Laurent Jouve

Gradual Soil Water Depletion Results in Reversible Changes of Gene Expression, Protein Profiles, Ecophysiology, and Growth Performance in Populus euphratica , a Poplar Growing in Arid Regions

The responses of Populus euphratica Oliv. plants to soil water deficit were assessed by analyzing gene expression, protein profiles, and several plant performance criteria to understand the acclimation of plants to soil water deficit. Young, vegetatively propagated plants originating from an arid, saline field site were submitted to a gradually increasing water deficit for 4 weeks in a greenhouse and were allowed to recover for 10 d after full reirrigation. Time-dependent changes and intensity of the perturbations induced in shoot and root growth, xylem anatomy, gas exchange, and water status were recorded. The expression profiles of approximately 6,340 genes and of proteins and metabolites (pigments, soluble carbohydrates, and oxidative compounds) were also recorded in mature leaves and in roots (gene expression only) at four stress levels and after recovery. Drought successively induced shoot growth cessation, stomatal closure, moderate increases in oxidative stress-related compounds, loss of CO2 assimilation, and root growth reduction. These effects were almost fully reversible, indicating that acclimation was dominant over injury. The physiological responses were paralleled by fully reversible transcriptional changes, including only 1.5% of the genes on the array. Protein profiles displayed greater changes than transcript levels. Among the identified proteins for which expressed sequence tags were present on the array, no correlation was found between transcript and protein abundance. Acclimation to water deficit involves the regulation of different networks of genes in roots and shoots. Such diverse requirements for protecting and maintaining the function of different plant organs may render plant engineering or breeding toward improved drought tolerance more complex than previously anticipated.

Concepts in plant stress physiology. Application to plant tissue cultures

Because the term stress is used, most often subjectively, with variousmeanings, this paper first attempts to clarify the physiological definition,andthe appropriate terms as responses in different situations. The flexibility ofnormal metabolism allows the development of responses to environmental changeswhich fluctuate regularly and predictably over daily and seasonal cycles. Thusevery deviation of a factor from its optimum does not necessarily result instress. Stress begins with a constraint or with highly unpredictablefluctuations imposed on regular metabolic patterns that cause bodily injury,disease, or aberrant physiology. Stress is the altered physiological conditioncaused by factors that tend to alter an equilibrium. Strain is any physicaland/or chemical change produced by a stress, i.e. every established condition,which forces a system away from its thermodynamic optimal state. The papersecondly summarises the Strassers state-change concept which is preciselythat suboptimality is the driving force for acclimation (genotype level) oradaptation (population level) to stress. The paper continues with the actualknowledge on the mechanisms of stress recognition and cell signalling. Briefly:plasma membranes are the sensors of environmental changes; phytohormones andsecond messengers are the transducers of information from membranes tometabolism; carbon balance is the master integrator of plant response; betwixtand between, some genes are expressed more strongly, whereas others arerepressed. Reactive oxygen species play key roles in up- and down-regulation ofmetabolism and structure. The paper shows finally that the above concepts canbeapplied to plant tissue cultures where the accumulating physiological andgenetical deviations (from a normal plant behaviour) are related to thestressing conditions of the in vitro culture media and ofthe confined environment. The hyperhydrated state of shoots and the cancerousstate of cells, both induced under conditions of stress in invitro cultures, are identified and detailed, because they perfectlyillustrate the stress-induced state-change concept. It is concluded that stressresponses include either pathologies or adaptive advantages. Stress may thuscontain both destructive and constructive elements : it is a selection factoraswell as a driving force for improved resistance and adaptive evolution.

Involvement of indole-3-acetic acid in the circadian growth of the first internode of Arabidopsis

Abstract. The extension rate of the first inflorescence node of Arabidopsis was measured during light/dark or continuous light exposure and was found to exhibit oscillations which showed a circadian rhythmicity. Decapitation induced a strong inhibition of stem extension. Subsequent application of IAA restored growth and the associated extension–rate oscillations. In addition, IAA treatments, after decapitation, re-established the circadian rhythmicity visible in the intact plants during free run. This indicates that the upper zone of the inflorescence has a major influence on the extension rate of floral stems and implies a role for auxin. Application of N-(1-naphthyl)phthalamic acid, an IAA transport inhibitor, to an intact floral stem inhibited growth and the rhythmicity in the extension rate oscillations, indicating that IAA polar transport may play a role in the dynamics of stem elongation. Furthermore, IAA-aspartate application, after decapitation, did not restore growth and rhythmicity. Nevertheless, biochemical analysis of IAA and IAA-aspartate demonstrated circadian fluctuations of the endogenous levels of both compounds. These observations suggest that IAA metabolism is an essential factor in the regulation of the circadian growth rhythm of Arabidopsis floral stems.

Arabidopsis thaliana floral stem elongation: Evidence for an endogenous circadian rhythm

Abstract The floral stem elongation of Arabidopsis thaliana, Landsberg erecta ecotype, was studied with a plant growth-measuring apparatus using linear voltage differential transformers as sensors. Elongation rate displayed a clear rhythm which could be synchronized by a L:D (12:12) or L:D (7:7) photoperiod. The rhythm persisted afterwards in continuous constant conditions (CL). When pre-synchronization was L:D (12:12), the period in CL was 23.5 h. After L:D (7:7) synchronization (equal light/dark photoperiod which was not in phase with the 24 h daily period) a period of 21.4 h was measured in CL. Moreover, this later treatment triggered a significant increase in the first internode length. Thus, these results showed clearly that the floral stem growth was under the control of an endogenous circadian rhythm.

Effect of alginate matrix composition on regrowth of in vitro-derived encapsulated apical microcuttings of hybrid aspen

Effect of alginate matrix composition on regrowth performance of encapsulated microcuttings of hybrid aspen (Populus tremula L. × P. tremuloides Mincx.) was studied. Both high regrowth frequency and viability of explants were registered in all encapsulation mixtures tested. Some ingredients of the matrix (nutrient medium salts, sugars, growth regulators) significantly affected the initial development of the microcuttings. Sucrose appeared to play an important role in the starting stage of the regrowth event.

Poplar acclimation to cold during in vitro conservation at low non-freezing temperature: metabolic and proteic changes

Summary Microcuttings of Populus tremula L. were successfully in vitro conserved for more than 1 year at 10 °C on Murashige and Skoog (MS) medium devoid of any growth regulator. During storage, an important limitation of growth was observed. Survival was unaffected and the recovery of multiplication ability after transfer to normal conditions was satisfactory. From the first days of treatment microcuttings cultured at 10 °C when compared with cultures grown at 23 °C presented important biochemical changes. Endogenous contents of ABA and proline were affected during cold exposure as well as activities of several free radicals scavenging involved enzymes such as superoxide dismutase (SOD), dehydroascorbate reductase (DHAR) or glutathione reductase (GR). Moreover, de novo synthesis and accumulation of two new proteins with a molecular weight of about 120 kDa were observed after 3 days of chilling treatment.

Dependence of Arabidopsis Thaliana Floral Stem Growth and Architecture on Photoperiod

The influence of the applied photoperiod during floral stem development has been studied. A clear relationship between the length of the photoperiod, the frequency of light/dark switches, and the dynamic of growth and the subsequent morphology and architecture has been found. An increase in the day length (L/D = 16/8) or an increase in frequency of light/dark transitions (L/D = 7/7) stimulated the inflorescence growth. The two treatments induced the same enlargement in the early inflorescence, but the L/D = 7/7 condition causes a greater increase in the late one. The treatments induced also a diminution in the number of lateral inflorescences, principally with the high frequency light-on/light-off condition. Moreover than differences in the growth along the early inflorescence, at the level of the internode, a gradual growth was observed from the basal part to the upper part of the internode. Finally, the floral stem growth dynamic showed that it could be adapted to the environmental light/dark signalling by a good extension rate synchronisation.

Are temperature-induced early changes in auxin and polyamine levels related to flowering in Phalaenopsis?

Summary Phalaenopsis plants flowered 31/2 months after passing from a 24/22°C day/night to a 22/17°C regime without changing the photoperiod (12:12). The new thermoperiodic treatment induced rapid IAA fluctuations (with a significant peaking between day 2 and day 5), and about the same fluctuation for putrescine. Since flowering occurred much later and because quite similar results were observed during plant cold acclimation, the relationships of the biochemical changes registered with flowering induction were questioned.