Strong light-induced reorganization of pigment-protein complexes of thylakoid membranes in rye (spectroscopic study)

The supramolecular reorganization of LHCII complexes within the thylakoid membrane in Secale cereale leaves under low and high light condition was examined. Rye seedlings were germinated hydroponically in a climate chamber with a 16 h daylight photoperiod, photosynthetic photon flux density (PPFD) of 150 μmol m⁻² s⁻¹ and 24/16 °C day/night temperature. The influence of pre-illumination of the plants with high light intensity on the PSII antenna complexes was studied by comparison of the structure and function of the LHCII complexes and organization of thylakoid membranes isolated from 10-day-old plants illuminated with low (150 μmol m⁻² s⁻¹) or high (1200 μmol m⁻² s⁻¹) light intensity. Aggregated and trimeric with monomeric forms of LHCII complexes were separated from the whole thylakoid membranes using non-denaturing electrophoresis. Analyses of fluorescence emission spectra of these different LHCII forms showed that the monomer was the most effective aggregating antenna form. Moreover, photoprotection connected with LHCII aggregation was more effective upon LHCII monomers in comparison to trimer aggregation. Light stress induced specific organization of neighboring LHCII complexes, causing an increase in fluorescence yield of the long-wavelength bands (centered at 701 and 734 nm). The changes in the organization of the thylakoid membrane under light stress, observed by analysis of absorbance spectra obtained by Fourier transform infrared spectroscopy, also indicated light-induced LHCII aggregation.     

Regulation by sucrose of storage compounds breakdown in germinating seeds of yellow lupine (Lupinus luteus L.), white lupine (Lupinus albus L.) and Andean lupine (Lupinus mutabilis Sweet): I. Mobilization of storage protein

Research of the regulatory function of sucrose in storage protein breakdown was conducted on isolated embryo axes, excised cotyledons and whole seedlings of three lupine species grown in vitro on medium with 60 mM sucrose or without the sugar. Sucrose stimulated growth of yellow, white and Andean lupine isolated embryo axes and cotyledons but growth of seedlings was inhibited. Dry matter content was higher in sucrose-fed isolated organs and in seedling organs. Ultrastructure research revealed that lack of sucrose in the medium caused enhancement in storage protein breakdown. Protein deposits in cotyledons were smaller as well as soluble portion content in all studied organs was lower when there was no sucrose in the medium. In the same conditions, the activity of glutamate dehydrogenase was significantly higher. Increase in vacuolization of cells of white lupine root meristematic zone cells was observed and induction of autophagy in young carbohydrate-starved embryo axes is discussed.     

Bottlenose dolphins exchange signature whistles when meeting at sea

The bottlenose dolphin, Tursiops truncatus, is one of very few animals that, through vocal learning, can invent novel acoustic signals and copy whistles of conspecifics. Furthermore, receivers can extract identity information from the invented part of whistles. In captivity, dolphins use such signature whistles while separated from the rest of their group. However, little is known about how they use them at sea. If signature whistles are the main vehicle to transmit identity information, then dolphins should exchange these whistles in contexts where groups or individuals join. We used passive acoustic localization during focal boat follows to observe signature whistle use in the wild. We found that stereotypic whistle exchanges occurred primarily when groups of dolphins met and joined at sea. A sequence analysis verified that most of the whistles used during joins were signature whistles. Whistle matching or copying was not observed in any of the joins. The data show that signature whistle exchanges are a significant part of a greeting sequence that allows dolphins to identify conspecifics when encountering them in the wild.     

Movement of the iron-sulfur head domain of cytochrome bc(1) transiently opens the catalytic Q(o) site for reaction with oxygen

Cytochrome bc(1), a key enzyme of biological energy conversion, generates or uses a proton motive force through the Q cycle that operates within the two chains of cofactors that embed two catalytic quinone oxidation/reduction sites, the Q(o) site and the Q(i) site. The Q(o) site relies on the joint action of two cofactors, the iron-sulfur (FeS) cluster and heme b(L). Side reactions of the Q cycle involve a generation of superoxide which is commonly thought to be a product of an oxidation of a highly unstable semiquinone formed in the Q(o) site (SQ(o)), but the overall mechanism of superoxide generation remains poorly understood. Here, we use selectively modified chains of cytochrome bc(1) to clearly isolate states linked with superoxide production. We show that this reaction takes place under severely impeded electron flow that traps heme b(L) in the reduced state and reflects a probability with which a single electron on SQ(o) is capable of reducing oxygen. SQ(o) gains this capability only when the FeS head domain, as a part of a catalytic cycle, transiently leaves the Q(o) site to communicate with the outermost cofactor, cytochrome c(1). This increases the distance between the FeS cluster and the remaining portion of the Q(o) site, reducing the likelihood that the FeS cluster participates in an immediate removal of SQ(o). In other states, the presence of both the FeS cluster and heme b(L) in the Q(o) site increases the probability of completion of short-circuit reactions which retain single electrons within the enzyme instead of releasing them on oxygen. We propose that in this way, cytochrome bc(1) under conditions of impeded electron flow employs the leak-proof short-circuits to minimize the unwanted single-electron reduction of oxygen.     

CELL PROLIFERATION DURING the COURSE of IMMUNOLOGICAL REJECTION of EHRLICH ASCITES TUMOUR CELLS

Ehrlich ascites tumours were transplanted from their normal hosts (mice) into rats, and studies made of the timing of cell cycle 120-170 hr after transplantation, when tumour regression was under way. There was no significant change in the duration of the cell cycle. Some increase was found in the average and spread of G₂ durations, largely compensated by a decrease in S duration. When taken together with previously published work the results suggest that the immunological pressure of transplantation into a heterologous host prolongs the G₂ period.     

The effect of hypermethylation on the functional properties of transfer ribonucleic acid. Ribosome-binding and polypeptide synthesis

1. Phenylalanyl-tRNA formed after chemical hypermethylation of Escherichia coli B tRNA was able to bind to ribosomes with the same efficiency as normal phenylalanyl-tRNA. 2. Under incubation conditions used in the ribosome-binding assay, hypermethylation of tRNA did not measurably decrease the stability of either inter-nucleotide phosphodiester bonds or the covalent bond between amino acid and tRNA in phenylalanyl-tRNA. 3. The ability of hypermethylated tRNA to take part in polyphenylalanine synthesis was inhibited progressively as the degree of hypermethylation increased. 4. Hypermethylation of tRNA affected polyphenylalanine synthesis at the stage of amino acid recognition and at a further point in the synthesis but not at the level of codon-anticodon recognition. 5. The formation of polylysine was more seriously affected by hypermethylation of tRNA than would be accounted for by inhibition of amino acid acceptance alone. 6. Polyproline formation was completely inhibited by the presence of 7mol% excess of methyl groups in tRNA. 7. The possibility of a link between amino acid acceptance and ribosome-binding was suggested for phenylalanyl-tRNA, but not for lysyl- or prolyl-tRNA.     

Photosynthetic activity of variegated leaves of Coleus × hybridus hort. cultivars characterised by chlorophyll fluorescence techniques

Different pigments often occur together and affect photosynthetic characteristics of the respective leaf portions. In this study, photosynthetic activity in variegated leaves of five cultivars of the ornamental and medicinal plant, Coleus × hybridus hort., was estimated by image analysis and point data measurements of major chlorophyll (Chl) fluorescence parameters and related to the amount of photosynthetic pigments measured with a Chl meter or spectrophotometrically in leaf extracts. Significant differences in Chl and carotenoid (Car) contents were noticed among differentially pigmented sectors of a leaf and among the cultivars. Although the higher Chl concentration was noticed in purple parts compared to green parts of the leaves, the values of minimal and maximal fluorescence yield at the dark- and light-adapted state (F₀, F_m, F₀', F_m', respectively) were a little lower than those in the green sectors, indicating photoprotective effects provided by anthocyanins and Car, more abundant in the red parts. The lowest Chl and Car content was detected in creamy-yellow and pink sectors and this contributed to low F₀, F_m, and F_m', maximal quantum yield of PSII photochemistry, and nonphotochemical and photochemical quenching but high PSII maximum efficiency and effective quantum yield of PSII photochemistry. Both methods of Chl fluorescence analysis revealed heterogeneity in capture, transfer, and dissipation of excitation energy but Chl fluorescence imaging was more suitable in examining very narrow pigmented leaf areas.