Studies on the control of cell division in a green alga,Ankistrodemus gracilids (Chlorococcales)

Abstract

The proliferation patterns of the green alga,Ankistrodesmus gracilis were investigated by electron microscopy. The multichotomically dividing phase, namely the type I phase was characterized by multichotomical nuclear division, whereas the dichotomically dividing phase, i.e., the type II phase was related to dichotomical nuclear division. Type I phase was controlled by a lower cell density and a diurnal light-dark rhythm of LD 14:10. Type II phase was induced by a cell density of more than 1.0×10⁷ cells/ml. Independent of the 2 types of proliferation patterns, the diurnal light-dark rhythms related to the autospore release from a mother cell. The diurnal light-dark rhythm of LD 14∶10 induced the scattered release of autospores. On the other hand, a rhythm of LD 18∶6 induced the release of a couple of tightly adhered autospores from a mother cell which had been observed apparently as a type II cell by light microscopy.