¹⁵N-Allocation of ¹⁵NH₄-N and ¹⁵NO₃-N to Nitrogenous Compounds at the Vegetative Growth Stage of Potato Plants

Abstract

Effect of NH₄ ⁺ and NO₃ ⁻on ¹⁵N-aIIocation to organs and nitrogenous compounds in potato plants (Solanum tuberosum L.) was examined in hydroponic culture using an automatic pH control system, and the results obtained were as follows.

1.	Growth of upper leaves was stimulated by NH4 + because 15NH4-N was preferentially distributed into upper leaves compared to 15NO3-N which was mainly distributed to lower leaves.
2.	At the vegetative growth stage, 15NH4-N and 15NO3-N distribution among organs was almost similar except for roots, whereas at the tuber swelling stage, 15NH4-N was distributed to stems and roots, and 15NO3-N was distributed to leaves.
3.	15N amino acid metabolism was affected by NH4 + or NO3 −, for example, in leaves grown in 15NH4-N, the contents of aspartic acid and asparagine (Asx) increased with growth, while those of glutamic acid and glutamine (Glx) decreased with growth. In leaves grown in 15NO3-N, the Asx content remained constant, but the Glx content increased with growth. In tubers, 15NH4-N was distributed to Asx at first, but 15NO3-N was distributed to Glx. Thus, the metabolism and translocation pattern of Asx and Glx were quite different depending on the nitrogen forms.

Key Words:

• amino acid
• asparagine
• glutamine
• nitrogen metabolism
• nitrogen translocation