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It has been pointed out that tea (Camellia sinensis (L.) O. Kuntze) prefers ammonium (NH 4 + ) over nitrate (NO 3 - ) as an inorganic nitrogen (N) source. 15 N studies were conducted using hydroponically grown tea plants to clarify the characteristics of uptake and assimilation of NH 4 + and NO 3 - by tea roots. The total 15 N was detected, and kinetic parameters were calculated after feeding 15 NH 4 + or 15 NO 3 - to tea plants. The process of N assimilation was studied by monitoring the dynamic 15 N abundance in the free amino acids of tea plant roots by GC-MS. Tea plants supplied with 15 NH 4 + absorbed significantly more 15 N than those supplied with 15 NO 3 - . The kinetics of 15 NH 4 + and 15 NO 3 - influx into tea plants followed a classic biphasic pattern, demonstrating the action of a high affinity transport system (HATS) and a low affinity transport system (LATS). The V max value for NH 4 + uptake was 54.5 nmol/(g dry wt min), which was higher than that observed for NO 3 - (39.3 nmol/(g dry wt min)). K M estimates were approximately 0.06 mM for NH 4 + and 0.16 mM for NO 3 - , indicating a higher rate of NH 4 + absorption by tea plant roots. Tea plants fed with 15 NH 4 + accumulated larger amounts of assimilated N, especially glutamine (Gln), compared with those fed with 15 NO 3 - . Gln, Glu, theanine (Thea), Ser, and Asp were the main free amino acids that were labeled with 15 N under both conditions. The rate of N assimilation into Thea in the roots of NO 3 - -supplied tea plants was quicker than in NH 4 + -supplied tea plants. NO 3 - uptake by roots, rather than reduction or transport within the plant, seems to be the main factor limiting the growth of tea plants supplied with NO 3 - as the sole N source. The NH 4 + absorbed by tea plants directly, as well as that produced by NO 3 - reduction, was assimilated through the glutamine synthetase-glutamine oxoglutarate aminotransferase pathway in tea plant roots. The 15 N labeling experiments showed that there was no direct relationship between the Thea synthesis and the preference of tea plants for NH 4 + . © 2013 Pleiades Publishing, Ltd.

Original publication

DOI

10.1134/S1021443712060180

Type

Journal article

Journal

Russian Journal of Plant Physiology

Publication Date

03/01/2013

Volume

60

Pages

91 - 99