Ethylene effects on cambial activity and cell wall formation in hypocotyls of Picea abies seedlings

Ethylene regulation of cell division in the vascular cambium and cell wall formation was studied in hypocotyls of Norway spruce ( Picea abies [L.] Karst.) seedlings. Cuttings from 6-week-old seedlings were placed in water culture to which compounds affecting the synthesis and action of ethylene were added. After a 3-week treatment period, growth, ethylene production, morphology and cell wall composition of the hypocotyls were determined. Addition of high concentrations of the potent ethylene releasing agent 2-chloroethylphosphonic acid (ethrel), which increased ethylene emission by more than twice compared to control plants, inhibited the expansion of xylem cells while stimulating the incorporation of cell wall material, especially cellulose. Addition of small amounts of ethrel, which slightly stimulated ethylene emission, led to increases in the size of xylem cells, the amount of phloem tissue and the number of intercellular spaces in the cortex, and thus to increased hypocotyl diameter. However, no significant change in cell wall composition was detected. When ethylene production was decreased by adding Co²⁺ to the nutrient solution, differentiation of new xylem was disturbed, but the rate of cell division was not affected. Although the incorporation of cell wall material was inhibited, the proportions of lignin and cellulose in the wall appeared to remain unchanged. Silver ions stimulated the expansion of both xylem and cortex cells, but had no significant effect on cell wall formation. We conclude that ethylene has a role in regulating the incorporation of wall carbohydrates.     

Effect of microspore stage and media on anther culture of peanut (Arachis hypogaea L.)

This study was designed to study the effects of stage of microspore development and culture medium on androgenic response in peanut (Arachis hypogaea L.). Anthers of various developmental stages were cultured for 7 days, then fixed and observed cytologically. Three sets of media, involving different basal media, growth regulators, sucrose levels and glutamine concentrations, were tested. In all experiments, the stage of development of the microspores at the time of culture was highly significant. The early uninucleate microspores stage was identified as producing the highest anther response rating. The effect of media was nonsignificant in all experiments. However, the stepwise modification of the media through the course of the study resulted in an almost 8 x increase in anther response rating. Numerically, the best media tested was N₆ basal medium with 1 mg 1^-1 NAA, 0.1 mg 1^-1 BA, 5.5% sucrose, and 3.5 g 1^-1 glutamine. While no haploids were obtained, four-nucleate cells were observed, indicating the potential in peanuts for an androgenic reponse.     

-alkoxyphenol leukotriene B4 receptor antagonists

A series of -alkoxyphenols containing a tetrazole acid sidechain have been prepared as antagonists of leukotriene B₄ receptors. These compounds were tested as receptor antagonists of human neutrophil and guinea pig lung membrane leukotriene B₄ receptors. Compounds in this series were found to be up to 18-fold more potent than LY255283. These results indicate that the acyl group of the 1,2,4,5 substituted hydroxyacetophenone class of LTB₄ antagonists is not critical to antagonist potency.     

Receptor sites for amino acids in the facial taste system of the channel catfish

1. Receptor sites for different amino acids in the facial taste system of the channel catfish, Ictalurus punctatus, were determined from in vivo electrophysiological cross-adaptation experiments. 2. Relatively independent receptor sites were indicated for L-proline, D-proline, D-arginine, L-histidine and L-lysine, as well as those previously reported for L-alanine, L-arginine and D-alanine. 3. The functional isolation of two nerve twigs that were more responsive to D-alanine than to L-alanine or to other test stimuli provided further evidence for the existence of D-alanine sites that are independent from those to L-alanine. 4. Under all cross-adaptation regimes, the taste responses to the majority of test stimuli were reduced. Various possible mechanisms accounting for this generalized reduction in action potential activity during adaptation are discussed.     

Cofactor interactions and the regulation of glutamate decarboxylase activity

More than 50% of glutamate decarboxylase (GAD) in brain is present as apoenzyme. Recent work has opened the possibility that apoGAD can be studied in brain by labeling with radioactive cofactor. Such studies would be aided by a compound that inhibits specific binding. One possibility is 4-deoxy-pyridoxine 5-phosphate, a close structural analog of the cofactor pyridoxal 5-phosphate. The effects of deoxypyridoxine-P on the cyclic series of reactions that interconverts apo- and holoGAD was investigated and found to be consistent with simple competitive inhibition of the activation of apoGAD by pyridoxal-P. As expected from the cycle GAD was inactivated when incubated with glutamate and deoxypyridoxine-P even though cofactor was present, but no inactivation was observed with deoxypyridoxine-P in the absence of glutamate. Deoxypyridoxine-P also stabilized apoGAD against heat denaturation. These effects were quantitatively accounted for by a kinetic model of the apo-holoGAD cycle. Deoxypyridoxine-P inhibited the labeling by [³²P]pyridoxal-P of GAD isolated from rat brain. Hippocampal extracts were labeled with [³²P]pyridoxal-P and analyzed by SDS-polyacrylamide gel electrophoresis. Remarkably few bands were strongly labeled. The major labeled band (at 63 kDa) corresponded to one of the forms of GAD. Other strongly-labeled bands were observed at 65 kDa (corresponding to the higher molecular weight form of GAD) and at 69–72 kDa. Labeling of the 63- and 65-kDa bands was inhibited by deoxypyridoxine-P, but the 69–72 kDa bands were unaffected, suggesting that the latter were non-specifically labeled. The results suggest that the 63-kDa form of GAD makes up the majority of apoGAD in hippocampus.Special issue dedicated to Dr. Eugene Roberts.     

A new species of solanum section geminata (Solanaceae) from western Mexico

Solanum malacothrix S. Knapp is described from the slopes of the Sierra Madre del Sur in the Río Balsas drainage in the state of Guerrero. It is apparently rare, and has been collected only twice. Its relationship to other species in Mexico and northern South America is discussed.     

Milligram to gram scale purification and characterization of dextransucrase from Leuconostoc mesenteroides NRRL B-512F

A sequence of dextranase treatment, DEAE-cellulose chromatography, affinity chromatography on Sephadex G-200, and chromatography on DEAE-Trisacryl M has been optimized to give a dextransucrase preparation with low carbohydrate content (1-100 micrograms/mg protein) and high specific activity (90-170 U/mg protein) relative to previous procedures, in 30-50% yield. Levansucrase was absent after DEAE-cellulose chromatography, and dextranase was undetectable after Sephadex G-200 chromatography. The method could be scaled up to produce gram quantities of purified enzyme. The purified dextransucrase had a pH optimum of 5.0-5.5, a Km of 12-16 mM, and produced the same lightly branched dextran as before purification. The purified enzyme was not activated by added dextran, but the rate of dextran synthesis increased abruptly during dextran synthesis at a dextran concentration of approximately 0.1 mg/mL. The enzyme had two major forms, of molecular weight 177,000 and 158,000. The 177,000 form predominated in fresh preparations of culture supernatant or purified enzyme, whereas the amount of the 158,000 form increased at the expense of the 177,000 form during storage of either preparation.     

Effect of an abiotic disturbance on a lotic predator-prey interaction

Summary A model derived from marine research, and recently applied to stream communities, suggests that community structure is more likely to be influenced by predators in benign versus harsh abiotic regimes. Experiments were conducted to determine if increasing the harshness of a particular regime would alter the impact of a stream invertebrate predator on prey densities in field enclosures. Density of a stonefly predator, Kogotus nonus, was varied in containers exposed to low (benign) and high (harsh) levels of fine sediment. As predicted by the model, the harsher regime eliminated predator effects in two of three experiments. In the third experiment, however, high levels of sediment actually enhanced the impact of the predator on the prey community. A consideration of the possible mechanisms underlying this model led to the conclusion that increasing the harshness of a regime can be expected to produce outcomes ranging from elimination to enhancement of predator effects, depending on how the regime is perceived by the predator versus the prey.     

Laboratory studies on salmonella-contaminated cheese involved in a major outbreak of gastroenteritis

Dried biomass of Streptomyces cyaneus NCIB 9616 harvested at 1, 3, 7, 10 and 14 d from a liquid culture was degraded by alkaline methanolysis and the fatty acid methyl esters released examined quantitatively by gas chromatography. Isoprenoid quinones were extracted with petroleum ether and methanolic saline, purified by thin-layer chromatography and quantified by high performance liquid chromatography. Data for each component were plotted against time. The results showed that at the beginning of logarithmic growth there was a small quantitative shift in the fatty acid composition but, the fatty acid profiles remained relatively constant during both the logarithmic and stationary phases of growth. In contrast, the isoprenoid quinone composition depended markedly on the stage of growth. These results indicate that valid comparison of isoprenoid quinone profiles requires that sampling take place at defined stages of the growth cycle.     

Steady state terrestrial ecosystems and the global carbon cycle

The assumption that landscapes dominated by mature vegetation are presently in carbon steady state with the atmosphere is challenged. Evidence suggests that the vegetation and soils of these landscapes are frequently disturbed and over short time periods (<300 yr) slowly sequester atmospheric carbon. The critical consideration in this argument is the time interval used to evaluate a steady state. Current models of carbon flux through the terrestrial biota limit their time considerations to 120 yr, a short and inadequate time interval for realistic assumptions about steady state in the carbon cycle of vegetation.Research performed under subcontract 19B-07762C with S. Brown and 19X-43326C with the Center for Energy and Environment Research of the University of Puerto Rico (A. E. Lugo) under Martin Marietta Energy Systems, Inc., contract DE-AC05-840R21400 with the U.S. Department of Energy.