Nitrate assimilation in the forage legume Lotus japonicus L.

Nitrate assimilation in the model legume, Lotus japonicus, has been investigated using a variety of approaches. A gene encoding a nitrate-inducible nitrate reductase (NR) has been cloned and appears to be the only NR gene present in the genome. Most of the nitrate reductase activity (NRA) is found in the roots and the plant assimilates the bulk of its nitrogen in that tissue. We calculate that the observed rates of nitrate reduction are compatible with the growth requirement for reduced nitrogen. The NR mRNA, NRA and the nitrate content do not show a strong diurnal rhythm in the roots and assimilation continues during the dark period although export of assimilated N to the shoot is lower during this time. In shoots, the previous low NR activity may be further inactivated during the dark either by a phosphorylation mechanism or due to reduced nitrate flux coincident with a decreased delivery through the transpiration stream. From nitrate-sufficient conditions, the removal of nitrate from the external medium causes a rapid drop in hydraulic conductivity and a decline in nitrate and reduced-N export. Root nitrate content, NR and nitrate transporter (NRT2) mRNA decline over a period of 2 days to barely detectable levels. On resupply, a coordinated increase of NR and NRT2 mRNA, and NRA is seen within hours

Biotechnological Strategies for Controlling Wine Oxidation

Apart from the controversial positive effects of moderate wine consumption on human health, wine antioxidant capacity plays a key role in winemaking technology. From juice extraction to bottle storage, oxygen management is one of the most critical points for making quality wines. In the past, the protection of juice and wine from oxidations was based on the sole use of sulfur dioxide; more recently, the toxicity and the allergenic potential of this additive, together with the increased knowledge on wine oxidation mechanisms, have given rise to new biotechnological approaches and producing trends, leading to a significant reduction of sulfites in winemaking. The aim of this paper is to review the oxidation mechanisms of grape juice and wine and to discuss the opportunities to reduce as much as possible sulfur dioxide addition by a proper management of alcoholic and malolactic fermentation and by the supplementation of some important yeast nutritional factors (e.g., thiamine). The use of natural antioxidants complementing the activity of sulfites (i.e., ascorbic acid, glutathione, yeast lees, and yeast derivatives) is also discusse

Effects on varietal aromas during wine making: a review of the impact of varietal aromas on the flavor of wine

Although there are many chemical compounds present in wines, only a few of these compounds contribute to the sensory perception of wine flavor. This review focuses on the knowledge regarding varietal aroma compounds, which are among the compounds that are the greatest contributors to the overall aroma. These aroma compounds are found in grapes in the form of nonodorant precursors that, due to the metabolic activity of yeasts during fermentation, are transformed to aromas that are of great relevance in the sensory perception of wines. Due to the multiple interactions of varietal aromas with other types of aromas and other nonodorant components of the complex wine matrix, knowledge regarding the varietal aroma composition alone cannot adequately explain the contribution of these compounds to the overall wine flavor. These interactions and the associated effects on aroma volatility are currently being investigated. This review also provides an overview of recent developments in analytical techniques for varietal aroma identification, including methods used to identify the precursor compounds of varietal aromas, which are the greatest contributors to the overall aroma after the aforementioned yeast-mediated odor release