Bromouracil mutagenesis in Escherichia coli evidence for involvement of mismatch repair.

Summary Bromouracil mutagenesis was studied in several strains of E. coli in combination with measurement of incorporation of bromouracil in DNA. For levels below 10% total replacement of bromouracil for thymine, mutagenesis was negligible compared with higher levels of incorporation. Such a nonlinear response occurred both when the bromouracil was evenly distributed over the genome and when a small proportion of the genome was highly substituted. Also, the mutation frequency could be drastically lowered by amino acid starvation following bromouracil incorporation. These observations suggest the involvement of repair phenomena. Studies of mutagenesis in recA ^– and uvrA ^– mutants, as well as studies of prophage induction, did not support an error prone repair pathway of mutagenesis. On the other hand, uvrD ^– and uvrE ^– mutants, which are deficient in DNA mismatch repair, had much increased mutation frequencies compared with wild type cells. The mutagenic action of bromouracil showed specificity under the conditions used, as demonstrated by the inability of bromouracil to revert an ochre codon that was easily revertable by ultraviolet light irradiation. The results are consistent with a mechanism of bromouracil mutagenesis involving mispairing, but suggest that the final mutation frequencies depend on repair that removes mismatched bases.     

The energy balance of leaves of the evergreen desert shrub Atriplex hymenelytra

Summary Atriplex hymenelytra is an evergreen shrub distributed in the hot deserts of parts of Mexico and the southwestern United States. The leaves of the species have a number of characteristics that are adaptive in a hot, dry environment, some of which change seasonally. Steeply angled leaves reduce midday solar interception, yet result in relatively high interception when solar angles are low and vapor pressure deficits are at a minimum. The leaves substantially reduce their absorptance of incident radiation during the hot periods of the year by changing their moisture and hence dissolved salt contents. At these times the light intensity required for saturation of photosynthesis is low and a reduction in the radiation absorbed by the leaves therefore results in a greater water-use efficiency.     

A new favreine coprolite (Crustacea,Decapoda) from the Jurassic of Iran and the Cretaceous of the Dinarids,Jugoslavia

Favreina tabasensis n. sp., a Crustacean (Decapoda) coprolite with numerous longitudinal canals is described from the Upper Jurassic of the Tabas area, east-central Iran. The same favreine form-species is also recorded and figured from the Neocomian of the Dinarids, Bata, Montenegro, Jugoslavia. Further, a lectotype is proposed forFavreina prusensis (Paréjas) from the Upper Portlandian of the region of Lake Apolyont, Turkey.Favreina montana Elliott from the Albian Qamchuqa formation, Gund-i-Shikavt, Erbil Liwa, northern Iraq, is considered as a nomen dubium non conservandum.     

Canarion,ein neues naphthochinon aus Usnea canariensis

The structure of canarione, a new naphthoquinone from the lichens Usnea canariensis and U. hookeri was elucidated by UV, ¹H-NMR, ¹³C-NMR, mass spectrometry, and chemical degradation as 5,8-dihydroxy-2-methyl-4H-naphtho [2,3b]-pyran-4,6,9 (6H, 9H)- trione.     

Quantum Yields for CO(2) Uptake in C(3) and C(4) Plants: Dependence on Temperature, CO(2), and O(2) Concentration

The quantum yields of C₃ and C₄ plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O₂ and in 2% O₂. At 30 C, the quantum yields of C₃ plants averaged 0.0524 ± 0.0014 mol CO₂/absorbed einstein and 0.0733 ± 0.0008 mol CO₂/absorbed einstein under 21 and 2% O₂. At 30 C, the quantum yields of C₄ plants averaged 0.0534 ± 0.0009 mol CO₂/absorbed einstein and 0.0538 ± 0.0011 mol CO₂/absorbed einstein under 21 and 2% O₂. At 21% O₂, the quantum yield of a C₃ plant is shown to be strongly dependent on both the intercellular CO₂ concentration and leaf temperature. The quantum yield of a C₄ plant, which is independent of the intercellular CO₂ concentration, is shown to be independent of leaf temperature over the ranges measured. The changes in the quantum yields of C₃ plants are due to changes in the O₂ inhibition. The evolutionary significance of the CO₂ dependence of the quantum yield in C₃ plants and the ecological significance of the temperature effects on the quantum yields of C₃ and C₄ plants are discussed.     

Initial phases of indoleacetic acid induced growth in coleoptile segments of Avena sativa L.

The intial phases of auxin-induced growth in coleoptile segments of Avena sativa L. were investigated using a high resolution growth recording technique, based on an angular position sensing transducer. The first response to the hormone is a slight, transient reduction of the growth rate lasting about 5 min. After this phase growth rate increases to a maximum. The duration of the increase and the maximum clearly depend on the concentration of the hormone. With increasing auxin concentration the duration of the growth rate increase is reduced from about 80 min in 10^-9 M indoleacetic acid (IAA) to about 14 min in 10^-4 M IAA. After the maximum the growth rate declines. Looking at the maximum of the growth rate, we obtained a dose-response curve with a sharp increase between 10^-9 M and 10^-6 M IAA and a slight decline between 10^-6 M and 10^-4 M IAA. This result is confirmed by growth rates measured one and two hours after the application of the hormone.Abbreviations IAA indoleacetic acid     

Cytophotometric investigation of DNA and RNA content in nuclei of active Strasburger cells in Pinus nigra var. austriaca (Hoess) Badoux

The nuclei of active, sieve cell-associated Strasburger cells in the secondary phloem of Pinus nigra var. austriaca (Hoess) Badoux have been studied for their structure and DNA and RNA content. No difference in size compared to those of ordinary ray cells was found. The nuclear surface is often increased by an ameboid or lobed shape. The amount of highly decondensed chromatin is greatly increased. Cytophotometric measurements of DNA content of both Feulgen and gallocyanine chromalum-stained nuclei showed normal DNA levels and proved absence of endomitotic polyploidization. RNA content, however, was significantly increased as compared to nuclei of young Strasburger cells and of ordinary ray parenchyma cells.Abbreviations StC₁ Strasburger cells in contact with young and immature sieve cells - StC₂ Srasburger cells in contact with mature and functionally active sieve cells - StC₃ dead Strasburger cells - eRPC pRPC erect and procumbent ray parenohyma cells, respectively - GCCA gallocyanine chromalum - T transmission - A absorbance Dedicated to Professor Dr. Wilhelm Halbsguth, Kiel, on the occation of his 65th birthday     

Production of specific antibodies to contractile proteins,and their use in immunofluorescence microscopy

Summary The injection of rabbits with insoluble or soluble G-actin from chicken smooth or striated muscle will produce antibodies that are equally reactive, and species and tissue non-specific in immunoprecipitation, immunofluorescence and actin-activated Mg²⁺-ATPase^** inhibition test. These antibodies have been used for the identification of actin-containing fibrils in a variety of tissues. When G-actins from chicken smooth or striated muscle are immobilized by chemical linkage to Affi-Gel 702 microbeads, their immunogenicity is increased, but the antibodies obtained against them are species-specific and will only react with actin and actin-containing structures from chicken and are therefore limited in use. It is concluded from this work that insoluble G-actin is the preferable immunogen to obtain precipitating antibodies for wide use.Abbreviations ATPase Adenosinetriphosphatase - FITC Fluoresceinisothiocyanate - SDS Sodiumdodecylsulfate This paper is dedicated to Dr. Dorothy M. Needham, University of Cambridge, England, in honour of her eightieth birthday     

Isolation and characterization of cells from rat adipose tissue developing into adipocytes.

To identify cells developing into adipocytes by accumulation of triglyceride, rat epididymal fat pad cells from small rats were exposed to (3)H-labeled chylomicron fatty acids in vivo and then liberated with collagenase. Tissue remnants were removed by filtration and mature fat cells by flotation. Aggregating cells were then removed by filtration through a 25- micro m nylon screen. Further purification of cells labeled in vivo was obtained by removing floating cells from those adhering to the bottom of a culture dish. The adhering cells multiplied to a confluent monolayer when cultured in Medium 199 containing serum, glucose, insulin, and a triglyceride emulsion. The cells then gradually enlarged due to granulation of the cytoplasm by a lipid-staining material. After about 2 weeks these granules had coalesced forming mature adipocytes of typical signet-ring appearance. Free adipocytes could then be recovered from the cultures by collagenase treatment. After about 2 weeks of culture these cells had the same size (about 30 micro m) as adipocytes recovered in the original collagenase preparation of the rat epididymal fat pad. They contained triglyceride lipase activity and incorporated glucose into triglycerides to the same extent as cells developed in vivo but had higher lipoprotein lipase activity. In vitro, heparin in a low concentration, prostaglandin E(1), isobutylmethylxanthine, and cholera toxin markedly promoted the development of these cells into adipocytes. This could be shown to occur almost completely indicating that this fraction of cells was homogeneous and consisted of cells with the capacity to form adipocytes. The duplication time was about 2 days and did not change with subculturing. Preadipocytes could be obtained by density gradient centrifugation, isolating triglyceride-containing cells either directly from the pad or after 3 days in culture. All of these cells developed into adipocytes as described above but did not multiply as readily. It was concluded that cells from the epididymal fat pad from small rats can be isolated in a homogenous fraction that develops in culture into cells of identical morphology and function as adipocytes formed in vivo. The differentiation of these cells into adipocytes may be manipulated in vitro.