Dark pretreatment improves adventitious shoot organogenesis from cotyledons of diploid watermelon

The influence of light incubation during embryo germination on shoot organogenesis from cotyledons of four diploid watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai cultivars was examined. Germinating embryos in darkness significantly improved the number of explants that produced harvestable shoots during the 6 week incubation period on shoot regeneration medium under a 16-h photoperiod. The percentage of explants with shoots more than doubled for `Crimson Sweet' and was about 1.5-fold greater for `Sweet Gem' and `Yellow Doll' when embryos were germinated in darkness. The percentage of explants with shoots was not significantly improved for `Minilee' by pretreating seedlings in darkness. This study demonstrates that optimal shoot regeneration can be obtained by germinating embryos in darkness before preparing cotyledon explants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Virus-specific glycoproteins associated with the nuclear fraction of herpes simplex virus type 1-infected cells.

Monospecific antisera to herpes simplex virus type 1 (HSV-1) glycoproteins gB, gC, and gD were used to identify the HSV-1-specific glycoproteins associated with the nuclear fraction as compared with those associated with cytoplasmic fraction, whole-cell lysates, and purified virions. The results indicate that a predominance of HSV glycoprotein precursors pgC(105), pgB(110), and pgD(52) is associated with the nuclear fraction. Treatment of the nuclear fraction with the enzyme endo-beta-N-acetylglucosaminidase H indicated that the lower-molecular-weight glycoproteins are sensitive to this endoglycosidase. These results suggest that in the nuclear fraction of HSV-1-infected cells virus-specific glycoproteins gB, gC, and gD are predominately in the high-mannose precursor form; however, detectable amounts of the fully glycosylated forms of gC and gD were also found.     

Identification of a glucocorticoid-induced nuclease in thymocytes. A potential "lysis gene" product

Glucocorticoids initiate a cytolytic process in lymphoid cells that is characteristic of programmed cell death. In vivo treatment of adrenalectomized rats with glucocorticoids results in the rapid degradation of the thymocyte genome at internucleosomal sites. This DNA degradation occurs prior to cell death, and considerable evidence indicates that this nucleolytic event is central to the initiation of lymphocytolysis. To further characterize this process, we have searched for the gene products in thymocytes which may be responsible for steroid-induced DNA degradation. Adrenalectomized rats were treated in vivo with dexamethasone or a vehicle control; nuclear thymocyte proteins were extracted with 0.6 M NaCl and analyzed for protein content or nuclease activity on sodium dodecyl sulfatepolyacrylamide gels containing calf thymus DNA. Glucocorticoid treatment resulted in the induction of two major protein families, a 30-32-kDa protein doublet and a series of 3-4 proteins of 12-19 kDa, both of which express prominent DNase activity. Induction of the lower molecular weight nucleases increased with time after steroid treatment and paralleled the time course of glucocorticoid-mediated DNA degradation. Nuclease induction was blocked by the glucocorticoid antagonist RU 486, indicating a steroid receptor-mediated process. When nuclei from glucocorticoid-resistant cells were incubated with nuclear extracts from glucocorticoid-treated rats, the DNA was cleaved at internucleosomal sites, whereas extracts from vehicle-treated animals were virtually inactive. Based on these findings we propose that glucocorticoids, acting via a receptor-mediated pathway, induce a nucleolytic "lysis gene" product(s) responsible for lymphocytolysis.     

Mammalian adipose tissue and muscle are major sources of lipid transfer protein mRNA

The plasma cholesteryl ester transfer protein (CETP) catalyzes the transfer of cholesteryl esters from high density lipoproteins (HDL) to triglyceride-rich lipoproteins and plays a major role in the catabolism of HDL. Lipoprotein lipase (LPL) is the rate-limiting enzyme for hydrolysis of circulating triglyceride and is involved in HDL formation. We show that tissues containing LPL are major sources of CETP mRNA in several mammalian species, including some with low cholesteryl ester transfer activity in plasma. In hamsters, adipose tissue and heart were found to be the richest sources of both CETP and LPL mRNA; in situ hybridization studies showed that the same cell types (i.e. adipocytes or myocytes) contained CETP and LPL mRNA in these tissues. Isolated adipocytes synthesized active CETP. Dietary studies revealed a complex pattern of response of CETP mRNA levels in different tissues, which showed partial similarity to the changes in LPL mRNA abundance. However, high cholesterol diets resulted in increased CETP mRNA abundance in adipose tissue, heart, and skeletal muscle, without equivalent changes in LPL mRNA. Plasma HDL cholesteryl ester levels showed strong inverse correlations with CETP mRNA abundance in adipose tissue. The results suggest a conserved function of CETP in adipose tissue and heart, such as a co-ordinate action with LPL to enhance HDL turnover. Although there is considerable overlap in the tissue- and cell-specific pattern of CETP and LPL gene expression, dietary studies revealed only limited parallelism in response at the mRNA level. The increase in CETP mRNA in peripheral tissues in response to increased dietary cholesterol suggests that local induction of CETP synthesis may help to recycle cholesterol deposited in these tissues during lipolysis of dietary lipoproteins.     

Studies on determining conformational order in n-alkanes and phospholipids from the 1130 cm−1 raman band

Conformational disorder in lipid bilayer systems is commonly measured with reference to the intensity of the 1130 cm^?1 Raman band. However, estimates of the concentration of gauche bonds may vary by a factor of six according to the model used to relate intensity and concentration. In an effort to narrow the wide range in these estimates, we have measured the intensity of the 1130 cm^?1 band of crystalline n-C₂₁H₄₄ in its orthorhombic and hexagonal phases. On transition to the hexagonal phase, the intensity of the 1130 cm^?1 band is much reduced. It is assumed that the observed intensity reduction results from the introduction of gauche bonds whose number can be independently estimated from other features in the Raman and infrared spectra. From these measurements we conclude that the intensity of the 1130 cm^?1 band is not linearly related to the concentration of gauche bonds and that a disproportionately large decrease in the 1130 cm^?1 band intensity results from the introduction of a low concentration of gauche bonds. Thus previous estimates of gauche bond concentrations based on the assumption of a linear relation have tended to greatly overestimate the gauche bond concentration. These results derived from experiment are in accord with those of Pink et al. (Pink, D.A., Green, T.J. and Chapman, D. (1980) Biochemistry 19, 349–356) derived from theory.     

Insertion of nonhomologous DNA into the yeast genome mediated by homologous recombination with a cotransforming plasmid

Bacterial plasmids containing no detectable homology with yeast DNA sequences were inserted into the yeast genome by cotransforming with a plasmid containing a yeast gene. Analysis of the yeast transformants confirmed that recombination events occurred between the prokaryotic sequences shared by the two plasmids and between the yeast sequences common to the cotransforming plasmid and to the genome. Multiple copies of the two plasmids, in both tandem and interspersed arrays, are inserted by this method. Populations of cells grown from individual transformants are heterogenous for the number of integrated sequences. The number of integrated bacterial sequences is greatly reduced after 100 generations of growth in the populations that initially contained large numbers of sequences, while it is stable in those populations that initially contained either a single or a small number of copies.     

Genetic studies in an exotic population of corn (Zea mays L.) grown under two plant densities

Summary Progenies of a Design II [Comstock and Robinson (1948)] using random S ₁ lines from an exotic population of corn (Zea mays L.) were evaluated in a randomized incomplete block design with two replications at two plant-population densities (1 7,222 plants/ha and 68,888 plants/ha) in 1970 and 1971, at Lincoln, Nebraska. Five traits were studied i.e. grain weight, number of ears, days to flower, plant height and ear height.Under both densities the estimates of additive genetic variance were much larger than those of dominance genetic variance for all traits. The ratio of dominance to additive genetic variance estimates was less than 0.5 suggesting that for the majority of loci controlling the traits, partial to complete dominance is likely.The estimates of additive genetic x year interaction variance were high and significantly different from zero under both densities, indicating that estimates of additive genetic variance in this population obtained from experiments conducted in only one year may be seriously biased. The estimates of dominance genetic x year interaction variance were not significant and most of them were negative.Under both densities high genetic inter-relationships were indicated between grain weight and number of ears, days to flower and plant height, days to flower and ear height, and plant height and ear height.Even though there was a large difference between the two densities used in the study, the differences between the estimates of genetic parameters were not significant in all cases.The sample size of S ₁ plants representing each S₀ parent in the crossing nursery used in the present study (11.75) caused a small upward bias in the estimates of additive genetic variance, but it caused an upward bias in the estimates of dominance genetic variance of 6–7% of the total genetic variance.It is suggested that a trait such as grain weight should be expressed on a unit area basis when genetic parameters (except for correlation and the ratio between two values) obtained from experiments with different plant-population densities are to be compared.Published as Paper Number 3542, Journal Series, Nebraska Agricultural Experimental Station. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph. D. degree.A. I. D. Participant.The work was supported in part by a grant from the Rockefeller Foundation.