Dependence of the gametogenesis induction, zygote formation and their germination on the culture density of the homothallic algaChlamydomonas geitleri Ettl

Abstract

The induction of gametogenesis has its beginning in the most diluted cell suspension after the transfer of the cells to a nitrogen-less medium. Here, the highest percentage frequencies of zygotes are formed within the same period of time in comparison with the less diluted cell suspensions. The zygotes formed in the mostly diluted cell suspensions mature relatively very slowly and germinate very irregularly. The induction of gametogenesis retards in the denser cultures probably due to the strongest homeostatic forces trying to return the cell population to its initial stage. In our experiments up to now, the effects of the changing irradiance of the cells inside the suspension were not separated from the effects of the changing number of the cells in the given volume of the culture. Neither were the ratios of distilled water to the amount of the zygotes, nor to the vegetative cells constant. Thus, it is necessary to consider the mentioned effects as the result of an interaction of both factors under consideration. Each of the cell populations behaved as an autonomous whole. Also the populations, starting after the transfer to a nitrogen-less medium of the same culture density, may sometimes differ significantly in the observed characteristic features at various phases of their growth. The discontinued supply of nitrogen obviously causes a change of the cell metabolism in favour of the nitrogen-less substances, especially in the more diluted cell suspension. This work completes and explains some earlier results obtained from the study of the life cycle inChlamydomonas geitleri.