ABA promotion of ethylene production in anther culture of Brussels sprouts (Brassica oleracea var. gemmifera) and its relevance to embryogenesis

Abscisic acid (ABA) inhibited embryogenesis in anther culture of Brussels sprouts. This was accompanied by enhanced ethylene production during the first half of the anther culture period followed by a reduction in ethylene during the latter half, when compared to anthers not treated with ABA. The enhancement of ethylene production by ABA 6 h and 48 h after the start of the culture period was counteracted by the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). Both AVG and the ethylene antagonist AgNO₃ removed much of the ABA inhibition of embryogenesis, suggesting that at least part of the ABA effect on embryo production is mediated through increased ethylene biosynthesis.
ABA promotion of ethylene production was reduced by high temperature: less ethylene evolved from ABA-treated anthers following a 24 h treatment at 35°C than from ABA-treated anthers incubated continuously at 25°C. A high temperature treatment such as this is invariably necessary for embryogenesis in Brussels sprouts anther culture.     

Diol sulfonamides: A potent and novel class of inhibitors of human renin

The syntheses and pharmacological activity of a series of diol sulfonamides which function as inhibitors of human renin are described. The most potent compound in this series, compound 20 (SQ 33,800), is a subnanomolar inhibitor of human renin (IC₅₀ = 0.35 × 10⁻⁹ M).     

Regulation of collagenase production by steroids in uterine smooth muscle cells: An enzymatic and immunologic study

An enzyme-linked immunosorbent assay (ELISA) has been developed for rat collagenase. The assay is capable of measuring the enzyme from a variety of rat cell sources at concentrations of 10–;50 ng/ml, approximately 500–;1,000-fold more sensitive than radiolabelled collagen fibril assay systems. The assay is specific to collagenase from the rat: enzymes from human, tadpole, mouse, and bacterial sources failed to cross-react significantly with rat enzyme. The assay is reproducible and accurate, and is capable of detecting enzyme in the presence of serum or tissue inhibitors. Using the ELISA, we have examined the effect of a variety of hormones on the production of collagenase by rat myometrial smooth muscle cells in culture. Of all the reproductive hormones examined, only progesterone and its synthetic derivative medroxyprogesterone acetate were capable of inhibiting the production of the enzyme by these cells. The maximally effective concentration of progesterone was 1 x 10^?6M, and that of medroxyprogesterone acetate was 1 x 10^?7M. The effect of the steroid was selective: no effect on cell proliferation or on general protein synthesis was observed. In addition to the progestational steroids, the glucocorticoids were also capable of inhibiting the production of collagenase by the cells at similar nominal concentrations. However, the myometrial cells were found actively to metabolize progesterone but not hydrocortisone in culture. Thus, the effective inhibitory concentration of progesterone was approximately ten-fold lower than that of hydrocortisone. The results of this study support the concept that progesterone plays a major role in preventing the production of collagenase in the rat uterus.     

Histories and Stories from Chiapas: Border Identities in Southern Mexico.

Histories and Stories from Chiapas: Border Identities in Southern Mexico. R. Aída Hernández Castillo. Texas: University of Texas Press, 2001. 317 pp.     

Adventitious regeneration of Juglans nigra L. (eastern black walnut)

Somatic embryos and adventitious shoots were initiated from immature cotyledons 10–14 weeks after anthesis. Maximum embryogenesis occurred 12 weeks after anthesis and maximum shoot organogenesis occurred 14 weeks after anthesis. The best treatment for induction of somatic embryos and adventitious shoots from immature cotyledon explants was on agar-solidified WPM supplemented with 0.1 M 2,4-D and 5.0 M TDZ and incubated in light for the first four weeks. Rooting of adventitious shoots was best if they were quickdipped in 2.5 mM IBA and 1.25 mM NAA in 1% dimethyl formamide and 3.9% ethanol (120 Wood's Rooting Compound: water, by volume). Plantlets from rooted adventitious shoots were acclimatized to the greenhouse.Abbreviations BA Benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - DKW Driver and Kuniyuki (1984) walnut medium - IBA indolebutyric acid - LP Long and Preece medium described herein - NAA naphthaleneacetic acid - PPF photosynthetic photon flux - TDZ thidiazuron - WPM Woody Plant Medium of Lloyd and McCown (1980)     

Isolation of a cDNA encoding a growth-arrest associated gene and characterization of its regulation

We are interested in understanding the molecular events associated with the growth-arrest of vascular SMCs. We constructed a subtracted cDNA library enriched in nucleotide sequences associated with quiescent SMCs. This library was screened with similarly subtracted ³²P-labeled cDNAs to identify growth-arrest associated cDNA clones. Characterization of 19 of these cDNA clones revealed that 9 hybridized to mRNAs that exhibited a 2–3 fold increase in growth-arrested SMCs. In addition, two other cDNAs hybridized to a 5 Kb mRNA that was elevated approximately 10-fold in high density growth-arrested SMCs. Genomic Southern blot hybridization and DNA sequencing analysis indicated that these cDNAs encoded the same gene (LG7) and that this gene may be a member of a multigene family or that it may contain a sequence shared by other unrelated genes. Augmented expression of LG7 was associated with both high cell density and serum deprivation induced growth-arrest. LG7 mRNA expression was down-regulated when SMCs were incubated with FBS or with reagents that arrest cells in early S-phase. Additional analysis with cell cycle specific inhibitors indicated that LG7 mRNA levels were also low when cells were blocked at the G₂ phase of the cell cycle but blockage at mitosis resulted in an elevated level of LG7 mRNA. We further demonstrated that the expression of LG7 was dependent on the presence of a relatively labile protein since protein synthesis inhibitors specifically blocked the expression of this mRNA but not the mRNA expression of α₁(III) collagen or ferritin H-chain. Finally, we demonstrated that Bt₂cAMP was able to induce mRNA expression of LG7 within 2 h, suggesting that this gene may be directly regulated via the cyclic-AMP-dependent protein kinase pathway.     

Reflective organelles in the anterior pigment epithelium of the iris of the European starling Sturnus vulgaris

The ultrastructure and chemical composition of reflective organelles in the anterior pigment epithelium of the iris of the European starling Sturnus vulgaris were examined. The reflective organelles produced a diffuse white reflectance at the iris mid-section which was visible only when the stroma was removed. The pigment granules were clear, angular, and birefringent under the light microscope. In electron micrographs the granules were irregular in shape and density, sometimes crystalline in appearance, but more often they were lost during sectioning or staining. Guanine was abundant in the modified pigment epithelium of the starling, but not in the pigment epithelia of other birds that lacked birefringent granules. Pteridines, such as xanthopterin and leucopterin, were present in small amounts. Pteridines were also present in the iris stroma which had no reflective organelles. The reflective organelles in the starling pigment epithelium resemble both the reflecting platelets of lower vertebrate chromatophores and the reflective granules in the tapeta of various vertebrates. Possible derivation of the organelles from these sources is discussed.