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Glucosylation of phosphorylpolyisoprenol and sterol at the plasma membrane of soya-bean (Glycine max) protoplasts.

ABSTRACT: Protoplasts were prepared from cells of soya-bean (Glycine max) suspension cultures and the plasma membrane was labelled with diazotized [G-3H]sulphanilic acid. Homogenates were fractionated by differential and isopycnic centrifugation, and membrane fractions in a density gradient were characterized by enzymic markers and the radioactive label. When fractions containing a large amount of protein were incubated with UDP-[U-14C]glucose, radioactive material soluble in chloroform/methanol was formed and this separated into acidic and neutral fractions on ion-exchange chromatograms of DEAE-cellulose. The acidic fraction was shown to consist of dolichol phosphate glucose, and the neutral fraction sterol glucosides and acylsterol glucosides. Optimum conditions for glucosylation of dolichol phosphate were established as 5 mM-MgCl2, pH 6.0, and the enzyme had a Michaelis constant of 1.5 x 10(-5) m-UDP-glucose. Optimum conditions for glucosylation of sterol were 5 mM-MgCl2, pH 8.0 GDP-[U-14C]glucose was a poor substrate for the synthesis of both acidic and neutral lipids. Although the synthesis of dolichol phosphate glucose and sterol glucosides occurred throughout the sucrose gradient, the specific activities of both glucosyltransferases were greatest in a fraction coincident with the radioactively labelled plasma membrane. Results are discussed in relation to the likely role fo these transglucosylase activities.

SUBMITTER: Chadwick CM

PROVIDER: S-EPMC1161591 | biostudies-other | 1980 Feb

REPOSITORIES: biostudies-other

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Project description:The transition metal tungsten (W) finds increasing application in military, aviation and household appliance industry, opening new paths for the heavy metal into the environment. Since tungsten shares certain chemical properties with the essential plant micro nutrient molybdenum, it is proposed to inhibit enzymatic activity of molybdoenzymes by replacing the Mo-ion bound to the co-factor. However, recent studies suggest the inhibition of enzymatic activity might not be the only effect W has on plants and that, much like other heavy metals, tungsten exerts toxicity on its own. Still, our understanding of the mechanisms behind the apparent phytotoxicity remains limited.This study investigates the effects of W on growth, nutrient levels (ionome, ICP-MS), starch levels and nitrogen nutrition (IRMS, enzyme activity assays) as well as root and nodule proteome (LC-MS/MS) of Glycine max cv. Primus. Plants were inoculated with Bradyrhizobium japonicum and grown in a semi hydroponic set up using three different tungsten concentrations (zero, 0.1 mM and 0.5 mM). To identify possible benefits of a functional bacterial symbiosis on W induced stress response, two different environmental growth conditions, one with suppressed N-fixation, supplied with Nitrate (10 mM KNO3) and one solely relying on symbiotic N-fixation (zero KNO3), were applied. Glycine max was able to take up considerable amounts of W (703 ± 136 mg kg-1). However, high W resulted in a strong reduction of shoot biomass of both N regimes and of root biomass (N fed only). Irrespective of N regime, NR activity and total N decreased with increasing W concentrations. Similarly, nitrogenase precursor levels as well as N2-fixation, nodule fixation activity (mg N g-1 nodule dry weight) and nodulation were reduced, indicating that nitrogenase synthesis and activity were negatively affected by W stress. However, along a N fix nodule specific induction of the secondary and phytohormone metabolism, it appears that N2 fixation of remaining nodules was not as severely affected by increasing levels of tungsten than nitrate reduction. Besides N metabolism, plants exhibited an imbalance in nutrient and a failure of carbon metabolic pathways accompanied by an accumulation of starch at high tungsten concentrations, independent of N-regime. Proteomic data demonstrated that the response to high W concentrations is independent of nodule functionality and dominated by several peroxidases and other general stress related proteins. Based on an evaluation of several W responsive proteotypic peptides, we identified a set of protein markers of W stress and possible targets for improved stress tolerance.

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Glucosylation of phosphorylpolyisoprenol and sterol at the plasma membrane of soya-bean (Glycine max) protoplasts.

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