Yosepha Shahak

Coloured shade nets can improve the yield and quality of green decorative branches of Pittosporum variegatum

Summary Many green decorative branches (“greens”), which form an important part of ornamental bouquets, originatefrom shade plants, and are commercially grown in Israel under black shade nets. We are studying the possibility to manipulate the nature of the vegetative growth of greens to improve the yield and quality desirable for various ornamental crops.The present paper summarizes the results obtained for Pittosporum variegatum grown under shade nets of various optical properties: green, red, blue, grey, black, and reflective. The knitting density and design of the nets were adjusted to give the same transmittance of sunlight in the PAR (photosynthetically active radiation, 400–700.nm) region. The experiments were carried out in a commercial plot. A single layer of 50% shade net covered the plot during thewinter season, and two layers in the summer, according to common practice. Data were collected mostly during the second growth year. The main results obtained included: (i) pronounced stimulation of branch elongation under the Red net; (ii) dwarfing under the Blue net; (iii) the Grey net markedly enhanced branching, resulting in “bushy”, dense plants with short side shoots and small leaves; (iv) the reflective, thermal net (Aluminet®) enhanced long branching. The results were reproducible over two successive harvesting years. We suggest that the coloured net technology can be applied to enhance commercially desired plant responses, thus substituting for the use of growth regulators or pruning.

Specific loss of LHCII phosphorylation in the Lemna mutant 1073 lacking the cytochrome b6/f complex

The thylakoid protein kinase(s) activity of Lemna perpusilla strain 6746 (wild type, WT) and the cytochrome (cyt) b 6/f‐less mutant 1073 was compared. Isolated thylakoids of both WT and mutant phosphorylated the polypeptides of 9–15, 29, 32–34 and 40–45 kDa. This kinase(s) activity was light‐dependent and could be elicited by addition of duroquinol in the dark. Thylakoids from both WT and mutant phosphorylated histone III‐S at comparable rates. However, the redox‐controlled phosphorylation of the LHCII polypeptide which could be demonstrated in vitro and in vivo in the WT thylakoids could not be detected under any experimental condition in the cyt b 6/f‐less thylakoids. Halogenated quinone analogues known to inhibit reduction of the cyt b 6/f complex inhibited both the electron flow and duroquinol‐activated LHCII phosphorylation, but had no effect on the duroquinol‐dependent phosphorylation of the other thylakoid polypeptides. These results indicate that the Lemna thylakoids contain at least two redox‐activated protein kinase(s). A quinone‐binding site is involved in the activation of the LHCII kinase system which is rendered inactive in the absence of the cyt b 6/f complex.

Sulfide quinone reductase (SQR) activity in Chlorobium

Membranes of the green sulfur bacterium, Chlorobium limicola f, thiosulfatophilum, catalyze the reduction of externally added isoprenoid quinones by sulfide. This activity is highly sensitive to stigmatellin and aurachins. It is also inhibited by 2‐n‐nonyl‐4‐hydroxyquinoline‐N‐oxide, antimycin, myxothiazol and cyanide. It is concluded that in sulfide oxidizing bacteria like Chlorobium, sulfide oxidation involves a sulfide‐quinone reductase (SQR) similar to the one found in Oscilatoria limnetica [Arieli, B., Padan, E. and Shahak, Y. (1991) J. Biol. Chem. 266. 104–111].

Electrogenic proton translocation by the chloroplast cytochrome b6/f complex reconstituted into phospholipid vesicles

When the cytochrome b 6/f complex from chloroplasts is incorporated into liposomes, reduction of external plastocyanin by plastoquinol is stimulated under uncoupling conditions. An extra H+/e− is ejected from the vesicles during the reaction, in addition to the scalar proton liberated from plastoquinol. This is stimulated by valinomycin/K+ and abolished under uncoupling conditions. Furthermore, the formation of a membrane potential during the reaction, negative inside the vesicles, is observed with the help of carbocyanine dyes. We conclude that the cytochrome b 6/f complex, like the cytochrome bc 1 from mitochondria, functions as an electrogenic proton translocator.

Electrogenic and Electroneutral Transport Modes of Renal Na/K ATPase Reconstituted into Proteoliposomes

SummaryThis paper describes measurements of electrical potentials generated by renal Na/K-ATPase reconstituted into proteoliposomes, utilizing the anionic dye, oxonol VI. Calibration of absorption changes with imposed diffusion potentials allows estimation of absolute values of electrogenic potentials.ATP-dependent Nacyt/Kexc exchange in K-loaded vesicles generates large potentials, up to 250 mV. By comparing initial rates or steady-state potentials with ATP-dependent22Na fluxes in different conditions, it is possible to infer whether coupling ratios are constant or variable. For concentrations of Nacyt (2–50mm) and ATP (1–1000 μm) and pHs (6.5–8.5), the classical 3Nacyt/2Kexc coupling ratio is maintained. However, at low Nacyt concentrations (<0.8mm), the coupling ratio is apparently less than 3Nacyt/2Kexc.ATP-dependent Nacyt/congenerexc exchange in vesicles loaded with Rb, Cs, Li and Na is electrogenic. In this mode congeners, including Naexc, act as Kexc surrogates in an electrogenic 3Nacyt/2congenerexc exchange. (ATP+Pi)-dependent Kcyt/Kexc exchange in K-loaded vesicles is electroneutral.ATP-dependent “uncoupled” Na flux into Na- and K-free vesicles is electroneutral at pH 6.5–7.0 but becomes progressively electrogenic as the pH is raised to 8.5. The22Na flux shows no anion specificity. We propose that “uncoupled” Na flux is an electroneutral 3Nacyt/3Hexc exchange at pH 6.5–7.0 but at higher pHs the coupling ratio changes progressively, reaching 3Na/no ions at pH 8.5. Slow passive pump-mediated net K uptake into Na- and K-free vesicles is electroneutral, and may also involve Kcyt/Hexc exchange.We propose the general hypothesis that coupling ratios are fixed when cation transport sites are saturated, but at low concentrations of transported cations, e.g., Nacyt in Na/K exchange and Hexc in “uncoupled” Na flux, coupling ratios may change.

Sulfide Oxidation from Cyanobacteria to Humans: Sulfide–Quinone Oxidoreductase (SQR)

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Adenosine triphosphate-generated transmembrane electric potential in chloroplasts

Abstract Utilizing oxonol VI as a transmembrane electric potential indicating dye, chloroplasts are shown to develop rapid transient light-induced and ATP-induced potentials. Following the large transient signal smaller steady-state potentials are maintained with either driving system. The ATP-induced potential in the dark depends upon preactivation of the light-triggered ATPase of the chloroplasts, and is inhibited by uncouplers, ionophores such as valinomycin, and energy-transfer inhibitors such as tentoxin, Dio-9 or DCCD. Nigericin increased the signal of both the light- and the ATP-induced reactions. The fact that relatively large transient membrane potentials are induced by either a dark-to-light transition or ATP in the dark provides an explanation for previously observed phenomena such as early kinetics of photophosphorylation and the ATP-induced luminescence.

Extra proton translocation and membrane potential generation—Universal properties of cytochrome bc1b6f complexes reconstituted into liposomes

Isolated cytochrome complexes from different sources like beef heart mitochondria, spinach chloroplasts, cyanobacteria, and photosynthetic bacteria were incorporated into liposomes by sonication as revealed by sucrose density gradient centrifugation and electron microscopy. The reconstituted cytochrome complexes show suppressed rates of quinol-cytochrome c/plastocyanin oxidoreduction which can be stimulated by ionophores and uncouplers. In addition, extra proton translocation out of the vesicles and membrane potential generation during electron transport were observed, suggesting a universal mechanism of electron and proton transport through all the tested cytochrome complexes.

Photophosphorylation studies with fluorescent adenine nucleotide analogs

The synthesis of fluorescent analogs of nucleotides with enzymic activity was recently reported [ 1 J . The fluorescence properties of 1 ,N6-ethenoadenosine diand triphosphate (eADP and eATP) promise to provide useful tools for the study of the interaction of adenine nucleotides with the energy conservation system of chloroplast membranes and the transport of nucleotides across these membranes, if these can replace nucleotides in the various chloroplast reactions. This communication deals with the activity of EADP as a substrate for photophosphorylation and of EATP as substrate for several hydrolytic and exchange reactions related to photophosphorylation. Significant differences in the capability of the e-adenine analogs to replace adenine nucleotides in the various reactions tested suggest that more than one type of site, with different specificity for the nucleotide phosphates, exists.

Irreversible disassembly of chiral macrodomains in thylakoids due to photoinhibition

We investigated the effect of photoinhibitory illumination on the chiral macroorganization of the chromophores in spinach thylakoid membranes. By measuring circular dichroism (CD), we found that prolonged (15 min) illumination of membranes with intense white light led to irreversible diminishment of the main CD bands originating from the chiral macroorganization of the chromophores. The irreversible decrease of the main CD bands showed a nearly linear correlation with the extent of photoinhibition which was determined by chlorophyll fluorescence induction. CD measurements also revealed that the excitonic CD bands, which are given rise by short-range interactions between the chromophores inside the complexes or particles, were largely insensitive to the photoinhibitory illumination of the membranes. These data show that, whereas photoinhibitory treatment has no perceptible effect on the molecular architecture of the bulk of the pigment–protein complexes, it leads to a disorganization of their macroarray, and an irreversible disassembly of the chirally organized macrodomains.