Dynamics of cell growth and endoreduplication during orchid flower development

Endoreduplication, a process to amplify nuclear DNA without cell division, is widespread in plants. This study aims to formulate endoreduplication process as a dynamic system using orchid flowers in favor of their slow growth rate. We analyzed the ploidy levels during orchid flower development and proposed an improved model to describe the relationship between endoreduplication and cell growth. Our model combined a logistic growth model with an endoreduplication model of Schweizer et al. [Proc. Natl. Acad. Sci. U.S.A. 92 (1995) 7070]. We found that using the Fermi function to describe the transition rates from one C value to next higher C value significantly improved simulation of changes in growth and endoreduplication. The growth rate, endoreduplication transition rates, and nuclei number of each C level at different developmental stages were computed. Our results indicated that cells with higher C values had lower transition rates and less potential for further endoreduplication, and the time that endoreduplication stopped occurred at the same time flower fresh weight stopped increasing. In addition, average cell fresh weight was positively correlated to average C value, suggesting that endoreduplication is a contributing factor to cell growth. (C) 2003 Elsevier Ireland Ltd. All rights reserved.