小兴凯湖的水生植被及其生态作用

本文论述了小兴凯湖水生植物的种类组成、植被类型、生物量及其在湖泊淤积和渔业中的作用。该湖属老年期湖泊,水生维管束植物共有25科56种,优势种为竹叶眼子菜、荇菜、芦、菰等。植被类型可划分为沉水植被、浮叶植被和挺水植被等三个亚型,包括12个主要植物群丛。全湖水生植物总生物量(湿重)为196380吨;以植物现存量计算,草食性鱼类的年生产力应为78.75吨。由于水生植物大量繁殖,为减缓湖泊的垫平作用,可适量放养草食性鱼类,控制住水生植物的过量繁殖;同时引种一些经济水生植物,压住水中杂草的生长。     

Decisionmaking competence and risk

Mark Wicclair criticizes Allen Buchanan's and my claim that determining an appropriate level of competence (Wicclair substitutes "decisional capacity" for "competence", the import of which I note briefly below) for health care treatment decisionmaking involves balancing respecting a patient's self-determination and protecting his or her well-being. The most important implication of this balancing is that a standard of competence should vary in significant part with the effects for the patient's well-being of accepting his or her choice. Wicclair's criticisms take two main forms. First, he considers and rejects four of the positive reasons we offer in support of a risk-related standard. Second, in rejecting our fourth reason he argues that a risk-related standard leads to faulty competence determinations -- too high a standard in some cases and too low a standard in others. If he is correct, there are no positive reasons for adopting a risk-related standard and there are as well specific reasons not to adopt such a standard in order to avoid mistaken competence determinations. My response will address both sorts of criticisms in turn.     

Immunocytochemical demonstration of tissue-type plasminogen activator in endocrine cells of the rat pituitary gland

We immunocytochemically stained rat pituitary glands using antibodies against plasminogen activators of the tissue type (t-PA) and the urokinase type (u-PA). A large population of endocrine cells in the anterior lobe of the gland displayed intense cytoplasmic immunoreactivity with anti-t-PA. In some areas of the intermediate lobe we found a weak staining, and we observed weakly staining granular structures in the posterior lobe. Controls included absorption of the antibodies with highly purified t-PA. In addition, SDS PAGE followed by immunoblotting of pituitary gland extracts revealed only one band with an electrophoretic mobility similar to that of t-PA when stained with anti-t-PA IgG. No u-PA immunoreactivity was detected in the rat pituitary gland. Sequential staining experiments using antibodies against growth hormone and t-PA demonstrated that the t-PA-immunoreactive cells constitute a large subpopulation of the growth hormone-containing cells. These findings represent the first direct evidence for the presence of t-PA in cell types other than endothelial cells in the intact normal organism. In this article we discuss the implications of the results for a possible role of t-PA in the posttranslational processing of prohormones.     

Photoacoustic and fluorescence measurements of the chilling response and their relationship to carbon dioxide uptake in tomato plants

The response of tomato plants to various chilling treatments was studied using two approaches for the measurement of photosynthetic activity. One involved the use of a portable fluorometer for the measurement of in-vivo chlorophyll fluorescence, while the other employed a newly introduced photoacoustic system which allowed changes in oxygen evolution to be followed in a leaf disc. A strong correlation was found between results obtained by each system and those obtained by a conventional open gas-exchange system for the determination of CO₂ uptake. Both systems of measurements could readily distinguish between the effects of chilling in the dark (at 3° C for 18 h) and chilling at high photon flux density (2000 mol m^-2 s^-1 for 5h at 5° C). Chilling in the dark had practically no effect on the quantum yield of oxygen evolution, chlorophyll fluorescence or CO₂ uptake, while chilling at excessively high photon flux density resulted in a sharp reduction (50–70%) in the quantum yields obtained. The results support the view that photosystem II cannot be the primary site of damage by chilling in the dark, although it is significantly affected by chilling at high light intensity.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PA photoacoustic - PFD photon flux density - PSII photosystem II     

The parasitoids of the aleyrodid Bemisia tabaci in Israel: development, host preference and discrimination of the aphelinid wasp Eretmocerus mundus

Developmental history and behavior of Eretmocerus mundus Mercet, a parasitoid of Bemisia tabaci was studied at 25°C. The eggs may be laid under all four nymphal instars but not under the pupa. Yet the second and third instars are preferred. The egg hatches only under the fourth instar or the pupa. Developmental medians at 25°C are: Instar I-2.5, II-4, II-4, prepupa-2 and pupa 8 days. When ovipositing, the female stands at an angle of 90° to the host, with wings raised and inserts the ovipositor under the whitefly nymph. The egg is laid close to the insertion point of the whitefly's proboscis into the leaf. After oviposition, the female apparently marks the host while drumming on it with her hind legs. She distinguishes already parasitized hosts from unparasitized ones and refrains from laying under the former. Discrimination is accomplished after antennal drumming only.

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Les parasitoïdes de Bemisia tabaci (aleyrodidae) en Israel: développement, ponte et sélection des hôtes ches Eretmocerus mundus (aphelinidae)

Résumé Le développment et le comportement de E. mundus, parasitoïde de B. tabaci, ont été étudiés à 25°C. Les oeufs sont pondus sous les quatre stades larvaires (les deuxième et troizième sont préférés) mais pas sous les nymphes. Les oeufs n'éclosent que sous les larves du quatrième stade ou les nymphes. Les temps de développement médiaux sont à 25°, les suivants: stade I: 2,5j; stade II: 4j; stade III: 4j et nymphe 8j. Pendant la ponte, la femelle est à 90° sur son hôte, les ailes dressées, et insère sa tarière sous la larve d'aleurode. L'oeuf est déposé près du point d'insertion de la trompe dans la feuille. Après l'émission, la femelle marque apparemment son hôte pendant qu'elle tambourine avec ses pattes postérieures. Elle distingue les hôtes parasités ou non, et limite sa ponte dans les premiers. La sélection est effectuée seulement après tambourinage antennaire.

     

Modes of endocytosis of latex particles in sinusoidal endothelial and Kupffer cells of normal and perfused rat liver

The endocytosis of latex particles (0.33, 0.46 and 0.80 micron in diameter) in the sinusoidal endothelial and Kupffer cells of the rat liver was studied electron microscopically. When the liver was perfused with serum-free oxygenated Krebs Ringer bicarbonate, latex particles of all three sizes were taken up by the endothelial cells. After a 10-min perfusion, particles were incorporated by the luminal cell surface of the perikarya or of the thick portion of the endothelial cells. A large patch of bristle coat was surrounding the ingested particle. The number of ingested particles in the endothelial cells, however, was much less than in the Kupffer cells. In in vivo experiments, no endocytosis of the latex particles was observed in the endothelial cells. In the Kupffer cells, particles were engulfed by the ruffled membranes or sank into the cytoplasm without a large patch of the bristle coat both in the perfusion system and in vivo. These observations show that at least 0.80 micron latex particles are taken up by the bristle-coated membranes in the sinusoidal endothelial cells of the perfused liver. The endocytic mechanism for latex particles in the endothelial cells is different from that of the Kupffer cells.     

Reversible addition of bisulfite buffer to the cytidine ring system

The rate constants for the reversible addition of protons and sulfite to the 5,6 double bond of cytidine and 3-methylcytidine have been spectrophotometrically measured under conditions (25°C, μ = 1.0 ) where the deamination of 5,6-dihydrocytidine-6-sulfonate is minimal. Both the addition and the elimination of sulfite from the ring system are subject to general catalysis of proton transfer. For the reaction in either direction, plots of the pseudo-firstorder rate constants against increasing buffer concentration are biphasic and indicative of at least a two-step reaction pathway with both steps being subject to general acid-base catalysis. Kinetic hydrogen-deuterium isotope effects were measured for both buffer-catalyzed steps of sulfite elimination from 3-methyl-5,6-dihydrocytidine-6-sulfonate and sulfite addition to 3-methylcytidine. Both H₂O and D₂O were used as solvent. For both the addition and the elimination of SO₃²⁻ values of k₂^H/k₂^D were 6.3–7.1 and 2.3–2.6 at low and high imidazole buffer concentration, respectively. The large isotope effects values in the range of 6–7 can be attributed to rate-determining proton transfer to carbon-5 of the cytidine ring system. The smaller values are more likely caused by proton transfer to a electronegative atom such as the oxygen on carbon-2 of the cytidine ring. The equilibrium constants for bisulfite buffer addition to 3-methylcytidine and cytidine at 25°C, μ = 1.0 , pH 7.2, are 10.2 and 1.3 ⁻¹, respectively.