RESUMO
To examine the difference between early kernels at different ear position in maize and the effect of nitrogen supply rates on kernel development, physiological indices in apical and mid-basal kernel 5-20 days after pollination in maize under different nitrogen supply rates (0, 120, 180 and 240 kg x ha(-1)) were determined with UV-Vis spectrophotometry. The results showed that nitrogen supply obviously increased the contents of soluble sugar, sucrose and starch, and the activities of enzymes related to sucrose inversion and starch synthesis. Twenty days after pollination, the kernel volume, dry weight and the contents of soluble sugar, sucrose and starch in apical kernel under nitrogen supply rate of 180 kg x ha(-1) were higher than those with other treatments. Five to twenty days after pollination, higher activities of acid sucrose invertase (AI), neutral sucrose invertase (NI), sucrose synthase (SS), ADPGase and starch synthase in apical kernel were also obtained under nitrogen supply rate of 180 kg x ha(-1), indicating that the sucrose utilization and starch synthesis were improved, the kernel development was promoted and the kernel abortion was reduced, which resulted in higher yield.