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The metabolic responses of the topshore cyanobacterium (blue-green alga) Rivularia atra (Roth) Born. et Flah. have been studied over the salinity range from 0 to 100% sea water. Photosynthetic competence is maintained throughout, showing only minor variation in response to salinity change. Nitrogenase activity is highest in hyposaline media (5 to 25% sea water), decreasing to approximately 55 to 60% in full-strength sea water. `The principal low molecular weight, ethanol-soluble carbohydrate present within cells of R. atra is the disaccharide trehalose, occurring at concentrations up to 232 mmol kg[sup-1] (cell water) within cells incubated in 100% sea water. Trehalose concentration was found to be dependent upon the salt concentration of the bathing medium, suggesting that it played a role in the maintenance of positive turgor under conditions of varying salinity. Approximately 10 to 12% of the total intracellular trehalose pool was released upon 'downshock' [transfer from 100% sea water to 0% (fresh water)]. Regular release of such quantities of carbohydrate in response to 'downshock', e.g. on exposure to rain or freshwater at low tide, may be locally important in providing fixed carbon for associated heterotrophic organisms, although it represents a negligible input of fixed carbon to the marine littoral environment. [ABSTRACT FROM AUTHOR]

The relationship between ATP and nitrogenase activity has been investigated using the obligate photoautotroph Anabaena cylindrica and Anabaenopsis circularis strain 6720, a photoautotroph which can also use exogenously supplied carbon. In the light photophosphorylation supports maximum observed rates of nitrogenase activity (0.60 and 1.2 μmoles C2H4 mg chl a-1 min-1 under aerobic and microaerobic conditions respectively). The ATP pools sustained under both conditions are similar at 160-200 nmoles mg chl a-1. Oxidative phosphorylation and substrate level phosphorylation are unimportant in supporting nitrogenase activity in the light. Cyclic photophosphorylation can supply all the necessary ATP provided fixed carbon compounds from photosynthetic CO2 fixation (Anabaena) or supplied exogenously (0.2%, w/v, fructose) (Anabaenopsis) are available. When the algae are placed in the dark nitrogenase activity declines. In Anabaenopsis, after an initial rapid drop, nitrogenase activity can be sustained in the presence of exogenous carbohydrate in the dark at up to 70% of the light rate under air, but under anaerobic conditions. This decreased nitrogenase activity in the dark is not due to a lack of nitrogenase synthesis or of penetration of fixed carbon into the cells, but appears to be due to an inherent inability of dark metabolism to generate sufficient ATP and/or reductant for maximum nitrogenase activity. The ATP pool can be sustained at maximum levels when photophosphorylation, cyclic photophosphorylation, and oxidative phosphorylation operate individually, and to a lesser extent when substrate-level phosphorylation operates. No consistent correlations were found between the ATP pool and nitrogenase activity, except under dark anaerobic conditions where there was a positive correlation. [ABSTRACT FROM AUTHOR]

Free-living and symbiotic phycobionts of Anthoceros punctatus and Blasia pusilla reduce acetylene and fix [sup15]N[sub2]; gametophytes and sporophytes without algae do not. Nitrogenase activity by free-living and symbiotic Nostoc is higher under microaerobic than aerobic conditions in the light, and is higher in the light than in the dark. The free-living Blasia phycobiont grows heterotrophically on sucrose and less well on fructose and glucose; heterotrophic growth on galactose is negligible. There is a transfer of [sup15]N from the alga, via the gametophyte to the sporophyte of Anthoceros. About 98% of the extracellular nitrogen liberated into the medium by excised Nostoc colonies is in the form of ammonia; there is negligible liberation of peptides and amino acids. The capacity to excrete ammonia is lost after 72 h of growth free from the liverwort, Excised Nostoc colonies show a negligible capacity to fix CO[sub2] photosynthetically and autoradiographic studies show a transfer of fixed carbon from Blasia gametophytes to the algal cavities. Sucrose may be the main extracellular carbon compound liberated by Blasia gametophytes. In Anthoceros, nitrogenase activity can be sustained for days when alga-containing gametophytes are placed in the dark, if the sporophytes remain exposed to the light. This indicates a transfer of photosynthate from the sporophyte, via the gametophyte, to the alga. [ABSTRACT FROM AUTHOR]

The Anthoceros punctatus-Nostoc and Blasia pusilla-Nostoc symbioses were investigated. In both associations the Nostoc colonies develop in mucilaginous cavities on the undersurface of the gametophyte. The sporophytes of Anthoceros have no Nostoc colonies; no sporophytes of Blasia were found. The symbiotic algae have been identified as Nostoc sphaericum ex. Born et Flah. The heterocyst frequency of the free-living isolates is 3-6% but this increases to 30% (Blasia) and 43% (Anthoceros) when the algae are growing symbiotically. On infecting alga-free gametophytes of Blasia pusillia with Nostoc, algal colonies develop in the cavities within 72 h. The developing Nostoc colonies stretch the cells of the cavity wall and there also arise from a point on the host cavity wall, usually opposite the cavity pore, septate, branched, filamentous protrusions, which increase the surface area of contact between phycobiont and host by about 30% within 4 weeks of colony formation. Such outgrowths may facilitate interchange of metabolites between the alga and liverwort. The Nostoc phycobiont of Anthoceros may infect Blasia and vice-versa, A strain of Nostoc punctiforme isolated from Gunnera also infects Blasia, but four other Nostoc isolates, including one from cycad root nodules, do not. Five other heterocystous algae, five non-heterocystous filamentous algae and one unicellular alga tested do not infect Blasia. The nitrogen contents of thalli with Nostoc colonies are significantly higher than those treated with algae which do not develop colonies. The symbiotic algae differ physiologically and biochemically from free-living algae. They show higher rates of nitrogenase activity (acetylene reduction assay), are depleted of nitrogen-storing phycobilin pigments and structured granules and although metabolically active do not evolve O[sub2] or fix CO[sub2] photosynthetically, but do have polyhedral bodies which contain the key CO[sub2]-fixing enzyme ribulose-1,5-diphosphate carboxylase. [ABSTRACT FROM AUTHOR]

The effects of temperature and salinity on the carbohydrate accumulation profiles of a range of unicellular cyanobacteria (blue-green algae) have been studied. Four isolates of Synechocystis sp. which usually accumulated glucosyl-glycerol produced a second carbohydrate, sucrose, when grown in a seawater-based medium at high temperature (35 °C). In contrast, three sucrose-accumulating isolates of Synechococcus, grown over a range of temperatures and salinities, did not produce a second detectable low molecular weight carbohydrate in any experimental treatment. The interaction of temperature and salinity was further examined in Synechocystis PCC 6714. Sucrose production was found to be favoured by high temperature and low salinity. The rate and extent of sucrose accumulation differed in cells grown at 20 and 37 °C reaching an upper asymptote 12 h after upshock at 37 °C and 24 h after upshock at 20 °C followed by a decrease to ah approximately constant level after 96 h. This is the first demonstration of the accumulation of sucrose as a second osmotically active carbohydrate in cyanobacteria. [ABSTRACT FROM AUTHOR]

The lichen Peltigera aphthosa consists of a green alga Coccomyxa, a fungus, and a N2-fixing Nostoc which is located in superficial packets (cephalodia). In symbiosis the Nostoc shows only low activities of glutamine synthetase, but the cephalodia show very high activities of glutamate dehydrogenase. Alanine dehydrogenase activity is rather similar in all components. The Nostoc liberates over 95% of the N2 which it fixes as NH4+, and fungal glutamate dehydrogenase in the cephalodia appears to be important in the assimilation of this NH4+. Exogenous NH4+(5 mM) has no effect on acetylene reduction activity by excised cephalodia but completely inhibits acetylene reduction by cephalodia attached to lichen discs (of fungus + Coccomyxa) within 24 h. This inhibition can be overcome by inhibiting main thallus glutamine synthetase activity by adding the glutamate analogue, L-methionine-SR-sulphoximine (MSX). On adding exogenous NH4+ to main thallus discs with cephalodia, glutamine accumulates in the cephalodia when main thallus glutamine synthetase is active but not when it is inactivated by MSX. Exogenous glutamine also specifically inhibits nitrogenase activity by the cephalodia although exogenous alanine and glutamate (all 5 mM) have no such effect. The data indicate that glutamine produced in the main thallus may be involved in the regulation of nitrogenase activity by the cephalodial Nostoc. [ABSTRACT FROM AUTHOR]

On adding NH4+ to nitrogen-fixing cultures of A nabaena cylindrica, the glutamine pool of the intact filament increases within seconds. Nitrogenase activity and then glutamine synthetase activity decline. There are no changes in the activities of glutamate-aspartate aminotransferase, or in the pools of alanine, glycine and aspartate during this period. Nitrogenase activity is usually inversely related to the size of the glutamine pool and shows little correlation with glutamine synthetase activity per se. There is no evidence of adenylylation or deadenylylation of glutamine synthetase (snake venom phosphodiesterase has no effect on activity, there is no serological homogeneity with the Escherichia coli enzyme which shows a covalent modification; the ratio of biosynthetic : transferase activity does not change markedly on the addition of NH4+ and the kinetics of decrease in glutamine synthetase activity are not consistent with adenylylation of the enzyme). Feed-back inhibition occurs, with alanine and glycine being particularly effective inhibitors and with some inhibition occurring with AMP, carbamoyl phosphate and aspartate. Histidine, lysine, ornithine, citrulline and arginine were non-inhibitory at the concentrations used. There is no evidence of inhibition of glutamine synthetase by glutamine. The addition of azaserine inhibits glutamine uptake by intact filaments and reduces the subsequent conversion of glutamine to glutamate within the filament by 77%. Such results are consistent with the operation of the glutamine synthetase--glutamate synthase pathway in A nabaena cylindrica. [ABSTRACT FROM AUTHOR]