Carbohydrate Metabolism in the Developing Kernel of Normal, Sweet Corn and Quality Protein Maize

Maize is an important food crop widely used in the milking stage for human consumption. Although some mutants like su1 and sh2 exhibits considerable amount of sweetness during milking stage, but the expression of sugars and the associated enzymes is not well understood in the developing maize kernel. The present study was planned to evaluate the time course expression of sugars (fructose, sucrose, glucose, sorbitol and starch) and enzymes (invertase, sucrose synthase and hexokinase) in the developing kernel of normal, sweet corn and quality protein maize. The results revealed higher concentrations of free sugars in the initial stages of kernel development. Sweet corn possesses significantly higher concentration of sugars and low concentrations of starch as compared to normal and quality protein maize (QPM) genotypes in the milking stage of kernel. The invertase activity was found to be maximum in the initial stages of kernel development and then showed a declining trend. In contrast, the activity of sucrose synthase was found low at 15 DAP but increased at 30 and 45 DAP. The activity of hexokinase was found low at the initial stages which further reduced significantly (47%) with increasing DAP. However, the activity of hexokinase was found lowest in sweet corn at 15 DAP but increased drastically and showed maximum content at 30 and 45 DAP.