The Effects of Various Light Intensities onNostoc Punctiforme(Kützing)

SUMMARYWe studied by light and electron microscopy the influence of different intensities and periods of illumination on the life cycle and morphogenesis of Nostoc punctiforme (Kütz.) grown in nitrogen-free medium. By using light intensities between 500 and 2800 lux it was observed that the developmental cycle of N. punctiforme consists of a complete heterocystous phase and o a truncated sporogenous phase. The first phase is characterized by aseriate, spherical, or elongated colonies formed by a filament of vegetative cells and heterocysts. The filament is always enveloped in a watery or firm sheath which forms a surface pellicle. The sporogenous phase stops with the formation of coccoid cells formed along the filament of aseríate colonies. The coccoid cell may be released or remain in the mother colonies where they germinate originating directly new aseríate colonies. The nature and functions of such particular cells, which are considered immature spores are discussed.The various light intensities influence the cultural growth, heterocyst frequency and sheath thickness, all the processes increased at the higher light intensities.The continuous light above 1200 lux determines an accentuated degenerative process.