Nonterminal incorporation of guanosine monophosphate from guanosine triphosphate by an enzyme system from spinach chloroplasts

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Protein synthesis by poly somes isolated from wheat leaves

When polysomes isolated from wheat (Triticum vulgare L., var. W2691) leaves are incubated with the soluble components of wheat germ protein synthesizing system (SI76 fraction), the in vivo initiated polypeptide chains are elongated and various size classes of polypeptides are radiolabelled. Under these conditions, there is little or no reinitiation of polypeptides by ribosomes that have completed the elongation of in vivo initiated chains. The time course of labelling and the large size of the polypeptides synthesized suggest that most of the polypeptides are elongated to completion in the cell-free system. The size classes of newly synthesized polypeptides thus reflect the size classes of wheat leaf polysomal mRNA populations.In the protein synthesizing system reconstituted with wheat leaf polysomes and S176 fraction from wheat germ, cydoheximide inhibits the elongation of certain size classes of polypeptides. At high concentrations (5 × 10 M and greater), it completely abolishes the translation of all size classes of polysomal mRNA. Chloramphenicol, on the other hand, preferentially inhibits the synthesis of certain classes of polypeptides including those that correspond in size to polypeptides known to be synthesized by isolated chloroplasts.These characteristics of cell-free translation suggest that analytical gel electrophoresis of the products of polysomal mRNA translation represents a potentially powerful biochemical tool for monitoring mRNA populations in plant tissues

Transcriptional changes in wheat leaf nuclei during the early and intermediate stages of rust infection

Nuclei isolated from wheat (Triticum aestivum L., var. Zenith) susceptible to race 126-ANZ-5,6,7,11 of the rust fungus (Puccinia graminis f.sp. tritici) are transcriptionally active in vitro. A comparison of RNA synthesis in nuclei isolated from uninfected and rust infected leaves has revealed that there is a significant increase in the synthesis of some high molecular weight species of RNA at 3 and 5 days after inoculation. On the basis of the effect of α-amanitin on nuclear transcription at 20 mM and 240 mM (NH)SO and hybridization of nuclear transcripts to cloned wheat 28S, 18S and 5S rRNA genes, we conclude that this increase in RNA synthesis is predominantly due to the activity of RNA polymerase II, the enzyme responsible for the synthesis of mRNA precursors. The possibility that the observed changes in transcription are due to differential degradation of newly synthesized RNA is unlikely in view of the finding that RNase inhibitor has no detectable effect on the size of RNA synthesized in the Percoll gradient-purified nuclei. These results suggest that alterations in host nuclear transcription due to changes in RNA polymerase II activity occur in wheat leaves during the early stages of rust infection

Messenger and ribosomal RNA hydrolysis by ribonucleases II. Changes in ribonuclease activities and ribosomes of barley leaves during the early stages of powdery mildew infection

We have monitored changes in the properties of two barley (Hordeum vulgare L.) leaf RNases with respect to their action on polysomal messenger RNA (mRNA) and the RNA of isolated ribosomes during the early stages of infection by the powdery mildew fungus (Erysiphe graminis f. sp. hordei). The results presented support the following conclusions. (i) At 48 hr after inoculation, the pH 5 insoluble RNase undergoes significant changes in its catalytic properties. This is evident from the finding that under limit digestion conditions, the enzyme from inoculated leaves hydrolyzes chloroplast polysomal mRNA and produces far greater quantities of chloroplast monosomes than does the corresponding enzyme from healthy leaves. (ii) The acid soluble oligonucleotide fragments produced by the soluble RNase from healthy and inoculated leaves (at 48 hr after inoculation) in the RNA of isolated ribosomes are quantitatively significantly different. This suggests a change in the properties of the soluble RNase during the initial stages of host-parasite interactions. (iii) As early as 24 hr after inoculation, there is a dramatic change in the distribution of the pH 5 insoluble and soluble RNase cleavage sites in the RNA of ribosomes indicating a readily detectable conformational change in the ribonucleoprotein particles. (iv) These changes in the RNases and ribosomes are only detectable in the susceptible cultivars of barley and not in a cultivar which is genetically resistant to race 3 of the powdery mildew fungus

A systematic approach to understand hydrogeochemical dynamics in large river systems: development and application to the River Ganges (Ganga) in India

Large river systems, such as the River Ganges (Ganga), provide crucial water resources for the environment and society, yet often face significant challenges associated with cumulative impacts arising from upstream environmental and anthropogenic influences. Understanding the complex dynamics of such systems remains a major challenge, especially given accelerating environmental stressors including climate change and urbanization, and due to limitations in data and process understanding across scales. An integrated approach is required which robustly enables the hydrogeochemical dynamics and underpinning processes impacting water quality in large river systems to be explored. Here we develop a systematic approach for improving the understanding of hydrogeochemical dynamics and processes in large river systems, and apply this to a longitudinal survey (> 2500 km) of the River Ganges (Ganga) and key tributaries in the Indo-Gangetic basin. This framework enables us to succinctly interpret downstream water quality trends in response to the underpinning processes controlling major element hydrogeochemistry across the basin, based on conceptual water source signatures and dynamics. Informed by a 2019 post-monsoonal survey of 81 river bank-side sampling locations, the spatial distribution of a suite of selected physico-chemical and inorganic parameters, combined with segmented linear regression, reveals minor and major downstream hydrogeochemical transitions. We use this information to identify five major hydrogeochemical zones, characterized, in part, by the inputs of key tributaries, urban and agricultural areas, and estuarine inputs near the Bay of Bengal. Dominant trends are further explored by investigating geochemical relationships (e.g. Na:Cl, Ca:Na, Mg:Na, Sr:Ca and NO3:Cl), and how water source signatures and dynamics are modified by key processes, to assess the relative importance of controls such as dilution, evaporation, water-rock interactions (including carbonate and silicate weathering) and anthropogenic inputs. Mixing/dilution between sources and water-rock interactions explain most regional trends in major ion chemistry, although localized controls plausibly linked to anthropogenic activities are also evident in some locations. Temporal and spatial representativeness of river bank-side sampling are considered by supplementary sampling across the river at selected locations and via comparison to historical records. Limitations of such large-scale longitudinal sampling programs are discussed, as well as approaches to address some of these inherent challenges. This approach brings new, systematic insight into the basin-wide controls on the dominant geochemistry of the River Ganga, and provides a framework for characterising dominant hydrogeochemical zones, processes and controls, with utility to be transferable to other large river systems