Effects of supplemental nitrogen on nitrogen-assimilation enzymes, free amino nitrogen, soluble sugars, and crude protein of rice

• Published in: Communications in soil science and plant analysis 1999-01, Vol.30 (5/6), p.711-724
• Main Authors: Souza, S.R, Stark, E.M.L.M, Fernandes, M.S, Magalhaes, J.R
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; amino nitrogen; ammonium nitrate; application rate; Biological and medical sciences; crop growth stage; crude protein; enzyme activity; flowering date; foliar application; free amino acids; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; leaves; nitrate reductase; nitrogen; Nitrogen fertilization; Nitrogen, phosphorus, potassium fertilizations; Oryza sativa; protein content; seed development; seed weight; Soil-plant relationships. Soil fertility. Fertilization. Amendments; solubility; sugars; urea
• ISSN: 0010-3624; 1532-2416
• DOI: 10.1080/00103629909370240

An upland rice variety IAC-47 was grown in a greenhouse to determine the effect of foliar nitrogen (N) supplementation during grain development on the activity of the N assimilation enzymes, nitrate reductase (NR) and glutamine synthetase (GS), on free amino-N content and leaf soluble sugars, and on grain crude protein content. At 10 and 20 days after anthesis (DAA), the leaves were fertilized with a liquid fertilizer containing 32% N as 12.8% urea, 9.6% ammonium (NH4), and 9.6% nitrate (NO3) in increasing rates corresponding to 0,20+20, 40+40, and 60+60 kg N ha-1. Leaves were collected twice (at 12 DAA and 14 DAA for GS activity, sugar and amino-N content, and at 11 and 13 DAA for NRA) after each application of leaf N. The late foliar application of N increased significantly grain crude protein without a corresponding decrease in grain weight. The NR activity (NRA) increased after the foliar application of N. In the flag leaf, 60+60 kg N ha-1 (21 DAA) resulted in higher NRA (20x over the control), while GS activity was smaller than the control. At 22 DAA there was an increase in GS activity in the flag leaf at 20+20 N level. However, the GS activity decreased as applied N levels increased. Also at the 20+20 level, there were increases in free amino-N in the flag leaf and second leaf at the final harvest. Throughout the experiment, plants at the 60+60 N level had the lowest levels of soluble sugars. Increases in crude protein were highest at 40+40 N level (27.9%), followed by 60+60(18.7%).