Comparative analysis of photosynthetic and respiratory parameters in the psychrophilic unicellular green alga Koliella antarctica, cultured in indoor and outdoor photo-bioreactors.

Effect of temperatures and illumination of temperate winter on photosynthesis and respiration was studied in the psychrophilic microalgae, Koliella antarctica (Trebouxiophyceae). Outdoor and indoor algal cultures were compared. Photosynthetic as well as respiration rates increased as light and temperature increased, until 35 °C, more in outdoor than in indoor cells, in agreement with the calculated Q 10 values. K. antarctica showed important strategy mechanisms of adaption to the several temperature and light conditions. These significant photo-acclimation and thermo-acclimation abilities make it possible to cultivate Koliella for different uses, under less expensive outdoor conditions. Therefore, K. antarctica shows important strategy mechanisms of adaption to various temperature and light conditions; moreover, by varying the culture conditions, it is possible to modulate and optimize the growth and accordingly the biomass production. This is a very interesting point since it has been proved that this microalga is a promising potential source of functional ingredients, such as polyunsaturated fatty acids and carotenoids, suitable for industrial purposes.

Glutamate synthase activities and protein changes in relation to nitrogen nutrition in barley: the dependence on different plastidic glucose-6P dehydrogenase isoforms.

In barley (Hordeum vulgare L. var. Nure), glutamate synthesis and the production of reducing power by the oxidative pentose phosphate pathway (OPPP) are strictly correlated biochemical processes. NADH-GOGAT was the major root isoform, whose activity increased on a medium supplied with NH4+ or NO3-; by contrast, no noticeable variations could be observed in the leaves of plants supplied with nitrogen. In the leaves, the major isoform is Fd-GOGAT, whose activity increased under nitrogen feeding. G6PDH activity increased in the roots supplied with nitrogen; no variations were observed in the leaves. Moreover, an increase of the P2 isoform in the roots was measured, giving 13.6% G6PDH activity localized in the plastids under ammonium, and 25.2% under nitrate feeding conditions. Western blots confirmed that P2-G6PDH protein was induced in the roots by nitrogen. P1-G6PDH protein was absent in the roots and increased in the leaves by nitrogen supply to the plants. The changes measured in cytosolic G6PDH seem correlated to more general cell growth processes, and do not appear to be directly involved in glutamate synthesis. The effects of light on Fd-GOGAT is discussed, together with the possibility for P2-G6PDH to sustain nitrogen assimilation upon illumination.

Temperature responses of growth, photosynthesis, respiration and NADH: nitrate reductase in cryophilic and mesophilic algae.

• Temperature effects on growth, photosynthesis, respiration and nitrate reductase (NR) were studied in the cryophilic algae Koliella antarctica and 'Chlorella'saccharophila, and in the mesophilic Chlorella sorokiniana. • Growth rate was measured as increase in optical density. Photosynthesis at saturating light and respiration in darkness were measured as O2 exchange. NADH : NR was assayed in crude extracts. • The two cryophilic algae grew below 15°C, and C. sorokiniana above 20°C. Photosynthetic and respiration rates of K. antarctica and 'C.' saccharophila were elevated at 5°C, and peaked at 30°C. Arrhenius plots from 5 to 25°C were linear in K. antarctica, whereas in 'C.' saccharophila and C. sorokiniana they exhibited breaks at 15 and 20°C, respectively. Values for activation energy (Ea ) and the factor by which the rate increases with raising the temperature 10°C (Q10 ) differed. Nitrate reductase had its optimum at 25°C in cryophilic algae and at 35°C in C. sorokiniana. • We conclude that growth of cryophilic algae at low temperature is favoured by elevated photosynthesis and respiration rates, but that it could be limited by a high respiration : photosynthesis ratio.

Glutamate synthesis in barley roots: the role of the plastidic glucose-6-phosphate dehydrogenase.

Evidence is provided for a close link between glutamate (Glu) synthesis and the production of reducing power by the oxidative pentose phosphate pathway (OPPP) in barley ( Hordeum vulgare L. var. Alfeo) root plastids. A rapid procedure for isolating organelles gave yields of plastids of over 30%, 60% of which were intact. The formation of Glu by intact plastids fed with glutamine and 2-oxoglutarate, both substrates of glutamate synthase (GOGAT), depends on glucose-6-phosphate (Glc-6-P) supply. The whole process exhibited an apparent K(m Glc-6-P) of 0.45 mM and is abolished by azaserine, a specific inhibitor of GOGAT; ATP caused a decrease in the rate of Glu formation. Glucose and other sugar phosphates were not as effective in supporting Glu synthesis with respect to Glc-6-P; only ribose-5-phosphate, an intermediate of OPPP, supported rates equivalent to Glc-6-P. Glucose-6-phosphate dehydrogenase (Glc6PDH) rapidly purified from root plastids showed an apparent K(m Glc-6-P) of 0.96 mM and an apparent K(m NADP)(+) of 9 micro M. The enzyme demonstrated high tolerance to NADPH, exhibiting a K(i) (NADPH) of 58.6 micro M and selectively reacted with antibodies against potato plastidic, but not chloroplastic, Glc6PDH isoform. The data support the hypothesis that plastidic OPPP is the main site of reducing power supply for GOGAT within the plastids, and suggest that the plastidic OPPP would be able to sustain Glu synthesis under high NADPH:NADP(+) ratios even if the plastidic Glc6PDH may not be functioning at its highest rates.