop protection - progress with two contrasting approaches. Opportunities for Molecular Biology in Crop Protection. BCPC Monograph. Aldoxime-forming microsomal enzyme systems involved in the biosynthesis of glucosinolates in oilseed rape Brassica napus leaves A - Papers appearing in refereed journals. Aldoxime-forming microsomal enzyme systems involved in the biosynthesis of glucosinolates in oilseed rape Brassica napus leaves. The biosynthesis of glucosinolates in oilseed rape C2 - Non-edited contributions to conferences. The biosynthesis of glucosinolates in oilseed rape.
The biochemical basis for the differential response of oilseed rape varieties to infection and stress. Physiology of Varieties. Aspects of Applied Biology. The biosynthesis of amino acids and amino acid-derived secondary metabolites in crop plants C2 - Non-edited contributions to conferences. The biosynthesis of amino acids and amino acid-derived secondary metabolites in crop plants.
Marquez, A. Analisis molecular de mutantes fotorrespiratorios de cebada deficientes en la biosintesis de glutamato. Pineda, M. Metabolismo del nitrogeno. Sociedad Espanola de Bioquimica, Madrid. Abiotic induction of glucosinolate synthesis in Brassica napus C2 - Non-edited contributions to conferences. Abiotic induction of glucosinolate synthesis in Brassica napus. Potential of secondary metabolites in genetic engineering of crops for resistance B - Book chapters etc edited externally. Potential of secondary metabolites in genetic engineering of crops for resistance.
Interactions of avocado Persea americana cytochrome P with monoterpenoids A - Papers appearing in refereed journals. Interactions of avocado Persea americana cytochrome P with monoterpenoids. Cytochrome P catalysed monoterpene hydroxylation in Nepeta mussinii A - Papers appearing in refereed journals.
Cytochrome P catalysed monoterpene hydroxylation in Nepeta mussinii. Carbon and nitrogen cycling between organelles during photorespiration. Tobin, A. Polymerase chain reaction amplification and cloning of complementary DNA for ferredoxin-dependent glutamate synthase from barley C2 - Non-edited contributions to conferences. Polymerase chain reaction amplification and cloning of complementary DNA for ferredoxin-dependent glutamate synthase from barley.
Plastid genes and parasitic plants G - Articles in popular magazines and other technical publications. Plastid genes and parasitic plants. Accumulation of glucosinolates in oilseed rape leaves as a result of fungal infection.
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Porter, A. Myrosinase activity and glucosinolate content in developing leaves of oilseed rape. Nitrogen fixation, assimilation and transport during the initial growth phase of Phaseolus vulgaris L. Hungria, M. Variation in the glucosinolate content of oilseed rape Brassica napus L. Response to infection by Alternaria brassicae Berk. Effect of leaf age and postition A - Papers appearing in refereed journals. Effect of leaf age and postition.
Enzymes of leucine, valine and isoleucine biosynthesis A - Papers appearing in refereed journals. Enzymes of leucine, valine and isoleucine biosynthesis. Methods in Plant Biochemistry. Molecular analysis of barley mutants deficient in chloroplast glutamine synthetase A - Papers appearing in refereed journals.
Freeman, J. Molecular analysis of barley mutants deficient in chloroplast glutamine synthetase. Plant Molecular Biology. The biosynthesis of amino acids in plants. B - Book chapters etc edited externally. British Crop Protection Council Monograph Copping, J. Secondary plant metabolites as targets for genetic modification of crop plants for pest resistance. Pesticide Science. The genetics of nitrate uptake in higher plants. Kinghorn, eds pp. Amino acid biosynthesis inhibitors. British Crop Protection Monograph Ferredoxin-glutamate synthase from barley leaves: rapid purification and partial characterization.
Physical and kinetic properties of lysine-sensitive aspartate kinase purified from carrot cell suspension culture. Relton, J. Some effects of oxygen on photosynthesis by photorespiratory mutants of barley Hordeum vulgare L. Sivak, M. Barley mutants lacking glutamine synthetase - biochemical and genetic analysis. Biochemical and molecular genetics of nitrogen assimilation and re-assimilation in barley.
G - Articles in popular magazines and other technical publications. The roles of glutamine synthetase and glutamate synthase in nitrogen metabolism of higher plants. Selection strategies for isolation of nitrate uptake deficient mutants in barley. Hasegawa, H. Selection screen for novel photorespiration mutants of barley.
Hall, N. Barley photorespiration mutants. Kendall, A. Ferredoxin-glutamate synthase from barley leaves - purification and properties. Altered feedback sensitivity of acetohydroxyacid synthase from valine-resistant mutants of tobacco Nicotiana tabacum L. Carbon and nitrogen metabolism in barley Hordeum vulgare L mutants lacking ferredoxin-dependant glutamate synthase.
Carbon and nitrogen metabolism in a barley Hordeum vulgare L. Biochemical characterisation of Nicotiana plumbaginifolia auxotrophs that require branched-chained amino acids. Plant Cell Reports. Effects of exogenous amino acids on growth and activity of four aspartate pathway enzymes in barley. Rognes, S. Plant Science. Biochemical characterisation of an auxotroph of Datura innoxia requiring isoleucine and valine. Glutamine synthetase-deficient mutants of barley Hordeum vulgare. Barley mutants deficient in chloroplast glutamine synthetase. Genetic analysis of photorespiratory mutants in barley.
Turner, J. Photorespiratory mutants of barley Hordeum vulgare. Isozymes of phosphoglycollate phosphatase missing in a photorespiratory mutant of barley. A barley mutant deficient in RuBP carboxylase. The isolation and characterisation of photorespiratory mutants of barley Hordeum vulgare L. Maris pink. Lea, P. Barley Genetics Newsletter. Acetohydroxyacid synthase in a valine-resistant mutant of nicotiana tabacum A - Papers appearing in refereed journals.
Acetohydroxyacid synthase in a valine-resistant mutant of nicotiana tabacum. Bright, S.
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Manipulation of key pathways in photorespiration and amino acid metabolism by mutation and selection. Genetic manipulation of plants and its application to agriculture Annual Proceedings of the Phytochemical Society of Europe, Clarendon Press, Oxford. Photosynthesis, photo-respiration and nitrogen-metabolism A - Papers appearing in refereed journals. Photosynthesis, photo-respiration and nitrogen-metabolism. The isolation of ferredoxin dependent glutamate synthase deficient, photorespiration mutants of barley A - Papers appearing in refereed journals.
The isolation of ferredoxin dependent glutamate synthase deficient, photorespiration mutants of barley. Intracellular-localization of aspartate kinase and the enzymes of threonine and methionine biosynthesis in green leaves A - Papers appearing in refereed journals. Intracellular-localization of aspartate kinase and the enzymes of threonine and methionine biosynthesis in green leaves.
The development of nad p h-dependent and ferredoxin-dependent glutamate synthase in greening barley and pea leaves A - Papers appearing in refereed journals. The development of nad p h-dependent and ferredoxin-dependent glutamate synthase in greening barley and pea leaves.
Localization and characterization of homoserine dehydrogenase isolated from barley and pea leaves A - Papers appearing in refereed journals. Sainis, J. Localization and characterization of homoserine dehydrogenase isolated from barley and pea leaves. Glutamine-metabolism in higher-plants A - Papers appearing in refereed journals.
Miflin, B. Glutamine-metabolism in higher-plants. Current Topics in Cellular Regulation.