Multiple origins of self-fertilization in tristylous Eichhornia paniculata (Pontederiaceae): Inferences from style morph and isozyme variation

Populations of Eichhornia paniculata (Pontederiaceae) exhibit a wide range of mating systems, from predominant outcrossing to high levels of self-fertilization. The origin of self-fertilization in this tristylous species is associated with the loss of style-length morphs from populations and the spread of self-pollinating, floral variants. We examined geographic variation in style morph and allozyme frequencies to determine whether the loss of style morphs and transition to selfing could have multiple origins in E. paniculata. Surveys of floral variation in 167 populations from six states in northeastern Brazil revealed that at least one style morph was absent from 29.3%. Non-trimorphic populations occurred in all states and ranged in frequency from 9% in Ceará to 68% in Alagoas. Selfing variants occurred in 8.5% and 55% of trimorphic and non-trimorphic populations, respectively, and were distributed among five of six states with primary concentrations in Alagoas and Pernambuco. A comparison of electrophoretic variation at 24 isozyme loci in 28 trimorphic, 13 dimorphic and 3 monomorphic populations indicated that non-trimorphic populations contained 84% of the allelic variation present in trimorphic populations and were markedly differentiated from one another. Analyses of genetic distance and the distribution of rare alleles indicated that non-trimorphic populations were often more similar to neighbouring trimorphic populations than to one another. Populations with selfing variants occurred at low frequency in three genetically distinct parts of the range. These results, in combination with genetic and morphological evidence suggest that style morphs are lost repeatedly from populations of E. paniculata and that selfing variants may have originated on at least three separate occasions in northeastern Brazil.     

The role of the neutrophil and formed elements of the blood in an in vitro model of reperfusion injury

Using The globally ischaemic isolated guinea-pig heart we conducted studies to assess the role of activated neutrophils (PMNs) and the role of the endothelium in reperfusion injury. Reperfusion injury was induced by a 20 min period of global ischaemia followed by a 30 min reperfusion with Krebs' buffer supplemented with f-Met-Leu-Phe (fMLP) and heparinized blood. Ischaemia alone or blood alone resulted in a complete recovery in contractile function measured by developed pressure, fMLP (500 muM) and blood, administered to normoxic hearts did not affect contractile function. The combination of 100 muM fMLP and blood beginning at reperfusion and continuing for 30 min decreased the recovery in contractile function (max. 33 +/- 6% reovery) while buffer and 100 pM fMLP resulted in a complete recovery in function. In hearts infused with buffer and neutropenic blood incubated with 100 muM fMLP a complete recovery in function was observed. Isolated peritoneal neutrophils, 7-70 x 10(5) PMN/ min, incubated with 100 muM fMLP and Krebs' solution decreased contractile function in a concentration-related manner (max. 44 +/- 11% recovery). Platelets, plasma or red blood cells alone incubated with fMLP did not decrease recovery in developed pressure. Platelets and PMN incubated with 100 muM fMLP did not, while red blood cells and PMN did, elicit a reduction in recovery in contractile function (34 +/- 4% recovery). A 20 min period of global ischaemia destroys the functional integrity of the endothelium (response to Ach). Pre-treatment of the heart with sufficient H(2)O(2) to functionally damage the endothelium, followed by infusion of Krebs' solution supplemented with blood and 100 muM fMLP also elicited a reduction in recovery of contractile function (42 +/- 15% recovery). In summary, partially activated neutrophils play a major role in reperfusion injury and there exists a cooperativity between the RBC and PMN in this model.     

Evolutionary breakdown of distyly to homostyly is accompanied by reductions of floral scent in Primula oreodoxa

Reproductive traits that function in pollinator attraction may be reduced or lost during evolutionary transitions from outcrossing to selfing. Although floral scent plays an important role in attracting pollinators in outcrossing species, few studies have investigated associations between floral scent variation and intraspecific mating system transitions. The breakdown of distyly to homostyly represents a classic example of a shift from outcrossing to selfing and provides an opportunity to test whether floral fragrances have become reduced and/or changed in composition with increased selfing. Here, we evaluate this hypothesis by quantifying floral volatiles using gas chromatography-mass spectrometry in two distylous and four homostylous populations of Primula oreodoxa Franchet, a perennial herb from SW China. Our analysis revealed significant variation of volatile organic compounds (VOCs) among populations of P. oreodoxa. Although there was no difference in VOCs between floral morphs in distylous populations as predicted, we detected a substantial reduction in VOC emissions and the average number of scent compounds in homostylous compared with distylous populations. A total of 12 compounds, mainly monoterpenoids and sesquiterpenoids, distinguished homostylous and distylous morphs; of these, (E)-β-ocimene was the most important in contributing to the difference in volatiles, with significantly lower emissions in homostyles. Our findings support the hypothesis that the transition from outcrossing to selfing is accompanied by the loss of floral volatiles. The modification to floral fragrances in P. oreodoxa associated with mating system change might occur because high selfing rates in homostylous populations result in relaxed selection for floral attractiveness.     

Mechanisms for species differences in receptor-mediated carcinogenesis

Species differences resulting from a number of mechanisms are common in receptor-mediated chemical carcinogenesis. In this review, examples of possible mechanisms underlying these differences are discussed, including ligand metabolism, receptor polymorphisms, receptor isoforms, receptor levels, and crosstalk between signal transduction pathways. In addition, a number of other mechanisms also are likely to be important. The developmental state of the animal will determine the expression of receptors in different tissues. The regulatory pathways for cell proliferation and cell death and cell cycle check point controls can vary among species and tissues. Adaptation or potentiation of responses during chronic exposures to chemicals can greatly influence species differences. The mechanisms of adaptive processes are poorly understood but probably highly important for chronic toxicities such as cancer. Finally, different species may have different stem cell populations that are the targets for neoplastic transformation, and this will influence receptor-mediated carcinogenic responses. The implications of species differences in receptor-mediated responses for risk assessment are discussed.     

Endocrine cells of the human gastrointestinal tract have no proliferative capacity

Summary There is compelling evidence that the epithelial cell lineages of the gastrointestinal tract are derived from a common stem cell precursor, but the details of the subsequent cellular hierarchies remain uncertain. In this context, it is important to know the arrangement of cell proliferation that gives rise to the final cell populations. In rodents, a number of studies have been performed examining the possible proliferative capacity of endocrine cells, but a wide range of technical problems makes interpretation of these data difficult. Continuous labelling studies suggest that there is potential for proliferation in endocrine cells but flash labelling studies have not been conclusive. In man there are no data on this issue. We have taken advantage of the ability to perform double immunostaining for operational markers of proliferation (Ki67 antigen) and endocrine cell phenotype (chromogranin expression). We demonstrate that there are no double-labelled cells in the normal stomach, small intestine or colon of fetal, neonatal or adult humans. Moreover, no double-labelled cells are found in pathological states associated with endocrine cell hyperplasia (gastritis, ulcerative colitis). These data indicate that the normal endocrine cells of the human gut have no proliferative capacity and that, in this cell lineage, population expansion precedes differentiation.     

Inhibition of cysteine proteinases and dipeptidyl peptidase I by egg-white cystatin.

The interactions between egg-white cystatin and the cysteine proteinases papain, human cathepsin B and bovine dipeptidyl peptidase I were studied. Cystatin was shown to be a competitive reversible inhibitor of cathepsin B (Ki 1.7 nM, k-1 about 2.3 X 10(-3) s-1). The inhibition of dipeptidyl peptidase I was shown to be reversible (Ki(app.) 0.22 nM, k-1 about 2.2 X 10(-3) s-1). Cystatin bound papain too tightly for Ki to be determined, but an upper limit of 5 pM was estimated. The association was a second-order process, with k+1 1.0 X 10(7) M-1 X s-1. Papain was shown to form equimolar complexes with cystatin. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of complexes formed between papain or cathepsin B and an excess of cystatin showed no peptide bond cleavage after incubation for 72 h. The reaction of the active-site thiol group of papain with 5,5'-dithiobis-(2-nitrobenzoic acid) at pH 8 and 2,2'-dithiobispyridine at pH 4 was blocked by complex-formation. Dipeptidyl peptidase I and papain were found to compete for binding to cystatin, contrary to a previous report. The two major isoelectric forms of cystatin were found to have similar specific inhibitory activities for papain, and similar affinities for papain, cathepsin B and dipeptidyl peptidase I. This, together with specific oxidation of the N-terminal serine residue with periodate, showed the N-terminal amino group of cystatin 1 to be unimportant for inhibition. General citraconylation of amino groups resulted in a large decrease in the affinity of cystatin for dipeptidyl peptidase I. It is concluded that the interaction of cystatin with cysteine proteinases has many characteristics similar to those of an inhibitor such as aprotinin with serine proteinases.     

Proteinase inhibitors of bovine nasal cartilage.

Extracts from bovine nasal cartilage with 1 M-guanidinium chloride were fractionated by ultrafiltration. Gel chromatography of the low-molecular-weight material resolved three distinct fractions with inhibitory activity against (a) collagenases (22000 mol.wt.), (b) thiol proteinases cathepsin B and papain (13000 mol.wt.), and (c) trypsin and other serine proteinases (7000 mol.wt.).     

Low velocity gradient flow birefringence and viscosity changes in hyaluronate solutions as a function of pH.

The flow birefringence and extinction angle over a velocity gradient range of approximately 5–100 sec^?1, and the zero shear-viscosity have been obtained from human umbilical cord hyaluronic acid at concentrations of 0.25, 0.125 and 0.0625%, and pHs 6.0, 6.5, 7.0, 7.5, 8.0, and 8.5 and constant ionic strength 0.1. The data indicate a large change in optical anisotropy as a function of pH, with most of the transition in the pH range 7.0–7.5, i.e., across the physiological range. The sign of the anisotropy changes between pH 8.0 and 8.5. These results, together with changes in the extinction angle and intrinsic viscosity as a function of pH, suggest a pH-dependent structural change in the system. Due to the abruptness of the transition, as evidenced by the intrinsic viscosity and flow birefringence, it is probable that the structural transition is cooperative. If the data are interpreted in terms of the Rouse-Zimm Gaussian subchain theory, a modification of the model in terms of the Haller-Cerf concept of internal viscosity is required. Thus, the demonstrated properties of hyaluronate solutions indicate a system with memory of stress. Due to the presence of large concentration effects discernible in the extinction angle measurements, hyaluronic acid probably exists as a network in solution. The results are discussed with respect to the mechanoelectrical transducing properties of hyaluronates and stress-dependent changes in ORD already reported.