The effect of established plants on recruitment in the annual forb Sinapis arvensis

Summary The germination response of Sinapis arvensis to the presence of established plants was investigated in a greenhouse experiment. Established conspecific and heterospecific plants were found to inhibit germination and reduce the probability of recruitment of those seeds that germinate. Established plants have no effect on seed mortality in the soil. Using a simple recruitment model, it is demonstrated that the combination of variance in germination time coupled with the interaction between buried seeds and established plants can generate density dependence. The implications of these results for community processes, such as succession, are discussed.     

Association of polymorphisms in the HLA-B region with extended haplotypes

Genomic probes from the HLA-B region of the major histocompatibility complex (MHC) were used to study the association of restriction fragment length polymorphisms (RFLPs) with various MHC alleles, complotypes, and extended haplotypes. The two DNA probes, M20A and R5A, were derived from previously cloned cosmids and are located 38 and 110 kilobases (kb) centromeric to HLa-B, respectively. Five different RFLP variants occuring in five different haplotypic combinations were detected within a panel of 40 homozygous-typing cells and cells from 21 families using Bst EII. In two informative families with HLA-B/DR recombinations the inheritance of the RFLP variants was consistent with their mapping between HLA-B and complotypes. The R5A/M20A haplotypic pattern 6.5 kb/3.0 kb (A) had a normal Caucasian frequency of approximately 0.43 and was found in all independent examples of the extended haplotypes [HLA-B8,SC01,DR3], [HLA-B18,F1C30, DR3], [HLa-Bw62,SC33,Dr4], [HLa-B44,SC30,Dr4], and [HLA-Bw47,FC91,0DR7]. The patterns of 6.9 kb/ 3.0 kb (B), 6.5 kb/4.7 kb (C), 1.45 kb/3.0 kb (D), and 6.9 kb/4.7 kb (E) had normal Caucasian frequencies of approximately 0.23, 0.15, 0.15, and 0.04 and were found on all independent examples of [HLA-B38,SC21, DR4], [HLA-Bw57,SC61,DR7], [HLA-B7,SC31,DR2], and [HLA-B44,FC31,DR7], respectively. Individual complotypes or HLA-B alleles which were markers of extended haplotypes showed variable associations. For example, HLA-B7 and the complotype SC31 were associated with all R5A/M20A RFLP haplotypes except haplotype E, although [HLA-B7,SC31,DR7] was associated exclusively with haplotype D. HLA-B27, not known to be part of an extended haplotype, was suprisingly exclusively associated with the 6.5 kb/4.7 kb or C haplotypic pattern in all five instances tested. These findings support the concept of regional conservation of DNA on independent examples of extended haplotypes. The results also further characterize these haplotypes.     

The root-knot nematode resistance gene (Mi) in tomato: construction of a molecular linkage map and identification of dominant cDNA markers in resistant genotypes

A dominant allele at the Mi locus on chromosome 6 of tomato (Lycopersicon esculentum Mill) confers resistance to three species of root-knot nematodes (Meloidogyne). The resistance, which is associated with a localized necrotic response, was originally introduced into tomato from the wild species Lycopersicon peruvianum. As a step towards the molecular cloning of Mi, we have identified closely linked DNA markers from both cDNA and genomic DNA libraries as restriction fragment length polymorphisms (RFLPs). DNA from tomato populations segregating for nematode resistance was analyzed to generate a high-resolution genetic map of this region. Additional information on gene order was obtained by comparing the size of the introgressed L. peruvianum chromosomal segment within a collection of nematode-resistant tomato lines. Among the four cDNA markers that are tightly linked to Mi, three are dominant, i.e. L. peruvianum-specific. One cDNA marker corresponds to a gene family comprising 20-30 members, one of which is diagnostic for all nematode-resistant genotypes tested. The presence of non-homologous sequences around the Mi gene may contribute to the suppression of recombination in this region of the genome in crosses heterozygous for Mi. The potential of 'walking' from closely linked markers to Mi is discussed.     

Activation of the inositol trisphosphate second messenger system by cAMP in a mouse fibroblast cell line

Intracellular Ca²⁺ mobilization events were assessed in mouse L cells, which contain native prostaglandin E₁ receptors and transfected human ₂ adrenergic receptors. Both Fura2 (single cell measurements) and Quin 2, (cuvette assays) were used to determine [Ca²⁺]_i levels. Our results demonstrate that in the transfected cells there is a dose-dependent increase in [Ca²⁺]_i in response to isoproterenol (0.1 nM–100 nM), which is inhibited by the -adrenergic antagonist, propranolol, and is a result of intracellular Ca²⁺ release. [Ca²⁺]₁ in these cells was also increased by prostaglandin E₁, 8 bromo cyclic AMP, and aluminum fluoride. Both 8 bromo cAMP and isoproterenol induced a rapid increase in the levels of IP₁, IP₂, and IP₃. The data presented demonstrate that the elevation of intracellular cyclic AMP induces an increase in IP₃ production which leads to an elevation in [Ca²⁺];. We propose that this cyclic AMP dependent activation of the IP₃ generating system occurs at a post-receptor site.Abbreviations cAMP Adenosine Cyclic 3-5-Monophosphate - [Ca²⁺]_i intracellular [Ca²⁺]_i - 8 Br cAMP 8 Bromo Adenosine Cyclic 3-5-Monophosphate - DAG Diacylglycerol - EGTA] [Ethylene Bis (oxyethylenenitrilo)] Tetracetic acid - BSA Bovine Serum Albumin - HBSS-H Hanks' Balanced Salt Solution buffered with HEPES to pH 7.4 - HEPES 4-(2-Hydroxyethyl)-1-piperazineethanesulfonic acid - PIP₂ Phosphatidylinositol 4,5-bisphosphate - IP₂ Inositol 4 Phosphate - IP₂ Inositol 4,5 Bisphosphate - IP₃ Inositol Trisphosphate - PGE₁ Prostaglandin E₁ - PBS Phosphate Buffered Saline Solution     

Aerial Dispersal and Epiphytic Survival of Pseudomonas syringae during a Pretest for the Release of Genetically Engineered Strains into the Environment

Prospective experimental field evaluation of genetically engineered microorganisms, such as microbial pest control agents, raises issues of how to properly ascertain their fate and survival in the environment. Field trials with recombinant organisms must reflect requirements for sampling and monitoring. Field trials were conducted at Tulelake, Calif., to monitor the numbers of viable cells of a nonrecombinant strain of Pseudomonas syringae that entered the atmosphere and landed on plants and soil during and after an aerosol spray application. An exponential decrease in numbers of viable cells deposited at increasing distances from three sprayed plots was observed. The relative rate of survival of cells sprayed directly on plants was more than 10 times higher than that of cells dispersed through the air to similar adjacent plants. Results are being used to gain experience with the characteristics of a release site that influence containment or dispersal and to develop appropriate sampling methodologies for evaluating survival and dispersal characteristics of genetically engineered bacteria released into the environment. The ability to make predictions about microbial dispersal and survival will reduce the uncertainties associated with environmental releases of recombinant organisms.     

Gibberellins in immature seeds and dark-grown shoots of Pisum sativum

Gibberellins (GAs) A₁₇, A₁₉, A₂₀, A₂₉, A₄₄, 2OH-GA₄₄ (tentative) and GA₂₉-catabolite were identified in 21-day-old seeds of Pisum sativum cv. Alaska (tall). These GAs are qualitatively similar to those in the dwarf cultivar Progress No. 9 with the exception of GA₁₉ which does not accumulate in Progress seeds. There was no evidence for the presence of 3-hydroxylated GAs in 21 day-old Alaska seeds. Dark-grown shoots of the cultivar Alaska contein GA₁, GA₈, GA₂₀, GA₂₉, GA₈-catabolite and GA₂₉-catabolite. Dark-grown shoots of the cultivar Progress No.9 contain GA₈, GA₂₀, GA₂₉ and GA₂₉-catabolite, and the presence of GA₁ was strongly indicated. Quantitation using GAs labelled with stable isotope showed the level of GA₁ in dark-grown shoots of the two cultivars to be almost identical, whilst the levels of GA₂₀, GA₂₉ and GA₂₉-catabolite were significantly lower in Alaska than in Progress No. 9. The levels of these GAs in dark-grown shoots were 10²- to 10³-fold less than the levels in developing seeds. The 2-epimer of GA₂₉ is present in dark-grown-shoot extracts of both cultivars and is not thought to be an artefact.Abbreviations cv cultivar - GA_n gibberellin A_n - GC gas chromatography - GC-MS combined gas chromatographymass spectrometry - HPLC high-pressure liquid chromatography - KRI Kovats retention index - MeTMSi methyl ester trimethylsilyl ether     

Lack of correlation between differentiation status and response to radiation of three murine squamous cell carcinomas

Summary The gross growth rate, histology, cellular kinetics, andin situ radiobiological response have been measured for three murine, keratinising squamous cell carcinomas that differed in their degree of differentiation. Growth rate was fastest in the least-differentiated tumour, slowest in the best-differentiated. However, the kinetics of the compartment of undifferentiated cells that are likely to be radiotherapeutically important, were the same for the three lines. There was no correlation between degree of differentiation and intrinsic or apparent radiosensitivity as measured by the growth delay assay. The radiobiologically best-oxygenated tumour was that which had the largest stromal component and this was not the best-differentiated tumour.     

Placental vascular responses to leukotriene receptor antagonist FPL 55712

We have previously shown that FPL 55712, a specific leukotriene receptor antagonist, potentiates estrogen induced uterine hyperemia in nonpregnant rabbits. We therefore chose to investigate the vascular responses of pregnant rabbits to leukotriene blockade. Nine unanesthetized animals carrying 46 viable fetuses were used in this study. Regional blood flows were measured by the radioactive microsphere technique. In 5 rabbits control blood flows were measured after vehicle administration and FPL 55712, 1 mg/kg bolus, followed by infusion of 100 ug/kg/min was given via the jugular vein. Regional blood flows were measured again after 10 minutes of infusion. The procedural order was reversed in the remaining 4 animals. Resistance was calculated as mean arterial pressure divided by total flow to an organ. FPL 55712 decreased the blood pressure from 83 ± 2 to 76 ± 3 mmHg (P<.001). Uterine resistance was not significantly changed (387 ± 44 to 362 ± 42 mmHg·ml⁻¹·min·gm), but renal resistance fell from 18.5 ± 1.1 to 15.1 ± 1.2 mmHg·ml⁻¹·min·gm (P<.01). FPL 55712 induced maternal placental vasodilatation with resistance decreasing from 291 ± 33 to 261 ± 31 mmHg·ml⁻¹·min·gm (P<.04). Vehicle administration did not cause dilation in any vascular bed. FPL 55712 appears to be a placental vasodilator whose action is most likely due to receptor blockade of the vasoconstrictive endogenous leukotrienes.     

Somatic embryogenesis and plant regeneration in Cichorium intybus L. (Witloof,Compositae)

Somatic embryogenesis of Cichorium intybus L. var. Carolus is induced using cubical pieces of mature tap roots with an intervening callus phase. A Murashige and Skoog's (MS) semi solid basal medium supplemented with 2,4-dichlorophenoxyacetic acid (0.02 or 0.2 mg/l) and benzylaminopurine (0.25 mg/l) and a liquid MS medium devoid of growth regulators are used respectively for induction of callus and somatic embryoids and for further development and germination. Regeneration from the nodular proembryonal stage to the full grown embryoids occurs following different morphological pathways depending on the physical and chemical environment of the culture. Further development of these embryos into plantlets and the possibilities of application of this technique in plantbreeding have been discussed.Abbreviations MS Murashige and Skoog medium - BAP benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid