Effect of Nitrogen and Phosphorus on the Amino Acids in Root Exudates and Grains of Rice During Grain Filling

Abstract

Nitrogen (N) and phosphorus (P) play important roles in regulating plant growth and development. The purpose of this study was to investigate how N and P nutrients affect amino acids in the root exudates and grains of rice ( Oryza sativa L.) using two cultivars, Yangdao 6 ( indica) and Yangjing 9538 ( japonica), with 5 treatments, 0N (without N), 1/2N (1/2 N of the standard Espino nutrition solution), 0P (without P), 1/2P (1/2 P of the standard Espino nutrition solution), and CK (standard Espino nutrition solution), during the grain filling period. The concentrations and components of amino acids in the root exudates and grains were measured, and their relations were analyzed. The results showed that the concentration of each amino acid in the root exudates decreased gradually during the process of grain filling. Nitrogen stress (0N) during grain filling significantly reduced the concentration of each amino acid in the root exudates and grains. Phosphorus stress (0P) significantly increased the concentrations of acidic and neutral amino acids in root exudates, but significantly reduced the contents of total amino acids, essential amino acids, and other amino acids in the grains. The concentrations of amino acids in the root exudates were significantly and negatively correlated with the relative content of amino acids in grains, and the concentration of alkali amino acids in the root exudates was significantly and negatively correlated with a 1000-grain-weight. The results suggested that the concentrations and components of amino acids in the root exudates were closely associated with those in grains as well as with the grain weight. Nitrogen and phosphorous nutrients played a significant role in regulating the concentrations/contents and components of amino acids in roots and grains, and accordingly, affect the grain yield and nutrient quality of rice.