ZINC AND COPPER TOLERANCE OF AGROSTIS STOLONIFERA L. IN TISSUE CULTURE

Callus tissue was induced from shoot meristematic tissue and root tips of a clone of the grass Agrostis stolonifera tolerant to both zinc and copper, and from a control clone tolerant to neither metal. Growth of the callus tissue on media containing zinc and copper showed that tolerance to both metals was maintained in tissue culture. The pattern of metal uptake in tissue culture resembled uptake by whole plants in that tolerant tissue took up more metal than nontolerant tissue. Plants regenerated from callus had the same copper and zinc tolerance as the original parental clones regardless of time of growth in tissue culture and shoot or root origin of the tissue. The results support previous evidence that metal tolerance is genetically determined and acts at the cellular level.     

The chromatin structure of specific genes: I. Evidence for higher order domains of defined DNA sequence.

When the chromatin of Drosophila is examined by digestion with DNAase I or micrococcal nuclease, no general structural organization above the level of the nucleosome is revealed by the cleavage pattern. In contrast, the DNAase I cleavage pattern of specific regions of the Drosophila chromosome shows discrete bands with sizes ranging from a few kilobase pairs (kb) to more than 20 kb. Visualization of such higher order bands was achieved by the use of the Southern blotting technique. The DNAase I-cleaved fragments were transferred onto a nitrocellulose sheet after size fractionation by gel electrophoresis. Hybridization was then carried out with radioactively labeled cloned fragments of DNA from D. melanogaster. For the five different chromosomal regions examined, each gives a unique pattern of higher order bands on the autoradiogram; the patterns are different for different regions. Restriction enzyme cleavage of the fragments generated indicates that the preferential DNAase I cleavage sites in chromatin are position-specific. The chromosomal regions bounded by preferential DNAase I cleavage sites are referred to as supranucleosomal or higher order domains for purposes of discussion and analysis. The micrococcal nuclease cleavage pattern of chromatin at specific loci was also examined. In the one case studied in detail, this nuclease also cleaves at position-specific sites.     

Mechanism of lethal action of 2,450-MHz radiation on microorganisms.

Various bacteria, actinomycetes, fungi, and bacteriophages were exposed to microwaves of 2,450 +/- 20 MHz in the presence and in the absence of water. It was found that microorganisms were inactivated only when in the presence of water and that dry or lyophilized organisms were not affected even by extended exposures. The data presented here prove that microorganisms are killed by "thermal effect" only and that, most likely, there is no "nonthermal effect"; cell constituents other than water do not absorb sufficient energy to kill microbial cells.     

Dry mass changes in germinating spores of Diplodia maydis

Summary The dry mass of two-celled Diplodia maydis spores was measured both before and after germination by quantitative interference microscopy. The dry mass of spores declined approximately 50% during germination. However, the dry mass of germinating spores plus the dry mass of their germ tubes was greater than the dry mass of spores before germination. We conclude that the germinating spores absorbed nutrients released from non-germinating spores.The dry mass of fungal spores can be estimated by weighing large numbers of spores and determining the mean from sample spore counts. Mumford and Pappelis(4) determined the total dry mass of individual spores of Fusarium roseum and the contained lipid bodies before and after spores germinated using quantitative interference microscopy. The mean spore dry mass before germination was 57 pg. Lipid bodies accounted for about 61% of that mass and decreased as spores germinated. The total dry mass of the spore and germ tube 24 hr later greatly exceeded that of the spore before germination. Quantitative interference microscopy has been used to measure the dry mass of various types of cells. Kulfinski and Pappelis (3) recently reviewed how this technique has been applied to plant cells. Technical aspects of interference microscopy have been described by Ross (6).The purpose of this study was to examine the dry mass changes in Diplodia maydis (Berk.) Sacc. with and without germ tubes through the use of interference microscopy.     

Influence of manufacturing variables on the characteristics and effectiveness of chitosan products. II. Coagulation of activated sludge suspensions

Chitosan samples manufactured under different conditions were compared for effectiveness of coagulating an activated sludge suspension grown on vegetable canning wastes. Computer analysis of data from Buchner funnel filterability tests resulted in quadratic polynomial equations describing the response curves for volume of filtrate versus dosage, expressed as g/liter chitosan/100 g sludge suspended solids (SSS). The quotient of the filtrate volume and dosage at the inflection points of the equations obtained for 10 test samples and 1 commercial chitosan sample were compared to evaluate the response (effectiveness) per unit amount for each chitosan product. The product made by a standard procedure (deproteinated with 3% NaOH at 100°C for 1 hr, demineralized with 1N HCL at ambient temperature for 30 min, and deacetylated with 50% NaOH at 145–150°C under N₂ for 5 or 15 min) gave the best performance as a coagulating agent for this activated sludge system. Other products, including the commercial preparation, required higher dosages to achieve the same effectiveness. Products deacetylated in the presence of sir rather than nitrogen decreased waste treatment effectiveness, which approximated the trends of reduced viscosity and molecular-weight distribution. The products containing minerals were less effective than products from which minerals had been removed prior to deacetylation, but they were more effective than the enzyme treated sample and the commercial product. In general, although chitosan products obtained after 15 min deacetylation were more effective than those receiving 5 min deacetylation, effectiveness did not correlate linearly with viscosity and molecular-weight distribution trends. However, chitosan products deacetylated for 15 min did show that the higher-molecular-weight products (0.65–1.1 × 10⁶) were more effective coagulating agents for activated sludge than the manufactured product having the lowest molecular weight (0.47 × 10⁶) and the commercial reference sample (0.56 × 10⁶). Thus, higher values for molecular weight were predictive of greater effectiveness for coagulation of activated sludge suspensions.     

Chemical flocculability of sludge organisms in response to growth conditions

The effect of waste characteristics on the removal of suspended solids and soluble phosphorus by alum, Al₂(SO₄)₃·18H₂O, was investigated in an activated sludge system with no cellular recycle. Under the conditions presently studied, it was found that sludge organisms grown in nitrogen- and phosphorus-restricted media possess exceptionally large capsules and produce a higher surface electric charge per unit of fry weight. Chemical demand for separation of these capsulated cells is obviously higher than those solids cultivated under a well-balanced nutrient condition. For phosphorus removal, the molar ratio of Al⁺³:P is a function of the initial concentrations of soluble phosphorus and suspended solids in solution. The relationship between percent phosphorus removal and the quantity of chemical coagulent used shows nonstoichiometric relationship; that is, the required molar ratio of Al⁺³:P is always greater than one and directly depends upon the content of suspended solids in the flocculated media. Moreover, the present study indicated that chemical separation of dispersed microorganisms occurred following phosphorus removal.     

Population biology of avena. VI. The role of genetic polymorphisms in the outcome of interspecific competition

Three different series of population samples of two Avena species cooccurring in California were grown for an analysis of the role of genetic variation in interspecies competition: I, samples from mixed fatua-barbata sites in nature, grown in mixed stands; II, samples from pure sites and grown in pure stands, and III, the same sites as in II but grown in mixed stands. Four macroenvironments and four densities were used giving a total of sixteen entries for each genetic/competitive unit in order to measure both mean and variance of survival and reproductive rates as fitness characters. Sites used in each series included low versus high levels of genetic polymorphism within each species. In general, high polymorphism favored A. fatua in competition with monomorphic A. barbata, and high polymorphism in A. barbata allowed it to compete better with monomorphic A. fatua observation fits well into the pattern of reduced polymorphism in natural mixed stands. Mean performance of polymorphic mixed stands was not consistently higher than the monomorphic combinations or pure stands but the greater relative stability over environments seemed to favor polymorphisms in one or both of the competitors. A relatively less regular pattern of density or competitive response in series III was interpreted as evidence for the lack of coadaptedness between samples drawn from pure sites. Several limitations characteristic of such controlled studies were briefly discussed; however, the tentative conclusions from laboratory studies provided several promising clues for more critical field studies.This work was supported in part by a grant from the National Science Foundation (GB 8627).