Synthesis of DNA and Mitosis in Relation to Cell Differentiation in the Roots ofVicia FabaandLactuca Sativa

Abstract

An analysis of mitotic index, labelling index and nuclear DNA content in differentiating cells of roots in Vicia faba and Lactuca sativa has shown a different behaviour of cell differentiation in the two species. In Vicia faba, the mitotic activity is almost wholly restricted to the meristem (two apical mm.), whilst the DNA synthesis occurs also in the root areas in which cell differentiation and elongation are taking place. This makes the nuclear DNA content of differentiated cells 4C and, in some cases, 8C. In Lactuca sativa, DNA synthesis occurs only in the meristem, and the mitoses which take place at the base of the meristem exhaust the cells in the G² (4C) phase of the mitotic cycle, so that the differentiated cells have a 2C nuclear DNA content.