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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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See detailStudy of bacterial determinants involved in the induction of systemic resistance in bean by Pseudomonas putida BTP1
Ongena, MARC ULg; Giger, A.; Jacques, Philippe ULg et al

in European Journal of Plant Pathology (2002), 108(3), 187-196

The ability of Pseudomonas putida BTP1 to induce resistance in bean to Botrytis cinerea was demonstrated in soil experiments on plants pre-inoculated at the root level with the bacteria before challenge ... [more ▼]

The ability of Pseudomonas putida BTP1 to induce resistance in bean to Botrytis cinerea was demonstrated in soil experiments on plants pre-inoculated at the root level with the bacteria before challenge with the leaf pathogen. As a first step to characterize the molecules from BTP1 responsible for induction of systemic resistance in bean, heat-killed cells and supernatant from culture in an iron-limited medium were tested for their protective effect. Most of the resistance-eliciting activity of the strain was retained in the crude cell-free culture fluid. In vivo assays with samples from successive fractionation steps of the BTP1 supernatant led, (i) to the conclusion that salicylic acid, pyochelin and pyoverdin, previously identified as Pseudomonas determinants for induced systemic resistance (ISR), were not involved in systemic resistance triggered by BTP1, and (ii) to the isolation of fractions containing one main metabolite that retained most of the resistance-inducing activity in bean. Although this molecule remains to be structurally characterized, its isolation is an addition to the range of determinants from plant growth-promoting rhizobacteria (PGPR) known to stimulate plant defences. [less ▲]

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See detailA specific role for spermidine in the initiation phase of somatic embryogenesis in Panax ginseng CA Meyer
Monteiro, Marta; Kevers, Claire ULg; Dommes, Jacques ULg et al

in Plant Cell, Tissue & Organ Culture (2002), 68(3), 225-232

Somatic embryogenesis of Panax ginseng CA Meyer was initiated from suspension aggregates of an embryogenic callus, in a liquid medium consisting of half strength Murashige and Skoog (1962) supplemented ... [more ▼]

Somatic embryogenesis of Panax ginseng CA Meyer was initiated from suspension aggregates of an embryogenic callus, in a liquid medium consisting of half strength Murashige and Skoog (1962) supplemented with the synthetic auxin benzoselenienyl-3 acetic acid. The addition of spermidine to this initiation medium significantly increased the production of somatic embryos. In this case, the total polyamine content of the embryogenic mass was higher than that of cultures without spermidine. At day 6 of the culture, a transient accumulation of free polyamines, mainly spermidine, was observed. After this peak, free and conjugated polyamines levels did not show significant variation nor did the polyamine oxidase activity. The results clearly demonstrated that spermidine supplied to the medium was oxidised by polyamine oxidase and partially metabolised into putrescine. The role of spermidine and its interaction with auxin in the initiation of the embryogenic process in Panax ginseng are discussed in relation to embryogenic potential. [less ▲]

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See detailBiosynthesis of peroxidases: a role as interplay between primary and hormonal metabolisms
Gaspar, Thomas ULg; Le Dily, Frédérique; Billard, Jean-Pierre et al

in Acosta, M.; Rodriguez-lopez, J.-N.; Pedreno, Maria-A (Eds.) Plant perodixases - Biochemistry and physiology - VI international plant peroxidase symposium Proceedings (2002)

Hyperhydric, fully habituated (growth independent from exogenous auxin and cytokinin), fully heterotrophic (achlorophyllous, dependent on sucrose supply, nevertheless able to fix CO2 non ... [more ▼]

Hyperhydric, fully habituated (growth independent from exogenous auxin and cytokinin), fully heterotrophic (achlorophyllous, dependent on sucrose supply, nevertheless able to fix CO2 non-photosynthetically) and non-organogenic (complete loss of any organogenic totipotency) sugarbeet cells in culture were characterized by a very low peroxidase activity, among other deficient heme compounds. This deficiency resulted from the lack of synthesis of the precursor aminolevulinic acid (ALA) through the chloroplastic Beale pathway; the low productive unusual ALA synthesis through the mitochondrial Shemin pathway (commonly used by animals and fungi) functioned but further at a limited rate due to inhibition of ALA-dehydratase by benzoic derivatives, predominant among the phenolic acids of these cells (compared to normal ones). A thorough investigation of the metabolic and hormonal functioning of these neoplastic cells showed that the above deviation originated from a disturbed nitrogen metabolism that diverted glutamate from the Kreb's cycle into polyamine (over) synthesis, which had also as consequence a low ethylene production. The Kreb's cycle could be replenished by oxaloacetate and malate deriving from the anaplerotic fixation of CO2 onto phosphoenolpyruvate. A privileged pentose phosphate pathway (PPP) allowed the formation of substrates for a non-limited biosynthesis of (endogenous) auxins and cytokinins. The PPP, through NAD(P)H formation, enhanced nitrogen metabolism, but also, together with a putative H2O2 accumulation (originated from high superoxide dismutase activity and high polyamine oxidation combined with low catalase activity), favoured the alternative respiratory pathway. These results not only illustrate a novel view of integration of hormonal metabolisms with the C and N primary and secondary ones but also allow to consider the biosynthesis of peroxidases in an interplay or mediating role between them. [less ▲]

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See detailCuttings of the non-rooting rac tobacco mutant overaccumulate phenolic compounds
Faivre-Rampant, Odile; Charpentier, Jean Paul; Kevers, Claire ULg et al

in Functional Plant Biology (2002), 29(1), 63-71

The auxin and phenolic contents, as well as phenylalanine ammonia-lyase (PAL) activity, were determined in in vitro cultured shoots of the recalcitrant-to-root rac mutant of tobacco, and compared with ... [more ▼]

The auxin and phenolic contents, as well as phenylalanine ammonia-lyase (PAL) activity, were determined in in vitro cultured shoots of the recalcitrant-to-root rac mutant of tobacco, and compared with wild-type shoots. The mutant and wild-type shoots showed similar auxin changes during the culture cycle, but with higher contents for the mutant. A transient peak of auxin (corresponding to the achievement of the rooting inductive phase) occurred at day 14 in both types of shoots, but earlier in the basal parts of the wild-type stems. The rac shoots contained more phenolics, corresponding with an increased PAL activity. The most abundant phenolic compound found in the two types of tobacco was chlorogenic acid, which was more abundant in the rac shoots. Rutin was also detected at a higher concentration in the mutant shoots. Basal parts of wild-type shoots treated with 10(-3) chlorogenic acid reacted by accumulating auxins and, unlike untreated controls, did not form adventitious roots. The relationships between those biochemical analyses in relation to the growth limitation of the rac mutant, and the inhibition of its root development, are discussed. [less ▲]

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See detailAuxins in the biology of roots
Gaspar, Thomas ULg; Faivre-Rampant, Odile; Kevers, Claire ULg et al

in Waisel, Yoav; Eshel, Amram; Kafkafi, Uzi (Eds.) Auxins in the biology of roots (2002)

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See detailIsolation of new metabolites from Pseudomonas putida involved in plant resistance induction
Ongena, Marc ULg; Budzikiewicz, H.; Jacques, Ph. et al

Poster (2001, September)

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See detailModified hormonal balance in rooting-recalcitrant rac mutant tobacco shoots
Faivre-Rampant, Odile; Kevers, Claire ULg; Dommes, Jacques ULg et al

in Plant Biosystems (2001), 135(1), 85-93

The rooting-recalcitrant rac tobacco mutant has been multiplied in vitro via outgrowth of axillary buds in parallel to the DS wild-type. The mutant shoots grew at a lower rate and did not root whatever ... [more ▼]

The rooting-recalcitrant rac tobacco mutant has been multiplied in vitro via outgrowth of axillary buds in parallel to the DS wild-type. The mutant shoots grew at a lower rate and did not root whatever the treatments, whereas the wild-type shoots rooted spontaneously during the culture cycle without auxin treatment. The mutant and wild-type shoots showed similar peroxidase variations along the culture cycle (21 days) but with higher levels of activity for the rac mutant: minimum peroxidase activity occurrey at day 14 in whole shoots of both tobacco genotypes, but already at day 7 in the basal parts of the stems (where roots appear) of the wild-type tobacco, while it was delayed in the mutant. Free and conjugated auxin and polyamine levels were also determined in whole shoots and basal parts of the stems. The rac mutant was characterised by higher auxin and polyamine contents. A peak of auxins and polyamines appeared at day 14 in the whole shoots whatever the tobacco genotype. This peak was delayed in the basal parts of the rac stems compared to the wild-type ones. The mutant shoots contained higher levels of benzyladenine and isopentenyladenosine at the end of the culture cycle, whereas zeatin riboside was more abundant in wild-type shoots. In response to increasing concentrations of indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA), only the wild-type shoots responded by an increase in growth rate followed by inhibition at high concentrations. The rac shoot responses were very low or nonexistent. Peroxidase activity was also measured in E basal parts of tobacco stems grown in the presence of IBA. Results suggest growth inhibition related to auxin accumulation, possibly combined with elevated putrescine content. Second, rooting induction seems to take place in both tobacco genotypes; however, the process of root formation is blocked in the mutant. The lack of initiation and expression phases of rooting in relation to auxin content in the mutant is discussed. [less ▲]

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See detailAre hyperhydric shoots of Prunus avium L. energy deficient?
Franck, Thierry ULg; Gaspar, Thomas ULg; Kevers, Claire ULg et al

in Plant Science (2001), 160(6), 1145-1151

The content of oxidized and reduced pyridine nucleotides and some enzymatic activities of the oxidative pentose phosphate and glycolytic pathways were compared in normal (NS, growing on agar) and ... [more ▼]

The content of oxidized and reduced pyridine nucleotides and some enzymatic activities of the oxidative pentose phosphate and glycolytic pathways were compared in normal (NS, growing on agar) and hyperhydric (HS, growing on gelrite) shoots of Prunus avium L. after 4 weeks of in vitro culture. The chlorophyll fluorescence from leaves and the redox capacity or the plasma membrane (reduction of exogenously added ferricyanide) of both types of shoots were recorded. The pool of oxidized and reduced pyridine nucleotides was lower in HS th;ln in NS. These results suggested a reduced metabolism of HS in comparison to normal ones. This hypothesis was also supported by other observations. First, chlorophyll fluorescence measurements showed a lower chlorophyll content and a slight reduction of the photosynthetic capacity in HS. Second, the low activity of some enzymes of oxidative pentose phosphate pathway (OPP) and glycolysis indicated a decline of these biochemical pathways in HS with the consequence of a reduced production of chemical energy in the form of NAD(P)H and ATP. Finally, the lower reduction of ferricyanide by I-IS suggested a lower rate of redox reactions at the level of the plasma membrane of these shoots in comparison to NS. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved. [less ▲]

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See detailSomatic embryogenesis of Panax ginseng in liquid cultures: a role for polyamines and their metabolic pathways
Kevers, Claire ULg; Le Gal, Nathalie; Monteiro, Marta et al

in Plant Growth Regulation (2000), 31(3), 209-214

A callus with embryogenic capacity was generated from root sections of Panax ginseng and used as an inoculum source for embryogenic liquid cultures in a three-step process: - a suspension culture of cell ... [more ▼]

A callus with embryogenic capacity was generated from root sections of Panax ginseng and used as an inoculum source for embryogenic liquid cultures in a three-step process: - a suspension culture of cell aggregates in the presence of an auxin/cytokinin mixture, - an induction medium containing auxin only (for 5 to 30 days), - a regeneration medium containing cytokinin only (for one month). Up to 25 embryos were recovered per 2.5 g of aggregates in these conditions. Incorporation of polyamines or their precursors arginine and ornithine into either the induction or regeneration media increased the number of embryos produced by up to 4 times. Inhibitors of both biosynthesis and biodegradation of polyamines reduced the number of embryos. These results support earlier findings of the role of polyamines in the process of somatic embryogenesis. The success of these liquid cultures opens up the possibility of producing somatic embryos of Panax ginseng in bioreactors. [less ▲]

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See detailIntegrating phytohormone metabolism and action with primary biochemical pathways. II. Interrelationships between disturbed nitrogen and carbon metabolism and changes in hormonal concentrations and sensitivities in tissue cultures
Gaspar, Thomas ULg; Bisbis, Badia; Kevers, Claire ULg et al

in Greppin, Hubert; Penel, Claude; Broughton, Walter (Eds.) et al Integrated Plant Systems (2000)

The paper begins with a review of the concept of neoplastic progressions in plant tissue cultures, with the progressive acquisition of (a relative) independence to the hormones auxins and cytokinins. It ... [more ▼]

The paper begins with a review of the concept of neoplastic progressions in plant tissue cultures, with the progressive acquisition of (a relative) independence to the hormones auxins and cytokinins. It takes advantage of the deviations of carbon and nitrogen metabolisms shown in these particular cases, to illustrate the interdependence with the metabolisms of the hormones (and increased sensitivities to) polyamines and ethylene. These results provide additional examples of the changing concepts in hormonology. [less ▲]

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See detailIntegrating phytohormone metabolism and action with primary biochemical pathways. I. Interrelationships between auxins, cytokinins, ethylene and polyamines in growth and development processes
Gaspar, Thomas ULg; Kevers, Claire ULg; Hausman, Jean-François et al

in Greppin, Hubert; Penel, Claude; Broughton, Walter (Eds.) et al Integrated Plant Systems (2000)

The paper begins with a review of the phytohormone (plant hormone) concept vs the sense of the mammalian hormones. The term "plant growth regulators" including new naturally occurring substances is ... [more ▼]

The paper begins with a review of the phytohormone (plant hormone) concept vs the sense of the mammalian hormones. The term "plant growth regulators" including new naturally occurring substances is discussed in regard to their effects on both growth and development processes, and possible different mechanisms of action in two different physiological directions. Mutual interactions between auxins, cytokinins, ethylene and polyamines are examined in several growth and development processes, showing the complexity of approach of the hormonal actions in plants . The indissociability of some hormonal relationships, and their obligatory integration with primary biochemical pathways is finally shown. [less ▲]

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