Intramembranous particles and chlorophyll complexes in chloroplasts

The size and population density of large and small particles from freeze-fractured chloroplasts of three wild-type algae and of normal spinach were determined.Computer analyses of low-temperature absorption spectra of chloroplast preparations from these species were performed, and a possible correlation between the occurrence of seven chlorophyll complexes and the aforementioned properties of the intramembranous particles was studied.It was found that only single-sized particles occur in a species containing neither chlorophyll b nor chlorophyll a-685 complexes. The three remaining species carry particles of two sizes, termed large and small particles. However, from quantitative considerations it is concluded that the chlorophyll content of none of the various pigment complexes is related to the size and the population density of the studied particles. If such a relationship exists, it seems likely to be due to the carrier moiety of the chlorophyll b · chlorophyll a-685 complex.     

Fluorescence emission spectra of chloroplasts and subchloroplast preparations at low temperature.

A study was made of the chlorophyll fluorescence spectra between 100 and 4.2 K of chloroplasts of various species of higher plants (wild strains and chlorophyll b mutants) and of subchloroplast particles enriched in Photosystem I or II. The chloroplast spectra showed the well known emission bands at about 685, 695 and 715--740 nm; the System I and II particles showed bands at about 675, 695 and 720 nm and near 685 nm, respectively. The effect of temperature lowering was similar for chloroplasts and subchloroplast particles; for the long wave bands an increase in intensity occurred mainly between 100 and 50 K, whereas the bands near 685 nm showed a considerable increase in the region of 50--4.2 K. In addition to this we observed an emission band near 680 nm in chloroplasts, the amplitude of which was less dependent on temperature. The band was missing in barley mutant no. 2, which lacks the light-harvesting chlorophyll a/b-protein complex. At 4.7 K the spectra of the variable fluorescence (Fv) consisted mainly of the emission bands near 685 and 695 nm, and showed only little far-red emission and no contribution of the band at 680 nm. From these and other data it is concluded that the emission at 680 nm is due to the light-harvesting complex, and that the bands at 685 and 695 nm are emitted by the System II pigment-protein complex. At 4.2 K, energy transfer from System II to the light-harvesting complex is blocked, but not from the light-harvesting to the System I and System II complexes. The fluorescence yield of the chlorophyll species emitting at 685 nm appears to be directly modulated by the trapping state of the reaction center.     

Fluorescence emission spectra of chloroplasts and subchloroplast preparations at low temperature

A study was made of the chlorophyll fluorescence spectra between 100 and 4.2 K of chloroplasts of various species of higher plants (wild strains and chlorophyll b mutants) and of subchloroplast particles enriched in Photosystem I or II. The chloroplast spectra showed the well known emission bands at about 685, 695 and 715–740 nm; the System I and II particles showed bands at about 675, 695 and 720 nm and near 685 nm, respectively. The effect of temperature lowering was similar for chloroplasts and subchloroplast particles; for the long wave bands an increase in intensity occurred mainly between 100 and 50 K, whereas the bands near 685 nm showed a considerable increase in the region of 50-4.2 K. In addition to this we observed an emission band near 680 nm in chloroplasts, the amplitude of which was less dependent on temperature. The band was missing in barley mutant no. 2, which lacks the lightharvesting chlorophyll a/b-protein complex. At 4.7 K the spectra of the variable fluorescence (F_v) consisted mainly of the emission bands near 685 and 695 nm, and showed only little far-red emission and no contribution of the band at 680 nm.From these and other data it is concluded that the emission at 680 nm is due to the light-harvesting complex, and that the bands at 685 and 695 nm are emitted by the System II pigment-protein complex. At 4.2 K, energy transfer from System II to the light-harvesting complex is blocked, but not from the light-harvesting to the System I and System II complexes. The fluorescence yield of the chlorophyll species emittting at 685 nm appears to be directly modulated by the trapping state of the reaction center.     

Fluorescence and energy transfer in phycobiliprotein-containing algae at low temperature

Fluorescence emission spectra of Anacystis nidulans, Porphyridium cruentum and Cyanidium caldarium, three phycobiliprotein-containing algae, were measured at temperatures between 4 and 120 K in the absence and in the presence of quinones as quenchers of chlorophyll fluorescence. In all species three major emission bands were observed in the chlorophyll a region, near 685 nm (F-685), 695 nm (F-695) and between 710 and 730 nm. Additional bands were observed at shorter wavelengths; these were preferentially excited by light absorbed by the phycobiliproteins and are presumably due to phycocyanins and allophycocyanins.

The amplitudes of F-685, F-695 and the long-wave emission showed a distinct increase upon cooling. For F-685 and F-695 the temperature dependence was similar to that earlier observed with spinach chloroplasts, for the long-wave emission it appeared to depend on the location of the emission bands, which was different for different species. All three bands were strongly quenched by quinones. These and other data suggest that the origin of these bands is the same as in higher plants, and that the fluorescence increase upon cooling can be explained by a lowering of the efficiency of energy transfer between chlorophyll molecules. It is concluded that at most a small percentage of the emission at 685 nm can be ascribed to allophycocyanin B, and that the efficiency of energy transfer between allophycocyanin B and chlorophyll a probably exceeds 99% both at 77 and 4 K. Experiments with isolated phycobilisomes suggest that energy transfer from allophycocyanin to allophycocyanin B occurs with an efficiency of about 90% at low temperature.

The effect of quenchers can be understood by the assumption that the quenching is caused by the formation of non-fluorescent traps in the bulk chlorophyll. Of three quinones tested, the strongest quenching was observed with dibromothymoquinone, which quenched F-685, F-695 and the long-wave emission approximately equally. Menadione and 1,4-naphthoquinone, however, preferentially quenched the long-wave bands, indicating a stronger interaction with Photosystem I than with Photosystem II chlorophylls.     

Model for fluorescence quenching in light harvesting complex II in different aggregation states

Low-temperature (77 K) steady-state fluorescence emission spectroscopy and dynamic light scattering were applied to the main chlorophyll a/b protein light harvesting complex of photosystem II (LHC II) in different aggregation states to elucidate the mechanism of fluorescence quenching within LHC II oligomers. Evidences presented that LHC II oligomers are heterogeneous and consist of large and small particles with different fluorescence yield. At intermediate detergent concentrations the mean size of the small particles is similar to that of trimers, while the size of large particles is comparable to that of aggregated trimers without added detergent. It is suggested that in small particles and trimers the emitter is monomeric chlorophyll, whereas in large aggregates there is also another emitter, which is a poorly fluorescing chlorophyll associate. A model, describing populations of antenna chlorophyll molecules in small and large aggregates in their ground and first singlet excited states, is considered. The model enables us to obtain the ratio of the singlet excited-state lifetimes in small and large particles, the relative amount of chlorophyll molecules in large particles, and the amount of quenchers as a function of the degree of aggregation. These dependencies reveal that the quenching of the chl a fluorescence upon aggregation is due to the formation of large aggregates and the increasing of the amount of chlorophyll molecules forming these aggregates. As a consequence, the amount of quenchers, located in large aggregates, is increased, and their singlet excited-state lifetimes steeply decrease.     

Subnuclear particles containing a small nuclear RNA and heterogeneous nuclear RNA

Five of the stable low molecular weight RNA species in the HeLa cell nucleus have been localized in RNP complexes in the cell nucleus. The two abundant species C and D and the three minor species F, G′ and H are found in RNP particles following two different methods of preparation. Sonication of nuclei releases the five small RNAs and also the hnRNA in RNPs that sediment in a range from 10 to 150 S. Alternatively, incubation of intact nuclei at elevated temperature and pH releases four of the small RNAs and degraded hnRNA in more slowly sedimenting structures.When nuclear RNPs obtained by sonication are digested with RNAase in the presence of EDTA, the hnRNA is degraded and the hnRNPs sediment at 30 S. The structures containing the small RNA species D are similarly shifted to 30 S particles by RNAase and EDTA but not by either agent alone. In contrast, the sedimentation of complexes containing species G′ and H are not altered by exposure to RNAase/EDTA and small RNA species C and F are unstable under these conditions.In isopycnic metrizamide/²H₂O gradients species D and hnRNA accumulate at a density characteristic of RNP particles. They have a similar but not identical distribution.Species D is released from large RNPs by salt concentrations of 0.1 m-NaCl or greater, while the hnRNA remains in large RNP particles. In contrast, the structures containing species G′ and H are stable in 0.3 m-NaCl. All five of the small nuclear RNA species and the hnRNAs are released from rapidly sedimenting complexes by the ionic detergent sodium deoxycholate.It is suggested that the low molecular weight RNA species play a structural role in RNP particles in the cell nucleus and that a subpopulation of species D may be associated with the particles that package the hnRNA.     

Composition of the photosystems and chloroplast structure in extreme shade plants

Chloroplasts were isolated from leaves of three species of tropical rainforest plants, Alocasia macrorrhiza, Cordyline rubra and Lomandra longifolia; these species are representative of extreme “shade” plants. It was found that shade plant chloroplasts contained 4–5 times more chlorophyll than spinach chloroplasts. Their chlorophyll a/chlorophyll b ratio was 2.3 compared with 2.8 for spinach. Electron micrographs of leaf sections showed that the shade plant chloroplasts contained very large grana stacks. The total length of partitions relative to the total length of stroma lamellae was much higher in Alocasia than in spinach chloroplasts. Freeze-etching of isolated chloroplasts revealed both the small and large particles found in spinach chloroplasts.

Despite their increased chlorophyll content, low chlorophyll a/chlorophyll b ratio, and large grana, the shade plant chloroplasts were fragmented with digitonin to yield small fragments (D-144) highly enriched in Photosystem I, and large fragments (D-10) enriched in Photosystem II. The degree of fragmentation of the shade plant chloroplasts was remarkably similar to that of spinach chloroplasts, except that the subchloroplast fragments from the shade plants had lower chlorophyll a/chlorophyll b ratios than the corresponding fragments from spinach. The D-10 fragments from the shade plants had chlorophyll a/chlorophyll b ratios of 1.78-2.00 and the D-144 fragments ratios of 3.54–4.07. We conclude that Photosystems I and II of the shade plants have lower proportions of chlorophyll a to chlorophyll b than the corresponding photosystems of spinach. The lower chlorophyll a/chlorophyll b ratio of shade plant chloroplasts is not due to a significant increase in the ratio of Photosystem II to Photosystem I in these chloroplasts.

The extent of grana formation in higher plant chloroplasts appears to be related to the total chlorophyll content of the chloroplast. Grana formation may simply be an means of achieving a higher density of light-harvesting assemblies and hence a more efficient collection of light quanta.     

Feeding Habits of Diaptomus ashlandi and Diaptomus sicilis in Lake Michigan

The herbivorous habits of Diaptomus ashlandi and Diaptomus sicilis were studied at a nearshore station in Lake Michigan. Filtering and feeding rates were measured from December 1975 to October 1976. Feeding was measured from the change in concentration in three size fractions of chlorophyll a. D. ashlandi fed only on particles in the smallest size class, while the larger D. sicilis consumed particles in all three size fractions. During the isothermal period (winter and spring), the feeding rates of both species were proportional to temperature or chlorophyll concentration. D. sicilis preferentially ingested particles in the largest size class, when this size class increased significantly during the spring bloom. During the summer the highest feeding rates of D. ashlandi occurred in the epilimnion. The highest feeding rates of D. sicilis were in the metalimnion, where large particles in a subsurface chlorophyll maximum were available for consumption. These results indicated the importance of the depth distributions of herbivores and phytoplankton for feeding.     

Isolation and characterization of photosystem I and II membrane particles from the blue-green alga, Synechococcus cedrorum.

Fractions enriched in either Photosystem I or Photosystem II activity have been isolated from the blue-green alga, Synechococcus cedrorum after digitonin treatment. Sedimentation of this homogenate on a 10--30% sucrose gradient yielded three green bands: the upper band was enriched in Photosystem II, the lowest band was enriched in Photosystem I, while the middle band contained both activities. Large quantities of both particles were isolated by zonal centrifugation, and the material was then further purified by chromatography on DEAE-cellulose. The resulting Photosystem II particles carried out light-induced electron transport from semicarbizide to ferricyanide of over 2000 mumol/mg Chlorophyll per h (which was sensitive to 3-(3,4-dichlorophenyl)-1, 1-dimethylurea), and was nearly devoid of Photosystem I activity. This particle contains beta-carotene, very little phycocyanin, has a chlorophyll absorption maximum at 675 nm, and a liquid N2 fluorescence maximum at 685 nm. The purest Photosystem II particles have a chlorophyll to cytochrome b-559 ratio of 50 : 1. The Photosystem I particle is highly enriched in P-700, with a chlorophyll to P-700 ratio of 40 : 1. The physical structure of the two Photosystem particles has also been studied by gel electrophoresis and electron microscopy. These results indicate that the size and protein composition of the two particles are distinctly different.     

Effect of Light Quality on the Composition, Function, and Structure of Photosynthetic Thylakoid Membranes of Asplenium australasicum (Sm.) Hook

The effect of light quality on the composition, function and structure of the thylakoid membranes, as well as on the photosynthetic rates of intact fronds from Asplenium australasicum, a shade plant, grown in blue, white, or red light of equal intensity (50 microeinsteins per square meter per second) was investigated. When compared with those isolated from plants grown in white and blue light, thylakoids from plants grown in red light have higher chlorophyll a/chlorophyll b ratios and lower amounts of light-harvesting chlorophyll a/b-protein complexes than those grown in blue light. On a chlorophyll basis, there were higher levels of PSII reaction centers, cytochrome f and coupling factor activity in thylakoids from red light-grown ferns, but lower levels of PSI reaction centers and plastoquinone. The red light-grown ferns had a higher PSII/PSI reaction center ratio of 4.1 compared to 2.1 in blue light-grown ferns, and a larger apparent PSI unit size and a lower PSII unit size. The CO₂ assimilation rates in fronds from red light-grown ferns were lower on a unit area or fresh weight basis, but higher on a chlorophyll basis, reflecting the higher levels of electron carriers and electron transport in the thylakoids.

The structure of thylakoids isolated from plants grown under the three light treatments was similar, with no significant differences in the number of thylakoids per granal stack or the ratio of appressed membrane length/nonappressed membrane length. The large freeze-fracture particles had the same size in the red-, blue-, and white-grown ferns, but there were some differences in their density. Light quality is an important factor in the regulation of the composition and function of thylakoid membranes, but the effects depend upon the plant species.

     

The conformation of apolipoprotein A-I in discoidal and spherical recombinant high density lipoprotein particles. 13C NMR studies of lysine ionization behavior.

To elucidate the molecular details of how high density lipoprotein (HDL) microstructure affects the conformation of apolipoprotein (apo) A-I in various classes of HDL particles, apoA-I structure in homogeneous recombinant HDL (rHDL) complexes containing palmitoyl-oleoyl phosphatidylcholine (POPC) and cholesteryl oleate has been investigated by NMR spectroscopy of [13C]lysine-labeled apoA-I. All Lys residues in rHDL apoA-I were labeled with 13C by reductive methylation, and then their ionization behavior was characterized by 13C NMR spectroscopy. Four discoidal particles were prepared to contain from 64 to 256 molecules of POPC and 2 molecules of apoA-I; their major diameters ranged from 9.3 to 12.1 nm. (13CH3)2-Lys resonances from apoA-I in discoidal complexes exhibit six distinct chemical shifts at pH 10. The various Lys have pKa values ranging from 8.3 to 10.5, indicating that they exist in different microenvironments. More than 80% of the Lys residues in small (9.3 nm) discoidal particles titrate at a significantly lower pH than in the large (12.1 nm) discoidal particles. This indicates that apoA-I has a different conformation on the differently size discs. Two spherical particles were prepared with POPC:cholesteryl oleate:apoA-I molar stoichiometries of 56:16:2 and 232:84:4 and diameters of 7.4 and 12.6 nm, respectively. On spherical rHDL, apoA-I (13CH3)2-Lys resonances exhibit five distinct chemical shifts at pH 10. The titration behavior of apoA-I Lys residues is the same in small and large spherical particles, indicating that apoA-I conformation is similar on the two particles. The Lys microenvironments indicate that the conformation of apoA-I in discoidal complexes is dependent on particle size and that these conformations are substantially different from that of apoA-I on spherical complexes. Lys microenvironments in discoidal complexes differ from that of spherical complexes by 4 to 5 ysines which titrate with relatively low pKa values on discs. This reflects apparent differences in conformation in the NH2-terminal one-third of apoA-I on discs and spheres.     

Lateral mobility of the light-harvesting complex in chloroplast membranes controls excitation energy distribution in higher plants

Chloroplast thylakoid protein phosphorylation produces changes in light-harvesting properties and in membrane structure as revealed by freeze-fracture electron microscopy. Protein phosphorylation resulted in an increase in the 77 °K fluorescence signal at 735 nm relative to that at 685 nm. In addition, a decrease in connectivity between Photosystem II centers (PS II) and a dynamic quenching of the room temperature variable fluorescence was observed upon phosphorylation. Accompanying these fluorescence changes was a 23% decrease in the amount of stacked membranes. Microscopic analyses indicated that 8.0-nm particles fracturing on the P-face moved from the stacked into the unstacked regions upon phosphorylation. The movement of the 8.0-nm particles was accompanied by the appearance of chlorophyll b and 25 to 29 kD polypeptides in isolated stroma lamellae fractions. We conclude that phosphorylation of a population of the light-harvesting chlorophyll $\text{a}\text{b}$ protein complexes (LHC) in grana partitions causes the migration of these pigment proteins from the PS II-rich appressed membranes into the Photosystem I (PS I) enriched unstacked regions. This increases the absorptive cross section of PS I. In addition, we suggest that the mobile population of LHC functions to interconnect PS II centers in grana partitions; removal of this population of LHC upon phosphorylation limits PS II → PS II energy transfer and thereby favors spillover of energy from PS II to PS I.     

Soil properties and the distribution of the endangered Juliana's golden mole

The endangered Juliana's golden mole Neamblysomus julianae occurs in three small, geographically isolated populations within South Africa. As a sand-swimmer, it is a habitat specialist and has a highly fragmented distribution within each population. There is a need for a conservation action plan for this species, but this is difficult because of the dearth of knowledge of its biology, including its habitat characteristics. To better understand its patchy distribution, we selected 48 plots that were occupied or unoccupied by golden moles and measured the soil properties in each plot. The size distribution of sand particles influenced the density and compactability of the soil, and both were positively correlated with the presence of golden moles. These soil characteristics are thus vital in understanding and describing the distribution of this cryptic species.     

Isolation and characterization of Photosystem I and II membrane particles from the blue-green alga, Synechococcus cedrorum

Fractions enriched in either Photosystem I or Photosystem II activity have been isolated from the blue-green alga, Synechococcus cedrorum after digitonin treatment. Sedimentation of this homogenate on a 10–30% sucrose gradient yielded three green bands: the upper band was enriched in Photosystem II, the lowest band was enriched in Photosystem I, while the middle band contained both activities. Large quantities of both particles were isolated by zonal centrifugation, and the material was then further purified by chromatography on DEAE-cellulose.The resulting Photosystem II particles carried out light-induced electron transport from semicarbizide to ferricyanide of over 2000 μmol/mg Chlorophyll per h (which was sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea), and was nearly devoid of Photosystem I activity. This particle contains β-carotene, very little phycocyanin, has a chlorophyll absorption maximum at 675 nm, and a liquid N₂ fluorescence maximum at 685 nm. The purest Photosystem II particles have a chlorophyll to cytochrome $\text{b-559}$ ratio of 50 : 1. The Photosystem I particle is highly enriched in $\text{P-700}$, with a chlorophyll to $\text{P-700}$ ratio of 40 : 1. The physical structure of the two Photosystem particles has also been studied by gel electrophoresis and electron microscopy. These results indicate that the size and protein composition of the two particles are distinctly different.     

Regulation of energy balance in photosystems in response to changes in CO2 concentrations and light intensities during growth in extremely-high-CO2-tolerant green microalgae

Regulation of energy balance in photosystems in response to extremely-high-CO2 (40%) and low-CO2 (0.04%) stress was studied in extremely-high-CO2-tolerant green microalgae, Chlorococcum littorale and Chlorella sp. UK001. To investigate the energy input process, we assessed an F714/F685-ratio in a 77K fluorescence emission spectrum induced by 440-nm excitation in intact cells, which represents a ratio of fluorescence intensities derived from light-harvesting chlorophyll complexes in PSI and PSII. The F714/F685-ratio increased in several days after transferring C. littorale cells from air to 40% CO2, from 3% to 40% CO2 and from 3% to air. In all cases, the increase in the F714/F685-ratio was observed in high cell density culture, but no or a little increase was apparent in sparse cell density culture, when these cultures were illuminated at 250 micromol photon m-2 s-1. Even in the sparse culture, however, a similar increase in the F714/F685-ratio was observed when C. littorale cells were transferred from 3% to 40% CO2 at 20 micromol photon m-2 s-1. The cell density did not affect the F714/F685-ratio when CO2 concentration was kept at 3%. The activity of PSI electron (e-) transport was much higher in 40% CO2-grown cells than in 3% CO2-grown cells irrespective of the cell density during the culture, whereas the difference in PSII activity between them was small. The PSI activity at high cell density was higher also in air-grown cells than that in 3% CO2-grown cells. In both dense and sparse culture, 40% CO2-grown cells and air-grown cells showed higher relative quantum yield of PSI in the presence of DCMU than 3% CO2-grown cells, suggesting an increase in cyclic electron flow around PSI. Likewise, the increase in the F714/F685-ratio in response to the transfer to 40% CO2 was observed also in another extremely-high-CO2-tolerant alga, Chlorella sp. UK001. The possible role of the increases in the F714/F685-ratio, PSI/PSII activity ratio and cyclic e- transport activity in extremely-high-CO2 acclimation is discussed in comparison with low-CO2 acclimation.     

Correlation between the "low"-salt-induced increase in the F730/F685 fluorescence emission ratio at 77 K in isolated chloroplasts, and the organization of chlorophyll in photosystem I pigment-protein complexes of thylakoids

Isolated pea or spinach chloroplasts suspended in "high"-salt phosphate buffer exhibit a low F730/F685 fluorescence emission ratio at 77 K; in contrast, removal of cations by incubation in "low"-salt Tricine buffer induces a drastic increase in the F730/F685 ratio. Parallel to the F730/F685 ratio increase, a gradual organization of chlorophyll (Chl) in the pigment-protein complexes of the Photosystem I, chlorophyll-protein complex Ia, and light-harvesting complex I (LHC-I), is observed. The kinetics of the two processes are closely correlated, all changes being completed within 5-10 min from Tricine addition. On the other hand, the inability of low-salt Tricine to induce any changes in the F730/F685 ratio in bean plastids, isolated and suspended in high-salt phosphate buffer, correlates with the lack of extensive changes in the organization of the Photosystem I complexes, and more specifically of LHC-I. The latter is attributed to the higher stability of complexes in bean, arising from stronger association of thylakoids in grana stacks in this species; this is probably due to higher levels of residual divalent cations present in the isolated thylakoids of bean compared to pea (or spinach). The results suggest that the F730/F685 ratio changes, observed in chloroplasts by manipulation of their ionic environment, reflect modulation of Chl organization within the pigment-protein complexes of the photosynthetic units.     

Population density and genetic diversity are positively correlated in wild felids globally

Aim

Insights into the biological and evolutionary traits of species, and their ability to cope with global changes, can be gained by studying genetic diversity within species. A cornerstone hypothesis in evolutionary and conservation biology suggests that genetic diversity decreases with decreasing population size, however, population size is difficult to estimate in threatened species with large distribution ranges, and evidence for this is limited to few species. To address this gap, we tested this hypothesis across multiple closely related species at a global scale using population density which is a more accessible measure.

Location

Global.

Time Period

Contemporary.

Major Taxa Studied

Wild felids in their natural habitats.

Methods

We obtained data from published estimates of population density assessed via camera trap and within-population genetic diversity generated from microsatellite markers on 18 felid species across 41 countries from 354 studies. We propose a novel method to standardize population density estimates and to spatially join data using K-means clustering. Linear mixed-effect modelling was applied to account for confounding factors such as body mass, generation length and sample size used for the genetic estimates.

Results

We found a significant positive correlation between population density and genetic diversity, particularly observed heterozygosity and allelic richness. While the confounding factors did not affect the main results, long generation length and large sample size were significantly associated with high genetic diversity. Body mass had no effect on genetic diversity, likely because large-bodied species were over-represented in our data sets.

Main Conclusions

Our study emphasizes how recent demographic processes shape neutral genetic diversity in threatened and small populations where extinction vortex is a risk. Although caution is needed when interpreting the small population density effect in our findings, our methodological framework shows promising potential to identify which populations require actions to conserve maximal genetic variation.     

Nuclear ribonucleoprotein particles in the cellular slime mold Dictyostelium discoideum

The nuclear ribonucleoprotein (RNP) particles containing rapidly labeled RNA were isolated from interphase cells of the cellular slime mold Dictyostelium discoideum and characterized. The size of the isolated RNP particles was small (10S to 50S) in comparison with that of nuclear RNP particles found in higher eukaryotes. These small RNP particles do not seem to be artifacts due to degradation during the preparation of nuclear extracts. The rapidly labeled RNA of the nuclear RNP particles was heterogeneous in size and a considerable amount contained polyadenylic acid sequences. Synthesis of RNA in the nuclear RNP particles was resistant to a relatively high concentration of actinomycin D. The protein component of the RNP particle consists of at least four proteins with molecular weights of 80,000, 66,000, 60,000, and 42,000. Thus it is suggested that almost all of the nuclear RNP particles containing rapidly labeled RNA in interphase cells are RNP complexes consisting of Heterogeneous nuclear RNA and several protein species.     

QUANTITATIVE VARIATION IN VULPINIC AND PINASTRIC ACIDS PRODUCED BY TUCKERMANNOPSIS PINASTRI (LICHEN-FORMING ASCOMYCOTINA,PARMELIACEAE)

Tuckermannopsis pinastri is a lichen species found commonly on rocks and tree branches in boreal and alpine habitats in the northern United States. Members of this species produce three yellow-pigmented phenolic compounds: usnic, pinastric, and vulpinic acids. The objective of our study was to quantify the variation in concentration of the latter two of these compounds in relation to substrate factors, chlorophyll content, and thallus size. Using high-performance liquid chromatography, we analyzed 120 thalli of T. pinastri collected randomly from a single large population located at Spruce Knob, West Virginia. Although individuals were sampled from both tree and rock substrates that differed markedly in light intensity, these environmental factors were not correlated with observed variations in vulpinic or pinastric acid concentrations. Instead, compound concentrations were correlated most closely with thallus size, with small rather than large thalli having the highest concentrations of the two compounds. Small thalli did not have higher concentrations of chlorophylls than large thalli, however, which suggests that the rate of production of secondary compounds by the fungus in T. pinastri is independent of algal biomass. Inasmuch as lichen secondary compounds serve a defensive role against microorganisms and herbivores, our results suggest that small, juvenile thalli are better defended than more mature thalli.