Germination in Pithophora Akinetes

Abstract

The green alga Pithophora was described at the close of the last century by Wittrock (1877). Wittrock noted that akinetes germinate parallel to the long axis of the cells, whereas later studies of Mothes (1930) and Ernst (1908) indicated that germination was at right angles to the long axis of the cells. Since past observations concerning akinete formation and development have been of a general nature, and little is known of the specific conditions under which these phenomena occur, a germination study of Pithophora varia Wille under controlled culture conditions was undertaken (Neal, 1965). MATERIALS AND METHODS The specific identity of the Indiana culture strain used was determined by Dr. G. W. Prescott to be Pithophora varia Wille. This strain was cultured, in mass, in soil-water medium modified from standard culture techniques (Pringsheim, 1946) only by autoclaving at 250 F. In addition, Bold's basal medium (Bishoff & Bold, 1963) was found to support rapid growth when the quantity of NaNO3 was doubled. Akinetes were formed in abundance in cultures three or more weeks old in both media. Cultures previously maintained in an 18 hr day length environment at 25 C were placed in a dark box at 21 C seven days prior to the experimental period. Square polystyrene utility boxes containing suspended filaments with mature akinetes were prepared. These were either unpainted, to allow light to enter from all directions, or painted in a manner to admit light through a small window from either one direction, or from two opposite directions. The boxes with mature akinetes were then placed in BOD incubators with a medium of soil-water supernatant at 28 C (determined to be the optimum temperature for germination by a series of preliminary studies) and light intensity of 420 ft-c provided by 30 w, cool, white, fluorescent lamps. In like manner, a set of controls was prepared under identical conditions in dark containers.