Studies on Genetic Male-Sterile Soybeans : IV. Effect of Male Sterility and Source of Nitrogen Nutrition on Accumulation, Partitioning, and Transport of Nitrogen

Soybean (Glycine max [L.] Merr.) germplasm, isogenic except for loci controlling male sterility (ms₁) and nodulation (rj₁), was used to investigate the effects of reproductive tissue development and source of nitrogen nutrition on accumulation, transport, and partitioning of nitrogen in a greenhouse experiment. Nodulated plants were supplied nitrogen-free nutrient solution, and nonnodulated plants were supplied nutrient solution containing 20 millimolar KNO₃. Plants were sampled from flowering until maturity (77 to 147 days after transplanting).

Accumulation rates of nitrogen in whole plants during reproductive growth were not significantly different among the four plant types. Nitrogen accumulation in the sterile, nonnodulated plants, however, ceased 2 weeks earlier than in fertile, nonnodulated or fertile and sterile, nodulated plants. This early cessation in nitrogen accumulation resulted in sterile, nonnodulated plants accumulating significantly less whole plant nitrogen by 133 days after transplanting (DAT) than fertile, nonnodulated plants. Thus, changing the site of nitrogen assimilation from nodules (N₂-fixing plants) to roots and leaves (NO₃-fed plants) resulted in similar whole-plant nitrogen accumulation rates in fertile and sterile plants, despite the absence of seed in the latter.

Leaflet and stem plus petiole tissues of both types of sterile plants had significantly higher nitrogen concentrations after 119 DAT than both types of fertile plants. Significantly higher concentrations and exudation rates of nonureide, reduced-nitrogen in xylem sap of sterile than of fertile plants after 105 DAT were observed. These latter results indicated possible cycling of nonureide, reduced-nitrogen from the downward phloem translocation stream to the upward xylem translocation stream in roots of sterile plants. Collectively, these results suggest a lack of sinks for nitrogen utilization in the shoots of sterile plants. Hence, comparison of nitrogen accumulation rates for sterile and fertile plants does not provide a definitive test of the hypothesis that reproductive tissue development limits photosynthate availability for support of N₂ fixation and nitrate assimilation in determinate soybeans.

Nitrogen assimilation during reproductive growth met a larger proportion of the reproductive-tissue nitrogen requirement of nitrate-dependent plants (73%) than of N₂-fixing plants (63%). Hence, vegetative-tissue nitrogen mobilization to reproductive tissue was a more prominent process in N₂-fixing than in nitrate-dependent plants. N₂-fixing plants partitioned nitrogen to reproductive tissue more efficiently than nitrate-dependent plants as the reproductive tissues of the former and latter contained 65 and 55%, respectively, of the whole-plant nitrogen at the time that nitrogen accumulation in reproductive parts had ceased (133 DAT).

     

A novel immunoassay with direct relevance to protection against organophosphate poisoning

Antiparaoxon immune sera were employed in a new immunoassay based on competition between acetylcholinesterase and antibodies for the binding ofparaoxon. Unlike radioimmunoassay, the new assay described herein can be extended to predict the feasibility of antibodies to confer in vivo protection of acetylcholinesterase against organophosphate poisoning. The toxicity of paraoxon was reduced in mice which were pre-injected with the immune sera.     

The effect of calcium supplements on plasma alkaline phosphatase and urinary hydroxyproline in postmenopausal women

Although calcium supplements are widely used in the treatment of osteoporosis, their beneficial effect is not conclusively established. We now report some effects of a calcium supplement (1 g/day) given for 6 to 12 weeks to 15 postmenopausal osteoporotic women. The mean fasting urinary hydroxyproline/creatinine ratio decreased from 0.021 +/- 0.002 to 0.015 +/- 0.001 (P less than 0.0025), indicating a significant reduction in bone resorption. The mean plasma alkaline phosphatase fell from 123 +/- 5 U/l to 104 +/- 3.1 U/l (P less than 0.01), probably representing some secondary reduction in bone formation following the inhibition of bone resorption. These results support the concept that calcium supplementation is useful in the treatment of postmenopausal osteoporosis.     

Epidermal cellular proliferation and differentiation in sexually mature male Salmo salar with androgen levels depressed by oil

Sexually mature male Salmo salar exhibit epidermal thickening and an increase in goblet cell concentration during the spawning season. The ventral skin, which is likely to experience most abrasive contact during the spawning period, has the thickest epidermis and the greatest goblet cell concentration. Following exposure to crude oil there is inhibition of cellular proliferation and elongation associated with epidermal thickening, and also inhibition of mucigenesis. Data on the androgen levels in these fish, and data from earlier studies involving treatment with hormones, indicate that oil-related epidermal effects during the spawning period are most likely systemic in origin, probably arising from reduced plasmatic androgen levels.     

Fluorine-19 nuclear magnetic resonance study of codon-anticodon interaction in 5-fluorouracil-substituted E. coli transfer RNAs.

Codon-anticodon interaction was investigated in fully active 5-fluorouracil-substituted E. coli tRNAVal1 (anticodon FAC) by 19F NMR spectroscopy. Binding of the codon GpUpA results in the upfield shift of a 19F resonance at 3.9 ppm in the central region of the 19F NMR spectrum, whereas trinucleotides not complementary to the anticodon have no effect. The same 19F resonance shifts upfield upon formation of an anticodon-anticodon dimer between the 19F-labeled tRNA and E. coli tRNATyr2 (anticodon QUA). These results permit assignment of the peak at 3.9 ppm to the 5-fluorouracil at position 34 in the anticodon of fluorouracil-substituted tRNAVal1. The methionine codon ApUpG also causes a sequence-specific upfield shift of a peak in the central part of the 19F NMR spectrum of fluorinated E. coli tRNAMetm. However, ApUpG has no effect on the 19F spectrum of 19F-labeled E. coli tRNAMetf, indicating possible conformational differences between the anticodon loop of initiator and chain-elongating methionine tRNAs. 19F NMR experiments detect no binding of CpGpApA to the complementary FpFpCpG (replaces Tp psi pCpG) in the T-loop of 5-fluorouracil-substituted tRNAVal1, in the presence or absence of codon, suggesting that the tertiary interactions between the T- and D-loops are not disrupted by codon-anticodon interactions.     

Reassembly of lipid-protein complexes of pulmonary surfactant. Proposed mechanism of interaction

We studied the interaction at 37 degrees C between a major apolipoprotein of pulmonary surfactant and 11 mixtures of lipids. The experiments were carried out in the presence of either 3 mM Ca2+ or 10 mM EDTA. The amount of apolipoprotein associated with lipid was independent of Ca2+. However the binding was sensitive to the percentage of gel-state lipid in the vesicles, and the amount of apolipoprotein in the recombinant lipoprotein complex decreased as the percentage of fully saturated phospholipid was reduced. Maximum association of the apolipoprotein occurred with lipid vesicles containing 85% 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 15% 1,2-dipalmitoyl-sn-glycero-3-phospho-1-glycerol or 1,2-dipalmitoyl-sn-glycerol. Fluorescence measurements on the apolipoprotein indicated that the tryptophan side chains were in a relatively hydrophobic environment, and that the wavelength of maximum fluorescence emission was not changed upon the binding of lipid. The results suggest that the principal mode of interaction between the apolipoprotein and lipids of surfactant is hydrophobic bonding. The most extensive binding occurs with lamellar lipids in a gel that would be expected to have inhomogeneities in packing density due to the presence of acidic phospholipids or other glycerolipids. The role of Ca2+ in this interaction has not been fully determined. Although it is not needed to effect the binding of the lipids and the apolipoprotein, it does influence the physical state of the complex, and possibly the stoichiometry of lipid to protein. Some of the processes mediated by Ca2+ in this interaction may be analogous to those observed in membrane fusion. Thus, Ca2+ probably causes segregation of the lamellar phospholipids into domains, inducing vesicular disruption and fusion. This lipid aggregates about hydrophobic sites on the protein, thereby forming high molecular weight reassembly complexes.     

Leaf Starch Metabolism during the Growth of Pepper (Capsicum annuum) Plants

Levels of starch and sugars, and the activities of amylase and starch phosphorylase were measured in expanding leaves harvested in early morning and early evening during the growth of pepper (Capsicum annuum L.; cv `Bellboy') plants. The differences between starch levels 1 hour after dawn and 1 hour after dusk increased during the period of initial fruit expansion. This diurnal starch difference was strongly correlated with post-dusk amylase activities in leaves at both stages of expansion. There was also a strong correlation between levels of amylase in immature and those in mature leaves throughout the experiment. Phosphorylase activity showed no direct relationship to leaf starch levels, and there was no similarity between activities in immature and mature leaves. An increase in photosynthesis during plant development was observed which could account for the increased starch synthesis at initial fruit expansion.     

Transport of nucleic acid bases into Escherichia coli

The uptake and retention of purine bases and of uracil requires both a protonmotive force and intracellular conversion to nucleotides. Inhibition of uptake by arsenate does not imply that ATP is required for the transport process because arsenate caused a rapid fall in the level of 5-phosphoribosyl 1-pyrophosphate. A mutation defective in high-affinity adenine transport has been identified and is designated purP. This mutation has been found to lie in the neighbourhood of mtl. Competition experiments indicate that at least two other systems are used to transport guanine, xanthine and hypoxanthine.