Stomatal response to leaf water potential in almond trees under drip irrigated and non irrigated conditions

Almond plants (Amygdalus communis L. cv. Garrigues) were grown in the field under drip irrigated and non irrigated conditions. Leaf water potential () and leaf conductance (g₁) were determined at three different times of the growing season (spring, summer and autumn). The relationships between and g₁ in both treatments showed a continuous decrease of g₁ as decreased in spring and summer. Data from the autumn presented a threshold value of (approx. –2.7 MPa in dry treatment, and approx. –1.4 MPa in wet treatment) below which leaf conductance remained constant.     

Growth characteristics of human epidermal melanocytes in pure culture with special reference to genetic differences

Human melanocyte cultures were established using disaggregated epidermal cell suspensions derived from foreskins and plated onto culture dishes in medium containing 2% fetal bovine serum, growth factors, hormones, and melanocyte growth factor (MGF) extracted from bovine hypothalamus (Wilkins et al., J.Cell. Physiol., 122:350, 1985). After 2 days in culture the cells were transferred to serum-free medium to eliminate keratinocyte and fibroblast growth. Melanocytes grew preferentially and pure melanocyte populations could be harvested after 12-16 days in vitro. Melanocytes were later subcultured in the presence of 1% FBS. Pure melanocyte cultures were characterized by light and electron microscopic criteria, as well as by cytochemical demonstration of the melanocyte-specific enzyme, tyrosinase. At the ultrastructural level, cultured melanocytes derived from black (negroid) neonatal skin (B-M) had numerous mature rod-shaped stage IV melanosomes, while white (caucasoid) skin-derived melanocytes (W-M) in culture contained no mature melanosomes. Growth rate, cell yield, and in vitro lifespan for B-M were more than twice that for W-M in pure melanocyte cultures in the presence of MGF. Our results suggest that MGF-dependent growth of B-M differs from that of W-M.     

Stability and motion of a hairpin and the corresponding mismatched duplex: a theoretical exploration using molecular mechanics and normal mode analysis of 2D NMR results on d(GCCGCAGC)

The oligomer d(GCCGCAGC) can adopt two different conformations: i) a duplex with two mismatched A.C base pairs and ii) a hairpin with two C.G base pairs and a single stranded loop. We report molecular mechanics, normal mode analysis, and thermodynamic stability calculations for both structures. We show that the energy-minimized structure and harmonic-dynamics results are in complete agreement with the observed NOE spectrum and imino proton exchange data. We conclude that the high stability of the hairpin structure over the duplex at low salt concentration is due to the higher vibrational entropy contribution to the system free energy by the single stranded loop and to the lack of minor groove phosphate/phosphate electrostatic repulsions that tend to destabilize the duplex.     

Redox-controlled,in vivo and in vitro phosphorylation of the α subunit of the light-harvesting complex I in Rhodobacter capsulatus

Labelling of Rhodobacter capsulatus cells with (³²P)Pi in a phototrophic culture results in phosphorylation of a membrane-bound polypeptide identified as the subunit of the LHI antenna complex of the photosynthetic apparatus. Phosphorylation of the same polypeptide was also observed by incubation of chromatophores with (³²P)ATP or under conditions of photophosphorylation with ADP and (³²P)Pi. The identity of the phosphorylated LHI- subunit was demonstrated by N-terminal protein sequencing of the phosphorylated polypeptide and by failure of labelling in LHI-defective mutants. Pre-aeration of the samples or addition of the oxidant potassium ferrcyanide stimulated the kinase activity whereas the presence of soluble cytoplasmic proteins impaired phosphorylation in an in vitro assay. No effect resulted from addition of reductants to the assay medium. The results indicate the presence of a membrane-bound protein kinase in R. capsulatus that phosphorylates the subunit of the LHI antenna complex under redox control.Abbreviations Pi inorganic phosphate - SDS-PAGE sodium dodecyl-sulfate polyacrylamide gel electrophoresis     

Analysis of the human regulators of complement activation (RCA) gene cluster with yeast artificial chromosomes (YACs).

The human regulators of complement activation gene cluster (RCA cluster) have been partially characterized with yeast artificial chromosomes (YACs). While the data confirm many points previously elucidated, the finer resolution of YAC mapping has allowed the discovery and/or localization of partial gene duplications, the determination of gene orientations, and the measurement of gaps between known genes. Here nine overlapping YACs that encompass a genomic region of 800 kb, encoding four RCA genes and three gene-like elements, are described. The encoded genes and two of the gene-like elements share the same orientation and are ordered (5' to 3') DAF, CR2, CR1, MCP-like, CR1-like, and MCP. A C4bp-like region lies upstream from DAF and is likely to correspond to one recently observed by F. Pardo-Manuel, J. Rey-Campos, A. Hillarp, B. Dahlback, and S. Rodriguez de Cordoba (1990, Proc. Natl. Acad. Sci. USA 87: 4529-4533). MCP-like, a new genetic element, was discovered and found to be homologous to the 5' portion of the MCP gene. Two large gaps of 85 kb (between CR2 and DAF) and 110 kb (between DAF and the C4bp-like element) could carry additional RCA genes. The arrangement of CR1, MCP-like, CR1-like, and MCP, in that order, strongly suggests that this region was generated by a single duplication of neighboring CR1/CR1-like and MCP/MCP-like forerunners. The RCA YACs will now serve as convenient DNA sources for the subcloning and further characterization of this region.     

Localization of the amphotropic murine leukemia virus receptor gene to the pericentromeric region of human chromosome 8.

The host range of retroviruses is determined primarily by the presence of specific receptors on target cells which are recognized by the retroviral envelope glycoprotein. Somatic cell hybrids have been used to determine the chromosomal locations of several retroviral receptors in mice prior to their molecular cloning. Here we report that by using human-Chinese hamster somatic cell hybrids and a retroviral vector, we have mapped the receptor for the amphotropic murine leukemia virus to the pericentromeric region of human chromosome 8.     

The life cycle ofAmblyomma parvum Aragao, 1908 (Acari: Ixodidae) under laboratory conditions

A colony ofAmblyomma parvum was started with engorged females collected from cattle in the Province of Salta (25°01 S, 63°56 W), Argentina. The progeny of those ticks were fed on rabbits and the non-parasitic stages maintained at 27±1°C, 83–86% RH in darkness. The life cycle (prefeeding period not evaluated) had a mean duration of 99.6 days. The mean time (days) for the different phases of the cycle were as follows: feeding period of females, 8.0; pre-oviposition period, 5.7; oviposition period, 17.5; minimum incubation period of the eggs, 31.8; feeding period of larvae, 3.2; premoult period to nymphs, 10.9; feeding period of nymphs, 4.7; premoult period to adults, 17.8. The oviposition pattern was typical of an ixodid tick, including a linear relationship between weights of engorged females and the number of eggs laid (r=0.8659). The males increased 18% in weight after feeding on hosts (P<0.01). The mean recovery rates of larvae, nymphs and females were 28.2%, 95.3% and 90.7%, respectively. The nymphs moulting to females were heavier (6.8±0.69 mg) than those moulting to males (3.2±0.29 mg) (P<0.01). A comparison of biological values ofA. parvum with American and non-AmericanAmblyomma species is presented.     

Spring and summer hosts for Pieris rapae in Southern Spain with special attention to Capparis spinosa

The suitability of different host plants for Pieris rapae L. in the South of the Iberian Peninsula, was studied in relation to host plant phenology, female behaviour, and larval development. Capparis spinosa is the only host plant available during the dry season of the year in the area studied. D. virgata, R. raphanistrum, H. incana and S. alba being suitable spring hosts. Comparative studies on mortality, larval development and larval growth between C. spinosa and the spring hosts revealed no significant differences.

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Résumé L'adéquation de différentes plantes comme hôtes de P. rapae a été examinée en fonction de la phénologie des végétaux, du comportement de la femelle et du développement larvaire dans le sud de la péninsule ibérique. Pendant la saison sèche, C. spinosa est la seule plant convenable dans la zone étudiée. Diplotaxis virgata, Raphanus raphanistrum, Hirschfeldia incana et Sinapis alba sont des hôtes printaniers convenables. La mortalité, le développement et la croissance larvaires ne sont pas différentes sur C. spinosa et sur les hôtes de printemps.

     

Sequential study of the synaptonemal complex in rat (Rattus norvegicus) oocytes by light and electron microscopy

The progression of first meiotic prophase and synaptonemal complex (SC) formation in female rats, Rattus norvegicus S.D., is described through the analysis of the different stages of the first meiotic prophase, and confirms the high synchrony of the process in this species. Leptotene is a stage of very short duration and since pairing of the homologues begins very early, only a leptotene-zygotene stage can be distinguished. The progression of pairing during zygotene is asynchronous. The morphology of the SCs is similar to that described in other species. During diplotene and before desintegration of the lateral elements, desynapsis takes place.In some oocytes a double or even multiple nature of lateral elements was seen. Associations between SCs and nucleoli or nucleolar filaments are frequent. The presence of fragmented SCs can be interpreted as a technical artifact.