Peculiarities of cell division in Nostoc muscorum CALU 304 in monoculture and associations with plant tissues

Light and transmission electron microscopy were used to study the morpholog y of Nostoc muscorum CALU 304 in pure cultures grown under standard conditi ons, in pure cultures grown in media for cultivating plant tissues (such cu ltures are hereafter termed monocultures), and in mixed cultures with night shade and rauwolfia tissues. Cyanobacterial populations in mono- and mixed cultures contained not only morphologically normal but also branched tricho mes (examination of ultrathin sections revealed cyanobacterial cells charac terized by several cell division planes, which is evidence of the existence of true branching). The results obtained are compared with earlier data on analogous phenomena occurring in natural symbioses. It is inferred that bi nary division in one plane with the formation of unbranched trichomes, whic h was considered a taxonomically significant characteristic of Nostocales r epresentatives, is an unstable trait under nonstandard conditions.