New records on morphological variation of Nostoc muscorum and Nostoc ellipsosporum on Benecks, and Modified Allens, media during their life cycle

As the morphological traits of cyanobacteria changes in different culture media, their taxonomical position has been argued in recent years. To determine a reliable taxonomic system concerning the culture media the main target is to have the highest rate of morphological stability in the medium where dimensions of filaments, trichomes, vegetative cells, heterocysts and spores have a normal frequency. Nostoc ellipsosporum and Nostoc muscorum which are the most frequent species of paddy fields in Golestan province were cultured on Allen’s and Benecks culture media. Morphological variations of length and width of heterocysts, akinetes and vegetative cells were measured from day first up to the end of the experiment (21 days) meeting the static phase of growth. Observations showed that vegetative cells of both species became reformatted on Benecks medium being spiral up to the end of experiment. Heterocystous also had a bony form while in Allen's medium the species had their natural form. The results of the statistical analysis of data obtained from factorial experiment in a completely randomized design and from Duncan test together with dendrograms showed significant differences in most measured characteristics at 95% level. Hence Allen medium is suggested to be used when less morphological variation and a normal distribution of the characteristics is expected. According to the results new taxonomic keys also were designed.