STARCH ACCUMULATION, SIZE DISTRIBUTION AND RELATED ENZYME ACTIVITY IN SUPERIOR AND INFERIOR KERNELS OF MAIZE UNDER DIFFERENT NITROGEN RATES

Compared to inferior kernels, superior kernels had significantly higher amount of starch accumulation in maize at maturity. The logistic simulation showed that the starting potential and mean accumulation rate were affected by kernel position in the regulation of starch accumulation. The contents of sucrose in inferior kernels were significantly higher than those in superior kernels during kernel growth. The activities of related enzymes, sucrose synthase (SS) and ADPG pyrophosphorylase (AGPase), in superior kernels were much higher compared to inferior kernels. The results suggested that high starch accumulation was caused by high activities of SS and AGPase but not by high starch synthase substrate levels in superior kernels compared to inferior kernels. Nitrogen could increase the degradation and utilization of sucrose and the level of starch synthesis, as well as accelerate the formation of small granules in maize. The volume percentages of granules 18 and 3, 3-18 and 18 ?m. These results suggest that it is more conducive to increase of individual volume of small and midsized starch granules in superior kernels within a maize ear. There was small difference on the mean AGPase activities during filling between superior and inferior kernels under normal nitrogen compared with low nitrogen. Thus, normal application decreased the variation on the starch accumulation and volume percentage of large starch granules in both kernels.