CARBON NUTRITION AND THE REGULATION OF UPTAKE HYDROGENASE ACTIVITY IN FREE‐LIVING AND SYMBIOTIC ANABAENA CYCADEAE

Abstract

SUMMARYAnabaena cycadeae was grown with N, as nitrogen source, either photoautotrophically in light or with glucose as carbon source in darkness. The rate of growth was much slower in darkness but the heterocyst frequency was much the same; nitrogenase activity (on a chlorophyll basis) was about half that of light-grown cells. Light-grown organisms contained uptake hydrogenase activity but dark-grown organisms did not. The addition of glucose to light-grown organisms was followed by the disappearance of uptake hydrogenase activity over the following 48 hours and the disappearance was independent of light. Heterocyst frequency and nitrogenase activity were much less affected by glucose addition.A. cycadeae growing symbiotically in cycad roots had much higher heterocyst frequency and nitrogenase activity than the free-living form but no detectable uptake hydrogenase activity.It is suggested that the rate of supply of carbohydrate to the heterocyst controls the development of uptake hydrogenase activity and that the absence of this activity in the symbiotic cyanobacteria indicates that the organisms in the cycad roots have an ample supply of carbohydrate.

N2-Fixation by Freshly Isolated Nostoc from Coralloid Roots of the Cycad Macrozamia riedlei (Fisch. ex Gaud.) Gardn.

“…The average, 5.8:1.0, as well as that of 4.3 for intact coralloid roots obtained in the present study, suggests that the symbiosis evolves H2 at rates at least equivalent to those of N2 reduction. These observations are consistent with those for the freshly isolated organism from C. circinalis, which appears to have lost uptake hydrogenase activity (14,20). The ratio of C2H2 reduced:N2 fixed by intact Azolla-Anabaena has been found to range from 3.2 in 0.3 atm N2 to 1.7 in 0.8 N2, while values for the freshly isolated cyanobacteria from this symbiosis vary from 4.4 to 2.5 (23).…”

“…Studies with freshly isolated symbiotic cyanobacteria from coralloid roots of Cycas circinalis (14,20) have shown high rates ofphotosynthetic O2 evolution as well as light-stimulated nitrogenase activity in excess of those found in cultured freeliving cyanobacteria originally isolated from the same source (20). In the above cycad, coralloid roots develop at or near the soil surface where cyanobacteria may be exposed to light.…”

The role of hydrogen metabolism in photoheterotrophic cultures of the cyanobacterium Nostoc sp. strain Cc isolated from Cycas circinalis L.

“…strain Cc is observed both under photo-and chemoheterotrophic conditions. This contrasts with the general opinion that organic carbon prevents the synthesis or expression of uptake hydrogenase, a regulatory phenomenon observed in several different heterotrophic (Schlegel & Eberhardt, 1972;Maier et al, 1979;Partridge et al, 1980) and phototrophic bacteria (Willison et al, 1983) and in one cyanobacterium (Kumar et al, 1986). However, Bradyrhizobiurn japonicum expresses uptake hydrogenase activity during heterotrophic growth (Graham et al, 1984;van Berkum, 1987).…”

Cyanobacterial hydrogenases: diversity, regulation and applications

“…Cells of N. punctiforme grown either photoor chemoheterotrophically reach both higher nitrogenase and hydrogen uptake activities than photoautotrophically grown cells . However, the effect of carbon substrates on the cyanobacterial uptake hydrogenase activity is difficult to assess, and apparently contradictory results are reported in the literature (Houchins, 1984;Kumar et al, 1986;Chen et al, 1989;Margheri et al, 1991).…”