Effects of applying different nitrogen form on cherry tomato nitrogen metabolism during fruit development.

A hydroponic experiment was conducted to study the effects of applying 100% NO₃^--N,100% NH₄⁺-N, and 75% NO₃^--N+25% NH₄⁺-N on the nitrogen metabolism and the nitrate reductase (NR) and glutamine synthetase (GS) gene expression of cherry tomato during its fruit development. Applying 75% NO₃^--N+25% NH₄⁺-N slightly increased the single fruit mass, and increased the fruit NH₄⁺-N, total amino acid, and total N contents and N accumulation significantly, compared with applying 100% NO₃^--N. In treatments 100% NO₃^--N and 75% NO₃^--N+25% NH₄⁺-N, the fruit NR activity and its gene expression had no significant difference, but were higher than those in treatment 100% NH₄⁺-N. The fruit GS activity was significantly higher in treatment 75% NO₃^--N+25% NH₄⁺-N than in treatment 100% NO₃^--N. In the three treatments, isozyme GS1 (Cytosolic type GS) and GS2 (Chloroplast type GS) expression was inconsistent with GS activity, suggesting that the effects of applied N on GS activity could be mainly reflected at posttranscriptional level. [ABSTRACT FROM AUTHOR]