STUDIES ON THE USE OF BACTERICIDAL RUBBER IN MILKING MACHINE CLUSTERS

SUMMARY: Bactericidal rubber containing tetramethylthiuram disulphide was used in milking machine clusters cleaned by immersion in caustic soda on four farms, and by ordinary chemical sterilization on eight farms. Some reduction in the bacterial content of clusters was brought about by the bactericidal rubber, but high bacterial counts were not prevented, particularly where cleaning was inadequate. 'Fatigue splitting' of bactericidal rubber liners occurred after two to six weeks use.     

Genetics of Crop Improvement

SYNOPSIS. Man has been engaged in the genetic manipulation ofcrop plants for millennia. At its most elemental level, plantgenetic manipulation has three requirements: (1) a source ofgenetic variability that can be utilized for plant improvement;(2) methods for propagating desirable plant genotypes; and (3)strategies for the transfer and selection of useful genes orgenecombinations. The modern science of genetics has providedmany new approaches to each of these three aspects of plantimprovement. Modern plant genetics has also led to a varietyof environmental, political and economic problems. These problemsinclude the loss of valuable plant genetic resources, the widespreadadoption of monocultures that may be unstable in the face ofpathogen epidemics, and the current political debates concerningthe regulation and environmental implications of plant geneticengineering. It is impossible tojudge these and related issueswithout a basic understanding of the ways in which geneticsis applied in improving crop plants. The goal of this articleis to provide an account of the applications of plant geneticsin crop improvement.     

Adhesion of phospholipid vesicles to Chinese hamster fibroblasts: Role of cell surface proteins

The adhesion of artificially generated lipid membrane vesicles to Chinese hamster V79 fibroblasts in suspension was used as a model system for studying membrane interactions. Below their gel-liquid crystalline phase transition temperature, vesicles comprised of dipalmitoyl lecithin (DPL) or dimyristoyl lecithin (DML) absorbed to the surfaces of EDTA- dissociated cells. These adherent vesicles could not be removed by repeated washings of the treated cells but could be released into the medium by treatment with trypsin. EM autoradiographic studies of cells treated with[(3)H]DML or [(3)H]DPL vesicles showed that most of the radioactive lipids were confined to the cell periphery. Scanning electron microscopy and fluorescence microscopy further confirmed the presence of adherent vesicles at the cell surface. Adhesion of DML or DPL vesicles to EDTA-dissociated cells modified the lactoperoxidase-catalyzed iodination pattern of the cell surface proteins; the inhibition of labeling of two proteins with an approximately 60,000- dalton mol wt was particularly evident. Incubation of cells wit h (3)H-lipid vesicles followed by sodium dodecyl sulfate (SDS)- polyacrylamide gel electrophoresis showed that some of the (3)H-lipid migrated preferentially with these approximately 60,000-mol wt proteins. Studies of the temperature dependence of vesicle uptake and subsequent release by trypsin showed that DML or DPL vesicle adhesion to EDTA- dissociated cells increased with decreasing temperatures. In contrast, cells trypsinized before incubation with vesicles showed practically no temperature dependence of vesicle uptake. These results suggest two pathways for adhesion of lipid vesicles to the cell surface-a temperature-sensitive one involving cell surface proteins, and a temperature-independent one. These findings are discussed in terms of current models for cell-cell interactions.