Viability of dried vegetative cells and the formation and germination of reproductive structures in Pithophora oedogonia, Cladophora glomerata and Rhizoclonium hieroglyphicum under water stress

All dried vegetative cells of Pithophora oedogonia died within 1 h, while those of Cladophora glomerata and Rhizoclonium hieroglyphicum retain viability to some extent for 1 and 8 d, respectively, under similar storage conditions. The viability of dried vegetative cells of either C. glomerata or R hieroglyphicum decreased more or less equally when stored either at 20 degrees C in light or dark or at 12 degrees C in dark, but was lost rapidly and drastically when stored at 0 degrees C in dark. Both dried and wet akinetes of P. oedogonia were equally more viable when stored at 20 degrees C in dark than in light, but they lost germination ability when stored either at 12 or 0 degrees C in dark; this might be either due to loss of viability or dormancy induction at low temperatures. The water stress imposed by growing vegetative filaments either on highly agarized media, in NaCl-supplemented liquid media or in media undergoing progressive air-drying to complete dryness did not induce, but reduced akinete formation in P. oedogonia, decreased zoosporangium formation in C. glomerata and R hieroglyphicum, decreased or totally suppressed akinete germination in P. oedogonia and zoospore germination in C. glomerata and R hieroglyphicum. Akinetes of P. oedogonia formed under water stress were equally viable, while zoosporangia of C. glomerata and R hieroglyphicum formed under water stress were comparatively less viable than those formed without any water stress. Akinete germination in P. oedogonia and zoospore germination in C. glomerata and R hieroglyphicum were comparatively more sensitive to water stress than the formation of akinetes and zoosporangia. The akinete germination in P. oedogonia was more sensitive to water stress than zoospore germination in C. glomerata and R hieroglyphicum and it might be either due to their large size, thick wall or dense content.