The radiosensitivity of cultured human and mouse keratinocytes

Clonogenic survival assays after gamma-radiation in vitro were performed on freshly isolated and subcultured keratinocytes from mouse skin, mouse tongue and human skin. Survival curves were constructed by fitting the data to a multi-target model of cell survival. When subcultured, keratinocytes from all sites produced survival curves which showed a reduced shoulder region and an increased D0 when compared with their freshly isolated counterparts. Freshly isolated human skin keratinocytes were more radiosensitive than mouse keratinocytes from either skin or tongue.     

A reproducible technique combining tritiated thymidine autoradiography with immunodetection of bromodeoxyuridine for double labelling studies of cell proliferation in paraffin sections of tissues

Abstract. A method is described to combine tritiated thymidine autoradiography with immunoperoxidase detection of bromodeoxyuridine on the same paraffin sections. It overcomes the varied technical artefacts we encountered when first attempting to combine these techniques and results in preparations with extremely low peroxidase and autoradiographic backgrounds. In particular, we find it is important to avoid the use of detergents during immunostaining, otherwise grain counts are reduced and autoradiograph exposures need to be greatly increased, and to avoid excessive peroxidase staining which makes it difficult to visualize silver grains in the overlying emulsion. The advantages of a method to remove emulsion films using acid-alcohol, allowing the same sections to be dipped twice with a long and a short autoradiographic exposure, are presented. The routine combination of high quality tritiated thymidine autoradiography with clean immunoperoxidase staining of bromodeoxyuridine-positive nuclei provides a new and powerful cell kinetic, double-labelling method to augment existing techniques e.g. by labelling the same cells undergoing DNA synthesis in successive cell cycles.     

Influence of pH,exchangeable aluminium and 0.02M CaCl2-extractable aluminium on the growth and nitrogen-fixing activity of white clover (Trifolium repens) in some New Zealand soils

The effects of soil acidity on the growth and N₂-fixing activity of white clover in seven acid topsoils and subsoils of New Zealand were investigated using a glasshouse experiment.The application of phosphate (Ca(H₂PO₄)₂) to the soils resulted in very large increases in white clover growth on all soils. The application of phosphate, as well as increasing P supply, also decreased 0.02M CaCl₂-extractable Al levels, but had little effect on exchangeable Al levels.Where adequate phosphate was applied, increasing rates of lime (CaCO₃) resulted in increased plant growth on most soils. N₂[C₂H₂]-fixing activity was increased by the first level of lime for one soil, but generally remained approximately constant or declined slightly at higher rates of lime. Up to the point of maximum yield, white clover top weight was more highly correlated with 0.02M CaCl₂-extractable soil Al than with exchangeable Al or pH. At pH values greater than 5.5, plant yield declined on some soils, apparently because of Zn deficiency. The data suggest that white clover is unlikely to be affected by Al toxicity at 0.02M CaCl₂-extractable Al levels of less than about 3.3 g g^–1. However, there were differences between soils in apparent plant tolerance to 0.02M CaCl₂-extractable Al, which appeared to be caused by differing C levels in the 0.02M CaCl₂ extracts.     

Kinetics of Cell Replacement In the Stratum Granulosum of Mouse Tongue Epithelium

Abstract. Sheet preparations of the stratum granulosum from the epithelium of the ventral surface of mouse tongue permit examination of cell replacement of this maturation compartment of the tissue. the cell transit rate/day is related to the cell desquamation rate and the cell production rate. the latter is approximately 6500-8000 cells/mm²/day, suggesting a 4-5-fold greater turnover compared with mouse dorsal skin epithelium. the use of [³H]IUdR and [³H]TdR at different times of day provides evidence for a reutilization of label from [³H]TdR released during nuclear degradation in the stratum granulosum. Flooding with unlabelled thymidine is not effective in suppressing this reutilization.     

Role of aminocyclopropane-l-carboxylic acid in ethylene release by distal tissues following localized application of ethephon in Cucurbita pepo

The application of ethephon to a single leaf of Cucurbita pepo L. cv. Trailing Marrow plants caused a huge increase in ethylene production from the treated organ and an increased rate of ethylene production from other parts of the plant. These increases were particularly marked in the shoot apex and expanding leaf. Prior treatment with aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor, blocked the increased production of ethylene at sites distant from the point of ethephon application. This strongly suggests that the increased ethylene production at these distant sites is due to ethylene biosynthesis and not a result of the translocation of ethylene released by the breakdown of ethephon at the site of application. Assays of 1-aminocyclopropane-l-carboxylic acid (ACC), an ethylene precursor, showed that it increased substantially after ethephon application but was at undetectable levels in the presence of AVG. It is proposed that the application of ethephon stimulates ethylene biosynthesis, but that transport through the plants is effected by ACC which is then converted to ethylene at the shoot apex and leaves.