ABSTRACT: The cell cycle approach has several advantages over other methods for estimating phytoplankton species-specific growth rates in situ. This method has been successfully used in field studies in which the S-G2-M phase was used as a terminal event in the growth rate equation. Recently, the method has been modified, and cell cycle proteins have been substituted as the terminal event marker. Unfortunately, many of these markers represent cell cycle phases other than a terminal event. Whether such a non-terminal event can be used in the cell cycle method will have a great impact on the extent of the application of this method. Our numerical analysis in this report showed that, with the original growth equation, use of a non-terminal event would overestimate the growth rate in most cases. The magnitude of the overestimation increased with the time interval between the non-terminal event and cell division as well as with growth rate. However, by solving an equation derived from existing ones, we were able to eliminate the overestimation. To test the validity of this approach, we simulated 33 populations with different growth rates, levels of synchrony, ratios of the duration of the G2-M phase to that of the S phase, and shapes of the S phase fraction curve. Estimates obtained with the S phase using the new equation were very close to those obtained with the terminal event (the S-G2-M phase) and to true growth rates, with an average underestimation of about 5% for the 24 rudimentary simulation cases. We conclude that, with the aid of this newly derived equation, a non-terminal event could perform as well as a terminal event in estimating growth rates. Using this approach for field investigation will only require accurately estimating the duration of the non-terminal event and the time interval between the non-terminal event and cell division.

KEY WORDS: Growth rate · Cell cycle approach · Non-terminal event · Phytoplankton · Population simulation

Published in MEPS Vol. 151 (1997) on May 22
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1997