Somatic embryogenesis and plant regeneration from zygotic embryo explants in mexican weeping bamboo,Otatea acuminata aztecorum

An efficient protocol has been developed for the in vitro propagation of Mexican Weeping Bamboo through somatic embryogenesis from zygotic embryo explants. Mature seeds and excised embryos were cultured in the light or in the dark on both Murashige and Skoog's and Gamborg's B5 basal media with various supplements. Optimal somatic embryogenesis and plant regeneration were obtained by culture in the dark on Murashige and Skoog's basal medium supplemented with 3 mg/1 2,4-dichlorophenoxyacetic acid, 0.5 mg/1 6-benzylaminopurine and 2.0% sucrose. More than 95% of the germinating somatic embryos developed shoots and roots, and were transferred to soil with 85% success.     

Behavioral,physiological, and morphological components of dominance and mate attraction in male green iguanas

This study investigated the morphological, physiological, and behavioral components of social dominance important for mate attraction in male green iguanas (Iguana iguana). A group of 9 male and 11 female adult green iguanas was studied in a large semi-natural enclosure during one reproductive season (October–January). Four of the nine males never initiated aggressive encounters; the other five were observed to display aggressively toward each other and were ranked in a linear dominance hierarchy. Head size was the most important factor influencing fighting success. Head size and display frequency were positively correlated with plasma testosterone levels. Dominance rank directly influenced ability to monopolize areas containing resources used by females. The quality of a male's home range, measured as his access to a large basking rock in the enclosure, was related to the proportion of potential mates found within his home range. One male greatly surpassed the others in his ability to defend a home range of high quality and attract potential mates. These data suggest that physiological and morphological factors, through their influence on social behavior, may ultimately affect male reproductive fitness. © 1992 Wiley-Liss, Inc.     

Characterization of endogenous and recombinant proviral elements of a highly tumorigenic AKR cell line

As an approach to evaluating the contribution of classes of endogenous viral sequences to leukemogenesis, a genomic library was prepared from the highly tumorigenic AKR SL12.3 cell line and screened for env-containing proviruses. An extensive battery of virus-derived probes and specific oligonucleotide probes were used to segregate 83 positive clones into related groups. The nonecotropic endogenous retroviruses were identified as members of the polytropic, modified polytropic, or xenotropic groups. At least three unique xenotropic proviruses were detected that differed from the published xenotropic sequence within a variable region of the 5' portion of env. Changes among the xenotropic proviruses included relative insertions and/or deletions that maintain an open reading frame and hence the potential to encode viable envelope gene products. Several recombinant viruses were also detected. Recombination was not random and primarily involved the formation of mink cell focus-inducing class I retroviruses via recombination between polytropic elements and ecotropic virus. One other recombinant was detected which contained ecotropic virus sequences in the 5' region encoding p15 of an otherwise xenotropic provirus. An interesting observation was the finding that certain clones contained more than one provirus within the average 20-kb cloned insert. This would not be expected if integration were totally random. The de novo recombinant proviruses identified here provide a series of potential candidates to be evaluated for their contribution to the tumorigencity of the SL12.3 cell line.     

Effect of straw on the behaviour of growing pigs

The effects of straw on the behaviour of young growing pigs were studied in two experiments. In Experiment 1, groups of three pigs, aged about 7 weeks, were housed in raised decks with or without straw bedding. Time-lapse video recording showed no major differences between treatments in the amount or daily pattern of overall activity and feeding. Detailed observations showed that bedding reduced the incidence of rooting and chewing on pen-mates, but had little effect on other social activities such as mounting and aggressive biting. Experiment 2 compared groups of eight growing pigs aged about 10 weeks, housed in floor pens with or without a small amount of straw provided daily in a rack. Pigs with straw concentrated more of their daily activity into the period when straw was fresh, but the total amount of overall activity and time spent feeding were not affected. Rooting and chewing of pen-mates were the only social activities reduced by the provision of fresh straw. In these studies, where straw was not required to compensate for deficiencies such as low temperatures or hunger, the one major function of straw was to provide a stimulus and outlet for rooting and chewing, with a resulting reduction in such activities directed at pen-mates.     

Cloning and sequencing of a gene encoding an aminoglycoside 6'-N-acetyltransferase from an R factor of Citrobacter diversus.

The aacA1 gene, which encodes a 6'-N-acetyltransferase [AAC(6')-I] mediating resistance to kanamycin, tobramycin, and amikacin, was cloned from the Citrobacter diversus R plasmid pBWH100 into the Escherichia coli vector pBR322. The complete nucleotide sequence of the gene and flanking regions was determined. A protein of approximately 21 kilodaltons was identified when the chimeric plasmid encoding the aacA1 gene was introduced into E. coli maxicells. This value is consistent with the size predicted for a protein translated from the open reading frame of the gene.     

Influence of molecular packing and phospholipid type on rates of cholesterol exchange

The rates of [14C]cholesterol transfer from small unilamellar vesicles containing cholesterol dissolved in bilayers of different phospholipids have been determined to examine the influence of phospholipid-cholesterol interactions on the rate of cholesterol desorption from the lipid-water interface. The phospholipids included unsaturated phosphatidylcholines (PC's) (egg PC, dioleoyl-PC, and soybean PC), saturated PC (dimyristoyl-PC and dipalmitoyl-PC), and sphingomyelins (SM's) (egg SM, bovine brain SM, and N-palmitoyl-SM). At 37 degrees C, for vesicles containing 10 mol% cholesterol, the half-times for exchange are about 1, 13, and 80 h, respectively, for unsaturated PC, saturated PC, and SM. In order to probe how differences in molecular packing in the bilayers cause the rate constants for cholesterol desorption to be in the order unsaturated PC greater than saturated PC greater than SM, nuclear magnetic resonance (NMR) and monolayer methods were used to evaluate the cholesterol physical state and interactions with phospholipid. The NMR relaxation parameters for [4-13C]cholesterol reveal no differences in molecular dynamics in the above bilayers. Surface pressure (pi)-molecular area isotherms for mixed monolayers of cholesterol and the above phospholipids reveal that SM lateral packing density is greater than that of the PC with the same acyl chain saturation and length (e.g., at pi = 5 mN/m, where both monolayers are in the same physical state, dipalmitoyl-PC and palmitoyl-SM occupy 87 and 81 A2/molecule, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of the structure of the lipid-water interface on the activity of hepatic lipase

Factors affecting the hydrolytic activity of purified rat hepatic lipase have been examined in mixed-monolayer systems. When nonsubstrate lipids [either egg sphingomyelin or beta-O-hexadecyl-gamma-O-(1-ocadec-9-enyl)-DL-phosphatidylcholine (OPPC-ether)] were used as inert matrices, hydrolytic activity for both triolein and dioleoylphosphatidylethanolamine was shown to decrease with increasing surface pressure (pi); negligible activity occurred at pi greater than or equal to 30 mN/m. Examination of the effect of introduction of cholesterol into either matrix containing 2 mol % triolein indicated that the mean molecular area decreased with increasing cholesterol and that, at pi = 24 mN/m, triolein was fully miscible in the sphingomyelin matrix at cholesterol concentrations less than or equal to 32.5 mol % and in the OPPC-ether matrix at cholesterol concentrations less than or equal to 49 mol %. Above these critical concentrations of cholesterol, the phase diagrams indicate transitions that suggest that triolein is forced out of the monolayer. Introduction of increasing amounts of cholesterol into either inert matrix increased the rate of hydrolysis of triolein by hepatic lipase, although by different degrees. There are at least two factors contributing to these effects: (1) condensation of the monolayer by cholesterol, thus increasing the total surface concentration of triolein at pi = 24 mN/m in the constant area surface balance, and (2) some change in triolein conformation and/or accessibility since at identical surface concentrations of triolein (8.7 +/- 0.1 pmol/cm2) and pi (24 mN/m) the rate of hydrolysis of triolein by hepatic lipase is 1.5-fold higher in the OPPC-ether matrix than in the egg sphingomyelin matrix.(ABSTRACT TRUNCATED AT 250 WORDS)