Factors affecting shoot proliferation and vitrification inDigitalis obscura cultures

Summary Variations of composition and consistency of the culture medium and time of exposure to growth regulators were assayed to optimize normal caulogenic response ofDigitalis obscura hypocotyls cultured in vitro. The effects of the culture conditions on physiologic changes related to vitrification of the regenerated plants were also investigated. Liquid medium increased the bud-forming capacity of the explants but induced buds failed to develop into shoots and showed symptoms of vitrification. On agar-solidified media, maximum multiplication rates were achieved with 0.7% agar. Increasing agar concentration reduced vitrification but lowered the propagation rate. Changes in the strength of the macronutrients of Murashige and Skoog did not significantly affect the bud-forming capacity of the explants. In contrast, a drastic inhibitory effect on both bud formation and shoot elongation was produced when NH₄NO₃ was omitted. Reduction of NH₄NO₃ to one-half or one-fourth of the level of the original formulation not only increased the bud-forming capacity ofD. obscura hypocotyls but also resulted in less vitrification. Modifications of time and method of exposure to growth regulators neither improved the multiplication rates nor overcame vitrification. Cardenolide content was lower in vitrified than in normal cultures and coincided with an overall reduction of photosynthetic pigments, lignin, and dry matter.     

pH mapping in transparent gel using color indicator videodensitometry

The colored pH indicator method introduced by Weisenseel et al. (1979) is particularly useful for localizing the zones along roots where acidification/alkalinization occurs. It can also be used to assess the direction and intensity of the proton fluxes. Because the method has not been quantitatively evaluated, however, it is nowadays little used or used in conjunction with other such as potentiometry. In the present study we examine the theoretical basis underlying this method of colorimetric visualization and show its similarity to spectrodensitometry. It thus becomes possible to quantify the luminous information and express it in terms of environmental pH. We describe the method used, emphasizing in particular the conditions required to achieve maximum accuracy of measurement, and an appropriate experimental device. pH distribution around roots can be mapped with a relative error of 0.03 pH units. The experimental device is easy to use and incorporates a computer-controlled video camera, thanks to which al acquisition and calculation procedures can be automated.     

Specifically UV-sensitive photoreactivable mutant of Salmonella abony

A new type of UV-sensitive mutant was isolated in Salmonella abony. The war 12 mutation causing UV sensitivity did not affect photoreactivability of UV damage or sensitivity to γ-rays, methyl methanesulfonate (MMS), mitomycin (MC) or 4-nitro-quinoline I-oxide (4NQO).Mutation uvr I2 appeared to be near the uvr B gene of Salmonella: the frequencies of contransduction of uvr B2 and uvr I2 mutations with gal were found to be 3% and 6% respectively.Close localization of the uvr I2 and uvr B2 mutations, the possibility of recombination between them and their phenotypic differences (both uvr B2 and uvr I2 mutants show quantitatively different Hcr phenotypes and different sensitivities to MC and 4NQO) suggest that the uvr B2 and uvr I2 mutations might be localized in different cistrons of an operon controlling the first step of excision repair.     

Quantification of cytotoxic hemocytes of Mytilus edulis using a cytotoxicity assay in agar

When a thin layer of agar containing a mixture of erythrocytes and Mytilus hemocytes is prepared on slides, the occurrence of plaques of lysed target cells can be observed around a limited number of hemocytes. These hemocytes remain completely intact cells and are viable as evidenced by their ability to phagocytose target cells and/or to form pseudopods. The number of hemocytes releasing cytotoxic molecules has been shown to vary greatly between different animals. The same holds true for the total number of circulating hemocytes, although no correlation exists between the number of hemocytes in the circulation and the percentage of cytotoxic blood cells.     

Agar from the red seaweed,Laurencia flexilis (Ceramiales,Rhodophyta) from northern Philippines

The worldwide production of the gelling agent agar mainly rely on the red algae of the order Gracilariales and Gelidiales for raw material. We investigate here the potential of a species from another red algal order, Ceramiales as an agar source. The agar from Laurencia flexilis collected in northern Philippines was extracted using native and alkali treatment procedures and the properties of the extracts were determined using chemical, spectroscopic and physical methods. The native agar, 26% dry weight basis, forms a gel with moderate gel strength (200 g cm^?2). Alkali‐treatment did not enhance the gel strength, indicating insignificant amounts of galactose‐6‐sulfate residue, the precursor of the gel‐forming 3,6‐anhydrogalactose (3,6‐AG) moieties. Furthermore, the Fourier transform infrared and chemical analysis showed low sulfate and high 3,6‐AG levels, not affected significantly by the alkali treatment. Nuclear magnetic resonance spectroscopic analysis revealed 3‐linked 6‐O‐methyl‐D‐galactose and 4‐linked 3,6‐anhydro‐L‐galactose as the major repeating unit of the native extract, with minor sulfation at 4‐position of the 3‐linked galactose residues. The native and alkali treated agars have comparably high gelling and melting temperatures, whereas the former exhibits higher gel syneresis. Laurencia flexilis could be a good source of agar that possesses physico‐chemical and rheological qualities appropriate for food applications. Due to the inability of alkali treatment to enhance the key gel qualities of the native extract, it is recommended that commercial agar extraction from this seaweed would be done without pursuing this widely‐used industrial procedure.     

Phycocolloid chemistry as a taxonomic indicator of phylogeny in the Gigartinales, Rhodophyceae: A review and current developments using Fourier transform infrared diffuse reflectance spectroscopy

The taxonomic significance of the polysaccharide structures of algal cell walls has been underscored several times over the past few decades but has never been pursued systematically. Many changes in red algal systematics and the biochemical analyses of phycocolloids have occured in recent years. The cell-wall composi-tion of representatives of 167 (24.7%) genera and 470 (11.5%) species of red algae has been documented.The method developed by Chopin and Whalen for carrageenan identification by Fourier transform infrared diffuse reflectance spectroscopy is extended to the study of phycocolloids for diverse species in many red algal orders. This paper focuses on the Gigartinales in which representatives of 28 (68.3%) families, 88 (50.6%) genera and 224 (27.9%) species have been analyzed. In light of recent molecular phylogenies, some patterns of distribution of key phycocolloid attributes, corresponding to familial and ordinal level groupings, are emerging; however, more species remain to be analyzed. The well-documented biochemical alternation of generations in the Phyllophoraceae, Petrocelidaceae and Gigartinaceae still holds (with two exceptions), but this pattern was not recorded in other families of Gigartinales.     

Acid production by Metarhizium anisopliae: Effects on virulence against mosquitoes and on detection of in vitro amylase,protease, and lipase activity

The imperfect fungus Metarhizium anisopliae infects and kills larvae of many insect species, including the mosquito Culex pipiens. Mutants of M. anisopliae selected for enhanced production of amylase have been found to have simultaneously acquired hypervirulence against C. pipiens larvae. In the present work, wild-type and some mutant strains of M. anisopliae were found to excrete an acid or acids which alter the pH of fungal cultures below that permissible for amylase activity. The amylase-enhanced hypervirulence mutants did not excrete acid. Detection of protease and lipase activities was complicated by the acid excretion. When this was taken into account, mutants having altered lipase or protease production were found to have no alteration in virulence against mosquito larvae. The link between acid excretion, amylase activity, and hypervirulence is discussed.     

Selective isolation of Yersinia pestis from plague-infected fleas

We evaluated Yersinia CIN agar for the isolation of Yersinia pestis from infected fleas. CIN media is effective for the differentiation of Y. pestis from flea commensal flora and is sufficiently inhibitory to other bacteria that typically outcompete Y. pestis after 48 h of growth using less selective media.