Relationship between oxygen and siderophore synthesis inPseudomonas aeruginosa

Pseudomonas aeruginosa strain PAO1, growing in low-iron medium, produces two siderophores, pyochelin and pyoverdin, in massive bursts as the culture shifts from logarithmic phase to stationary phase. Two medium components, oxygen and iron, prolonged the logarithmic phase when they were added to the medium. Oxygen and iron appeared to be in demand during this period because, as heme synthesis increased in response to the low oxygen concentration in the medium, a situation resulting from the high density of bacteria present in the medium during late log phase, the iron content of the bacteria decreased. These phenomena resulted in the production of massive amounts of siderophores late in the log phase to supply iron for the increased heme synthesis.     

Microheterogeneity of bovine myelin basic protein studied by nuclear magnetic resonance spectroscopy

Myelin basic protein isolated from bovine white matter is known to consist of a mixture of three or more “charge isomers”, which can be separated by cation-exchange chromatography. We are using 360-MHz ¹H-nmr spectroscopy to establish the chemical and structural differences among them. Preliminary studies by difference spectroscopy between two of the isomers suggest (a) all aromatic residues, and probably their nearest-neighbors, are unchanged; (b) the less cationic isomer lacks one (or two) of its C-terminal Arg residues; and (c) a significant fraction of the two Met residues in the less cationic isomer is present as methionine sulfoxide.     

Preservation of fine structure in vibratome-cut sections of the central nervous system stained for light microscopy

A technique without negative effects on tissue preservation that allows precise identification and subsequent removal of central nervous system nuclei for ultrastructural analysis is described. The procedure uses 200 microns thick Vibratome-cut sections of glutaraldehyde fixed brains. These sections are stained for 25 seconds with a methylene blue solution and stored for 4 hours in 0.2 M pH 7.4 phosphate buffer in 4% sucrose for optimal visualization at the light microscopic level. The stock solution of 1 g methylene blue and 1 g sodium borate in 100 ml of distilled water, is filtered through a Millipore filter and diluted 5:95 with distilled water immediately prior to use. Regions of specific interest are then processed for electron microscopy.     

Effect of Ferricyanide, Ferrocyanide and KCN on Growth and Flowering in the Short-Day Plant Lemna paucicostata 6746

Flowering in the short-day plant Lemna paucicostata 6746 canbe induced under continuous light by the addition of ferricyanie,ferrocyanide or KCN to M-sucrose medium. Each substance is nearly10 times more effective when the flasks are covered by glassbeakers than when cotton plugs are used. By contrast, when floweringis induced under continuous light by copper or by short-daytreatment, neither flowering nor growth are affected by whetherglass beakers or cotton plugs are used. Ferricyanide, ferrocyanideand KCN are also able to induce long-day flowering when theplants are grown on Msucrose medium in small beakers that areplaced in a covered storage dish that also contains a solutionof one of these compounds. Addition of a KOH trap to the storagedish completely blocks the flowering induced by these compounds.If [¹⁴C]ferrocyanide is added to the storage dish both the M-sucrosemedium and the plants contain significant amounts of radioactivity,the amount of radioactivity being proportional to the floweringresponse. These results indicate that ferricyanide, ferrocyanideand KCN break down to release HCN and that it is the HCN whichis responsible for inducing flowering in L. paucicostata 6746under continuous light. ¹Present address: Department of Biology, Osaka Kyoiku University,Ikeda, Osaka 563, Japan. ²Present address: Institute of Horticulture, The Volcani Center,P. O. B. 6, Bet-Dagan, Israel. (Received January 17, 1983; Accepted March 24, 1983)     

Studies on the mechanism of polyethylene glycol-mediated cell fusion using fluorescent membrane and cytoplasmic probes

The mechanism by which polyethylene glycol (PEG) mediates cell fusion has been studied by examining the movements of membrane lipids and proteins, as well as cytoplasmic markers, from erythrocytes to monolayers of cultured cells to which they have been fused. Fluorescence and freeze-fracture electron microscopy and fluorescence recovery after photobleaching have yielded the following results: (a) In the presence of both fusogenic and nonfusogenic PEG membranes are brought together at closely apposed contact regions. (b) Fluorescent lipid probes quickly spread from the membranes of erythrocytes to cultured cells in the presence of both fusogenic and nonfusogenic PEG. (c) Proteins of the erythrocyte membranes were never observed to diffuse into the cultured cell membrane. (d) Water-soluble proteins did not diffuse from the erythrocyte interior into the target cell cytoplasm until the PEG was removed. These data suggest that the coordinate action of two distinct components is necessary for fusion as mediated by PEG. Presumably, the polymer itself promotes close apposition of the adjacent cell membranes but the fusion stimulus is provided by the additives contained in commercial PEG.     

Larval development of Diploptera punctata reared alone and in groups

Larvae of the cockroach Diploptera punctata were reared in isolation, in pairs, or in groups of 8–10. Duration of larval development, age at each ecdysis, weights at birth and ecdyses, and adult head-capsule width were measured. Duration of larval development was longer and adult size was larger in isolated animals than in animals reared in pairs and groups. The effect of isolation on development was more pronounced in males. All females had 4 larval instars, whereas males had 3 or 4 instars. The proportion of males with 4 larval instars was higher among animals reared in isolation. There was no difference in the duration of larval development or adult size between pair- and group-reared animals. The sex of animals in the group did not affect adult size or the duration of larval development. Males which underwent 3 or 4 larval instars had different schedules of moulting. Rates of growth of males of both instar types reared in isolation and pairs were similar. Greater adult weight of isolated animals and 4-instar-type males was a result of their longer duration of larval development. Both a higher rate of growth and longer duration of larval development contribute to the larger adult size of females than males.     

Implication of Triticum searsii as the B-genome donor to wheat using DNA hybridizations

In vitro DNA:DNA hybridizations and hydroxyapatite thermal chromatography were employed to help identify the species ancestral to the B genome of the polyploid wheats. We hybridized 3H-Triticum aestivum DNA to the unlabeled DNAs of T. urartu, T. speltoides, T. sharonensis, T. bicorne, T. longissimum, and T. searsii, 3H-Labeled DNA of T. urartu was hybridized with the DNA of a synthetic tetraploid. AADD. The heteroduplex thermal stabilities indicated that T. searsii was most closely related to T. aestivum (ABD) and that the genome of T. urartu was more closely related to the A genome than the B genome. The degree of reassociation which may have occurred between the six diploid species and the D genome of T. aestivum was evaluated by hybridizing 3H-T. tauschii DNA with the DNAs of the diploids. The results indicated that T. urartu had the least sequence homology to T. tauschii, the D-genome donor lending additional support to the conclusion that T. urartu is related to the A genome. Thus, it is highly probable that T. searsii is the B-genome donor to the polyploid wheats or a major chromosome donor if the B genome is, in fact, polyphyletic in origin.