Genetic diversity of Nostoc symbionts endophytically associated with two bryophyte species

The diversity of the endophytic Nostoc symbionts of two thalloid bryophytes , the hornwort Anthoceros fusiformis and the liverwort Blasia pusilla, was examined using the tRNA(Leu) (UAA) intron sequence as a marker. The results confirmed that many different Nostoc strains are involved in both associat ions under natural conditions in the field. The level of Nostoc diversity w ithin individual bryophyte thalli varied, but single DNA fragments were con sistently amplified from individual symbiotic colonies. Some Nostoc strains were widespread and were detected from thalli collected from different fie ld sites and different years. These findings indicate a moderate level of s patial and temporal continuity in bryophyte-Nostoc symbioses.