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 Q10 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.

The mixed effects of nitrogen nutrition and sulphate assimilation were investigated in barley plants (Hordeum vulgare var. Alfeo) that were subjected to long-term sulphur and/or nitrogen starvation, by measuring the O-acetylserine(thio)lyase (OASTL-EC 4.2.99.8) activity, changes in -SH compounds and amino acid levels.The growth of barley plants cultured in the hydroponic vessels was severely affected by altered nutrient levels. The barley plants grown in medium deprived of nitrogen and/or sulphur sources for 21 days showed increase in both root length and weight. In contrast, the shoot growth was reduced in nitrogen-starved plants and was unaffected by sulphur deprivation. Sulphur starvation affected the level of proteins in barley plants more than nitrogen deprivation. The decline in the protein levels observed under sulphur-deficient conditions was coupled with the accumulation of glutamine, asparagine and serine, mainly in the roots; additionally, a nitrogen deficiency in the roots promoted a decrease in both glutathione and cysteine levels.The simultaneous deprivation of nitrogen and sulphur in plants leads to an alteration in their metabolism; high levels of glutathione (GSH) in the shoots could signify the induction of a mechanism intended for coping with stressful conditions.Sulphate deprivation enhanced OASTL activity, mainly in the roots; on the other hand, OASTL increases observed under S deprivation were clearly dependent on the nitrogen availability in the culture medium. In fact, the nitrate supply to the N and S starved plants that showed OASTL activity very low, rapidly recovered the OASTL activities to the levels typical of control plants. Nevertheless, the ammonium supply had negligible effects on the OASTL activity only observed after three days in the roots.Our results support the hypothesis that in barley plants, a portion of S assimilation (up to cysteine biosynthesis) occurs in the roots, and a reciprocal influence of nitrogen assimilation on cysteine synthesis occurs. (C) 2010 Elsevier B.V. All rights reserved.

Unicellular algae represent an interesting source of bioactive food ingredients. In this study, fatty acids and carotenoids of Koliella antarctica, a psychrophylic Antarctic unicellular alga, were investigated. K. antarctica was cultivated at different temperatures and harvested at the early exponential growth phase and at the late exponential growth phase. After 240h, at the end of the late exponential growth phase, the cell biomass concentration was 1.1gL−1 at 10°C while it was 2.2gL−1 at 15°C. The lipid profile of K. antarctica was rich in polyunsaturated fatty acids (PUFA) particularly at the early exponential phase (50.8% of total fatty acids). The comparison of data obtained from algae cultivated at 10°C and 15°C, showed at 15°C a strong increase in saturated lipids and a decrease in PUFA. At the same time the presence of EPA and DHA was marginally affected, with a percentage decrease around 15–20%. The productivity of EPA and DHA was similar at the two growth temperatures with maximum values of 0.6mgL−1day−1 and 1.3mgL−1day−1, at 10 and 15°C, respectively.

In Chlorella sorokiniana (211/8k), glucose-6 phosphate dehydrogenase (G6PDH—EC 1.1.1.49) activity is similar in both N-starved cells and nitrate-grown algae when expressed on a PCV basis. A single G6PDH isoform was purified from Chlorella cells grown under different nutrient conditions; the presence of a single G6PDH was confirmed by native gels stained for enzyme activity and by Western blots. The algal G6PDH is recognised only by antibodies raised against higher plants plastidic protein, but not by chloroplastic and cytosolic isoform-specific antisera. Purified G6PDH showed kinetic parameters similar to plastidic isoforms of higher plants, suggesting a different biochemical structure which would confer peculiar regulative properties to the algal G6PDH with respect to higher plants enzymes. The most remarkable property of algal G6PDH is represented by the response to NADPH inhibition. The algal enzyme is less sensitive to NADPH effects compared to higher plants G6PDH: KiNADPH is 103 μM for G6PDH from nitrogen-starved C. sorokiniana, similarly to root plastidic P2-G6PDH. In nitrate-grown C. sorokiniana the KiNADPH decreased to 48 μM, whereas other kinetic parameters remained unchanged. These results will allow further investigations in order to rule out possible modifications of the enzyme, and/or the expression of a different G6PDH isoform during nitrate assimilation.

Temperature responses of nitrate reductase (NR) were studied in the psychrophilic unicellular alga, Koliella antarctica, and in the mesophilic species, Chlorella sorokiniana. Enzymes from both species were purified to near homogeneity by Blue Sepharose (Pharmacia, Uppsala, Sweden) affinity chromatography and high-resolution anion-exchange chromatography (MonoQ; Pharmacia; Uppsala, Sweden). Both enzymes have a subunit molecular mass of 100 kDa, and K. antarctica NR has a native molecular mass of 367 kDa. NR from K. antarctica used both NADPH and NADH, whereas NR from C. sorokiniana used NADH only. Both NRs used reduced methyl viologen (MVH) or benzyl viologen (BVH). In crude extracts, maximal NADH and MVH-dependent activities of cryophilic NR were found at 15 and 35 degrees C, respectively, and retained 77 and 62% of maximal activity, respectively, at 10 degrees C. Maximal NADH and MVH-dependent activities of mesophilic NR, however, were found at 25 and 45 degrees C, respectively, with only 33 and 23% of maximal activities being retained at 10 degrees C. In presence of 2 microM flavin adenine dinucleotide (FAD), activities of cryophilic NADH:NR and mesophilic NADH:NR were stable up to 25 and 35 degrees C, respectively. Arrhenius plots constructed with cryophilic and mesophilic MVH:NR rate constants, in both presence or absence of FAD, showed break points at 15 and 25 degrees C, respectively. Essentially, similar results were obtained for purified enzymes and for activities measured in crude extracts. Factors by which the rate increases by raising temperature 10 degrees C (Q10) and apparent activation energy (E(a)) values for NADH and MVH activities measured in enzyme preparations without added FAD differed slightly from those measured with FAD. Overall thermal features of the NADH and MVH activities of the cryophilic NR, including optimal temperatures, heat inactivation (with/without added FAD) and break-point temperature in Arrhenius plots, are all shifted by about 10 degrees C towards lower temperatures than those of the mesophilic enzyme. Transfer of electrons from NADH to nitrate occurs via all three redox centres within NR molecule, whereas transfer from MVH requires Mo-pterin prosthetic group only; therefore, our results strongly suggest that structural modification(s) for cold adaptation affect thermodynamic properties of each of the functional domains within NR holoenzyme in equal measure.

Reversible inactivation of nitrate reductase by ammonia in intact cells ofCyanidium caldarium is described. In this organism the phenomenon occurs in the light or in the dark, in contrast with green algae where it is reported that it occurs only in the light and in the presence of CO2.

A fairly general method is described for analysing thermodynamic parameters for protonation and metal complex formation from logK, Delta H degrees and Delta C(p)degrees data at different temperatures and ionic strengths using the appropriate computer program. The method was applied to the protonation of THAM [or tris, tris(hydroxymethyl)methylamine], in NaCl, and the fluoride ion, in NaClO4. Recommended values for protonation thermodynamic parameters are reported.

The protonation of 1,10-phenanthroline has been studied potentiometrically in different aqueous salt media (LiCl, NaCl, KCl, Me4NCl, Et4NI, MgCl2, CaCl2, SrCl2, and BaCl2) in the ionic strength range 0≤1≤1 M. This ligand forms two protonated species, [H(phen)]+ and [H(phen)2]+; the monoligand species shows protonation constants strongly dependent on the medium. Medium effects were explained by the formation of some weak species: [H(phen)Cl]0, [M(phen)]2+ (M=alkaline earth metal cations). Formation thermodynamic parameters are reported.

"Effect of Ammonium on the Respiration of Roots in Young Barley Plants Grown under Nitrogen Deprivation." Plant Biosystem, 129(4), pp. 983–984

The hydrolysis of iron(III) was studied potentiometrically at different ionic strengths in KNO(3) aqueous solutions, at 25 degrees C, to determine the dependence of hydrolysis constants on ionic strength (nitrate media), to check the existence of nitrate-ferric ion interactions, and to confirm the formation of high polymeric species. Under the experimental conditions 0.03 I (KNO(3)) 1M, 0.3 C 12 mM, the species Fe(OH)(2+), Fe(2)(OH)(4+)(2), Fe(OH)(+)(2) and Fe(12)(OH)(2+)(34) were found, and the hydrolysis constants log beta(11) = 2.20, log beta(12) = -2.91, log beta(22) = -5.7, log beta(12,34) = -48.9 (I = 0M) were calculated. The ionic strength dependence of hydrolysis constants is quite close to that found for several protonation and metal complex formation constants reported elsewhere.

We report the results of a potentiometric study on the formation of weak complexes between imidazole (im) and acetate, malonate, and citrate (L), at T=25°C. Formation of protonated species Hj (im)(L), in which j=1 for acetate, j=1, 2 for malonate and j=1, 2, 3 for citrate, was found. The formation of weak complexes between N-ligands and O-ligands may be used to interpret the behavior of these classes of compounds in natural fluid and/or in biological systems, as regards inter-or intra-molecular interactions.