Salt-tolerance in plants. I. Ions, compatible organic solutes and the stability of plant ribosomes

Abstract Polysomes and ribosomes recovered from a number of plant species were tested for stability when incubated at 25°C in salt solutions in the absence of ATP and initiation factors. Stability was assessed by sucrose density gradient analysis. The stability was inversely proportional to salt concentrations above 125 mol m⁻³ KCl. Polysomes were less stable in the presence of Na⁺ than K⁺ salts, and were much less stable in Cl⁻ than in acetate salts. Polysomes from Triticum aestivum. Hordeum vulgare, Capsicum annuum, Helianthus annuus. Pisum sativum, Atriplex nummularia, Beta vulgaris, Cladophora sp., Enteromorpha sp. and Corallina cuvieri were similarly sensitive to KCl. Polysomes from Ulva lactuca were more sensitive than the other species. Cytoplasmic and plastid polysomes from T. aestivum were similarly unstable in 500 mol m⁻³ KCl. Unprogrammed ribosomal subunit couples from T. aestivum, B. vulgaris and U. lactuca showed Mg²⁺-dependent conformational instability and dissociation in KCl. Slight differences in ribosomal stability were observed between species, but these were unrelated to the salt tolerances of the plants. The ‘compatible’ organic solutes, glycinebetaine and proline, failed to reduce ion-induced instability. Ribosome yield and polysome profiles were similar in leaves of B. vulgaris containing significantly different levels of both Na⁺ and Cl⁻ after growth in media containing 50 or 200 mol m⁻³ NaCl. The results are consistent with the hypothesis that plants maintain a cytoplasmic solute environment that is compatible with ribosomal stability.     

Streptomycin retards the phenotypic maturation of chick myogenic cells

Summary As part of an effort to optimize conditions required for the complete maturation of muscle cells in vitro, we have investigated the effects of the antibiotics penicillin, streptomycin, and Fungizone (amphotericin B) on the development of cultured chick embryo skeletal muscle. It is shown that even low dosages of streptomycin, but not penicillin or Fungizone, retard protein synthesis and accumulation in these cultures. Myosin accumulation was also reduced and the appearance of striations in fused cells was delayed in myotubes formed in medium containing streptomycin. Additional data suggest that this overall retardation of myogenesis is due to the influence of streptomycin on maturing myotubes rather than early proliferation and cell fusion. These results are discussed with regard to recent efforts to promote the full maturation of muscle cells grown in culture. This research was supported by National Institutes of Health Grant NS 155882 and a Task Force on Drug Development Research Contract from The Muscular Dystrophy Association.     

Three-step preparation and purification of phosphorus-33-labeled creatine phosphate of high specific activity

Rabbit heart mitochondria were used as a source of enzymes for the synthesis of phosphoruslabeled creatine phosphate. This method is based on the coupled reaction between mitochondrial oxidative phosphorylation and mitochondrial-bound creatine kinase. It is possible to convert more than 90% of the inorganic phosphate (P_i) to creatine phosphate. The method used only small amounts of adenine nucleotides which led to a product with only slight nucleotide contamination. This could be removed by activated charcoal extraction. For further purification, a method for the removal of residual P_i is described.     

Coordinated synthesis of the nuclear protein cyclin and DNA in serum-stimulated quiescent 3T3 cells

Quantitative two-dimensional gel electrophoretic analysis (IEF) of the nuclear polypeptide cyclin together with autoradiographic studies have revealed a coordinate synthesis of cyclin and DNA after serum stimulation of quiescent 3T3 cells. These results strengthen the notion that cyclin may be a central component of the pathway(s) that regulate cell proliferation.     

Transferrin as a donor of iron to mitochondria Effect of pyrophosphate and relationship to mitochondrial metabolism and heme synthesis

Rat liver mitochondria accumulate iron mobilized from transferrin by pyrophosphate. The uptake has a very low energy dependence, but it is highly dependent on a functioning respiratory chain. Reduction of the ferric-iron-pyrophosphate complex is not linked to any specific respiratory complex. Half of the amount of iron accumulated is passed into heme. Iron once accumulated is very little accessible to chelation by added ferric or ferrous iron chelators. Iron uptake and heme synthesis are maximal if a suitable porphyrin substrate is added simultaneously with iron. The results represent further evidence that pyrophosphate is a possible candidate for intracellular iron transport. Also, the results suggest that iron uptake is coupled to simultaneous porphyrin uptake and heme synthesis.     

Roles of auxin and gibberellic acid in growth and maturation of epicotyls of Vigna angularis: Cell wall changes

The effects of auxin and gibberellic acid on cell wall composition in various regions of epicotyls of azuki bean ( Vigna angularis Ohwi and Ohashi cv. Takara) were investigated with the following results. (1) Young segments excised from apical regions of the epicotyl elongated in response to added 10⁻⁴ M indole-3-acetic acid (IAA). When the segments were supplied with 50 m M sucrose, the IAA-induced segment growth was accompanied by enhanced overall synthesis of cell wall polysaccharides, such as xyloglucans, polyuronides and cellulose. This IAA effect on the cell wall synthesis is a consequence of extension growth induced by IAA. Gibberellic acid (GA) at 10⁻⁴ M synergistically enhanced the IAA-induced cell wall synthesis as well as IAA-induced extension growth, although GA by itself neither stimulated the cell wall synthesis nor extension growth. In the absence of sucrose, cell wall synthesis was not induced by IAA or GA. (2) In mature segments excised from basal regions of the epicotyl, no extension growth was induced by IAA or GA. GA enhanced the synthesis of xylans and cellulose when the segments were supplied with 50 m M sucrose. IAA had no effect on the cell wall synthesis. These findings indicate that synthesis of polyuronides, xyloglucans and cellulose, which occurs during extension growth of the apical region of the epicotyl, is regulated chiefly by auxin whereas synthesis of xylans and cellulose during cell maturation in the basal region of the epicotyl is regulated by GA.     

Some properties of diacylglycerol acyltransferase in a particulate fraction from maturing safflower seeds

The activity of diacylglycerol acyltransferase of a subcellular particulate fraction from maturing safflower seeds was remarkably stimulated by the addition of 1, 2-diacylglycerols which were previously emulsified in a gelatin solution by sonication. Metal ions were inhibitory to the reaction. Deoxycholate and diisopropyl fluorophosphate were the most effective inhibitors. Sulfhydryl groups seemed to be of limited significance in the enzyme. Both 1, 2-dioleoyl-sn-glycerol and 2, 3-dioleoyl-sn-glycerol were good substrates of diacylglycerol acyltransferase, but the 1, 3-isomer did not serve as an acyl acceptor. The enzyme showed broad specificity for synthetic rac-1, 2-diacylglycerols containing various fatty acids. However, rac-1, 2-diacetylglycerol and rac-1, 2-dibutyrylglycerol, which are soluble in water, were ineffective. The enzyme exhibited no significant specificity for saturated and unsaturated fatty acyl-CoA thioesters as acyl donors. This suggests that the fatty acid composition at the 3-position of the glycerol molecule of safflower triacylglycerols may depend on the composition of the endogenous acyl-CoA pool.     

The preparation of a sarcolemmal fraction from evacuated muscle slices

A novel procedure is described for preparing a plasma membrane fraction from skeletal muscle (i.e., sarcolemma). The procedure entails evacuating the myoplasm from muscle slices as a preliminary step to homogenization and fractionation. The evacuated muscle slices are composed of a stroma-containing sarcolemma, which is then homogenized and fractionated, utilizing a sequence of differential and discontinuous sucrose density gradient centrifugations. On the basis of electron microscopy, selective enzyme markers and α-bungarotoxin binding in innervated and denervated muscles, the fraction most enriched with sarcolemma is recovered from the 0.5/0.7 M interface of a discontinuous sucrose gradient.     

Cell free synthesis of some storage protein subunits by polyribosomes and RNA isolated from developing seeds of pea (Pisum sativum L.)

Polyribosomes which have template activity in the wheat germ system have been isolated from developing pea seeds. Some of the translation products have identical mobilities to the vicilin and legumin subunits by SDS-PAGE. Certain products were specifically immunoprecipitated with antisera prepared against purified vicilin and legumin fractions. Various RNA fractions including poly A-rich RNA have also been isolated from polyribosomes and shown to direct the synthesis of polyripeptides whose properties are similar to the storage protein subunits. The results are discussed in relationship to other investigations with seed storage protein biosynthesis in vitro.Abbreviations DTT dithiothreitol - SDS-PAGE SDS-polyacrylamide gel electrophoresis - TCA tricarboxylic acid