The leaves plasma membranes could be implicated in flowering induction process. Comparative studies have been carried out with a short day plant, Chenopodium rubrum, and a long day plant, Spinacia oleracea. Electron microscopic observations have shown modifications of membrane thickness and structure. A modification of plasmalemma sterols content also appeared during floral transition. Implications of these phenomena on plant physiology were discussed. MARTINEC, Jan, et al. Plasma membrane thickness and flowering induction in Chenopodium rubrum and in Spinacia oleracea. Archives des Sciences, 1993, vol. 46, no. 2, p. 233-248 DOI : 10.5169/seals-740453

Les premiers botanistes anatomistes n'avaient pu décrire de glandes endocrines à l'image de celles observées et fonctionnelles dans des organismes animaux, disposant d'un système sanguin irriguant tous leurs organes. Le concept d'hormone végétale n'émergea qu'avec les recherches sur les tropismes et la perceptibilité particulière des apex (aussi bien caulinaires que racinaires), aussi avec la découverte de la distribution polarisée, et des croissances sous-jacentes engendrées, d'où le terme premier d'hormone (sinon de substance) de croissance. L'agriculture se mit à rechercher des composés synthétiques en quête d'activités contrôlées... et plus efficaces, et en trouva. L'application externe des unes et des autres sur différents organes sous diverses conditions expérimentales aboutit progressivement à plusieurs découvertes et conclusions importantes pour la suite des recherches. Une même substance peut avoir des effets positifs et négatifs sur la croissance différant en importance selon la supposée "sensibilité" des organes traités, mais surtout selon les concentrations utilisées. Dans la partie "inhibition" des courbes dose-réponse caractéristiques, on parla de concentrations "sus-optimales" atteintes de l'hormone en question, mais rares furent ceux qui vérifièrent que la dite hormone appliquée pénétrait bien comme telle sans être modifiée, pour venir grossir le pool endogène; on se rendit notamment compte plus tard que la plante réagit à des applications qualifiées de sus-optimales d'agents extérieurs par une adaptation de ses systèmes cataboliques (les auxine-oxydases sont les premières en cause), sans se poser la question du devenir et des effets des produits générés; d'où l'ingénierie chimique synthétisant des homologues moins "attaquables" par les systèmes naturels de régulation (nos dérivés séléniés entre autres vraisemblablement). Les effets "rhizogènes" d'une auxine naturelle ou synthétique furent rapidement mis en évidence. Mais une hormone de croissance pouvait-elle seule provoquer un type de développement spécifique? D'où le concept de l'hormone de développement (en l'occurrence la rhizocaline) sous forme d'un complexe auxine + un sucre, des phénols, une oxydase, ...). Il en fut de même plus tard avec le "florigène" à plusieurs composants dont la gibbérelline, une autre hormone de croissance découverte entretemps. L'évidence des cytokinines (importantes celles-là pour la division cellulaire, plutôt que pour l'élongation favorisée par les auxines) mais surtout le rôle joué par la "balance" entre ces deux dernières conduisit à des avancées nouvelles et modifia aussi le concept d'hormone végétale de croissance: chaque type d'hormone pouvait être synthétisé dans tout type de cellule vivante; des gradients des différentes hormones, instaurés sous l'effet des conditions environnementales tout le long de la plante, sont vraisemblablement plus déterminants dans le comportement de la plante qu'une seule hormone dans l'orientation de leur croissance et de leur développement. C'est que, même les botanistes avaient un peu oublié que croissance et développement, dans une embryogénèse sans fin chez les végétaux, étaient intimement liés. Les hormones de développement se firent oublier pour laisser place au terme de PHYTOHORMONES. Ce qui posa immédiatement problème dans la question des phases de développement (induction, initiation ou évocation, expression) spatio-temporelles. Où le terme de dédifférenciation vint sur le tapis "objectivement". A notre connaissance, cette dédifférenciation ne fut réellement observée que dans des processus tératologiques (hyperhydricité dans des cals ou des pousses feuillées), qui par ailleurs mirent en évidence la complexité du vrai rôle des hormones (les couples auxines-cytokinines et polyamines-éthylène) reliées et conditionnées par les métabolismes primaires et secondaires et par les stress. Nous ne sommes pas certains que les biologistes moléculaires actuels tiennent compte de l'état physiologique général (déterminant dans un processus organogénétique) sous l'effet d'une hormone qu'ils croient spécifique, ni que les séquences de gènes allumés ou éteints soient les mêmes spatio-temporellement. L'ingénierie génétique en a déjà fait les frais (par exemple les tomates au mûrissement retardé mais sans saveur!), mais elle devra ramener des physiologistes-hormonologistes à d'autres réalités que les premiers concepts pourtant difficultueusement émergés.

Plant excitability, as measured by the appearance and circulation of action potentials (APs) after biotic and abiotic stress treatments, is a far lesser and more versatile phenomenon than in animals. To examine the genetic basis of plant excitability we used different Arabidopsis thaliana accessions. APs were induced by wounding (W) with a subsequent deposition (D) of 5μL of 1M KCl onto adult leaves. This treatment elicited transient voltage responses (APs) that were detected by 2 extracellular electrodes placed at a distance from the wounding location over an experimental time of 150min. The first electrode (e1) was placed at the end of the petiole and the beginning of the leaf, and the second (e2) electrode was placed on the petiole near the center of the rosette. All accessions (Columbia (Col), Wassilewskija (Ws) and Landsberg erecta (Ler)) responded to the W & D treatment. After W & D treatment was performed on 100 plants for each accession, the number of APs ranged from 0 to 37 (median 8, total 940), 0 to 16 (median 5, total 528) and 0 to 18 (median 2, total 296) in Col, Ws and Ler, respectively. Responding plants (>0 APs) showed significantly different behaviors depending on their accessions of origin (i.e., Col 91, Ws 83 and Ler 76%). Some AP characteristics, such as amplitude and speed of propagation from e1 to e2 (1.28mms(-1)), were the same for all accessions, whereas the average duration of APs was similar in Col and Ws, but different in Ler. Self-sustained oscillations were observed more frequently in Col than Ws and least often in Ler, and the mean oscillation frequency was more rapid in Col, followed by Ws, and was slowest in Ler. In general, Col was the most excitable accession, followed by Ws, and Ler was the least excitable; this corresponded well with voltage elicited action potentials. In conclusion, part of Arabidopsis excitability in AP responses is genetically pre-determined.

Abstract : This contribution will pursue two goals : on one hand suggesting a systernic and ecological approach to fit the coaction between human activities and the natural physical and biological ones and, on the other hand to take stock of the main questions that concerned authorities are asked about geographical and political singularity resulting from the French-Valdo-Geneva Basin historical partition (BFVG).

Environment and sustainable development in Switzerland: confederation, states and metropolitan zones. – The ecological footprint and local biocapacity of the different states and the 5 metropolitan zones of Switzerland is presented. An important diversity and heterogeneity is apparent. This adds to the complex Swiss climatic pattern that is currently under change. The achievement of a global and local sustainable development will need new adaptations both at the institutional level and for the scientific approach of this territorial and economic reality (confederation, states, metropolitan areas, cities), as well as with the dynamics of the private economical sector, if one wants to eliminate growing socio-economical dispari­ties and not to worsen the state of the environment.

The ecological footprint and local biocapacity of the different states and the 5 metropolitan zones of Switzerland is presented. An important diversity and heterogeneity is apparent. This adds to the complex Swiss climatic pattern that is currently under change. The achievement of a global and local sustainable development will need new adaptations both at the institutional level and for the scientific approach of this territorial and economic reality (confederation, states, metropolitan areas, cities), as well as with the dynamics of the private economical sector if one wants to eliminate growing socio-economical disparities and not to worsen the state of the environment.

Four different methods to account for complex relationships between regional and local viability/sustainability and vulnerability have been investigated. The ecological footprint technique, emergy analysis, natural capital evaluation and compensation areas methods are used to infer and synthesize different sustainability/viability aspects of the Swiss territory. The results of this study and assay suggest coherency and complementarity of the multiple methodology used. Furthermore, bio-geographical, bio-physical and economic particularities of Switzerland, that differ largely from canton to canton, determine an important variation of local sustainability levels and capacity of response to climate forcing in action. We thus propose next to a general Swiss approach of sustainability, a subsequent differential treatment of cantons, based on spatial inequalities that are linked to primary physical, biological and economical structures and potentials. Despite of a unifying, global and federal approach, the implementation of sustainability measures and laws should be afterwards modulated in the case of each canton, by accounting for all these physical, biological, and anthropogenic disparities (equity treatment).

This paper explores the methodological background in climate change impact assessment, focusing on the coupling and co-action between the climate system, the biosphere, and human activities. The aim of this study is to shape a methodological framework to assess regional sensitivity/ vulnerability to climate change, by introducing the ombrothermic diagram technique as a basis for analysis. Some aspects of the possible outcome for Switzerland depending on the future climate evolution have been analysed within this framework.

Le but de cette publication est de suggerer un point de vue different dans l'approche integrative : biosphere-societe-environnement, a travers le concept d'enveloppe de viabilite physique, chimique, geologique, biologique et ecologique de l'activite humaine et de variables sentinelles permettant un suivi annuel du sens de cette evolution. Le developpement durable, local et generalise, ne peut se faire, pour le moins, que dans le cadre de la satisfaction de la logique elementaire et des contraintes absolues de cette enveloppe extra-culturelle. C'est en relation avec le programme WP4 (CUEH et LOGILAB ; GENEVE) du Centre de Competence National de la Recherche sur le Climat (NCCR ; BERNE), etudiant les consequences possibles du changement climatique en Suisse, que cette demarche a ete realisee. Mme Ana Maria PRICEPUTU, diplomee en Biologie et Genetique moleculaire (IASI), s'est specialisee, a Geneve, en Ecologie humaine et Sciences de l'Environnement, Geomatique (SES ; Geographie), Gestion de l'Entreprise et Environnement (HEC ; Logilab). Elle travaille actuellement a la Maison Internationale de l'Environnement (UNEP / DEWA /GRID-EUROPE: Dr R. WITT). Mr Robert DEGLI AGOSTI, Dr es Sciences, est Charge de cours a l'Universite de Geneve (Dep. : Botanique et Biologie vegetale; Chronobiologie et Physiomatique) et professeur a la HES-SO de Lullier (Agronomie et Production vegetale, Physiomatique). Mr Hubert GREPPIN, Dr es Sciences, est professeur honoraire a l'Universite de Geneve ; il a ete directeur du Centre d'Ecologie humaine et des Sciences de l'Environnement, et aussi du Departement de Botanique et Biologie vegetale. Il a dirige de nombreuses recherches sur 1 'interaction entre 1 'environnement et les organismes vivants (http://www.unige.ch/sciences/biologie/Plantsciences et http://www.unige.ch/sciences/LABPV/perox.html ).

A relatively low-cost computer-assisted image analysis system is described. Software has been specifically written for the continuous monitoring of absorbance readings on cryostat sections of plant tissues incubated in media to reveal enzyme activities. The equipment was tested by quantifying glucose-6-phosphate dehydrogenase activity in cryostat sections from shoot apices of spinach plants. The reaction rate of the dehydrogenase activity was monitored at two incubation temperatures, 20 degrees C and 30 degrees C. Control incubations were performed in media lacking substrate. The specific test minus control reaction at 30 degrees C was twice that at 20 degrees C. Variation of the substrate concentration at 30 degrees C yielded a Km value of 0.37 mM. These preliminary results show that our image analysis system can be used for kinetic measurements of dehydrogenase activity in frozen tissue sections and constitute a new approach for enzyme histochemistry in the shoot apical meristem.

The suggestion that ethylene plays a role in the transition from vegetative growth to flowering started with the observation of the promoting effect of fire smoke on flowering of pineapples. That idea was rapidly confirmed for the bromeliads with the use of ethylene analogs, precursor, inhibitors of biosynthesis and measurements of ethylene release. In the long-day rosette plant spinach, we found in the 1980s that there was a burst of ethylene release when plants were induced to flower by long days, but not when they were induced by gibberellin application (7, 8). The identification in Arabidopsis in recent years of several independent genetic pathways promoting flowering, together with the discovery that gene ACS10 related to ethylene biosynthesis is specifically up-regulated by activation of the long-day promotion pathway, have shed a new light on our physiological observations in spinach. In addition, recent work with Arabidopsis mutants of the ethylene transduction pathway demonstrated that ethylene sensitivity is required in wild-type plants for a normal flowering time. New doors are by the same occasion opened for the understanding of ethylene cross-talkings with other regulators (auxin, polyamines, jasmonate) and nutritional metabolites (glucose, sucrose) involved in the control of flowering.

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, canlocaline, 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.

Thermic and atmospheric phase plot as an expression of the climatic homeostatic capacity, and viable development.- A systemic and cybemetic approach of the most important effectors contributing to climate control has been made, with the view of a representation mode!. The thermic and gaseous (C02) phase space were proposed as sentinel variables to rapidly follow the passage or not toward a more viable and sustainable development.

The plasma membrane-associated NADH oxidase (NOX) of spinach leaf disks is characterized by oscillations in activity with a regular period length of ca. 24 min. Within a single population of plants exposed to light at the same time, NOX activities of all plants function synchronously. Exposure of plants transferred from darkness to blue light (495 nm, 2 min, 50 mum mol m(-2) s(-1)) resulted in a complex response pattern but with a new maximum in the rate of NOX activity 36 (24 + 12) min after illumination and then with maxima in the rate of NOX activity every 24 min thereafter. Transient maxima in NOX activity were observed as well after 9.3 +/- 1.4 and 20.7 +/- 2.1 min. The blue light response differed from the response to red (650 nm, 10 min, 50 mum mol m(-2) s(-1)) or white light where activity maxima were initiated 12 min after the light exposure followed by maxima every 24 min thereafter. Green or yellow light was ineffective. The light response was independent of the time in the 24-min NOX cycle when the light was given. The net effects of blue and red light were ultimately the same with a new maximum in the rate of NOX activity at 12 + 24 = 36 min (and every 24 min thereafter), but the mechanisms appear to be distinct.

Decapitation of Arabidopsis floral stern suppresses elongation and any associated rate oscillation. This growth inhibition also appeared after application on intact plants of IAA transport inhibitors such as NP A. A subsequent IAA paste application on the cut surface restored growth and circadian oscillations in extension rate. These results indicate that the upper zone of the inflorescence has a major influence on floral stem extension rate and give a particular importance to auxin. Furthermore, measurement of endogenous contents of IAA and IAA-aspartate conjugate displayed that they were subjected to a circadian rhythm during Arabidopsis floral stern growth. All together, these data point out lAA as an essential factor in circadian growth rhythm regulation of Arabidopsis floral stem

Viability Envelopes of Romania.- A general and heuristic methodology for sustainable development estimation is presented. An application is made concerning the interaction in Romania of population with environment and society, surrounded by physical, chemical and biological extra-cultural envelopes of viability and sustainability (climate: temperature, water, atmospheric composition; biosphere; forests, agriculture, etc.). A comparison with other lands is set out. Keywords: Viablity, Sustainable development, environment, Romania

Leaf disks, 1 cm in diameter, were punched from leaves of market spinach and used for assay of NADH oxidase. The disks exhibited a steady state rate of NADH oxidation of about 1 nmole/min/disk. The activity was proportional to time of incubation and to the number of disks. The activity was stimulated by the synthetic auxin 2,4-D to a maximum near 1 muM 2,4-D. The disks provide a convenient system to measure the cell surface NADH oxidase in leaves.