Lars Hällbom

Aluminium Uptake by Anabaena cylindrica

Summary: Atomic absorption spectrophotometry was used to characterize aluminium uptake by the cyanobacterium Anabaena cylindrica. An EDTA-washing procedure was used to distinguish between adsorbed and intracellular aluminium. The intracellular aluminium content increased with increasing external concentration and time. The phosphorus concentration in the growth medium did not affect the rate of aluminium uptake nor did dark treatment or addition of CCCP, an uncoupler of phosphorylation. We therefore conclude that aluminium toxicity is due to intracellular aluminium rather than to interactions with nutrients in the growth medium and that aluminium uptake is independent of phosphorus uptake. The accumulation of aluminium in polyphosphate granules and cell walls of phosphorus-rich cells noted earlier is rather due to an increased binding capacity in these cellular compartments. Also, the rapid uptake of aluminium by A. cylindrica mainly occurs via passive diffusion.

Influence of certain herbicides and a forest fertilizer on the nitrogen fixation by the lichen Peltigera praetextata

SummaryEffects of herbicides (Garlone 3A, MCPA, 2,4-D and Krenite) and nitrogen fertilizer (NH4NO3), commonly used in Swedish forestry, on nitrogen fixation (C2H2-reduction) by Peltigera praetextata (Sommerf.) Zopf. (field and laboratory) and its phycobiont Nostoc sp. (laboratory) were studied. The alga was affected by the herbicides 2,4-D and Krenite and the fertilizer, with a decrease in nitrogenase activity. Nitrogen fixation by the lichen was not affected by herbicides but treatment with NH4NO3 led to depression of nitrogenase activity and serious disturbance of the symbiosis, the latter effect due to the fertilizers lethal effects on the mycobiont (electron microscopy).

Glycollate Excretion by N2-fixing Cyanobacteria Treated With Photorespiratory Inhibitors

Summary We have examined the effects of various inhibitors of glycollate metabolism on glycollate excretion, photosynthetic CO2 assimilation and N2 fixation by cyanobacteria. α-HPMS (α-hydroxy-α(2-pyridyl)-methane sulphonate) increased the rate of glycollate excretion by Anabaena cylindrica considerably, but also inhibited net CO2 photoassimilation and N2 fixation. α-HPMS inhibted glycollate dehydrogenase in A. cylindrica extracts but did not affect ribulose bisphosphate carboxylase or phosphoglycollate phosphatase activities. Diamox (5 acetamido-1,3,5-thiadizaole-S-sulphonamide) also stimulated glycollate excretion, inhibited CO2 fixation and caused a low inhibition of N2 fixation. INH (isonicotinic acid hydrazide) enhanced glycollate excretion by A. cylindrica, suggesting the metabolism of glycollate via the glycineserine pathway, but again inhibited CO2 fixation and N2 fixation. Glyoxylate also stimulated glycollate excretion by A. cylindrica, Anabaena variabilis and Nostoc muscorum. The data are discussed in terms of the specificity of glycollate metabolism inhibitors in cyanobacteria and the regulation of glycollate metabolism in these organisms.

Effects of inorganic nitrogen on C2H2 reduction and CO2 exchange in the Peltigera praetextata-Nostoc and Peltigera aphthosa-Coccomyxa-Nostoc symbioses

Uptake of NH4+and NO3-by the N2-fixing lichens Peltigera praetextata (two-component lichen) and P. aphthosa (three-component lichen) was studied. In addition, the effects of these ions, separately and in combination, on C2H2 reduction and CO2 exchange were examined. Both NH4+and NO3-were utilized by the lichens. NH4NO3 caused an increased liberation of NO3-from the lichens as compared to the release observed in untreated lichen thalli. NH4+and NO3-led to reduced C2H2 reduction by P. praetextata, which, however, was less pronounced than when the two ions were given in combination. In P. aphthosa the C2H2 reduction was inhibited by NH4+and NH4NO3, but not by NO3-alone. NH4+and NO3-had no effect on the net photosynthesis of P. praetextata, while, in combination, they led to inhibition, although only at a concentration higher than that inhibitory to the C2H2 reduction of P. aphthosa. The photsynthesis was inhibited by all salts, but only initially, probably a “salt effect”. Effects of NH4+on the membrane potential of the cyanobiont are suggested as an important factor causing the depression of net photosynthesis.

Krebs Cycle Intermediates Revert the NH4+-inhibition of C2H2 Reduction in Anabaena cylindrica

Summary α-ketoglutarate, citrate, malate + pyruvate, and pyruvate were capable of reverting or partly reverting the NH 4 + -inhibition of N 2 -ase activity in Anabaena cylindrica . It is proposed that the reason for this is an increased availability of carbon skeletons for the GOGAT reaction (glutamine + α-ketoglutarate → 2 glutamate) and thereby a decreased intracellular glutamine concentration. The results stress the importance of the carbon shuttle for products of the photosynthesis to α-ketoglutarate in the regulation of N 2 -ase synthesis in A. cylindrica .