UV microbeam irradiation of chromosomes during mitosis in endosperm

Abstract

1. 1. Using endosperm of Haemanthus katharinae as material, some hundred kinetochores and chromosome arms in different stages of mitosis have been irradiated with heterochromatic UV microbeams 2 and 4 μ in diameter. 2. 2. It was found that, if the dose is high enough, a pale spot appears and is followed by a sticky bridge in the irradiated place during anaphase. Pale spot shows a tendency to swell and spread. 3. 3. In experiments with much higher doses effects on the whole cell, such as formation of restitution nuclei, very irregular anaphases, death of cell, etc., were obtained. 4. 4. Chromosomes with kinetochores irradiated during prophase, prometaphase and metaphase do not show any striking difference in respect to their movements as compared to non-irradiated ones, until the anaphase begins. In anaphase they have a tendency to occupy the equatorial position until formation of the phragmoplast. 5. 5. Normal activity of previously irradiated kinetochores is also proved by the way they are stretched during prometaphase and anaphase. 6. 6. Chromosomes with kinetochores irradiated during anaphase change their normal behavior and show some features of prometaphase chromosomes, e.g., they have a strong tendency to move towards the equatorial position. 7. 7. Some explanations of chromosome behavior after irradiation have been suggested.