TRANSITION TO SEXUAL REPRODUCTION AND CONTROL OF INITIAL CELL SIZE IN NITZSCHIA LANCEOLATA

Abstract

Induction of gametogenesis in some diatoms occurs after a change in illumination. The amount of light energy supplied and the pattern of supply not only condition the physiological status of the cells, but can also switch the mitotic cycle into meiosis. Previous studies have dealt with monoecious species. Here, the transition to sexual reproduction was studied in the dioeciously reproducing species Nitzschia lanceolata, where a compatible partner must be present for vigorous auxosporulation. Successful completion of auxospore development is ultimately dependent on light energy captured through photosynthesis, although sufficient storage material can be accumulated before sexual interaction or the shift to meiosis to allow initial cells to be formed without any further supply of energy. However, if the gametes lack sufficient stored energy then auxospore development ceases. The fact that the cells can exit from the mitotic cycle in the beginning of the Gl phase indicates that possession of a particular material stock is not essential for sexual induction. Factors inducing gametogenesis do not influence the growth of the auxospores or initial cell formation. In N. lanceolata, the lengths of the initial cells are correlated with the lengths of the gametangia. However, for a given parent pair, initial cell size is ± constant and appears to conform to the principle “all or nothing”.