PHYSIOLOGICAL CHANGES DURING GERMINATION OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AKINETES1

Abstract

ABSTRACTAkinetes of Pithophora oedogonia (Mont.) Wittrock, formed in stationary phase cultures, were induced to germinate by transfer to fresh media. Changes in various physiological parameters were monitored during the first 20 d of germination. Ungerminated akinetes contained a greater percentage of lipid, starch, and dry matter and exhibited lower photosynthetic rates than did vegetative cells. Germination consisted of four phases. Phase I (day‐0 to day‐1) was marked by a rapid increase in respiratory rates. Phase II (day‐2 to day‐6) involved protrusion of the germination tube and was insensitive to cyanide, a respiratory inhibitor, and simazine, a photosynthetic inhibitor. Phase III (day‐7 to day‐14) was marked by rapid elongation of the germination tube, increasing photosynthetic rate, increasing chlorophyll and water content and declining levels of lipid and starch. Germination tube elongation during phase III was not inhibited by simazine, but was cyanide sensitive. Phase IV (day‐15 to day‐20) was characterized by a reduction in respiratory rate and an abrupt increase in the ratio of photosynthesis to respiration. Germination tube elongation during phase IV was inhibited by simazine. The data indicate that germination in Pithophora oedogonia akinetes consists of an extensive period (phases I, II and III) during which reserve materials are respired. Utilization of internal food reserves apparently permits akinetes to germinate and supports the initial growth of the germination tube in light limited microenvironments.