The structure of the centromere in relation to metabolic activity

Summary

• 1. Considerable controversy exists in relation to the single or doubled nature of the centromeric region of chromosomes at metaphase of mitosis and metaphase II of meiosis. Until comparatively recently it was considered single by most workers, but observations on treated and some untreated material led others to conclude that it was double.

• 2. Relevant information regarding these two concepts was obtained from observations made on tapetal tissue in the anthers of two intervarietal hybrids ofHordeum vulgare, which revealed numerous cellular and nuclear abnormalities.

• 3. These abnormalities included-peristent meristematic activity of the cells; polyploid nuclei, uni- and multi-nucleate cells; chromosome stickiness and sticky anaphase bridges, as well as certain abnormal centromeric features such as overcharging of the centromeric chromomeres; divided centromeres at mitotic prophase; precocious repulsion of daughter centromeres.

• 4. All nuclear and cellular abnormalities were attributed to an upset in the nucleic acid metabolism within the cell.

• 5. Examples of some of the known effects of the centromere on n. a. organization and of n. a. metabolism on centromeric behaviour are discussed.

• 6. From a consideration of these effects, and the observed effect of an unusual n. a. metabolism on the centromeres ofH. vulgare chromosomes, it is suggested that whilst most organisms have an undivided centromere at mitotic metaphase and metaphase II of meiosis, others have divided centromeres at these stages, due either to innately differing metabolic activities or to treatment with e.g. c-mitotic substances.