Viability of dried vegetative trichomes, formation of akinetes and heterocysts and akinete germination in some blue-green algae under water stress.

Almost all dried vegetative trichomes ofAnabaena iyengarii, Westiellopsis prolifica andNostochopsis lobatus died within 1 h, while those ofOscillatoria acuminata retained viability to some extent for 1 d under similar storage conditions. The viability of dried vegetative trichomes ofO. acuminata decreased about equally on storage at 20 degrees C in the light or in the dark, but dropped rapidly at 12 and 0 degrees C in the dark. Vegetative trichomes ofA. iyengarii, N. lobatus andW. prolifica were more sensitive to frost than those ofO. acuminata, and this correlated with their low resistance to desiccation because both types of exposure involved osmotic stress. Both dried and wet akinetes ofA. iyengarii, W. prolifica andN. lobatus were about equally viable when stored at 20 degrees C in the light or the dark or at 12 and 0 degrees C in the dark, but their germination ability decreased on storage at 0 degrees C. The water stress imposed on growing vegetative trichomes either in high-agar media or in NaCl-supplemented liquid media reduced the survival ofO. acuminata trichomes, decreased or totally suppressed akinete and heterocyst formation and akinete germination inA. iyengarii, W. prolifica andN. lobatus. The sensitivity decreased in the sequenceA. iyengarii <W. prolifica ~N. lobatus. The akinete germination in all three blue-green algae was more sensitive to physiological water stress than their formation. In all of them, akinetes formed under water stress were equally viable as those formed under normal conditions. Trichomes ofO. acuminata became broader when grown in 0.5-0.8 mol/L NaCl-supplemented media, probably due to polyol accumulation, and they also developed a thin sheath-like structure.