On the nature of the photosynthetic energy storage monitored by photoacoustic spectroscopy

The photosynthetic energy storage yield of uncoupled thylakoid membranes was monitored by photoacoustic spectroscopy at various measuring beam intensities. The energy storage rate as evaluated by the half-saturation measuring beam intensity (i₅₀) was inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea, by heat inactivation or by artificial electron acceptors specific for photosystem I or photosystem II; and was activated by electron donors to photosystem I. The reactions involving both photosystems were all characterized by a similar maximal energy storage yield of 16±2 percent. The data could be interpreted if we assumed that the energy storage elicited by the photosystems at 35 Hz is detected at the level of the plastoquinone pool.Abbreviations PS photosystem - Tes N-Tris [hydroxymethl] methyl-2-aminoethanesulfonic acid - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCIP 2,6-dichlorophenolindophenol - FeCN potassium ferricyanide - DCBQ 2,5-dichlorobenzoquinone - TMPD N,N,N-tetramethyl-p-phenilenediamine     

Ultrastructural localization of fibronectin mRNA in chick embryo by in situ hybridization using 35S or biotin labeled cDNA probes

We have studied the expression of the fibronectin gene in 7 day-old chick embryo (stage 32) by in situ hybridization at the light and electron microscope levels, using a 397 base-pairs chicken cDNA, labeled by radioisotope or biotin-11dUTP. Cryostat sections of whole chick embryos displayed a selective label on the upper layer of the dermis, fibrous sclera and mesenchymal cells but not on cartilagenous sclera cells. These results show that the expression of the fibronectin gene varies in relation to the morphogenetic events. Hybridization at the ultrastructural level on thin sections of sclera embedded in Lowicryl K4M showed a selective labelling on various cell compartments. Biotin-11dUTP and radiolabeled probes were compared. The labeling was found precisely on the membrane of the rough endoplasmic reticulum and on the nuclear envelope. A few silver grains were located on the nucleus and in the perinucleolar region. This study shows that the postembedding in situ hybridization is a powerful procedure to study the expression of the extracellular protein genes and gives further information on the localization of mRNA.     

鸡胚肝乳糖凝集素专一性的研究——SEM-ARG技术的应用

本文利用扫描电镜放射自显影(SEM-ARG)技术研究鸡胚肝凝集素的专一性。该凝集素经乳糖尿素液抽提和离心分离后,再用DE-52纤维素柱和蓝色葡聚糖柱进一步纯化。纯化后的鸡胚肝凝集素用 ¹²⁵Ⅰ标记。以标记的 ¹²⁵Ⅰ-凝集素为探针再标记来自不同组织的细胞。标记的细胞经过放射自显影,用扫描电镜对细胞表面凝集素受体的位点进行直接观察。实验结果表明鸡胚肝凝集素对细胞的凝集作用具有相对的专一性。     

Effects of cesium on in vitro myoblast differentiation: An electron microscopic study

Summary This paper describes the microscopic evidence supporting a cesium-induced delay in the fusion of chick embryo myoblast membranes during in vitro myogenic differentiation. We have recently demonstrated that the sharp decrease in the conductivity and permittivity of the membranes of these myogenic cells at the time of fusion is delayed 30 h by the addition of cesium to the culture medium (Santini et al., Biochim. Biophys. Acta 945:56–64; 1988). We report here that this delay in fusion is substantiated by direct microscopic observation and that cesium also induces ultrastructural changes in the myoblast cells themselves. Possible mechanisms by which cesium may cause both the delay in fusion as well as the ultrastructural changes observed are discussed. This investigation was partially supported by an Italian Consiglio Nazionale delle Ricerche grant 85.00.304.02 (to P. L. I.).     

Free Radical Formation by Ultrasound in Aqueous Solutions. A Spin Trapping Study

Our recent spin trapping studies of free radical generation by ultrasound in aqueous solutions are reviewed. The very high temperatures and pressures induced by acoustic cavitation in collapsing gas bubbles in aqueous solutions exposed to ultrasound lead to the thermal dissociation of water vapor into H atoms and OH radicals. Their formation has been confirmed by spin trapping. Sonochemical reactions occur in the gas phase (pyrolysis reactions), in the gas-liquid interfacial region, and in the bulk of the solution (radiation-chemistry reactions). The high temperature gradients in the interfacial regions lead to pyrolysis products from non-volatile solutes present at sufficiently high concentrations. The sonochemically generated radicals from carboxylic acids, amino acids, dipeptides. sugars, pyrimidine bases. nucleosides and nucleo-tides were identified by spin trapping with the non-volatile spin trap 3.5-dibromo-2.6-dideuterio-4-nitrosobenzenesulfonate. At low concentrations of the non-volatile solutes. the spin-trapped radicals produced by sonolysis are due to H atom and OH radical reactions. At higher concentrations of these non-volatile solutes, sonolysis leads to the formation of additional radicals due to pyrolysis processes (typically methyl radicals). A preferred localization of non-volatile surfactants (compared to analogous non-surfactant solutes) was demonstrated by the detection of pyrolysis radicals at 500-fold lower concentrations. Pyrolysis radicals were also found in the sonolysis of aqueous solutions containing only certain nitrone spin traps. The more hydrophobic the spin trap, the lower the concentration at which the pyrolysis radicals can be observed. The effect of varying the temperature of collapsing transient cavities in aqueous solutions of different rare gases and of N₂O on radical yields and on cell lysis of mammalian cells was investigated.     

Radical Cations in Aromatic Hydrocarbon Carcinogenesis

Most carcinogens, including polycyclic aromatic hydrocarbons (PAH), require metabolic activation to produce the ultimate electrophilic species that bind covalently with cellular macromolecules to trigger the cancer process. Metabolic activation of PAH can be understood in terms of two main pathways: one-electron oxidation to yield reactive intermediate radical cations and monooxygenation to produce bay-region diol epoxides. The reason we have postulated that one-electron oxidation plays an important role in the activation of PAH derives from certain common characteristics of the radical cation chemistry of the most potent carcinogenic PAH. Two main features common to these PAH are: 1) a relatively low ionization potential, which allows easy metabolic removal of one electron, and 2) charge localization in the PAH radical cation that renders this intermediate specifically and efficiently reactive toward nucleophiles. Equally important, cytochrome P-450 and mammalian peroxidases catalyze one-electron oxidation. This mechanism plays a role in the binding of PAH to DNA. Chemical, biochemical and biological evidence will be presented supporting the important role of one-electron oxidation in the activation of PAH leading to initiation of cancer.     

Two-compartment model for rabbit skin organ culture

Summary A new method was developed for rabbit skin organ culture. In a two-compartment model, skin discs were cultured on a Millicell-HA insert unit with a microporous membrane which allows transport of culture medium via the dermis into the epidermis, whereas the epidermal side remains free of direct contact with culture medium. In this relatively simple two-compartment organ culture model, rabbit skin could be cultured for 7 d in RPMI 1640 medium supplemented with fetal bovine serum, or for 2 d in RPMI 1640 medium supplemented with cofactors. The histomorphology and ultrastructure of 7-d cultured rabbit skin discs was essentially similar to that of freshly isolated rabbit skin. Keratinocytes in the stratum basale continued to divide during organ culture. The terminal differentiation of the epidermis continued in vitro as was found by the presence of keratohyalin granules, the intact stratum corneum, and keratin expression. Furthermore, glucose consumption continued until culture Day 7, but thereafter it declined rapidly. Concomitantly, degenerative changes were found. At the end of the 7-d culture period the distance between single dermal collagen fibrils had increased as compared to noncultured skin. This model of skin organ cultures can be used to study biological processes, dermal toxicity, and penetration and metabolism of xenobiotics in intact skin. Furthermore, within certain limits, processes responsible for repair and regeneration of damaged skin can also be studied in this model because the rabbit skin can be cultured for 7 d. The present study was financially supported by grants of Duphar B. V. (Weesp, Netherlands), the European Community, and the Dutch animal welfare organizations Samenwerkingsverband van de Nederlandse Vereniging tot Bescherming van Dieren en de Nederlandse Bond tot Bestrijding van de Vivisectie, Anti-Vivisectie Stichting en Stichting Schoonheid Zonder Wreedheid.     

反复电针对慢性痛的累加治疗作用及其机制研究

本研究从基础和临床两方面观察了反复电针对慢性痛的累加治疗作用,并结合疼痛患者及慢性痛动物模型中几种神经肽的放射免疫测定及相应受体拮抗剂的药理学研究结果,探讨了产生累加效应的可能机制。结果表明,在临床脊髓损伤性痉挛患者,１００Ｈｚ穴位体表电刺激有效地缓解痉挛并有累加效应;在临床慢性痛患者,２／１５Ｈｚ变频ＴＥＮＳ刺激有效地治疗疼痛并具有累加效应。在关节炎模型大鼠,电针刺激能产生明显的镇痛并具有累加效     

Photosynthetic electron transport in thylakoids from cotton cultivars (Gossypium sp.) differing in tolerance to prometryn

A method to determine photosynthetic electron transport in thylakoid membranes is described for Gossypium barbadense (cv. Pima S-7) and G. hirsutum (cv. DP 5415). These cultivars differed markedly in tolerance to prometryn, a PS II inhibitor. The rates of photosynthetic electron transport obtained were 245 mole oxygen mg^–1 chl h¹. Plant age and leaf size influenced the activity of the thylakoid preparations. Thylakoids from leaves of plants 24 to 37 d and 50–70 mm in diameter had the highest activities; thylakoids from cotyledons, fully expanded leaves and young leaves had low activity. Thylakoids from both species had similar photosynthetic activities and I₅₀'s for prometryn, atrazine and diuron. Thus, tolerance to prometryn was not due to differential binding at D1 protein.Abbreviations PSII photosystem II - DAP day after planting - DQ duroquinone - DBMIB dibromothymoquinone - DMBQ 2,5-dimethyl-p-benzoquinone - I₅₀ concentration to inhibit reaction by 50% - Q_A quinone A - Q_B quinone B