Different Levels of N Supply Impacts on Seed Yield by Modulating C and N Metabolism in <i>Brassica Napus</i>

Abstract

Oilseed rape is known to crop having low nitrogen use efficiency (NUE) but requires high levels of N fertilizer. NUE is associated with N remobilization from source to sink organ, consequently affects seed yield. Remobilization of leaf N is also related to transport of C/N metabolites in phloem. However, interaction between seed yield and phloem transport was not fully documented. In response to seed yield, N and C metabolites and their transport into seed from bolting to pod filling stage investigated in two contrasting genotypes (Capitol and Pollen) cultivated under ample (HN) or limiting nitrate (LN) supply. Seed yield was significantly reduced in N limitation and its reduction rate was much lower in Capitol than in Pollen compared to HN treated plants. Amino acid and protein content was higher in Capitol than in Pollen at bolting stage. They gradually decreased during plant development but not significant between two cultivars and/or two treatments. Glucose, fructose and sucrose content were 1.8-,1.6- or 1.25-fold higher in LN condition than in HN condition, respectively. Amino acid and sucrose content in phloem were largely higher in Capitol than in Pollen under LN condition. These results indicate that the higher seed yield might be related to greater transport ability of amino acid and sucrose in phloem under LN condition.