Ultrastructure,polypeptide composition and photochemical activity of chloroplasts during foliar senescence of a non-yellowing mutant genotype of Festuca pratensis Huds.

A study was made of the structure and function of senescent chloroplasts from a non-yellowing (NY) mutant of Festuca pratensis. Electron microscopy suggested that the stroma matrix was destroyed but that thylakoid membranes persisted in a loose, unstacked condition. By contrast, chloroplasts from the normal (Y) genotype lost both stroma and recognizable thylakoid systems. Fraction 1, the major protein of the stroma, disappeared from Y and NY at similar rates during senescence. The activities of photosystems I and II from NY also declined at a similar rate to Y photosystems. Polypeptides of chloroplast membranes were separated by SDS gel electrophoresis into at least 30 components. There was considerable heterogeneity in rates of breakdown of the different protein species of the membranes. Of the five major polypeptide components, two had kinetics of breakdown similar to those of stroma proteins and were lost from NY and Y at about the same rate, whereas the remaining three (one of which was tentatively identified as the apoprotein of the light-harvesting chlorophyll-protein complex) were more stable in NY than in Y. These results are discussed in relation to the mechanism and function of chloroplast disintegration during leaf senescence.Abbreviations RuDPC ribulose diphosphate carboxylase - NY and Y non-yellowing and normal genotypes of Festuca, respectively - PSI and PSII photosystems I and II, respectively - SDS sodium dodecyl sulphate - MW molecular weight - CF coupling factor     

The uptake of choline by Streptococcus pneumoniae.

Uptake of choline, a structural component of pneumococcal C- and F-teichoic acids, into bacteria growing in a defined medium was very efficient with an uptake constant ([S]10 5) of 3.2 microns. It was inhibited by iodoacetate, dinitrophenol and oligomycin but not by structural analogues of choline. Ethanolamine, however, was transported in the absence of choline but with a reduced affinity ([S]0.5 71.4 microns). The same constitutive system was probably used by both ethanolamine and choline. It is suggested that this system required ATP and probably involved choline kinase.     

BIOCHEMICAL EFFECTS IN MAN and RAT OF THREE DRUGS WHICH CAN INCREASE BRAIN GABA CONTENT

Abstract— Brain amino acids were measured in rats given aminooxyacetic acid (AOAA) by mouth, and in rats given sodium dipropylacetate (DPA) both orally and by intraperitoneal injection. Brain GABA content was significantly elevated by AOAA doses of 10mg/kg/day, but not by 5mg/kg/day. Approximately 4 times as much AOAA is required by mouth as by parenteral injection to raise brain GABA content in the rat. DPA (400mg/kg) increased brain GABA and lowered brain aspartate content significantly 1 h after a single injection. However, DPA given orally (350 mg/kg/day) produced no alterations of any amino acids in rat brain.
Amino acids were measured in plasma and urine from patients treated orally with isonicotinic acid hydrazide (INH) or DPA, and from a volunteer who took AOAA. INH (10–21 mg/kg/day) increased concentrations of β -alanine and ornithine in plasma, as well as urinary excretion of β -alanine. DPA had no such effect. AOAA in oral doses ranging from 1.25 to 5.0 mg/kg/day increased plasma concentrations of β -alanine, ornithine, β -aminoisobutyric acid, proline and hydroxyproline, and produced massive urinary excretion of β -alanine, β -aminoisobutyric acid, and taurine.
Both INH and AOAA, given in doses practical for human use, inhibit the transamination of β -alanine and ornithine in liver, and may also inhibit the transamination of GABA in brain. In addition, AOAA interferes with the catabolism of β -aminoisobutyric acid, proline, and hydroxyproline. AOAA, in the lowest dose employed, appeared more effective than INH as an inhibitor of GABA aminotransferase in man, and might therefore be useful in the treatment of neurological diseases in which brain GABA is deficient.     

Com Yield Increases Relative to Nonfumigant Chemical Control of Nematodes

Corn yields were measured after application of nematicides in 16 experiments, mostly in medium-to-heavily textured soil, at 12 locations in Iowa during 1973-1976. The average maximum yield increase in plots treated with nematicides was 21% over yields in untreated plots. Yields were correlated negatively with nematode numbers or nematode biomass in nearly all comparisons. Correlations of nematode numbers in the soil with yield averaged -0.56 for Helicotylenchus pseudorobustus, -0.45 for Hoplolaimus galeatus, -0.51 for Pratylenchus spp., and -0.64 for Xiphinema americanum. Correlation coefficients for numbers of nematodes in the roots and yield averaged -0.63 for Pratylenchus spp. and -0.56 H. galeatus. Correlation coefficients for yield and total number of nematodes averaged -0.65 in roots and -0.55 in soils. Negative correlations also were greater for comparisons of yield with total parasitic-nematode biomass than with numbers of individual nematodes of a species or total numbers of parasitic nematodes.     

HE TURNOVER RATE OF TUBULIN IN RAT BRAIN

The turnover rate of tubulin in rat brain was determined from the decay in specific radioactivity of the protein after pulse-labeling. When precursors were administered by a parenteral route, the shortest half-life, 9.8 days, was obtained with [¹⁴C]NaHCO₃; the longer half-lives obtained with [U-¹⁴C]glucose or [4,5-³H]leucine suggest significant reutilization of label. Furthermore, with leucine as precursor maximal specific radioactivity of tubulin was not obtained until eight days after administration of label. Labeling and decay kinetics obtained with [4,5-³H]leucine were markedly different when the isotope was administered directly into the lateral ventricle. The difference between the turnover rates of the -α and β subunits of tubulin purified by means of high resolution polyacrylamide gel electrophoresis was not statistically significant. A half-life for tubulin of 6.2 days was measured by continuous intravenous infusion of [U-¹⁴C]tyrosine.     

MEASUREMENTS OF PHYTOPLANKTON-PROTEIN CONTENT WITH THE HEATED BIURET-FOL1N ASSAY1,2

The heated biuret-Folin method for determining protein consistently measures 90% of the total nitrogen of filtered algae samples as protein-N without the need of mechanical disruption as long as the heating period in biuret is 100 min at 100 C. Data indicate this protein assay measures total protein on all species tried and for naturally occurring mixtures of species plus detritus. Dilute algal suspensions with as little as 0.05 μg-atom particulate protein N.liter ^-1 can he concentrated by fltration on glass fiber filters to 1.0 μg-atom particulate protein-N per filter, the optimal amount of sample for a 5 ml volume of biuret. The filtered algae samples can be stored for several weeks frozen before assaying, if necessary.     

A model for sucrose transport in the maize scutellum

A model originally developed for transport of neutral substrates in bacterial systems was tested for its suitability for depicting sucrose transport across the plasmalemma of the maize scutellum cell. The model contains a sucrose—proton symporter, a negatively-charged free carrier and a neutral sucrose—proton—carrier complex. Sucrose transport is driven by the sucrose gradient and by a proton electrochemical gradient set up by a proton-translocating ATPase. The results of experiments on sucrose uptake in scutellum slices are in accord with predictions based on the model. Evidence was obtained for an electrogenic proton pump in the plasmalemma, for sucrose—proton symport and for a sucrose transport mechanism driven by both electrical potential and pH gradients. It was found that treatments (dinitrophenol, N-ethylmaleimide or HCl) causing a net proton influx into the slices also caused an efflux of sucrose. Interpretations of these results compatible with the model are given.     

Initial organic products of assimilation of [N]ammonium and [N]nitrate by tobacco cells cultured on different sources of nitrogen

Glutamine is the first major organic product of assimilation of ¹³NH₄⁺ by tobacco (Nicotiana tabacum L. cv. Xanthi) cells cultured on nitrate, urea, or ammonium succinate as the sole source of nitrogen, and of ¹³NO₃⁻ by tobacco cells cultured on nitrate. The percentage of organic ¹³N in glutamate, and subsequently, alanine, increases with increasing periods of assimilation. ¹³NO₃⁻, used for the first time in a study of assimilation of nitrogen, was purified by new preparative techniques. During pulse-chase experiments, there is a decrease in the percentage of ¹³N in glutamine, and a concomitant increase in the percentage of ¹³N in glutamate and alanine. Methionine sulfoximine inhibits the incorporation of ¹³N from ¹³NH₄⁺ into glutamine more extensively than it inhibits the incorporation of ¹³N into glutamate, with cells grown on any of the three sources of nitrogen. Azaserine inhibits glutamate synthesis extensively when ¹³NH₄⁺ is fed to cells cultured on nitrate. These results indicate that the major route for assimilation of ¹³NH₄⁺ is the glutamine synthetase-glutamate synthase pathway, and that glutamate dehydrogenase also plays a role, but a minor one. Methionine sulfoximine inhibits the incorporation of ¹³N from ¹³NO₃⁻ into glutamate more strongly than it inhibits the incorporation of ¹³N into glutamine, suggesting that the assimilation of ¹³NH₄⁺ derived from ¹³NO₃⁻ may be mediated solely by the glutamine synthetase-glutamate synthase pathway.     

Cytokinins in tRNA Obtained from Spinacia oleracea L. Leaves and Isolated Chloroplasts

Cytokinin-active ribonucleosides have been isolated from tRNA of whole spinach (Spinacia oleracea L.) leaves and isolated spinach chloroplasts. The tRNA from spinach leaf blades contained: 6-(4-hydroxy-3-methyl-2-butenylamino)-9-β-d-ribofuranosylpurine (cis and trans isomers), 6-(3-methyl-2-butenylamino)-9-β-d-ribofuranosylpurine, and 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-β-d -ribofuranosylpurine (cis and trans isomers). A method for isolation of large amounts of intact chloroplasts was developed and subsequently used for the isolation of chloroplast tRNA. The chloroplast tRNA contained 6-(3-methyl-2-butenylamino)-9-β-d-ribofuranosylpurine and 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-β-d -ribofuranosylpurine (the cis isomer only). The structures of these compounds were assigned on the basis of their chromatographic properties and mass spectra of trimethylsilyl derivatives which were identical with those of the corresponding synthetic compounds. The results of this study indicate that ribosylzeatin was present in spinach leaf tRNA, but absent from the purified chloroplast tRNA preparation.