345 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
Effects of anaerobiosis as probed by the polyphasic chlorophyll a fluorescence rise kinetic in pea (Pisum sativum L.)
No full textWe analysed the changes of the chlorophyll (Chl)a fluorescence rise kinetic (from 50 μs to 1 s) that occur when leaves or chloroplasts of pea ( Pisum sativum L.) are incubated under anaerobic conditions in the dark. In control leaves, Chl a fluorescence followed a typical O-J-I-P polyphasic rise [Strasser et al. (1995) Photochem Photobiol 61: 32–42]. Anaerobiosis modified the shape of the transient with the main effect being a time-dependent increase in the fluorescence yield at the J-step (2 ms). Upon prolongation of the anaerobic treatment (> 60 min), the O-J-I-P fluorescence rise was eventually transformed to an O-J (J = P) rise. A similar transformation was observed when pea leaves were treated with DCMU or sodium dithionite. Anaerobiosis resulted in a 10–20% reduction in the maximum quantum yield of the primary photochemistry of Photosystem II, as measured by the ratio of the maximal values of variable and total fluorescence (FV/FM). When the leaves were returned to the air in the dark, the shape of the fluorescence transient showed a time-dependent recovery from the anaerobiosis-induced change. The original O-J-I-P shape could also be restored by illuminating the anaerobically treated samples with far-red light but not with blue or white light. Osmotically broken chloroplasts displayed under anaerobic conditions fluorescence transients similar to those observed in anaerobically treated leaves, but only when they were incubated in a medium comprising reduced pyridine nucleotides (NADPH or NADH). As in intact leaves, illumination of the anaerobically treated chloroplasts by far-red light restored the original O-J-I-P transient, although only in the presence of methyl viologen. The results provide additional evidence for the existence of a chlororespiratory pathway in higher plant cells. Furthermore, they suggest that the J-level of the fluorescence transient is strongly determined by the redox state of the electron carriers at the PS II acceptor side
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
Effects of anaerobiosis as probed by the polyphasic chlorophyll a fluorescence rise kinetic in pea (Pisum sativum L.)
No full textWe analysed the changes of the chlorophyll (Chl) a fluorescence rise kinetic (from 50 μs to 1 s) that occur when leaves or chloroplasts of pea ( Pisum sativum L.) are incubated under anaerobic conditions in the dark. In control leaves, Chl a fluorescence followed a typical O-J-I-P polyphasic rise [Strasser et al. (1995) Photochem Photobiol 61: 32-42]. Anaerobiosis modified the shape of the transient with the main effect being a time-dependent increase in the fluorescence yield at the J-step (2 ms). Upon prolongation of the anaerobic treatment (> 60 min), the O-J-I-P fluorescence rise was eventually transformed to an O-J (J = P) rise. A similar transformation was observed when pea leaves were treated with DCMU or sodium dithionite. Anaerobiosis resulted in a 10-20% reduction in the maximum quantum yield of the primary photochemistry of Photosystem II, as measured by the ratio of the maximal values of variable and total fluorescence (FV/FM). When the leaves were returned to the air in the dark, the shape of the fluorescence transient showed a time-dependent recovery from the anaerobiosis-induced change. The original O-J-I-P shape could also be restored by illuminating the anaerobically treated samples with far-red light but not with blue or white light. Osmotically broken chloroplasts displayed under anaerobic conditions fluorescence transients similar to those observed in anaerobically treated leaves, but only when they were incubated in a medium comprising reduced pyridine nucleotides (NADPH or NADH). As in intact leaves, illumination of the anaerobically treated chloroplasts by far-red light restored the original O-J-I-P transient, although only in the presence of methyl viologen. The results provide additional evidence for the existence of a chlororespiratory pathway in higher plant cells. Furthermore, they suggest that the J-level of the fluorescence transient is strongly determined by the redox state of the electron carriers at the PS II acceptor sid
The Fo and the O-J-I-P Fluorescence Rise in Higher Plants and Algae
No full textThe variable chlorophyll (Chl) a fluorescence yield is related to the photochemical activity of photosystem II (PS II) of the oxygen evolving organisms. The kinetics of the fluorescence rise from the minimal yield Fo to the maximal yield Fm is a monitor of the accumulation of net reduced Qa with time in both active (Qb-containing) and inactive (non-Qb) PS II centers. The measurements of true Fo and that of the complete fluorescence transient from true Fo to Fm are useful in obtaining a kinetic picture of PS II activity. Using a shutter-less system (Plant Efficiency Analyzer, Hansatech, UK) that is capable of providing the first measured point at about 20 microseconds and that allows data accumulation over several orders of magnitude of time, we have measured the complete fluorescence transient in low and moderate (up to 700 W m⁻²) light intensities in several photosynthetic systems (higher plant leaves and chloroplasts; and the cell suspensions of green alga Chlamydomonas reinhardtii and several of its herbicide-resistant mutants, altered in single amino acids in its Dl protein). In all cases, the fluorescence transient follows a regular pattern of 0-J-I-P--T, where two intermediate inflections J (at about 2 ms) and I (at about 20 ms) appear between Fo and Fm levels. Furthermore, the ratio of Fm to Fo is about 5 in all cases and the lowered published ratio in several cases is suggested to be due to the J level being mistaken for Fo. We also present data on the effects of varying the dark times between preillumination and measurements of the transient, on the intensity dependence, and on the effect of the addition of diuron. The relationship of the 0-J rise to the fast fluorescence rise observed by other investigators will also be discussed
Polyphasic rise of chlorophyll a fluorescence in herbicide-resistant D1 mutants of Chlamydomonas reinardtii
No full textChlorophyll (Chl) a fluorescence transient, a sensitive and non-invasive probe of the kinetics and heterogeneity of the filling up of the electron acceptor pool of Photosystem II (PS II), was used to characterize D1-mutants of Chlamydomonas reinhardtii. Using a shutter-less system (Plant Efficiency Analyzer, Hansatech, UK), which provides the first measured data point at 10 μs and allows data accumulation over several orders of magnitude of time, we have characterized, for the first time, complete Chl a fluorescence transients of wild type (WT), cell wall less (CW-15) C. reinhardtii and several herbicide-resistant mutants of the D1 proteins: D1-V219* A251V, F255Y, S264A G256D and L275F. In all cases, the Chl a fluorescence induction transients follow a pattern of O-J-I-P where J and I appear as two steps between the minimum Fo (O) and the maximum Fmax (Fm, P) levels. The differences among the mutants are in the kinetics of the filling up of the electron acceptor pool of PS II (this paper) in addition to those in the re-oxidation kinetics of Q-A to QA, published elsewhere (Govindjee et al. (1992) Biochim Biophys. Acta: 1101: 353-358; Strasser et al. (1992) Archs. Sci. Genève 42: 207-224) and not in the ratio of the maximal fluorescence Fm to the initial fluorescence Fo. The value of this experimental ratio is Fm/Fo = 4.4±0.21 independent of the mutation. At 600 W m-2 of 650 nm excitation, distinct hierarchy in the fraction of variable Chl a fluorescence at the J level is observed: S264A > A251V ∼ G256A > L275F ∼ V219I > F255Y ∼ CW-15 ∼ WT. At 300 and 60 W m-2 excitation, a somewhat similar hierarchy among the mutants was observed for the intermediate levels J and I. Addition of bicarbonate-reversible inhibitor formate did not change the O to J phases, slowed the I to P rise, and in many cases, slowed the decay of fluorescence beyond the P level. These observations are interpreted in terms of formate effect being on the acceptor rather than on the donor side (S-states) of PS II. The formate effect was different in different mutants, with L275F being the most insensitive mutant followed by others (V219I, F255Y, WT, A251V and S264A). Further, in the presence of high concentrations of DCMU, identical transients were observed for all the mutants and the WT.The quantum yield of photochemistry of PS II, calculated from 1-(Fo/Fm), is in the range of 0.73 to 0.82 for the WT as well as for the mutants examined. Thus, in contrast to differences in the kinetics of the electron acceptor side of PS II, there were no significant differences in the maximum quantum yield of PS II, among the mutants tested. We suggest that earlier photochemistry yield values were much lower (0.4-0.6) than those reported here due to either higher measured values of Fo by instruments using camera shutters, or due to the use of cells grown in less than-optimal conditions
Regulation of antenna structure and electron transport in Photosystem II of Pisum sativum under elevated temperature probed by the fast polyphasic chlorophyll a fluorescence transient: OKJIP
No full textAbstractChlorophyll a (Chl a) florescence induction kinetics from the minimum yield F0 to the maximum yield Fm provide information on the filling up of the plastoquinone pool with reducing equivalents. In this paper, we have examined the effect of high temperature (above 40°C) on Chl a fluorescence rise kinetics starting from 40 μs (to 1 s) in pea leaves (Pisum sativum). The variable Chl a fluorescence is strongly quenched after heat treatment. With increasing temperature or the duration of heat treatment a typical O-J-I-P transient (Strasser et al. (1995) Photochem. Photobiol., 61, 32–42) is transformed into an O-K-J-I-P transient, with an additional rapid step called K detected in the 200–300 μs range. After prolonged heat treatment, the K-step becomes a dominant peak in the Chl a fluorescence transient followed by a large dip. We have investigated the origin and the possible interpretation of these changes by using NH2OH which acts as an electron donor to PS II, and DCMU which is known to block the PS II electron transport chain by displacing QB. From the present data we propose that the appearance of this K-step is due to two effects: (1) inhibition of the water splitting system that leads to a much slowed turn over of the reduction of QA; (2) changes in the architecture of the antenna of PS II which affect the energy migration properties within the photosynthetic unit. The K-step can thus be used as an indicator of the heterogeneity of photosynthetic units and as an indicator for the physiological state of the photosynthetic sample
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