Ethylene-promoted adventitious rooting and development of cortical air spaces (aerenchyma) in roots may be adaptive responses to flooding in Zea mays L

The roots and stem base of intact, 10 day old maize (Zea mays L. cv. LG11) plants, grown in nutrient solution, were continuously aerated either with ethylene (5 μl l(-1)) in air or with air alone. Ethylene treatment hastened the emergence of adventitious (nodal) roots from the base of the shoot, but slowed their subsequent extension. Ethylene also promoted the collapse of cells in the cortex of these roots, with lysigenous development of prominent air spaces (aerenchyma). Non-aeration of the nutrient solution caused endogenously produced ethylene to accumulate in the roots, and stimulated both the emergence of adventitious roots and the formation of cortical air spaces in them. With non-aeration the concentration of oxygen did not fall below 1% in the equilibrium gas phase (air=20.8%). Complete deoxygenation of the nutrient solution, produced by passing oxygen-free nitrogen gas, prevented both air space formation and the evolution of ethylene by root segments.These results suggest that adventitious rooting and cortical air space formation in nodal roots in Zea mays may be stimulated by enhanced concentrations of endogenous ethylene arising either from entrapment of the gas by unstirred water layers around the roots and/or by increased biosynthesis. These responses are considered conducive to survival in waterlogged soil.

Properties and biosynthesis of cyclopropane fatty acids in Escherichia coli

The lipid phase transition of Escherichia coli phospholipids containing cyclopropane fatty acids was compared with the otherwise homologous phospholipids lacking cyclopropane fatty acids. The phase transitions (determined by scanning calorimetry) of the two preparations were essentially identical. Infection of E. coli with phage T3 inhibited cyclopropane fatty acid formation over 98%, whereas infection with mutants which lack the phage coded S-adenosylmethionine cleavage enzyme had no effect on cyclopropane fatty acid synthesis. These data indicate that S-adenosylmethionine is the methylene in cyclopropane fatty acid synthesis.

Phase behavior of lipids from Halobacterium halobium

Mixtures of dipalmitoylphosphatidylcholine with purple membrane lipids, red membrane lipids, or total lipids of Halobacterium halobium have been studied with differential scanning calorimetry. A comparison of red and purple membrane lipids reveals no difference in their phase behavior, indicating that lipid phase behavior plays no role in the in vivo separation of red and purple membranes. The effects of variation of the salt content of the suspending solution have also been examined. Studies of the melting behavior of these mixtures as H. halobium lipid content is varied suggest that the gel to liquid-crystal transition does not occur in the lipids of H. halobium.

An estimate of the minimum amount of fluid lipid required for the growth of Escherichia coli

The lipid phase transition of Escherichia coli was studied by high sensitivity differential scanning calorimetry. A temperature sensitive unsaturated fatty acid auxotroph was used to obtain lipids with subnormal unsaturated fatty acid contents. From these studies it was concluded that E. coli can grow nromally with as much as 20% of its membrane lipids in the ordered state but that if more than 55% of the lipids are ordered, growth ceases. Studies with wild-type cells show that the phase transition ends more than 10 degrees C below the growth temperature when the growth temperature is either 25 degrees C or 37 degrees C.

Gaucher's disease and pregnancy

Two patients with Gaucher's disease during pregnancy are reported. In one there were severe puerperal hemorrhagic complications attributable to thrombocytopenia secondary to infiltration of the reticuloendothelial system by Gaucher cells. The conclusion as reported in previous literature, which is reviewed, regarding the absence of hemorrhagic complications is disputed since on of the cases reported here showed that these may be severe and occur late in the puerperium.

Phase transitions of the purple membranes of Halobacterium halobium

Purple membranes of Halobacterium halobium were studied by differential scanning calorimetry. No transition was detected at temperatures below 70 degrees C. A small endothermic transition was seen at about 80 degrees C and a larger one at 100 degrees C. The larger transition is the irreversible denaturation of bacteriorhodopsin. The smaller transition is accompanied by a change in the visible absorption spectrum and is believed to be reversible, involving a cooperative change in crystalline structure of the membrane.

Studies of the lipid phase transitions of Escherichia coli by high sensitivity differential scanning calorimetry

High sensitivity adiabatic differential scanning calorimetry was performed on lipids, membrane vesicles, and whole cells of Escherichia coli enriched in particular unsaturated fatty acids by genetic means. Information concerning the shape of the transition is discussed. Transitions with an asymmetric shape reminiscient of a second order transition were observed. Comparison between the lipid transition observed in whole cells, membrane vesicles, and extracted lipids enriched in elaidate reveal some basic similarities. Studies of synthetic lipids were undertaken in an attempt to interpret the shapes of these transitions as a function of the lipid components of the membrane.

Oligopeptide transport in proline peptidase mutants of Salmonella typhimurium

Investigations of peptide transport in Salmonella typhimurium are presented. A strain designated proB25, a proline auxotroph, grew on a variety of di, tri-, and tetrapeptides containing proline. In contrast (Pro)6, peptides acylated on the NH2 terminus and Ala-Pro-D-Ala did not satisfy the nutritional requirement of proB25 for proline because they were not transported. A derivative of proB25, strain TN87, deficient in a proline aminopeptidase and an X-Pro dipeptidase, was able to utilize only four of 25 proline-containing peptides investigated. The inability of TN87 to grow on most of these peptides was due to the lack of the requisite peptidase activity. Evidence for a functional dipeptide transport system in this strain is indicated by growth on Pro-Leu and Pro-Ala, and by growth inhibition by certain X-Pro dipeptides. Leu-Pro, Val-Pro, Met-Pro, and Arg-Pro cause temporary growth inhibition of strain TN87 whereas Gly-Pro, Ala-Pro, and Pro-Pro have no effect on growth. Evidence for a functional oligopeptide transport system is indicated by growth on Pro-Val-Gly and Pro-Gly-Gly and by uptake of label from L-methionyl-L-methionyl-L-[14C]methionine and L-alanyl-L-prolyl-[14C]glycine. The presence of multiple oligopeptide transport systems for certain proline-containing peptides was demonstrated using triornithine-resistant mutants (oligopeptide permease deficient) and competition experiments. Finally L-Ala-L-Pro-[14C]Gly is shown to be transported intact into strain TN87.

A beta-coupled gauche kink description of the lipid bilayer phase transition

A statistical-mechanical model for a lipid bilayer was built around the assumption that beta-coupled gauche kinks are the only nonstraight hydrocarbon chain configurations allowed. Packing of these chains was considered and expressions for the energy and entropy are developed based on those considerations. A solution was obtained which was not exact but was still accurate enough to be useful. In addition, an intermolecular potential was formulated which includes the attractive and repulsive forces between the hydrocarbon chains, the polar group repulsions, and hydrophobic forces. Combining the solution to the kinking model and the intermolecular potential, we obtain the total free energy of the lipid bilayer, which exhibits a first-order phase transition at a characteristic temperature. The theoretical heat of transition indicates that kinks alone can provide enough disorder for the transition to occur. Other physical quantities can be calculated, including order parameters. The order parameters calculated here give a picture of chains which are rigid near the polar group and more fluid near the methyl group.

Production of ethylene by excised segments of plant tissue prior to the effect of wounding

A delay of 20 to 30 min precedes a rapid increase in the production of ethylene when segments are excised from the petioles of tomato plants. Measurements made during this early phase may be better estimates of production by petioles on the intact plant than those made at later times.

The terminal sequences of Bombyx mori 18S ribosomal RNA

The 5' and 3' terminal T1 oligonucleotides of 32p-labelled B. mori 18S ribosomal RNA were isolated by a two dimensional electrophoretic (diagonal) technique. Nucleotide sequence analysis showed that the 3' terminal fragment, (G)AUCAUUAOH, is identical to that previously obtained from the 18S rRNA of several other eukaryotic species. The sequence of the B. mori 5' terminal fragment is pUCCUCG.

The reaction of isocyanates with bisulphite salts

Aliphatic isocyanates react rapidly and quantitatively with aqueous bi- sulphite solutions to form stable water-soluble adducts which are salts of N-alkyl-carbamyl sulphonio acids. Phenyl isocyanate gives lower yields of the corresponding adduct which is less stable in water. The rate of reaction of n-butyl isocyanate with bisulphite increases with increasing pH and is proportional to [OH-]over the pH range from 5 to 8. The rate of decomposition of the butyl isocyanate-bisulphite adduct increases with increasing temperature and pH. A plot of the logarithm of the initial first-order rate constant for the decomposition of the adduct against pH is linear over the pH range from 2 to 7 and has a slope of 0.57 � 0.05. Water-insoluble polymers with aliphatic isocyanate groups do not form bisulphite adducts under the conditions which are suitable for simple isocyanates. However, the addition of water-soluble organic solvents such as dioxan and the lower alcohols enables the preparation of water-soluble bisulphite adducts which are indefinitely stable at room temperature and low pH. The relative quantity of the organic solvent must be kept within specific limits which depend on the nature of the prepolymer, the solids content of the final product, and the nature of the organic co-solvent.