Seed vigor, aging, and osmopriming affect anion and sugar leakage during imbition of maize (Zea mays L.) caryopses

Conductivity was significantly increased by aging and decreased by osmopriming of maize (Zea mays L.) caryopses. Chloride, phosphate, and sulfate were the main anions that leaked out of maize seeds; their leakage was closely related to conductivity, increased by aging, and decreased by osmopriming. The anion leakage of isolated embryos correlated closely to seed vigor and was more sensitive to aging and priming than that of the whole seed. Anion leakage may be a more sensitive measure for seed vigor than bulk conductivity readings. Aging did not increase the sugar leakage of whole seeds but significantly increased the sugar leakage of isolated embryos. Sugar leakage was not closely related to total soluble sugar content of seeds. While priming decreased seed conductivity, the decreased anion and sugar leakage of the primed seeds was mainly caused by the washing effect during priming. The total anions or sugars left in the polyethylene glycol (PEG) solution after priming and in the conductivity solution of the primed seeds was almost the same as in the conductivity solution of the unprimed seeds alone

The electrical potential as a gauge of photosynthetic performance in plant chloroplasts : a patch-clamp study

The earliest events in the energisation of the photosynthetic membrane upon light capture are the formation of a transmembrane electrical potential (AV) and a transmembrane proton gradient (ΔpH). In this thesis ΔΨis employed for the study of the bioenergetics of chloroplast photosynthesis and its regulation by ΔpH in the shade adapted plant peperomia ( Peperomia metallic a) and the high-light adapted plant spinach ( Spinacia oleracea ). Electrochromism (P515) was used and a patch-clamp method was developed yielding two complementing tools for the detection of ΔΨ. The patch-clamp method enables the detection of relatively large light- induced currents (photocurrents) or potentials (photopotentials) of a single P. metallica chloroplast. An electrical equivalent scheme is introduced incorporating amongst others the thylakoid membrane resistance and capacitance and an access resistance which, at least partly, is supposed to be associated with low (lateral) conductance phases of thylakoid lamellae. The light-induced electrical responses reflect the operation of the photosynthetic current-generators and the way generated current is distributed throughout the chloroplast conductance network. Simultaneous measurements of light- and current-induced responses allow the separation of electrogenic events from changes in chloroplast conductances. A kinetically well defined slow secondary phase (R1 /Q) could be distilled from the flash- induced photocurrent/-potential which is related to the turnover of the cyt. b 6 f complex (Q-cycle). Generally, the rise of R1/Q was sigmoidal. This biphasic rise is modelled by a consecutive reaction scheme with two relaxation times of 13 and 28 ms which likely reflect the oxidation of plastoquinol and reduction of plastoquinone at the lumen and stroma membrane/water interface of the b 6 f complex, respectively. A P515 fraction (Rl /RC f ) of about 20 % is inadequately stabilised in dark-adapted spinach chloroplasts and decays rapidly with a relaxation time of 1 - 2 ms. A fast dissipation of ΔΨas generated by photosystern (PS) II is suggested to cause R1/RC f . It is hypothesised that adequate charge stabilisation depends on efficient energy coupling between PS II and the cyt. b 6 f complex which is only guaranteed in superclusters composed of both protein complexes. Energisation causes a suppression of about 50 % of PS II-dependent charge separation which is dark reversible with a relaxation time of about 20 s and is likely induced by the low lumenal pH created by lightdriven proton pumping. The results are best explained by a reaction center quenching model in which a fraction of PS II centers exhibits a rapid charge recombination. Flash-induced changes in chloroplast conductances are first demonstrated. The seal conductance decreases transiently upon a brief flash with a minimum of 0.3 - 5 % at 50 - 200 ms after the flash and a slow relaxation in 1 - 10 s. It is proposed that an important part of the conductance changes is intimately associated with changes in the lateral conductances of thylakoids, in particular those of the narrow spaced grana thylakoids.<br/

Are Interaction-free Measurements Interaction Free?

In 1993 Elitzur and Vaidman introduced the concept of interaction-free measurements which allowed finding objects without ``touching'' them. In the proposed method, since the objects were not touched even by photons, thus, the interaction-free measurements can be called as ``seeing in the dark''. Since then several experiments have been successfully performed and various modifications were suggested. Recently, however, the validity of the term ``interaction-free'' has been questioned. The criticism of the name is briefly reviewed and the meaning of the interaction-free measurements is clarified.Comment: 11 pages, 3 eps figures. Contribution to the ICQO 2000, Raubichi, Belaru

High-efficiency quantum interrogation measurements via the quantum Zeno effect

The phenomenon of quantum interrogation allows one to optically detect the presence of an absorbing object, without the measuring light interacting with it. In an application of the quantum Zeno effect, the object inhibits the otherwise coherent evolution of the light, such that the probability that an interrogating photon is absorbed can in principle be arbitrarily small. We have implemented this technique, demonstrating efficiencies exceeding the 50% theoretical-maximum of the original ``interaction-free'' measurement proposal. We have also predicted and experimentally verified a previously unsuspected dependence on loss; efficiencies of up to 73% were observed and the feasibility of efficiencies up to 85% was demonstrated.Comment: 4 pages, 3 postscript figures. To appear in Phys. Rev. Lett; submitted June 11, 199

The electrical potential as a gauge of photosynthetic performance in plant chloroplasts : a patch-clamp study

The earliest events in the energisation of the photosynthetic membrane upon light capture are the formation of a transmembrane electrical potential (AV) and a transmembrane proton gradient (ΔpH). In this thesis&nbsp;ΔΨis employed for the study of the bioenergetics of chloroplast photosynthesis and its regulation by&nbsp;ΔpH in the shade adapted plant peperomia ( Peperomia metallic a) and the high-light adapted plant spinach ( Spinacia oleracea ). Electrochromism (P515) was used and a patch-clamp method was developed yielding two complementing tools for the detection of&nbsp;ΔΨ. The patch-clamp method enables the detection of relatively large light- induced currents (photocurrents) or potentials (photopotentials) of a single P. metallica chloroplast. An electrical equivalent scheme is introduced incorporating amongst others the thylakoid membrane resistance and capacitance and an access resistance which, at least partly, is supposed to be associated with low (lateral) conductance phases of thylakoid lamellae. The light-induced electrical responses reflect the operation of the photosynthetic current-generators and the way generated current is distributed throughout the chloroplast conductance network. Simultaneous measurements of light- and current-induced responses allow the separation of electrogenic events from changes in chloroplast conductances. A kinetically well defined slow secondary phase (R1 /Q) could be distilled from the flash- induced photocurrent/-potential which is related to the turnover of the cyt. b 6 f complex (Q-cycle). Generally, the rise of R1/Q was sigmoidal. This biphasic rise is modelled by a consecutive reaction scheme with two relaxation times of 13 and 28 ms which likely reflect the oxidation of plastoquinol and reduction of plastoquinone at the lumen and stroma membrane/water interface of the b 6 f complex, respectively. A P515 fraction (Rl /RC f ) of about 20 % is inadequately stabilised in dark-adapted spinach chloroplasts and decays rapidly with a relaxation time of 1 - 2 ms. A fast dissipation of&nbsp;ΔΨas generated by photosystern (PS) II is suggested to cause R1/RC f . It is hypothesised that adequate charge stabilisation depends on efficient energy coupling between PS II and the cyt. b 6 f complex which is only guaranteed in superclusters composed of both protein complexes. Energisation causes a suppression of about 50 % of PS II-dependent charge separation which is dark reversible with a relaxation time of about 20 s and is likely induced by the low lumenal pH created by lightdriven proton pumping. The results are best explained by a reaction center quenching model in which a fraction of PS II centers exhibits a rapid charge recombination. Flash-induced changes in chloroplast conductances are first demonstrated. The seal conductance decreases transiently upon a brief flash with a minimum of 0.3 - 5 % at 50 - 200 ms after the flash and a slow relaxation in 1 - 10 s. It is proposed that an important part of the conductance changes is intimately associated with changes in the lateral conductances of thylakoids, in particular those of the narrow spaced grana thylakoids.&nbsp

Isolated tin fluoride molecules in a copper lattice

A Mössbauer absorber was made by simultaneous evaporation of copper and implantation of119Sn, and postimplantation of F. A large fraction of Sn4+ was formed, assigned to the formation of SnF4