The heterocysts of blue-green algae. III. Differentiation and nitrogenase activity

Abstract

The course of heterocyst development in Anabacna cylindrica was studied in relation to the ability to fix nitrogen. When non-differentiated filaments, grown in the presence of ammonium-N, were transferred into a medium free from combined nitrogen and incubated under photosynthetic conditions, the cellular C:N ratio increased from 4.5:1 to 8:1 before the percentage heterocyst frequency and nitrogenase activity reached a steady value. The initial stages of differentiation were observed 24 h after transfer into nitrogen-free medium, but nitrogenase activity was only detected when the formation of the first heterocysts was completed. The transformation of a vegetative cell into a heterocyst is characterized by the dissolution of storage granules, the deposition of a multilayered envelope, the breakdown of photosynthetic thylakoids and the formation of new membraneous structures. The latter appear to develop by the coalescence of small newly formed vesicles arising in regions of pre-existing thylakoids. The course of heterocyst development was paralleled by that of nitrogenase activity both under aerobic and anaerobic conditions. Anaerobic incubation enhanced heterocyst production as well as nitrogenase activity. The results suggest that nitrogenase synthesis in Anabaena cylindrica is associated with heterocyst formation and that the primary factor which may regulate both processes is the cellular C:N balance of the alga.

Heterocyst envelope thickness, heterocyst frequency and nitrogenase activity in Anabaena flos-aquae: influence of exogenous oxygen tension

“…These results imply an inducible nature of heterocyst envelope thickness in response to PO, which can protect nitrogenase by mediating inward O2 diffusion. Our observation is in agreement with previous reports of poor development of heterocyst walls in Anabaena species under anaerobic or microaerobic conditions (Kulasooriya et al, 1972;Rippka & Stanier, 1978). Heterocyst envelope components, such as the laminated glycolipid layer and the homogeneous polysacc haride layer, have been shown to be important as gas diffusion barriers (Murry & Wolk, 1989).…”

“…Heterocyst frequency of Anabaena cylindrica under highly elevated C 0 2 levels with no O2 was shown to be higher than that in air (Kulasooriya et al, 1972). However, we are unaware of reports on the effect of varied PO, alone on heterocyst frequency.…”

“…This observation also implies a degree of recovery from physiological stress at 40 kPa p02. Kulasooriya et al (1972) showed that short-term anaerobic growth of A . cylindrica with highly elevated C 0 2 levels increased nitrogenase activity, followed by a rapid decline.…”

“…This phenomenon has not been reported among cyanobacterial heterocysts, except for the observation that in Anabaena spp. the heterocyst envelope is poorly developed under low-PO, and anaerobic conditions (Kulasooriya et al, 1972;Rippka & Stanier, 1978). Only short-term effects of PO, or 02-supersaturation on nitrogenase activity in cyanobacteria have been reported (Murry et al, 1984;Paerl, 1978).…”

The Effects of Anaerobiosis on Nitrogenase Synthesis and Heterocyst Development by Nostocacean Cyanobacteria

“…In the special case of heterocystous cyanobacteria, heterocyst differentiation is also largely, and often totally, repressed under these conditions (Fogg, 1949). Removal of the nitrogen source causes a small fraction (5 to 10%) of the vegetative cells that compose the filaments to differentiate into heterocysts; and if the process takes place under aerobic conditions, the formation of mature heterocysts is closely correlated with the development of nitrogenase activity in the filament population (Neilson, Rippka & Kunisawa, 1971;Kulasooriya, Lang & Fay, 1972).…”