Journal of the Marine Biological Association of India

Volume 29 Issue 1&2

Progressive cell size decrement and auxospore formation in cultures of diatoms.

A. Duraisamy and V. N. R. Rao

Achnanthes brevipes v. intermedia (Kutz.) Cleve, Amphiprora alata (Ehr.) Kiitz., Amphiprora ornata Bailey, Amphiprora paludosa Wm. Sm., Amphiprora paludosa v. pimctulata Grun., Melosira dubia Katz., Synedra tabulata (Agardh) Kutz., Thalassiosira fluviatilis Hustedt and Triceratium dubium Brightwell isolated from marshes, estuaries or coastal regions were made axenic and used in studies on progressive size diminution and auxospore formation.

Rates of progressive size diminution were studied in cells grown in different salinities for 36 subcultures and frequency curves, mean length of apical, transapical and pervalvar axes were obtained. Reduction in dimension of transapical and pervalvar axes was negligible when compared to reduction in apical axis of pennate diatoms. In A. paludosa and S. tabulata, where it was possible to study the rate of size diminution, apical axis decrement was greater in high saline media and in large cells. Concomitant with decrease in cell diameter there was a corresponding increase in pervalvar axis in centric diatoms and this feature was more obvious in T. fluviatilis.

Three types of behaviour were noted in these diatoms as regards auxospore formation. In A. brevipes v. intermedia, M. dubia and T. dubium auxospores were frequently observed in all salinity media. On the other hand, T. fluviatilis auxosporulated only as a response to changes in salinity of the media. A. paludosa and S. tabulata showed progressive size diminution with no induction of auxospores even with periodic changes in salinity. Occasional large cells appeared though in cultures of these and other diatoms and the cause of their occurrence was not quite clear.

Date : 31-12-1987