Amino Acids (1997) 13:183-188 Amino Acids © Springer-Verlag 1997 Printed in Austria Incorporation of nitrate nitrogen in rice seedlings transferred to anaerobic conditions Short Communication R. Reggiani *, F. Bertini 2, and M. Mattana ~ 11stituto Biosintesi Vegetali and 2 Istituto Chimica Macromolecole, C.N.R., Milano, Italy Accepted March 13, 1997 Summary. Incorporation of 15NO3 into amino acids was studied in 3-day-old aerobic rice seedlings (with coleoptile and root) subjected for 24h to anaerobic conditions. The incorporation of 15N into glutamate, glutamine and alanine accounted for 89% and 84% of total incorporation in coleoptile and root, respectively. These findings indicate that, after the primary incorpora- tion of 15N into glutamate and glutamine, the main fate of nitrate nitrogen in rice seedlings subjected to anoxia is alanine. Keywords: Amino acids - Anoxia - Coleoptile - Nitrate nitrogen - Rice - Root Introduction Nitrate assimilation is one of the main reductive processes occurring in plant tissues during aerobic metabolism. The importance of this pathway under anaerobiosis is controversial. Rice plants grow well and withstand anaerobiosis better with nitrate as the sole nitrogen source when cultured on liquid nutrient media (Malavolta, 1954). Under such condition, nitrate is better than ammonium with respect to plant growth, grain yield, some meta- bolic activities and cation absorption of the roots (Yamasaki and Seino, 1965). Contrasting data are provided by the literature on the nitrate assimilation under anaerobic conditions. Investigations carried out on nitrate assimilation under anoxia have revealed that this pathway is partially or completely blocked at the nitrite reductase (NiR) step (Ferrari and Varner, 1971; Lee, 1978; Reggiani et al., 1985). Thus, the anaerobic nitrite production (Jaworski, 1971) or the loss of endogenous nitrate (Gray and Cresswell, 1984) has been used for the nitrate reductase (NR) in situ assay in different plant organs (Ferrari et al., 1973).