Surface charge on isolated maize-coleoptile amyloplasts

Whole amyloplasts were isolated from Zea mays L. coleoptiles. Electron microscopy confirmed that their envelopes consisted of two intact membranes. Their surface charge was quantified through electrokinetic measurements employing a vertically oriented cataphoresis cell. Amyloplasts from coleoptiles of different ages (5–9 d) and degree of exposure to light (0–9 d) all had negative zeta potentials (mean of -19.4 mV). Isolated starch granules had comparable values. The net negative surface charge was confirmed ultrastructurally by the binding of cationised ferritin to both amyloplasts and starch grains. Cationised ferritin tagged with a fluorescent label (fluorescein isothiocyanate) showed binding to some amyloplasts but not to starch grains. These results are discussed in the context of a hypothesized role for statolith charge in plant graviperception.     

Geotropism and the lateral transport of auxin in the corn mutant amylomaize

Summary In coleoptiles of the amylomaize corn mutant (AM), the amyloplasts are much reduced in size in comparison with the wild type corn (WT), permitting a comparison of geotropic responsiveness as related to lateral displacement of amyloplasts and lateral transport of auxin. The amyloplasts of AM showed 30–40% lesser lateral redistribution in response to horizontal exposure in comparison with WT. With geotropic stimulation, the lateral transport of auxin in the direction of growth was 40–80% less, and the geotropic curvature by the coleoptiles was also significantly less in the mutant as compared with WT. These correlations support the hypothesis that the starch plastids serve as gravity sensors in the geotropic responses of coleoptiles.     

Physical forces in dormancy and germination of xanthium seeds

The germination of seeds of Xanthium pensylvanicum Wallr. occurs in 2 phases, an initial passive phase of water uptake followed by an active phase of growth. These 2 phases have been separated experimentally, and shown to occur similarly in isolated cotyledons and embryonic axes. Measurements of the physical thrust generated by the entire seed and its separate components of cotyledon and axis reveal that non-dormant Xanthium seeds develop more than twice the thrust of dormant seeds, and that this difference develops principally in the second phase of enlargement of the axis. Measurement of the forces required for piercing the testa of these seeds establishes that whereas the thrust developed by non-dormant seed is adequate to cause testa rupture, that developed by dormant seeds is not. It is concluded that the dormancy of Xanthium involves an inadequacy in the embryo for rupture of the testa.     

Lateral movement of auxin in phototropism

Lateral movement of indoleacetic acid-1-¹⁴C in corn coleoptiles was measured as radioactivity moving laterally following unilateral application of the auxin. The data suggest that there is an endogenous lateral movement of auxin, and that phototropic stimulation of the coleoptile depresses lateral movement towards the light and enhances lateral movement away from the light. The lateral movement was found to be principally as indoleacetic acid. In experiments using sunflower hypocotyl sections, evidence is also presented to support the suggestion that lateral redistribution of auxin may be effected by a deflection of auxin around a barrier to basipetal transport.     

Postprandial hyperlipemia inhibits platelet aggregation without affecting prostanoid metabolism

The objective of this work was to characterize changes in platelet aggregability during postprandial hypertriglyceridemia with special emphasis on arachidonic acid metabolism. Ten healthy young men consumed 100 g fat after a fasting period of 12 hr. In-vitro platelet aggregation induced by ADP and collagen was measured at 0, 3, 5, and 9 hours after the fat intake. The major arachidonic acid metabolites, 12-hydroxyeicosatetraenoic acid (12-HETE), thromboxane A2 (TXA2), prostaglandin F2 alpha (PGF2a), and prostaglandin E2 (PGE2) produced during collagen-induced platelet activation were quantified by gas chromatography/mass spectrometry. A significant decrease in platelet aggregability induced by both ADP and collagen was detected during the postprandial hyperlipemia. No significant changes could be found in the prostanoid pattern of collagen activated platelets. There was no correlation between the degree of the inhibition of platelet aggregation and the relative or absolute increase of triglyceride-levels in the plasma during the postprandial hyperlipemia.     

Outer Membrane Protein Heterogeneity within Pseudomonas fluorescens and P. putida and Use of an OprF Antibody as a Probe for rRNA Homology Group I Pseudomonads

The electrophoretic patterns of outer membrane proteins of strains representing the biovars of Pseudomonas fluorescens and Pseudomonas putida were analyzed by gel electrophoresis. The outer membrane protein profiles were variable, and they were not useful for assigning strains to a specific biovar. However, three or four predominant outer membrane proteins migrating at 42 to 46 kDa, 33 to 38 kDa, and 20 to 22 kDa were conserved among the strains. They could be tentatively identified as OprE (44 kDa), OprF (38 kDa), OprH (21 kDa), and OprL (20.5 kDa), which are known proteins from Pseudomonas aeruginosa. A 37-kDa OprF-like protein was purified from P. fluorescens DF57 and used to raise a polyclonal antibody. In Western blot (immunoblot) analysis, this antibody reacted with OprF proteins from members of Pseudomonas rRNA homology group I but not with proteins from nonpseudomonads. The heterogeneity in M(infr) of OprF was greater among P. fluorescens strains than among P. putida strains. Immunofluorescence microscopy of intact cells demonstrated that the antibody recognized epitopes that were accessible only after unmasking by EDTA treatment. The antibody was used in a colony blotting assay to determine the percentage of rRNA homology group I pseudomonads among bacteria from the rhizosphere of barley. The bacteria were isolated on 10% tryptic soy agar, King's B agar, and the pseudomonad-specific medium Gould S1 agar. The estimate of OprF-containing CFU in rhizosphere soil obtained by colony blotting on 10% tryptic soy agar was about 2 and 14 times higher than the values obtained from King's agar and Gould S1 agar, respectively, indicating that not all fluorescent pseudomonads are scored on more specific media. The colonies reacting with the OprF antibody were verified as being rRNA homology group I pseudomonads by using the API 20NE system.     

The role of ATP as a mediator in the action of iron complexes on cellular calcium homeostasis

The effects of the interaction between low molecular weight iron complexes (citrate, lactate, and ATP complexes) with ATP and proteins, on the modification of Ehrlich carcinoma cell calcium homeostasis have been studied. In that modification the ferric-ATP complex shows much higher activity than the others. Sodium ATP, by iron translocation from citrate and lactate, increases their activity. This phenomenon implicates ATP as a mediator on the cellular activity of the complexes. Proteins, particularly ferritin, appear to moderately reduce their activity, whereas glutathione and ascorbic acid, acting as lipid peroxidation-inhibitors, show only a slight reduction of the iron complex’s effects on cellular calcium uptake.