Studies on the relationships between cell population and growth kinetics of root meristems

Abstract

Experiments were performed with three varieties of Pisum sativum (Alaska, Weitor, and Witham Wonder), Helianthus annuus and Vicia faba to further study the relationship between cell population and growth kinetics of root meristems. The duration of the mitotic cycle, DNA synthesis (S period), pre-DNA synthetic period (G1), post-DNA synthetic period (G2) and mitosis were measured by simultaneously marking meristematic cells with colchicine and 3H-thymidine. Autoradiography was used to distinguish the cells labeled with 3H-thymidine. The number of proliferating cells was estimated mathematically from cell population kinetic data and cell counts; the number of cell files was determined from cross sections of the meristem; the growth rate was measured once daily. The results indicated that the mitotic cycle, S, G1, G2, and mitotic duration were very similar in all varieties of Pisum; that Helianthus had the shortest G2 period of all plants tested, and that Vicia had a longer S and cycle duration. Root growth rate was shown to be the reflection of the rate of cell proliferation per file and the average cell length at maturity and that the latter can be estimated by cell population and growth kinetics. The studies also demonstrated that neither mitotic cycle duration, root growth, cell counts, nor mitotic indices exclusively measure the growth and proliferative capacity of a tissue but rather a combination of all four parameters are necessary for an accurate estimation.