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The influence of the source of inorganic nitrogen (KNO3, ( N H 4 ) 2 S O 4 and NH4NO3) and its concentration (5, 10, 20 and 30 mM N) on total N incorporation, as well as on N distribution into different fractions (ammoniacal, amino, amide and protein) and on free amino acid levels has been determined in grape vine explants cultured in vitro.Increasing concentrations of the nitrogen source resulted in increased total N content in tissues. This effect was small for KNO3, higher for (NH4)2SO 4 and maximal for NHaNO 3. In addition, nitrate promoted an increase in amino-N only, whereas ammonium increased both the ammoniacal-N and the amino-N fractions. Incorporation of N into amide-N and protein-N were not affected significantly by the N sources tested.The application of increasing quantities of N enhanced the accumulation of most free amino acids, especially arginine, alanine and proline, but to different extents, depending on both the N source and its concentration. The combination of ammonium and nitrate resulted in a higher accumulation of amino acids than that observed with either one of the two forms alone.

Growth and mineral composition of grapevine explants (13.3 EVEX rootstock) cultured on a basal medium with 10.4 mM of NO;, and respective additions of 5, 10, 15, 20 and 25 mM of NH 4 N0 3 were analysed. Low N-availability (10.4 mM) induced low shoot formation. Addition of NH 4 N0 3 up to 15 mM increased number, quality and N levels of shoots. Further increase of N in the medium induced very high contents of N and water in tissues, and led to abad shoot quality (large and abnormally shaped leaves and dark colour-fragile tissues, difficult to handle in further propagations). The content of K in explants was negatively affected by the concentration of NH 4 N0 3 in the substrate and by the level of N in tissues.

NaN0 3 treatments. induced an important accumu1ation of Na (r=0.986) caused by the presence of Na ion in the sa1t and a sma11 increase of N (r=0.953) and decrease of Ca (r=-0.904). The other nutrients considered were not altered. (NH4)2S04 treatments caused a very 1arge accumu1ation of N (r=0.974), P (r=0.967) and Fe (r=0.985) and at the same time an important decrease of K (r=-0.959).