A simple model relating photoinhibitory fluorescence quenching in chloroplasts to a population of altered Photosystem II reaction centers

A model is presented describing the relationship between chlorophyll fluorescence quenching and photoinhibition of Photosystem (PS) II-dependent electron transport in chloroplasts. The model is based on the hypothesis that excess light creates a population of inhibited PS II units in the thylakoids. Those units are supposed to posses photochemically inactive reaction centers which convert excitation energy to heat and thereby quench variable fluorescence. If predominant photoinhibition of PS II and cooperativity in energy transfer between inhibited and active units are presumed, a quasi-linear correlation between PS II activity and the ratio of variable to maximum fluorescence, F_VF_M, is obtained. However, the simulation does not result in an inherent linearity of the relationship between quantum yield of PS II and F_VF_M ratio. The model is used to fit experimental data on photoinhibited isolated chloroplasts. Results are discussed in view of current hypotheses of photoinhibition.Abbreviations F_M maximum total fluorescence - F₀ initial fluorescence - F_V maximum variable fluorescence - PS Photosystem - Q_A, Q_B primary and secondary electron acceptors of Photosystem II     

Organization of the biosynthesis genes for the peptide antibiotic gramicidin S.

A recombinant bacteriophage containing the intact Bacillus brevis gene for gramicidin S synthetase 1, grsA, and the 5' end of the gramicidin S synthetase 2 gene, grsB, was identified by screening an EMBL3 library with anti-GrsA antibodies. This clone, EMBL315, has a 14-kilobase (kb) insert that hybridizes to the previously isolated 3.9-kb fragment of the grsB gene, which encodes the 155-kilodalton ornithine-activating domain of gramicidin S synthetase 2. Deletion and subcloning experiments with the 14-kb insert located the grsA structural gene and its putative promoter on a 4.5-kb PvuII fragment which encoded the full-length 120-kilodalton protein in Escherichia coli. In addition, hybridization analysis revealed that the 5' end of the grsB gene is located approximately 3 kb from the grsA structural gene. Furthermore, these studies indicated that grsA and grsB are transcribed in opposite orientations.     

Activation of 2-5A-dependent RNase by analogs of 2-5A (5'-O-triphosphoryladenylyl(2'----5')adenylyl(2'----5')adenosine ) using 2',5'-tetraadenylate (core)-cellulose

A variety of 2-5A (px(A2'p)nA; x = 2 or 3, n greater than or equal to 2) analogs were assayed for their abilities to activate murine 2-5A-dependent RNase (subsequently "the nuclease") using a recently developed method. This technique consists of immobilizing and partially purifying the nuclease using core-cellulose [A2'p)3A-cellulose) and then monitoring the breakdown of poly(U)-3'-[32P]Cp into acid-soluble fragments. Several 5'-adenosinecapped analogs of 2-5A (containing a tetra-, tri-, or diphosphate) were analyzed, and it was found that reducing the number of phosphoryl groups between the 5' to 5'-diadenosine linkages resulted in a progressive loss of activity. Because A5' pppp(A2'p)3A was a potent activator of the nuclease yet stable during the assay these results suggested that a free 5'-phosphoryl group may not be required for the activation of the nuclease. A number of 8-bromoadenosine-substituted analogs of 2-5A were also studied. Curiously, the brominations decreased the activities of the 5'-di- and triphosphorylated molecules while substantially increasing the activities of the 5'-monophosphorylated species. The results indicated that a tri- or diphosphate moiety on the 5'-end of 2-5A or the presence of ATP is not absolutely required for the nuclease to be active. Furthermore, the ATP analog, beta, gamma-methylene ATP, did not inhibit the activity of the nuclease. Finally, a 3',5'-phosphodiester linkage isomer of 2-5A and a 3'-deoxy (cordycepin) analog of 2-5A were tested, and both were found to be completely without activity.     

Translation efficiency of zein mRNA is reduced by hybrid formation between the 5'- and 3'-untranslated region

The secondary structure of zein mRNA affects its translation potential. Here we show that in a cell-free system the translation efficiency of zein mRNA containing inverted repeats in the 5'- and 3'-untranslated regions is reduced. This translational block is released after deletion of the 3'-inverted repeat. We conclude that the translational block is caused by hybrid formation between the two inverted repeats. The translational efficiency of zein mRNAs, is also affected by varying the length or the primary structure of the 5'-untranslated region.     

Modelling individual growth of the Antarctic krill Euphausia superba Dana

Summary Growth of the Antarctic krill, Euphausia superba, is not easily determined from net catches nor from laboratory experiments. Therefore, in support of these methods, a phenomenological model was constructed which in its present state describes the growth of a single krill specimen under periodically limiting food conditions with summer seasons of variable lengths. Published data of krill body length vs. age and of the annual cycle of primary production of algae in the Drake Passage were used to formulate equations and to calculate growth curves. At 1,000 days after hatching, the model predicts a body length of 63 mm, growth being delayed by 380 days compared with constant, optimal feeding conditions. Final length, weight and time delay are related to the amount of food supplied and compared with published population growth curves.     

Characterization of chlorophyll fluorescence quenching in chloroplasts by fluorescence spectroscopy at 77 K II. ATP-dependent quenching

In intact, uncoupled type B chloroplasts from spinach, added ATP causes a slow light-induced decline ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≈ 3}\text{min}$) of chlorophyll a fluorescence at room temperature. Fluorescence spectra were recorded after fast cooling to 77 K and normalized with fluorescein as an internal standard. Related to the fluorescence quenching at room temperature, an increase in Photosystem (PS) I fluorescence (F₇₃₅) and a decrease in PS II fluorescence (F₆₉₅) were observed in the low-temperature spectra. The change in the $\text{F}{}_{735}\text{F}{}_{695}$ ratio was abolished by the presence of methyl viologen. Fluorescence induction at 77 K of chloroplasts frozen in the quenched state showed lowered variable (F_v) and initial (F₀) fluorescence at 690 nm and an increase in F₀ at 735 nm. The results are interpreted as indicating an ATP-dependent change of the initial distribution of excitation energy in favor of PS I, which is controlled by the redox state of the electron-transport chain and, according to current theories, is caused by phosphorylation of the light-harvesting complex.     

Volatile components of developing tomato fruit grown under field and greenhouse conditions

Volatile components of field- and glass greenhouse-grown tomatoes(Lycopersicon esculentum MILL., variety, V. R. Moscow) of differentmaturities were studied by gas-liquid and thin-layer chromatography.The following components were separated and identified: isobutylalcohol, isopentyl alcohol, hexyl alcohol, 2-methyl-3-hexanol,isovaleraldehyde, caproaldehyde, benzaldehyde, furfural, isopentylacetate, isopentyl butyrate, isopentyl isovalerate, butyl hexanoate,hexyl hexanoate, methyl salicylate and -pinene. Chromatogramswere consistent for both field- and greenhouse-grown tomatoesat all stages of maturity. Except for isovaleraldehyde and hexylalcohol, the biosynthesis of volatile components increased alongwith the growth of fruit. Isovaleraldehyde and hexyl alcohol,presumed to give the "green leafy" aroma of tomatoes, were foundto be in their highest concentrations at the breaker and thelarge-green stages, respectively. ¹This research was supported by a research grant—UI 00449—fromthe National Center for Urban and Industrial Health, U. S. PublicHealth Service.     

Electron microscopic observations on isolated mitochondrial membranes,prepared by various histological methods

Summary The pictures of isolated mitochondrial membranes, as seen on the electron-microscope, depend very much on the method of specimen preparation. Subunits of linear dimensions of about 25 m, (electron transport particles) are observed in carbon-replicas of the membranes and in specimens treated with trypsin or pepsin (0.02% for 30 mins) and shadowed with platinum. A three-layered structure of the unit membrane is seen in sections of specimens fixed with osmium tetroxide or formalin followed by post-fixation with osmium tetroxide. But fixation with potassium permanganate or with formalin, followed by post-fixation with potassium permanganate reveals an electron-dense globular structural element in the unit membrane. An electron-transparent ultrastructural element of the unit membrane is observed after treatment with trypsin (0.2% for 5 mins) and fixation with osmium tetroxide. Unsectioned specimens treated with 0.02% trypsin for 30 mins show a honeycomb-like structure of the membrane. Thus, part of the results appear to support the concept of a mosaic-like structure of the unit membrane, whereas other results are in agreement with the classical concept of a three-layered structure.The authors wish to express their gratitude to Dr. Sina Rosenthal, Department of Physiological Chemistry, Humboldt University, Berlin, who prepared the isolated membranes, to Mr. E. Fischer, Head Technician of the Department of Electron Microscopy, Greifswald University, who took most of the electron micrographs, to Mr. G. Bartsch, Department of Electron Microscopy, Greifswald University, and especially to Prof. W. Bargmann and to Doz. E. Lindner, Department of Anatomy, Kiel University, for many valuable suggestions.