Papers by Yaroslav de Kouchkovsky
Comptes rendus des séances de la Société de biologie et de ses filiales, 1968
Photosynthesis, two centuries after its discovery by Joseph Priestley, 1972
It is doubtless that the question of the events driving to the exciton capture and hence to the p... more It is doubtless that the question of the events driving to the exciton capture and hence to the photochemical activity should be considered as involving the structure of the thylakoid membrane supporting the pigment systems. In this regard, chlorophyll fluorescence is a good witness of many processes.
Current Plant Science and Biotechnology in Agriculture, 1998
In Rhizobiwn-legume nitrogen-fixing symbiosis, host plant lectins have been suggested to mediate ... more In Rhizobiwn-legume nitrogen-fixing symbiosis, host plant lectins have been suggested to mediate specific recognition and binding of bacteria to the root surface. This work concerns the nature of lectins from Medicago sativa roots.
Comptes rendus des séances de la Société de biologie et de ses filiales, 1968
Progress in Photosynthesis Research, 1987
The previously proposed microchemiosmotic scheme, in which a resistive proton pathway is separate... more The previously proposed microchemiosmotic scheme, in which a resistive proton pathway is separated from the bulk medium by diffusion barriers, implies that their lowering should delocalize the coupling between redox chains and F0F1-ATPases. This was already obtained by various treatments (osmotic, ionic) and now also by the use of permeant amines. The latter point explains the discrepancy of results found in literature.
Journal of Electroanalytical Chemistry, 1999
The anion PW 12 O 3 − 40 is very sparingly soluble in concentrated mineral acid solutions. This s... more The anion PW 12 O 3 − 40 is very sparingly soluble in concentrated mineral acid solutions. This shortcoming has impeded the kind of study that demonstrated the merging of the first two waves of SiW 12 O 4 − 40 and P 2 W 18 O 6 − 62 by an EEC mechanism in aqueous solutions. Entrapment of PW 12 O 3 − 40 in protonated slightly quaternized poly(4-vinylpyridine) films (QPVP) or in polyaniline films (PANI) has now permitted such a study. As also observed previously, a negative potential shift of the first redox wave of the heteropolyanion is obtained when the acid concentration in the bathing solution increases. All the results are compared with those obtained for QPVP-SiW 12 O 4 − 40 , QPVP-P 2 W 18 O 6 − 62 , PANI-SiW 12 O 4 − 40 and PANI-P 2 W 18 O 6 − 62 composites. In each case, the same EEC mechanism is operative. EQCM experiments were also very useful in this issue. Except for the case of PW 12 O3 − 40 which could not be studied in concentrated acid solutions, all other systems show that the merging of waves necessitates higher acid concentrations in solution than when the heteropolyanions are entrapped in polymer matrices. This observation was termed the 'microenvironment effect'. In the present work, confocal microscopy measurements of fluorescence intensity variation between bathing solutions and appropriate composites show directly the existence of differences of pH between the two phases. The results concord with predictions from Donnan effects, and reinforce such an explanation for the 'microenvironment effect'.
Photosynthetica
We thank Péter Maróti for his wonderful reminiscence of Jean Lavorel. We are grateful to Rajni Go... more We thank Péter Maróti for his wonderful reminiscence of Jean Lavorel. We are grateful to Rajni Govindjee and Sandra Stirbet for reading this tribute and making valuable suggestions, before its publication.
Auger Pierre, De Kouchkovsky Yaroslav, Passadeos Christos, Niang Souleimane, Morazé Charles. Déba... more Auger Pierre, De Kouchkovsky Yaroslav, Passadeos Christos, Niang Souleimane, Morazé Charles. Débats. In: Tiers-Monde, tome 20, n°78, 1979. Découverte et innovation scientifiques au service du tiers monde. Colloque Henri Laugier. pp. 263-265
Yvette, France Received 4 March 1983; revision received 25 March 1983 In thylakoids system II wat... more Yvette, France Received 4 March 1983; revision received 25 March 1983 In thylakoids system II water-splitting proton generation is mainly localized in grana stacks, whereas system I plastoquinol reoxidation, is essentially restricted to non-appressed regions, such as stromal lamellae; the same is true for the coupling factor. For a given mean proton gradient, a system II chain was found to be less able to drive phosphorylation than a system I or a system I + II chain. These results support our microchemiosmotic hypothesis, based on the existence of lateral resistances to H+ movements. They confirm that the proton gradients at the redox chain and at the coupling factor are unequal and that both are different from their mean experimentally measured value. Electron transfer Proton gradient Phosphorylation Membrane topography Microchemiosmosis
Photosynthesis Research
This paper is a tribute to a great scientist and an authentic "honest man" that was Jea... more This paper is a tribute to a great scientist and an authentic "honest man" that was Jean Lavorel (1928-2021). He was a pioneer in research on the primary events of photosynthesis in algae, plants, and photosynthetic bacteria. He focused his attention on chlorophyll fluorescence and luminescence, and also on oxygen evolution, both experimentally (with laboratory-built refined apparatus) and theoretically. Many of his results are classical now. Besides a survey of his main achievements, most of them obtained by him alone, different reminiscences on the researcher and the person he was illustrate the rich personality of Jean Lavorel.
This article is not a survey of all the research made during the last half century at the ‘Labora... more This article is not a survey of all the research made during the last half century at the ‘Laboratoire de Photosyn-thèse ’ of the ‘Centre National de la Recherche Scientifique ’ (CNRS) in Gif-sur-Yvette, but rather some personal recollections, as faithful as possible. Not all people could be mentioned and the scientists named here are mainly those who, at different stages of the laboratory’s evolution, created their research teams, within or outside the laboratory. The laboratory, closed now as an administrative entity, was founded in 1953 by the CNRS in Gif-sur-Yvette, near Paris. Besides the emerging research groups in Paris and at Saclay, it was then the only one in France to be entirely dedicated to photosynthesis. Initially, the focus was on metabolic biochemistry of photosynthesis in whole plants and unicellular algae. In 1959, biophysics of primary and associated processes was added and in 1966, the laboratory was enlarged to include molecular genetics and, somewhat later, st...
Photochemistry and Photobiology, 1967
ABSTRACT Abstract Oxygen evolution and fluorescence have been studied with isolated chloroplasts ... more ABSTRACT Abstract Oxygen evolution and fluorescence have been studied with isolated chloroplasts illuminated, in the absence of Hill reagents, by flashes or continuous light. As in whole cells, at least two substances are involved in the primary process leading to the oxygen evolution. The first, called E, probably is the photochemical “complex” of System II. After a long period of darkness, E is not active. It is activated in two steps. Step one is a photochemical reaction, induced by a quantum of light absorbed by pigment-system II, which results in the production of E in a reduced state. Step two is a dark oxidation of the reduced E by the second substance, A. The oxidized E can then enter the normal photochemical cycle of system II. Reduced E might alternatively be oxidized by oxygen, this reaction being responsible for a very rapid and brief light-induced oxygen uptake. Substance A is measured by the oxygen burst and is present in the chloroplasts at the approximate ratio of 1 molecule for 70 molecules of total chlorophyll while E is at the ratio of about 1/2800. This gives a E over A value of 1/35 which is much smaller than the one found in whoe cells (ca. 1/10). This independent behavior of E and A suggests that chloroplast extraction destroys some photochemical centers without having a direct impact on A, which might diffuse from one center to another. Besides the brief light-induced oxygen uptake above mentioned, there is another one which is related to System I functioning.The kinetics of the oxygen evolution and of the fluorescence have been compared. During the activation process of the oxygen evolving ability, rate of oxygen evolution and fluorescence yield increase in a parallel way. After the maximum velocity of the oxygen burst is reached (i.e. after activation), the fluorescence yield keeps growing up until the steady-state is attained (with an intermediary plateau), whereas the rate of oxygen emission slows down. The time-course curves of fluorescence obtained with inactivated or activated chloroplasts are essentially different in that the initial yield is higher in the latter case.
Photosynth Res, 1993
Two genotypes of Lupinus albus L., resistant and susceptible to drought, were subjected to water ... more Two genotypes of Lupinus albus L., resistant and susceptible to drought, were subjected to water deficiency for up to two weeks. Such treatment progressively lowered the leaf water content from about 85% to about 60% (water potential from-0.8 to-4.3 MPa). Light-saturation curves of the uncoupled electron transport were analyzed according to a simple kinetic model of separated or connected reversible photoreactions. It gives an extrapolated maximum rate (Vmax) and the efficiency for capturing light (Ira, which is the light intensity at Wmax/2). For Photosystem 2, Vr, ax and, less markedly, Ira, declined with increasing severity of drought treatment; the artificial donor, diphenylcarbazide, could not restore the activity. One cause of this Photosystem 2 inhibition could be the loss of active Photosystem 2 centers. Indeed, their concentration relative to chlorophyll, estimated by flash-induced reduction of dimethylquinone, was halved by a medium stress. To the extent that it was still not restored by diphenylcarbazide, the site of Photosystem 2 inactivation must have been close to the photochemical trap, after water oxidation and before or at plastoquinone pool. By relating electron transport rate to active centers instead of chlorophyll, no inhibition by drought was detected. Therefore, water stress inactivates specifically Photosystem 2, without impairing a downhill thermal step of electron transport. On the other hand, the decrease of I~ suggests that antennae connected to inactive centers may transfer their excitation energy to active neighbors, which implies that antenna network remains essentially intact. Gel electrophoresis confirmed that the apoproteins of the pigment complexes were well conserved. In conclusion, the inactivation of Photosystem 2 may not be a physical loss of its centers and core antennae but probably reflects protein alterations or conformational changes. These may result from the massive decrease of lipids induced by drought (Meyer et al. 1992, Photosynth. Res. 32: 95-107). Both lupin genotypes behaved similarly but, for a same deficiency, the resistant seemed unexpectedly more sensitive to drought.
Photosynthesis Research, Apr 30, 1992
Bioenergetic properties of thylakoids from plants submitted to a water stress stress (watering st... more Bioenergetic properties of thylakoids from plants submitted to a water stress stress (watering stopped for 6-15 days) have been measured in two lupin genotypes characterized as resistant or susceptible to drought. This energy coupling was assessed by flow-force relationships relating the phosphorylation rate to the magnitude of the proton gradient A~H+. The fluorescent probe 9-aminoacridine was used to express, as a ApH, the whole A~H. by calibrating fluorescence quenching against the phosphate potential AGp in 'state 4', i.e., when ATP synthesis is strictly balanced by its hydrolysis. This calibration procedure was shown to be unaffected by treatments. At equal energization (iso-ApH), ATP synthesis was halved by a medium stress and disappeared for a more severe stress, whereas ApH at equal energy input (light) declined only under a severe drought. For an identical ApH, PS 1-driven phosphorylation is always more efficient than PS2, both in control and stressed plants. Thus, uncoupling is not the cause of the phosphorylation decline; moreover, retention of a 'micro-chemiosmotic' type of coupling implies that the distribution of photosystems and ATPases is unchanged. Parallel to these functional alterations, the lipid content of thylakoids dramatically dropped. As galactolipids fell strongly, neutral lipids rose slightly. Fatty acids decreased then increased with stress, yet phosphorylation did not recover in the latter case and membrane permeability to protons remained unaffected. Overall, these observations suggest a preserved thylakoid structure and this was indeed observed on electron micrographs, even for a severe stress. Therefore, the membrane integrity is probably preserved more by the protein network than by the lipid matrix and the loss of the phosphorylating activity mainly reflects a loss of ATPases or at least their inactivation, possibly due to their altered lipid environment. Finally, from the bioenergetic point of view, the susceptible genotype was unexpectedly less affected by drought than the resistant.
Botany, 1972
Two clones of Nicotiana tabacum in liquid suspension culture were grown photosynthetically using ... more Two clones of Nicotiana tabacum in liquid suspension culture were grown photosynthetically using air plus 2% CO2 as carbon source, and agitation. In general, the transfer from heterotrophic to autotrophic growth in these cells was accompanied by an increase in the concentration of photosynthetic pigments, an increase in the N, C, and H contents and in the N:C ratio, an increase in the photosynthetic oxygen evolution capacity, and a decrease in the respiratory rate. The limiting factors are discussed.Several clones were also grown photosynthetically on agar slants and the development of their photosynthetic pigments studied. Results showed that one cannot accurately predict the photosynthetic capability of tobacco cells from their appearance in heterotrophic culture conditions.
Photochem Photobiol, 1966
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Papers by Yaroslav de Kouchkovsky