Appropriate Ammonium/Nitrate Mitigates Low Light Stress in Brassica pekinensis by Regulating the Nitrogen Metabolism and Expression Levels of Key Proteins

Abstract

Low light intensity is always the important factor that influences the growth and development of Brassica pekinesis during winter seasons. We have found out that appropriate ammonium/nitrate ratio mitigated low light intensity in the previous study. In the present study, the nitrogen metabolism and proteomic responses of Brassica pekinensis to light intensities and ammonium/nitrate were further investigated to find out the mitigation mechanism. The activities of nitrate reductase (NR) and glutamine synthetase (GS) and the relative expression of GS1 as well as the content of nitric oxide (NO) were significantly higher in the NH4+:NO3− (15:85) treatment than in the NH4+:NO3− (0:100) treatment under normal light intensity. However, under low light intensity condition, the activities of NR and GS and relative expression of NR as well as the NO level in seedlings fertilized with NH4+:NO3− (10:90) were significantly higher compared with those fertilized with NH4+:NO3− (0:100). In addition, we found thirty-six protein spots, which exhibited significant changes in abundance using similarity searches across the uniprot database of Brassica. The proteins identified were classified into ten functional groups including photosynthesis, carbon and energy metabolism, stress/defense, protein folding, and modification and degradation response. We concluded that appropriate ammonium nitrate ratio improves the tolerance of mini Chinese cabbage seedlings to low light intensity by regulating the nitrogen metabolism and expression levels of some key proteins.