A CYTOLOGICAL ANALYSIS OF THE NOSTOC‐BRYOPHYTE RELATIONSHIP

Abstract

SUMMARY A comparative light and electron microscope study has been made of the Nostoc colonies within the thalli of Blasia pusilla and the three British species of Anthoceros, and also of the Nostoc isolated from each bryophyte. From their morphology in culture two taxa of Nostoc have been identified; N. sphaericum from Anthoceros punctatus, A. husnotii and A. laevis, and N. calcicola from other gatherings of Anthoceros laevis and Blasia. These findings support the notion that the algal‐bryophyte associations are none specific. Within bryophyte thalli, the Nostoc trichomes are closely packed and specific features cannot be recognized. Mucilaginous sheaths are much less extensive and there is no evidence that the alga thrive in mucilage produced by the adjacent bryophyte cells. Heterocyst frequencies as high as 50% in the bryophytic Nostoc spp. strikingly recall the Azolla, Gunnera and cycad‐blue‐green algal symbioses. Akinetes, readily produced in culture were only seen in the Nostoc from dormant Anthoceros. The absence of phycobilisomes and high heterocyst frequencies in the bryophytic Nostoc spp. corroborates physiological data that the algae receive organic carbon from their hosts which enable them to fix nitrogen heterotrophically. The Nostoc colonies in both Blasia and Anthoceros are extensively penetrated by multi‐cellular bryophytic filaments. Whereas in Anthoceros these comprise highly vacuolate, thin‐walled cells, which sometimes contain intracellular Nostoc trichomes, in Blasia the filaments are thick‐walled and often develop labyrinthine wall ingrowths. This transfer cell morphology may be interpreted as an adaptation facilitating interchange of metabolites between Blasia and Nostoc. Its absence in Anthoceros perhaps indicates a far less harmonious relationship or may be related to the higher nutrient status of the habitats where the Anthoceros spp. were collected.

The anthocerote chloroplast: a review

“…7C, Duckett et al, 1977;Honegger, 1980). Similarly, the piastids in cells of Phaeoceros infected by mycorrhizai fungi are less developed than the chloropiasts of uninfected parenchyma ceiis and lack starch and a pyrenoid (Ligrone, 1988).…”

“…Similarly, the piastids in cells of Phaeoceros infected by mycorrhizai fungi are less developed than the chloropiasts of uninfected parenchyma ceiis and lack starch and a pyrenoid (Ligrone, 1988). Most likely, these changes in piastid structure reflect physiologicai interactions with the symbionts (Duckett et al, 1977;Ligrone, 1988).…”

Photosynthetic CO2 fixation and ribulose bisphosphate carboxylase/oxygenase activity of Nostoc sp. strain UCD 7801 in symbiotic association with Anthoceros punctatus

“…In A. punctatus, the symbiotic cyanobacteria develop as macroscopic colonies in small cavities in the gametophyte thallus (8,27). Colonies of symbiotic Nostoc sp.…”

Genetic Diversity of Nostoc Symbionts Endophytically Associated with Two Bryophyte Species

“…In these endophytic associations, the symbiotic Nostoc colonies are housed in special cavities, or domatia, located on the ventral surface of the gametophyte. The bryophyte produces the symbiotic structures before infection, and motile Nostoc filaments, or hormogonia, enter these structures through stomata or slime pores (4,18). As the symbiosis is restricted to the gametophyte, each bryophyte generation needs to be infected by new cyanobacteria.…”

“…Although many studies have been performed with these systems, relatively few have addressed questions of cyanobiont identity and specificity. Early studies relied on phenotypic characters for identification of the cyanobiont (4,8,10,18), but recently, molecular methods have also been used (21). Cyanobacterial symbionts from the hornwort Phaeoceros laevis were compared using different PCR amplification techniques, including those employing either short arbitrary primers or primers specific for the regions flanking the 16S-23S rRNA internal transcriber spacer.…”