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See detailResistance induced in cucumber and tomato by a non-pathogenic Pseudomonas putida strain
Adam, Akram; Jourdan, Emmanuel ULg; Ongena, MARC ULg et al

in Parasitica (2005), 61

Some plant growth promoting rhizobacteria are able to stimulate inducible defense mechanisms that render the host plant less susceptible to a subsequent pathogen attack. This phenomenon, called induced ... [more ▼]

Some plant growth promoting rhizobacteria are able to stimulate inducible defense mechanisms that render the host plant less susceptible to a subsequent pathogen attack. This phenomenon, called induced systemic resistance (ISR), can occur in several plant species against a wide range of bacterial, viral and fungal pathogens. Despite extensive work, many aspects of the molecular basis underlying this rhizobacteria-mediated ISR remain unclear. In this context, we have studied for several years the ISR-mediated protective effect of a particular strain, Pseudomonas putida BTP1. In this paper, we present the results obtained by using BTP1 for disease reduction against anthracnose caused by Colletotrichum lagenarium on cucumber and grey mold caused by Botrytis cinerea on tomato. As a result of cucumber treatment with BTP1, we observed an enhanced hydroperoxide lyase activity that could restrict pathogen ingress since this enzyme, acting downstream in the so-called oxylipin pathway, forms short chain aldehydes considered as “volatile phytoalexins”. By contrast, this phenomenon is not involved in the protective effect afforded by the strain in tomato. In this case, disease reduction is more seemingly associated with an early accumulation of antifungal compounds stimulated by the bacterium, showing that specific ISR-related metabolic pathways may be activated in different plants by the same microorganism. [less ▲]

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See detailOptimisation of Panax ginseng liquid cell cultures for biomass accumulation and ginsenoside production.
Kevers, Claire ULg; Bare, Gislain; Gaspar, Thomas ULg et al

in HVOSLEF-EIDE, Anne Kathrine; PREIL, Walter (Eds.) Liquid Culture Systems for in vitro Plant Propagation (2005)

Solid calli and derived liquid cell cultures were initiated from one-year-old roots of Panax ginseng CA Meyer. Half-strength Murashige and Skoog medium supplemented classically with an auxin and a ... [more ▼]

Solid calli and derived liquid cell cultures were initiated from one-year-old roots of Panax ginseng CA Meyer. Half-strength Murashige and Skoog medium supplemented classically with an auxin and a cytokinin did not appear favourable for biomass accumulation nor for a high ginsenoside content. Changes in the levels of mineral nutrients, sucrose and growth regulators were preliminary investigated here to improve growth and ginsenoside production in liquid cultures. The hypothesis that ginseng cells released growth inhibitors in the medium was not supported by the results obtained in experiments involving frequent transfers to fresh growth medium [less ▲]

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See detailStimulation of the lipoxygenase pathway is associated with systemic resistance induced in bean by a nonpathogenic Pseudomonas strain
Ongena, MARC ULg; Duby, Franceline ULg; Rossignol, Fanny et al

in Molecular Plant-Microbe Interactions (2004), 17(9), 1009-1018

Systemic defense reactions induced in bean by the nonpathogenic Pseudomonas putida BTP1 strain reduced disease caused by Botrytis cinerea. Phenylalanine ammonialyase activity and the level of endogenous ... [more ▼]

Systemic defense reactions induced in bean by the nonpathogenic Pseudomonas putida BTP1 strain reduced disease caused by Botrytis cinerea. Phenylalanine ammonialyase activity and the level of endogenous free sallicylic acid were compared in plant growth-promoting rhizobacteria-treated versus control plants, but no significant differences were detected. Furthermore, no enhanced fungitoxicity was detected in methanolic leaf extracts, suggesting that accumulation of bean phytoalexins was not part of the stimulated defense mechanisms. However, BTP1-inoculated plants showed increased levels of both linoleic and linolenic acids. On this basis, we further investigated whether the lipoxygenase pathway, leading to antifungal phytooxylipins, could have been stimulated. Two key enzymatic activities of this metabolic route, namely lipoxygenase and hydroperoxidelyase, were significantly stimulated during the first four days after challenging BTP1-treated plants with the pathogen. This was observed in parallel with a more rapid consumption of the respective substrates of these enzymes, as revealed by measurements of endogenous concentrations of linolenic acid and their hydroperoxide derivatives. Moreover, headspace-gas chromatography analyses showed significantly higher concentrations of the fungitoxic final product Z-3-hexenal in leaves from BTP1-inoculated beans as compared with control plants. Taken together, these results strongly suggest that the oxylipin pathway can be associated with enhanced disease resistance induced in bean plants by nonpathogenic rhizobacteria. [less ▲]

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See detailCloning and Expression Analysis of Cdnas Corresponding to Genes Activated in Cucumber Showing Systemic Acquired Resistance after Bth Treatment
Bovie, C.; Ongena, MARC ULg; Thonart, Philippe ULg et al

in BMC Plant Biology (2004), 4

BACKGROUND: Infection of plants by necrotizing pathogens can lead to the rapid and localized induction of a complex set of defense responses resulting in a restriction of pathogen growth and spread ... [more ▼]

BACKGROUND: Infection of plants by necrotizing pathogens can lead to the rapid and localized induction of a complex set of defense responses resulting in a restriction of pathogen growth and spread. Subsequently, an increase of plant resistance against a broad spectrum of pathogens is observed systemically. This plant immunity is known as Systemic Acquired Resistance. To identify components of the transduction pathway, we cloned and analysed the expression pattern of several mRNAs accumulating in cucumber plants after induction of Systemic Acquired Resistance. RESULTS: We tested on cucumber different compounds known to induce systemic acquired resistance. Among these, BTH (benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester) proved to be very effective. mRNA RT-PCR differential display was used to identify mRNA sequences induced 24 hours after the application of 10 microM BTH to cucumber plants. A cDNA library constructed from cucumber plants sprayed with 10 microM BTH was screened to get corresponding full length cDNAs. Among the identified cDNAs were those coding for a putative ras-related GTP-binding protein, a putative beta-1,4-N-Acetylglucosaminyltranferase III and a putative pathogenesis related protein. The time course of accumulation of the three corresponding mRNAs was analysed by northern blotting in plants treated by BTH or in plants infected by Colletotrichum lagenarium. CONCLUSIONS: The mRNA RT-PCR differential display technique allowed the identification of three genes possibly involved in Systemic Acquired Resistance in cucumber. Pathogenesis-related proteins are known to be involved in plant defence against pathogens. GTP-binding protein and N-acetylglucosaminyltranferase III have been reported to be components of signal transduction pathways in mammals and plants. [less ▲]

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See detailHyperhydricity of Prunus avium shoots cultured on gelrite: a controlled stress response
Franck, Thierry ULg; Kevers, Claire ULg; Gaspar, Thomas ULg et al

in Plant Physiology & Biochemistry (2004), 42(6), 519-527

Hyperhydricity is a physiological disorder frequently affecting shoots vegetatively propagated in vitro. Hyperhydric shoots are characterised by a translucent aspect due to a chlorophyll deficiency, a not ... [more ▼]

Hyperhydricity is a physiological disorder frequently affecting shoots vegetatively propagated in vitro. Hyperhydric shoots are characterised by a translucent aspect due to a chlorophyll deficiency, a not very developed cell wall and a high water content. Hyperhydricity of Prunus avium shoots was expressed in vitro in one multiplication cycle by replacing the gelling agent agar (normal shoots: NS) by gelrite (hyperhydric shoots: HS). P. avium shoots evolving towards the hyperhydric state produced higher amounts of ethylene, polyamines (PAs) and proline, which are substances considered as stress markers. A higher activity of glutathione peroxidase (GPX; EC 1.11.1.9), involved in organic hydroperoxide elimination, suggested an increased production of these compounds in HS. The unchanged free fatty acid composition indicated no HS membrane damages compared to NS. The ploidy level of HS nuclei was not affected, but the bigger size and the lower percentage of nuclei during the S phase suggested a slowing down of the cell cycle. The results argued for a stress response of the HS, but no signs of oxidative damages of lipid membrane and nucleus were observed. The discussion points out paradoxical results in a classical analysis of stress and suggests an alternative way of defense mechanisms in HS, involving homeostatic regulation and controlled degradation processes to maintain integrity and vital functions of the cell. (C) 2004 Elsevier SAS. All rights reserved. [less ▲]

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See detailHyperhydricity of micropropagated shoots: a typically stress-induced change of physiological state
Kevers, Claire ULg; Franck, Thierry ULg; Strasser, Reto et al

in Plant Cell, Tissue & Organ Culture (2004), 77(2), 181-191

Hyperhydricity of micropropagated shoots, formerly called vitrification, undoubtedly results from growth and culture conditions, subjectively reputated as stressing factors: wounding, infiltration of soft ... [more ▼]

Hyperhydricity of micropropagated shoots, formerly called vitrification, undoubtedly results from growth and culture conditions, subjectively reputated as stressing factors: wounding, infiltration of soft culture medium, generally of a high ionic strength, rich in nitrogen and in growth regulators in a special balance, in a humid and gaseous confined atmosphere. Stress is (objectively) defined as a disruption of homeostasis resulting from a constraint escaping the usual flexibility of metabolism. It induces another temporary (reversible) or definitive (irreversible) thermodynamic physiological state. The state-change concept developed by Strasser (1988) and Strasser and Tsimilli-Michael (2001) is applicable to the phenomenon of hyperhydricity. An appraisal of the redox capacities of hyperhydrated shoots together with a study of some enzymic activities that catalyse pentose phosphate and glycolytic pathways has indeed shown that such shoots have evolved towards a temporary state of lower differentiation or a juvenile state with a sufficient activity to survive and to defend themselves. [less ▲]

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See detailWood formation in in vitro propagated walnut shoots in relation with root formation and development
Kevers, Claire ULg; Bisbis, Badia; Crèvecoeur, Michèle et al

in Acta Botanica Gallica : Bulletin de la Société Botanique de France (2004), 151(1), 45-53

Lignification and xylem cell multiplication for wood formation were examined in in vitro propagated walnut shoot cuttings after transfer on an auxin-containing rooting medium for one week and subsequently ... [more ▼]

Lignification and xylem cell multiplication for wood formation were examined in in vitro propagated walnut shoot cuttings after transfer on an auxin-containing rooting medium for one week and subsequently during root development in vermiculite in the absence of growth regulators. Lignification in the shoot stems started immediately after the exogenous auxin treatment which implied changes in peroxidase activity and in free IAA levels. Sustained lignification required the completion of the following rooting phases. The lignin was exclusively located in xylem cells, the number of which increased with the number of developing roots. The mutual interactions between the aerial parts of the plants and their roots are discussed. [less ▲]

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See detailComparative titration of ginsenosides by different techniques in commercial ginseng products and callus cultures
Kevers, Claire ULg; Jacques, Philippe; Gaspar, Thomas ULg et al

in Journal of Chromatographic Science (2004), 42(10, Nov-Dec), 554-558

The ginsenoside content of different ginseng species (Panax ginseng, P. quinquefolium, and P. vietnamensis) from different sources (roots from field-grown plants or from in vitro cultures, cells from ... [more ▼]

The ginsenoside content of different ginseng species (Panax ginseng, P. quinquefolium, and P. vietnamensis) from different sources (roots from field-grown plants or from in vitro cultures, cells from solid calluses or from liquid cultures, commercial powders, and suspensions) is evaluated by means of a new high-performance thin-layer chromatography (HPTLC) technique combining an automatic TLC sampler and scanner. The results are compared with those obtained through more classical gross spectrometric and high-performance liquid chromatography (HPLC) techniques. HPTLC and HPLC allow the separation and estimation of the different ginsenosides. For this, HPTLC is faster and simpler than HPLC. Both techniques determine less amounts of ginsenosides than spectrophotometry, which displays overestimated values caused by light absorption by contaminating osides. In vitro cultured cells and roots contain the same ginsenosides as those produced by their mother plants, although at quite lower levels. The culture media also accumulates ginsenosides. [less ▲]

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See detailSynthesis and activity of another seleniated auxin: 2,4-dichlorophenylselenoacetic acid
Tadino, Vincent; Faez, Juan Mareque; Christiaens, Léon ULg et al

in Plant Growth Regulation (2003), 40(3), 197-200

The synthesis of 2,4-dichlorophenylselenoacetic acid (2,4-D-Se) may be completed in three steps starting from 2,4-dichloroaniline. The selenium is inserted in the molecule by reaction of a diazonium salt ... [more ▼]

The synthesis of 2,4-dichlorophenylselenoacetic acid (2,4-D-Se) may be completed in three steps starting from 2,4-dichloroaniline. The selenium is inserted in the molecule by reaction of a diazonium salt with potassium selenocyanate. 2,4-D-Se has been tested as an auxin in several bioassays including the regeneration of somatic embryos, adventitious root formation and the associated temporary increase of endogenous auxins at the induction phase, and callus formation, and compared with the natural auxin indoleacetic acid (IAA), the classical synthetic auxin(s) naphthaleneacetic acid (NAA) and/or 2,4-dichlorophenoxyacetic acid (2,4-D), and with the synthetic seleniated IAA, 3-(benzo[b] selenienyl) acetic acid, BSAA. These biological assays classified 2,4-D-Se together with BSAA among the most powerful synthetic auxins. The role of selenium is briefly discussed. [less ▲]

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See detailDifferential gene expression in two potato lines differing in their resistance to Phytophthora infestans
Evers, Danièle; Ghislain, Marc; Hausman, Jean-François et al

in Journal of Plant Physiology (2003), 160(6), 709-712

Horizontal resistance to late blight in the potato is a primary objective of many breeding programs. Knowledge of the physiological and biochemical mechanisms underlying it, however, is scarce. The ... [more ▼]

Horizontal resistance to late blight in the potato is a primary objective of many breeding programs. Knowledge of the physiological and biochemical mechanisms underlying it, however, is scarce. The purpose of the present study was the identification of these physiological and biochemical factors in plant material obtained by crossing a late blight resistant Solanum phureja clone with a susceptible dihaploid of S. tuberosum subsp. tuberosum. The mRNA RT-PCR differential display method was used to compare the gene expression patterns of a resistant hybrid with that of a susceptible one. By sequence homology, we identified several genes with diverse functions, including genes known to be involved in resistance or stress responses and genes known to be involved in primary or secondary metabolism. [less ▲]

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See detailRooting blockage in the tobacco rac mutant occurs at the initiation phase, and induces diversion to xylem differentiation
Faivre-Rampant, Odile; D'Angeli, S.; Falasca, G. et al

in Plant Biosystems (2003), 137(2), 163-174

The rac mutant of Nicotiana tabacum L. cv. Xanthii is impaired in adventitious root formation. The objective of the present study was to determine whether or not the root induction phase occurs in the rac ... [more ▼]

The rac mutant of Nicotiana tabacum L. cv. Xanthii is impaired in adventitious root formation. The objective of the present study was to determine whether or not the root induction phase occurs in the rac mutant, and if so, to determine what causes the induced cells to become incapable of organising root primordia. To this end, rac and wild-type shoots were cultured in vitro for 7 days under conditions suitable for obtaining roots in the wild-type (i.e., exposure to 5 muM indole-3-butyric acid for 4 h, and then transfer to hormone-free medium), and then histologically and biochemically analysed during culture. The variations in peroxidase activity, and in cellular levels of auxins and polyamines revealed that the induction phase occurs in rac shoots, although it lasts longer than in the wild-type ones. Furthermore, both auxin and polyamines were consistently higher in rac shoots compared to the wild-type. After induction, auxin and putrescine levels abruptly decreased in the wild-type shoots, whereas they decreased much more slowly in the rac mutant. The histological analysis of the wild-type shoots showed that the abrupt decrease in auxin and polyamine levels were correlated with a normal initiation phase. In fact, wild-type shoots showed cell divisions in the procambium already at day 2, resulting in the formation of root primordia at day 4, and in root emergence between days 5 and 7. In rac shoots, despite the fact that the procambium cells were activated to undergo cell division, the initiation phase was highly perturbed, and the procambial cells developed tracheary elements instead of adventitious roots. The different morphogenic responses of the two genotypes are discussed in the light of the differences in auxin content after the induction phase. [less ▲]

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See detailRestart of lignification in micropropagated walnut shoots coincides with rooting induction
Bisbis, Badia; Kevers, Claire ULg; Crèvecoeur, Michèle et al

in Biologia Plantarum (2003), 47(1), 1-5

The lignin content of walnut shoots did not change during in vitro shoot Multiplication. Lignin content started to increase as soon as shoots were passed to a rooting medium with auxin. Exogenous auxin ... [more ▼]

The lignin content of walnut shoots did not change during in vitro shoot Multiplication. Lignin content started to increase as soon as shoots were passed to a rooting medium with auxin. Exogenous auxin (applied for rooting) Caused a transient elevation of the endogenous free indoleacetic acid (IAA) content with a Simultaneous decrease of peroxidase activity. These events typically marked the completion of the rooting inductive phase (before any visible histological event. that is before the cell divisions beginnin- the rootin- initiation phase). This meant that either the given exogenous auxin or the endogenous IAA has served as signal for the stimulation of lignification. Continued increase of lignification in the shoots required completion of root formation; this increase indeed was slown down when root emergence did not occur. It was further shown that lionification varied conversely to the content of the Soluble Phenol Content. itself apparently being related to the activity of phenylalanine ammonia-lyase activity. [less ▲]

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See detailChanging concepts in plant hormone action
Gaspar, Thomas ULg; Kevers, Claire ULg; Faivre-Rampant, Odile et al

in In Vitro Cellular & Developmental Biology-Plant (2003), 39(2, MAR-APR), 85-106

A plant hormone is not, in the classic animal sense, a chemical synthesized in one organ, transported to a second organ to exert a chemical action to control a physiological event. Any phytohormone can be ... [more ▼]

A plant hormone is not, in the classic animal sense, a chemical synthesized in one organ, transported to a second organ to exert a chemical action to control a physiological event. Any phytohormone can be synthesized everywhere and can influence different growth and development processes at different places. The concept of physiological activity under hormonal control cannot be dissociated from changes in concentrations at the site of action, from spatial differences and changes in the tissue's sensitivity to the compound, from its transport and its metabolism, from balances and interactions with the other phytohormones, or in their metabolic relationships, and in their signaling pathways as well. Secondary messengers are also involved. Hormonal involvement in physiological processes can appear through several distinct manifestations (as environmental sensors, homeostatic regulators and spatio-temporal synchronizers, resource allocators, biotime adjusters, etc.), dependent on or integrated with the primary biochemical pathways. The time has also passed for the hypothesized 'specific' developmental hormones, rhizocaline, caulocaline, and florigen: root, stem, and flower formation result from a sequential control of specific events at the right places through a coordinated control by electrical signals, the known phytohormones and nonspecific molecules of primary and secondary metabolism, and involve both cytoplasmic and apoplastic compartments. These contemporary views are examined in this review. [less ▲]

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See detailCarbohydrates and resistance to Phytophthora infestans in potato plants
Evers, Danièle; Dommes, Jacques ULg; Hausman, Jean-François

in Acta Physiologiae Plantarum (2003), 25(2), 171-178

Plants generally deal with biotic or abiotic stresses by altering components as for example cell wall constituents and metabolites. Infection by Phytophthora infestans, the causal agent of late blight ... [more ▼]

Plants generally deal with biotic or abiotic stresses by altering components as for example cell wall constituents and metabolites. Infection by Phytophthora infestans, the causal agent of late blight, constitutes a stress condition for the plants and they react to it with changes arising in their metabolism depending on the resistance level of the plants. The present work compares two potato hybrids differing in their level of horizontal resistance to late blight. Carbohydrate content in stems and leaves of infected and uninfected plants was determined by HPLC. Some carbohydrates accumulated in the stems of the resistant hybrid infected by P. infestans, whereas they remained unchanged in the susceptible hybrid. On the other hand, in the leaves, these carbohydrates accumulated only in the infected susceptible hybrid. [less ▲]

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See detailHow hyperhydric shoots try to survive
Franck, Thierry ULg; Kevers, Claire ULg; Gaspar, Thomas ULg et al

in Free Radical Research (2003), 37(Suppl. 1), 74-74

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See detailMorphological and hormonal characterisation of strawberry vitroplants raised through axillary or stipular adventitious shooting
Jemmali, Ahmed; Elloumi, Nedra; Kevers, Claire ULg et al

in Plant Growth Regulation (2002), 38(3), 273-278

Adventitious stipular bud formation occurred in vitro in many strawberry cultivars during the proliferation phase on medium containing Knop macronutrients, MS micronutrients, vitamins, aminoacids, 2.22 ... [more ▼]

Adventitious stipular bud formation occurred in vitro in many strawberry cultivars during the proliferation phase on medium containing Knop macronutrients, MS micronutrients, vitamins, aminoacids, 2.22 muM BAP, 2.46 muM IBA and 0.29 muM GA(3). As described previously for cultivar Gorella, cultivar Elsanta also showed adventitious stipular buds developing on the abaxial median zone between the stipule tips. To compare the shoots produced from both types of buds, clonal propagation was initiated from stipular buds and from axillary buds on the above mentioned medium. Stipular buds were separated from the meristem-tip initiated plantlet and cultivated in the presence of a lower BAP concentration (1.33 muM) to prevent further stipular bud formation. During proliferation cycles, stipular originated propagules were very easily distinguished by their specific leaf phenotype and light green colour in comparison to plantlets cloned for an axillary bud. Their multiplication rate and cytokinin content were also higher than for axillary buds. No significant difference was observed in auxin content. [less ▲]

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See detailThe beneficial role of different auxins and polyamines at successive stages of somatic embryo formation and development of Panax ginseng in vitro
Kevers, Claire ULg; Gaspar, Thomas ULg; Dommes, Jacques ULg

in Plant Cell, Tissue & Organ Culture (2002), 70(2), 181-188

The production of viable plantlets via somatic embryogenesis in Panax ginseng requires different culture media corresponding to successive developmental stages. The effects of several auxins and ... [more ▼]

The production of viable plantlets via somatic embryogenesis in Panax ginseng requires different culture media corresponding to successive developmental stages. The effects of several auxins and polyamines have been tested at various steps. Multiplication of the embryogenic root-derived callus has been optimized on half-strength MS medium supplemented with 3-(benzo[b]selenyl)acetic acid (BSAA, a synthetic auxin) and kinetin; exogenously applied polyamines were deleterious at this stage, causing browning of the callus, diminished capacity of embryo initiation, and an increased tendency to hyperhydricity. BSAA again appeared to be the most favourable auxin at the initiation stage, but here its action was reinforced by the presence of polyamines, spermidine being the most efficient. Among the auxin needed at the next step, i.e., for the regeneration of embryos, the two seleniated auxins BSAA and seleniated 2,4-dichlorophenoxyacetic acid (2,4-D-Se) were the more efficient. For the harmonious development of plantlets, i.e., the simultaneous outgrowth of shoots and roots, the polyamines were favourable, with a greater efficiency for spermine. [less ▲]

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See detailConcepts in plant stress physiology. Application to plant tissue cultures
Gaspar, Thomas ULg; Franck, Thierry ULg; Bisbis, Badia et al

in Plant Growth Regulation (2002), 37(3), 263-285

Because the term stress is used, most often subjectively, with various meanings, this paper first attempts to clarify the physiological definition, and the appropriate terms as responses in different ... [more ▼]

Because the term stress is used, most often subjectively, with various meanings, this paper first attempts to clarify the physiological definition, and the appropriate terms as responses in different situations. The flexibility of normal metabolism allows the development of responses to environmental changes which fluctuate regularly and predictably over daily and seasonal cycles. Thus every deviation of a factor from its optimum does not necessarily result in stress. Stress begins with a constraint or with highly unpredictable fluctuations imposed on regular metabolic patterns that cause bodily injury, disease, or aberrant physiology. Stress is the altered physiological condition caused by factors that tend to alter an equilibrium. Strain is any physical and/or chemical change produced by a stress, i.e. every established condition, which forces a system away from its thermodynamic optimal state. The paper secondly summarises the Strasser's state-change concept which is precisely that suboptimality is the driving force for acclimation (genotype level) or adaptation (population level) to stress. The paper continues with the actual knowledge on the mechanisms of stress recognition and cell signalling. Briefly: plasma membranes are the sensors of environmental changes; phytohormones and second messengers are the transducers of information from membranes to metabolism; carbon balance is the master integrator of plant response; betwixt and between, some genes are expressed more strongly, whereas others are repressed. Reactive oxygen species play key roles in up- and down-regulation of metabolism and structure. The paper shows finally that the above concepts can be applied to plant tissue cultures where the accumulating physiological and genetical deviations (from a normal plant behaviour) are related to the stressing conditions of the in vitro culture media and of the confined environment. The hyperhydrated state of shoots and the cancerous state of cells, both induced under conditions of stress in in vitro cultures, are identified and detailed, because they perfectly illustrate the stress-induced state-change concept. It is concluded that stress responses include either pathologies or adaptive advantages. Stress may thus contain both destructive and constructive elements: it is a selection factor as well as a driving force for improved resistance and adaptive evolution. [less ▲]

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