Low Agar Concentration Research Articles

Effects of agar concentration on water status and growth of rose plants cultured in vitro

Rose (Rose hybrida cv. Madame G. Delbard) was micropropagated in vitro on agar at varying concentrations: 0, 4, 5.5, 6, 7.5, 8, 9 and 15 g l−1. Water status of the culture medium, leaf water potential, plant growth and propagation rate were investigated.Water potential of the medium was lincar function of agar concentration, and gel strength increased linearly from zero as agar concentration increased from 5 to 15 g l−1.Except for liquid medium, where shoot proliferation (total shoot number) was imparied by vitrification, fresh and dry weights and unmber of tatal shoots decreased linearly with increasing agar concentration. At low agar concentration, where water potential of the gelled medium was high, only few among numerous shoots that had attained a length of >0.3 cm were usable. Number of usable (elongated) shoots was significanly higher at a moderate level of agar, namely 7.5 g l−1. This can be explained in terms of the antagonistic actions of cytokinin and water on shoot elongation.At low agar concentration, leaf water potential and absolute water content were high. At high agar concentration, under gel water deficit, leaf water potential and absolute water content were low but an osmotic adjustment maintained turgor pressure. At moderate agar concentration, when the number of usable shoots was high, lower leaf turgor was found.

Suberization and bud formation in tobacco explants

SUMMARYWound‐healing and floral bud formation were studied in explants of Nicotiana tabacum L. Examination of sectioned material by conventional light microscopy, fluorescence microscopy and electron microscopy showed that suberin is formed in cells at the cut surface in close contact with the medium, after 4–7 days of culture.The number of cells depositing suberin depended on the agar concentration in the medium. In explants cultured on a medium with low agar concentration (0‐2 % agar), fewer cells showed suberin deposition and more callus cells without suberin were found. Explants cultured on a medium with high agar concentration (5 % agar) formed a complete layer of cells with suberin deposition.In tobacco explants floral determination occurred within 4 days after explantation. The inability of the explants to form floral buds after this period is probably due to barrier formation by suberin.

Effects of agar brand and concentration on the tissue culture medium

In tissue‐cultured Cynara scolymus L. (globe artichoke) vitrification (hyperhydric transformation) can only be overcome by increasing the concentration of agar. However, with increasing concentrations of Difco Bacto agar (8–15 g/I) the availability of labelled kinetin is decreased. There is some evidence for postulating that cytokinins under inductive conditions of low agar concentration or high matrix potential are evocators of vitrification.Both the brand and concentration of agar also affect the chemical and physical characteristics of a culture medium.Impurities introduced with the agar are responsible for significant differences in the concentration of an element in comparable media with different levels of agar, and are easily detected by conductance.Penetrometer measurements also show large ranges in solidity of media with increasing concentrations, not only within the type of agar, but also for the same concentration within different brands.

Mutants of Chlamydomonas reinhardii with altered sensitivity to antimicrotubular agents

Nine new colchicine-resistant, three vinblastine-resistant, two colchicine-sensitive and one colchicine-dependent mutant of Chlamydomonas reinhardii have been isolated. Some of the mutants have abnormal cell morphology in the absence of the drug. Some of the mutants have altered levels of resistance to puromycin and to caffeine, which may indicate that their phenotypes involve a non-specific permeability change. However, uptake of labelled colchicine is indistin-guishable from wild type in all of these mutants except two. The discrepancy between these two results is discussed. All the resistant mutants except one behave as if they have a single gene defect in crosses to wild type, although zygote germination is consistently very poor. Strains carrying certain pairs of resistance mutations are much more resistant than those carrying single mutations indicating that gene effects are additive. Recombination frequencies between some genes have been measured. The colchicine-sensitive mutations are thought not to be cell wall deficient mutations because of their appearance in the electron microscope, growth on low agar concentrations and their colony morphology. The colchicine-dependent strain had a very low viability even in the presence of optimal concentrations of colchicine.

THE SELF-DIFFUSION COEFFICIENTS OF 45CA AND 2,4-DICHLOROPHENOXYACETIC ACID

The agar method and the cell diffusion method were used to measure the self-diffusion coefficients of 45Ca in CaCI2 solution and 14C-labelled 2,4-Dichlorophenoxyacetic acid. Both methods gave results that were in agreement with theoretical considerations. Problems were experienced with the agar method. Difficulties encountered were preparation of stable media of low agar concentration and inability to properly account for physical properties of the matrix through which diffusion occurred, such as tortuosity, adsorption by the agar, and density gradients with associated viscosity gradients in the agar. The cell diffusion method was simple to use and gave results that were in agreement with values calculated from ionic mobilities. The diffusivities measured with the cell diffusion method were: for 45Ca in CaCl2 solution, K = 0.70 cm2/day and for 14C-labelled 2,4-D, K = 0.69 cm2/day.

Reversion to the streptococcal state of enterococcal protoplasts, spheroplasts, and L-forms.

A method is described for predetermining whether lysozyme-damaged enterococci grow as either the parent strain or as L-forms. Organisms treated with lysozyme grew as L-forms on media solidified with low concentrations of agar, or the damaged cells grew as streptococci on media solidified with high concentrations of gelatin. After induction, some of the L-forms reverted to the parent strain, but most did not during three routine subcultures. Continued spontaneous reversion occurred through approximately 30 subcultures after induction. However, subsequent progeny did not revert, even when subjected to conditions such as the gelatin medium which strongly favors growth in the streptococcal phase.

Bacteriocins from human and rodent streptococci

Thirteen strains of streptococci, representing cariogenic and non-cariogenic isolates from humans and rodents were examined for synthesis of bacteriocins. Six strains were found to produce bacteriocins that were active against other streptococci, including strains of Strep. pyogenes and enterococci, but not against unrelated bacteria. There was no correlation between production of bacteriocins and the cariogenicity of the organisms. Several types of bacteriocins could be delineated on the basis of their activity spectrum, the morphology of inhibition zones, and their sensitivity to heat, ether, chloroform, and various enzymes. Several organisms appeared to form more than one type of bacteriocin. All bacteriocins were affected by proteolytic enzymes and some by lipase, suggesting they contain peptide and lipid moieties. They were of low molecular weight, as indicated by their ability to diffuse through a dialysis membrane. Bacteriocin activity was readily demonstrated in agar agarose or starch plate assays, but activity could not be demonstrated in broth cultures. This indicated that the bacteriocins were extremely labile in liquid media, but they were found to be stabilized by low concentrations of agar, starch, glycerol or dextran.

SIMPLE CONDITIONS FOR GROWTH OF UNICELLULAR BLUE-GREEN ALGAE ON PLATES(1, 2).

The efficiencies of plating of 2 cultures of unicellular blue-green algae, 1 coccoid and 1 rod-shaped, were studied systematically. Reproducible colony growth and accurate viable counts are dependent on the use of a low agar concentration, and on the sterilization of the agar separately from the mineral components of the medium.

Bacteriologic investigations of the oral spirochetal flora in ulcerative stomatitis (Vincent's infection)

A method was presented for routine isolation and cultivation of certain of the oral spirochetes associated with lesions in cases of ulcerative stomatitis. The technique was based primarily upon the use of a-well for holding the spirochetel-containing inoculum in the confines of a highly nutritious medium of low agar concentration, which favors rapid multiplication and penetration of the medium by the spirochetes. Numerous strains of the smaller oral treponemes and three strains of Bor. vincenti were obtained by this method. Agglutination studies were undertaken. Media and techniques were devised both for mass cultivation of organisms for intravenous inoculation of rabbits and for use as antigen in performing microscopic agglutination reactions. Strains of T. pallidunt and various strains of the oral spirochetes were shown to be highly antigenic. The agglutination titres of immune serums of rabbits when tested against homologous strains of spirochetes ranged between 1: 1,000 and 1: 1,000,000.