We investigated the effect of exogenous cytokinins and marine bioactive substances containing seaweed extracts (marketed by the ROULLIER Group under the trade name N PRO TM. ) on nitrate reductase activity in Arabidopsis. Cytokinins, applied either directly in the growth medium or as a foliar spray, did not significantly influence nitrate reductase activity in extracts from in vitro grown Arabidopsis plants. Conversely, Arabidopsis grown in the presence of or sprayed with N PRO had increased nitrate reductase activity. This stimulatory effect of N PRO was even higher when the plants were grown on low nitrate concentration, suggesting that these marine bioactive substances may be beneficial for plant growth in adverse nutritional conditions.

No abstract

We found that the deletion of a conserved stretch of acidic residues led to an active NR protein that was more thermosensitive than the wild-type enzyme, but it was relatively insensitive to the inactivation by phosphorylation in the dark. Therefore, the removal of this acidic stretch seems to have the same effects on NR activation state as the deletion of the N-terminal domain. A hypothetical explanation for these observations is that a specific factor that impedes inactivation remains bound to the truncated enzyme. A synthetic peptide derived from this acidic protein motif was also found to be a good substrate for casein kinase II.Most higher plants obtain the nitrogen metabolites needed for growth and development by taking up and assimilating nitrate. After active transport into the cell, nitrate is reduced to nitrite by NR (EC 1.6.6.1-2), a cytosolic enzyme. Subsequently, nitrite is reduced to ammonium by nitrite reductase, which is localized in the chloroplast.The expression of the NR gene is highly regulated at the transcriptional level by many endogenous and environmental factors, including hormones, light, nitrogen source, and carbohydrates (for review, see Hoff et al., 1994;Crawford, 1995). These transcriptional regulations probably determine the long-term fluctuations in the NR protein level. On the other hand, a reversible posttranslational regulation of the NR protein involving protein phosphorylation allows short-term modulation of the enzyme activity in response to light-dark transitions, variations in photosynthetic activity, CO 2 level, intracellular pH, or oxygen availability (Kaiser and Fö rster, 1989;

A study was undertaken to explore the use of computer imaging to assess the color of cured meat products. Wiener sausages were manufactured to produce a color gradient. Increasing amounts of red carmine were added to the raw sausage emulsion (0, 50, 65, 100, 125, and 150 ppm) so that the extreme shades (0 and 150 ppm carmine) were clearly different, while the smallest color difference (e.g. 50 and 65 ppm carmine) was barely perceptible. Slices of the sausages containing 0, SO, 100, 125, atzd 15O ppm of carmine were presented to a group of 10 trained panelists in a standard lightbooth (065 lighting, 978 ± 21 lux; ASTM 1996) and the panelists were asked to evaluate the relarive color difference between each sausage and a reference sausage (65 ppm carmine), using the standard R‐index multiple comparison test. The panelists were also asked to make the same evaluation while looking at digitalized images of the sausage slices on a high quality color computer screen. In general, small differences in shade (Δa* 1.0–1.8) were more ofen perceived by panelists when these were looking at slice images on the computer screen than when observing the actual slices in the lightbooth.