Advancements in Nitrogen Metabolism in Grapevine

Nitrogen (N) plays the most important role of all soil mineral nutrients in plant growth and development. In grapevine, nitrogen is most likely to be deficient al-though it is the main fertlizer commonly applied to vineyards to increase produc-tivity (Keller et al. 1998) and to influence grape juice composition (Ough and Bell 1980). Considerable new information has been obtained over the past twenty years on the uptake, translocation, distribution, partitioning, and storage of ni-trogenous compounds in grapevines as well as new insights toward a better un-derstanding on the regulation of the synthesis and degradation of amino acids and other nitrogenous compounds and of the enzymes associated with these reactions. However, in spite of the widespread usage of nitrogen fertilization in vineyards, the physiological and biochemical effects of nitrogen on shoot and fruit growth, fruit bud initiation, flowering, fruit set, and crop yield are still poorly understood. Grapevines differ from herbaceous plants and many other woody plants in that they do not form terminal buds at the end of shoots, but they can continue to grow late into the season. The individual flower parts are formed after bud break, unlike most deciduous fruit trees. Nitrate and ammonium ions are the most common forms of nitrogen avail-able to plants in soils. The relative importance and concentration of each of these two ions depends on the genetic, developmental, and physiological status of each