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Author

Jaya Bansal

Date of Award

7-1975

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Supervisor

Dr. D. Davidson

Abstract

Cells in root meristems of Vicia faba are heterogeneous for cell cycle duration, nuclear volume and cell shape. The present study was made: (1) to determine volumes of meristem cell nuclei, (2) to analyze changes in nuclear volumes during a cell cycle in a marked population of tetraploid cells in the meristems of long lateral roots.

The results show that there is also heterogeneity in nuclear volume, growth rates of nuclei, protein content and shapes of nuclei. The degree of heterogeneity is different in meristems of roots at different developmental stages. The results also reveal that there is no definite correlation between the volume of a nucleus and its age in interphase. Furthermore, nuclei of non-cycling cells also appear to grow.

The data on the marked population of tetraploid cells provide specific information about changes in nuclear volumes during one cell cycles. The range in nuclear volumes is large even in early G1. Nuclei grow at different rates: 1) within any one subphase of interphase, 2) between different subphases. Even the volumes of prophase nuclei from cells with more or less the same cell cycle duration (i.e., fast cycling cells) appear to be variable. This indicates variability in nuclear growth rates even among the cells that take approximately the same time to complete a cell cycle.

From the volumes of metaphase chromosome complements, an estimate can be made of minimum possible volume of nuclei at the beginning of interphase. The variability of these values suggest that there is a range of volumes among the nuclei at the very beginning of interphase. Hence, one of the factors affecting nuclear growth could be the volumes and, therefore, the chemical composition of the chromosome complements from which the nuclei are formed.

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