Abstract: The strong- and weak-gluten cultivars are two typical patterns of high-quality wheat for different end-uses, between which many differences exist in the synthesis, accumulation, concentration, and components of both protein and starch in grain. The experiment was conducted at Tai’an experimental station of Shandong Agricultural University in 2005–2006 growth season. A strong-gluten cultivar Gaocheng 8901 and a weak-gluten cultivar Yumai 50 were used to compare the contents of NO₃^−-N, NH₄⁺-N and activities of enzymes relating to nitrogen metabolism, sucrose and starch syntheses and the starch accumulation dur-ing grain filling, and to characterize the relationship between nitrogen and carbon metabolisms during grain development. The results indicated that the activities of sucrose synthase (SS), sucrose-phosphate synthase (SPS), adenosine diphosphorate glucose pyrophrylase (AGPP), soluble starch synthase (SSS), granule-bound starch synthase (GBSS), and starch branching enzyme (SBE) performed in the pattern of a single-peak curve during grain filling. The peak values of SS, SPS, SSS, GBSS, and SBE activities were higher in Yumai 50 than in Gaocheng 8901 except AGPP. The accumulation rate of amylopectin was highly significantly correlated with the activities of SS (r=0.9377**), SPS (r=0.8857**), AGPP (r=0.6489**), and SBE (r=0.5980**) in Gaocheng 8901, however, the accumulation rate of amylose was highly significantly correlated with the activities of SS (r=0.7616**) and SPS (r=0.7750**). The accumulation rate of amylopectin was significantly or highly significantly correlated with the activities of SS (r=0.8182**), SPS (r=0.6762**), AGPP (r=0.7028**), GBSS (r=0.8749**), and SBE (r=0.5433*) in Yumai 50, and the accumulation rate of amylose was highly significantly correlated with the activities of SS (r=0.8528**), SPS (r=0.8428**), and SBE(r=0.8603**). The activities of both nitrate reductase (NR) and glutamine synthetase (GS) exhibited a gradually decreased trend in the processs of grain filling in both cultivars, the activities of NR and GS in Gaocheng 8901 were higher than those in Yumai 50. The contents of NO3−-N and NH₄⁺-N were highly significantly positively correlated with the activities of NR and GS in both cultivars. In Gaocheng 8901, the activities of NR and GS were negatively correlated with the activities of SS and SPS, but in Yumai 50 only the negative correlation of the activities between GS and SPS was significant (r = -0.5212*). Based on the results mentioned-above it was found that the starch synthesis and accumulation in grains of the different cultivars were influenced by the activities of the enzymes involved in nitrogen metabolism. The higher activity of NR caused the activities of both SS and SPS to be decreased, resulting in the decline of starch accumulation rate. This finding here supported the assumption that the ratio of SPS to NR plays an important role in starch synthesis and accumulation in wheat grains.

Key words: Winter wheat (Triticum aestivum L.), Strong gluten, Weak gluten, Nitrogen metabolism, Starch, Enzyme activity