IS THE NUCLEAR DNA CONTENT OF MATURE ROOT CELLS PRESCRIBED IN THE ROOT MERISTEM?

Abstract

Cells of the mature root exhibit arrest within the G1 and G2 periods of the mitotic cycle. The number of cells arrested with a 2C or 4C DNA amount in mature tissue was compared with that in meristems of excised primary root tips deprived of carbohydrate. Results from four plant species are described. Cells in mature tissue of seedling roots of Vicia and Pisum exhibited arrest predominately at the 4C while those of Triticum and Helianthus arrested preponderantly at the 2C DNA level. The proportion of cells arrested at the 2C and 4C levels in mature root tissue was specific for each species tested. In each species the cycle stage where most cells arrested was the same in carbohydrate‐deficient root meristems as in mature root tissue; consequently, most meristematic cells are preconditioned or predetermined to arrest in a specific mitotic period. A test system was developed in Pisum in which the predominant period of arrest was altered by the removal of the cotyledons. The predominant arrest period changed from 4C to 2C in both mature root tissue and carbohydrate‐deficient root meristems with cotyledon removal and indicated that mature root cells are preconditioned while meristematic as to where they will eventually arrest in the mitotic cycle.