1,059 research outputs found
Collective intelligence as a Challenge to Approach Interdisciplinary Topics in Plant Biology
No full textStrasser Reto J. Collective intelligence as a Challenge to Approach Interdisciplinary Topics in Plant Biology. In: Bulletin de la Classe des sciences, tome 14, n°7-12, 2003. pp. 261-263
Équivalence entre la théorie des flux et la théorie des relations entre proportions de pigments pour la description de la répartition de l'énergie lumineuse absorbée par les membranes photoactives
No full textSironval Cyril, Strasser Reto J., Brouers M. Équivalence entre la théorie des flux et la théorie des relations entre proportions de pigments pour la description de la répartition de l'énergie lumineuse absorbée par les membranes photoactives. In: Bulletin de la Classe des sciences, tome 67, 1981. pp. 248-259
Tree diversity affects chlorophyll a fluorescence and other leaf traits of tree species in a boreal forest
No full textAn assemblage of tree species with different crown properties creates heterogeneous environments at the canopy level. Changes of functional leaf traits are expected, especially those related to light interception and photosynthesis. Chlorophyll a fluorescence (ChlF) properties in dark-adapted leaves, specific leaf area, leaf nitrogen content (N) and carbon isotope composition (δ13C) were measured on Picea abies (L.) H.Karst., Pinus sylvestris L. and Betula pendula Roth. in monospecific and mixed boreal forests in Europe, in order to test whether they were affected by stand species richness and composition. Photosynthetic efficiency, assessed by induced emission of leaf ChlF, was positively influenced in B. pendula by species richness, whereas P. abies showed higher photosynthetic efficiency in monospecific stands. Pinus sylvestris had different responses when it coexisted with P. abies or B. pendula. The presence of B. pendula, but not of P. abies, in the forest had a positive effect on the efficiency of photosynthetic electron transport and N in P. sylvestris needles, and the photosynthetic responses were positively correlated with an increase of leaf δ13C. These effects on P. sylvestris may be related to high light availability at the canopy level due to the less dense canopy of B. pendula. The different light requirements of coexisting species was the most important factor affecting the distribution of foliage in the canopy, driving the physiological responses of the mixed species. Future research directions claim to enhance the informative potential of the methods to analyse the responses of pure and mixed forests to environmental factors, including a broader set of plant species’ functional traits and physiological response
Effects of acute O3 stress on PSII and PSI photochemistry of sensitive and resistant snap bean genotypes (Phaseolus vulgaris L.), probed by prompt chlorophyll “a” fluorescence and 820 nm modulated reflectance
No full textThe response of PSII and PSI photochemistry to acute ozone (O3) stress was tested in a “model plant system”, namely the O3 sensitive (S156) and O3 resistant (R123) genotype pairs of Phaseolus vulgaris L., during a phenological phase of higher O3 sensitivity (pod formation). The modulation of the photosynthetic activity during O3 stress was analysed by measuring gas exchanges, Prompt Fluorescence (PF, JIP-test) and 820 nm Modulated Reflectance (MR), a novel techniques which specifically detects the changes in the redox state of P700 and plastocyanin. The results showed that, coherently with genotypic-specific O3 sensitivity, the response of the two snap bean genotypes differed for the intensity and time of onset of the considered physiological changes. In fact, despite leaf injury and gas exchanges reduction appeared concurrently in both genotypes, S156 showed a PSII down regulation already after the first day of fumigation (DOF), and an enhancement of Cyclic Electron Flow of PSI after the second DOF, whereas R123 showed only slight adjustments until the third DOF, when the activity of both photosystems was down-regulated. Despite these differences, it is possible to distinguish in both genotypes an early O3 response of the photochemical apparatus, involving PSII only, and a following response, in which PSI activity and content are also modulated. The measurement of the MR signal, performed simultaneously with the PF measurements and the JIP-test analysis, has allowed a better understanding of the role that PSI plays in the O3 stress response of the S156/R123 model plant system
Differential response of photosynthetic electron transport and CO2 assimilation in sensitive (S156) and resistant (R123) Phaseolus vulgaris L. (bush bean) genotypes to chronic ozone exposure. (http://www.satnt.ac.za/index.php/satnt/article/view/684/1501)
No full textTroposferiese osoon (O3) word beskou as een van die belangrikste lugbesoedelstowwe
aangesien dit wêreldwyd meer skade aan landbougewasse aanrig as al die ander
besoedelstowwe saam. Weens die oksiderende aard daarvan verooraak O3
blaarskade en ’
n afname in fotosintese. Bestandheid van gewasse teen O3
verskil aansienlik tussen spesies
en genotipes. Met hierdie studie is nuwe inligting oor die fisiologiese en biochemiese
grondslag van die skadelike effek van O3
verkry deur chroniese blootstelling van twee
bosboongenotipes met bekende gevoeligheid vir O3
, naamlik S156 (gevoelig) en R123
(bestand), aan onderskeidelik houtskool-gefiltreerde lug en 80 dpm O3
. Die studie is
uitgevoer in oop-dek-groeikamers (OTCs) vir die volle groeiperiode tot wasdom. Die
status van die fotosintetiese apparaat van die proefplante is bepaal deur analise van
chlorofil a-fluoressensiekinetika en CO2
-afhanklikheidskrommes (A:Ci
). Fisiologiese effekte
is by S156 waargeneem lank voor die verkyning van nekrotiese vlekke op die drieledige
blare. Fotosintese is aansienlik gerem in S156, hoofsaaklik weens ontkoppeling van
die suurstofvrystellingskompleks (OEC), remming van fotosintetiese elektronoordrag,
gevolglike afname in die reduksie van eind-elektronontvangers (ferredoksien, NADP+)
en die gepaardgaande afname in die karboksilering en die regenerering van ribulose-1,5-
bisfosfaat. Saad- en peulopbrengs het nou ooreengestem met die fotosintetiese gedrag van
die proefplante. Ofskoon blare van albei genotipes sigbaar aangetas was, was dit S156 wat
ernstige nekrotiese vlekke vertoon het. Hierdie data bied nuwe inligting en komplementeer
bestaande kennis oor die prosesse onderliggend aan die fitotoksisiteit van O3
, nodig vir die
ontwikkeling van bestande genotipesTropospheric ozone is currently regarded as one of the most important air pollutants, since it causes more damage to vegetation world-wide than all the other pollutants combined (Ashmore and Bell 1991). Due to its oxidative nature ozone causes leaf damage and a decrease in photosynthesis. Ozone tolerance varies widely between species and genotypes. The aim of this study was to identify and quantify the physiological and biochemical constraints imposed by chronic ozone exposure of two bush bean (Phaseolus vulgaris L.) genotypes with known difference in sensitivity, namely S156 (sensitive) and R123 (resistant), to charcoal-filtered air and 80 nmol.mol-1 O3. The study was conducted in open-top growth chambers (OTCs) over the entire growth period by measuring chlorophyll a fluorescence (JIP-test) and photosynthetic gas exchange of the test plants weekly. The status of the photosynthetic apparatus was assessed by analysis of chlorophyll a fluorescence kinetics (JIP test) and CO2 response curves (A:Ci). O3-induced physiological effects were detected in S156 long before appearance of necrotic spots on the trifoliate leaves. Photosynthesis was substantially inhibited in S156, mainly due to disengagement of the oxygen evolving complex (OEC), inhibition of intersystem electron transport and the reduction of end-electron acceptors of PSI (ferredoxin, NADP+), causing the concomitant decrease in the carboxylation and regeneration of ribulose-1,5-bisphosphate. Seed and pod yield closely reflected the photosynthetic response of the test plants. Although leaves of both the genotypes were affected visually, it was S156 that displayed severe necrotic ozone injury on the trifoliate leaves. Our data contribute to and complement the existing knowledge on the processes underlying the phytotoxicity of O3 needed for development of tolerant genotype
Formulae and glossary of terms used by the JIP-test (modified after Strasser et al. 2004).
No full text<p>Formulae and glossary of terms used by the JIP-test (modified after Strasser et al. 2004).</p
Coral life as probed by their fluorescence emission
No full textCoral health was assessed by monitoring the photosynthetic activity of their zooxanthellae using the fast chlorophyll a fluorescence rise 0-J-I-P (Strasser et al. 2000). This type of measurement has the advantage of being non-invasive. Three species of recently collected Anthozoa were being studied: two species of Actinodiscus from Bali (Indonesia) and one colony of Porites porites from St Lucia (Lesser Antilles). The collected data were analysed according to the JIP-test (Strasser et al. 2000). Clear circadian rhythms were found in all calculated fluorescence parameters. The measurements are sensitive to random noise caused by for example movements of the polyps. We chose to study the maximum quantum efficiency of PSII (ϕPo) for its relative insensivity to this noise and the performance index (PIABS) as a reflection of all photosynthetic processes in PSII. The peaks and troughs of the circadian oscillations did not coincide with the rhythm of the ambient light in the aquarium. Long-term experiments with light cycles are reported
The possible role of pheophytine in the fast fluorescence rise OKJIP
No full textConforming to the quencher theory published as early as 1963 (Duysens and Sweers, 1963), and considered as a dogma by the majority of the researchers, the chlorophyll a fluorescence induction in viva is attributed to the photoreduction of a fluorescence quencher, the bound quinone QA, to its nonquenching form, QA-· With our actual knowledge about the PSII center, another component, the primary acceptor pheophytine Pheo, can also be included in the biochemical modeling of this phenomenon. A theoretical discussion based on numerical simulation and fitting of the experimental data, shows three possible approaches of the fluorescence signal, all being derived from the same reaction scheme of the electron transfer around PSII. The fluorescence rise in two of these models was based on the conventional assumption, that the presence of QA- determines the high fluorescence state. However, in the second model, the contribution to the fluorescence yield of the centers which have both Pheo and QA reduced has been considered higher (Vredenberg, 2000). The third model is based solely on the photochemical charge separation in the reaction center complex where P680Pheo- forms have a high fluorescence yield and P680+Pheo- create a dip (Strasser and Stirbet, 2000 and 2001)
Hyperhydricity of micropropagated shoots: a typically stress-induced change of physiological state
No full textpeer reviewedHyperhydricity 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
Opportunistic survival strategy of<i>Welwitschia mirabilis</i>: recent anatomical and ecophysiological studies elucidating stomatal behaviour and photosynthetic potential
No full textWe present new findings on leaf and stomatal apparatus anatomy and ecophysiology of Welwitschia mirabilis Hook.f. that are relevant to survival in the desert. We show that the structure of the stomatal apparatus with thin areas in the guard cell walls is a key feature enabling an opportunistic survival strategy through reversible quick switch-over from water conservation to CO2assimilation. Desert environment and greenhouse data demonstrated that stomatal conductance increased almost immediately after dawn to reach a maximum within approximately an hour, whereupon a steep decrease occurred. After discontinuation of induced drought in potted plants, fast recovery of stomatal conductance occurred while copious new root hairs developed within 50 h. Stomatal limitation proved to be the main photosynthetic constraint under induced drought. Under severe drought stress, biochemical limitation came into play. Chlorophyll fluorescence data of in-situ plants showed that the photosynthetic potential of leaf tissue is highest near the basal meristem, but although it decreases with age, it retains activity up to the leaf apex at the end of the green part. The photosynthetic potential of potted plants was optimal at 20 °C, analogous to mesophytic plants. Our data confirms our hypothesis that leaf surface and stomatal structure play a crucial role in moisture conservation and moderating leaf temperature for desert survival.</jats:p
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