Interconversion of Free Sugars, Starch and the activity of Invertase and Sucrose-UDP (ADP) Glucosyl Transferase in the Storage Organ of a Pennisetum hsybrid

Abstract

Summary Changes in free sugars, starch and the activity of invertase, sucrose-UDP glucosyl transferase and sucrose-ADP glucosyl transferase were studied in the storage organs of Pennisetum (Napier-Pearl millet) hybrid NB21 during continuous and intermittent growth (cuttings) of the plant. The relative level of reducing sugars decreased with a concomitant increase in the level of non-reducing sugars during continuous growth of the plant. During intermittent growth, the total free sugar levels decreased in alternate cuttings with the corresponding increase in the level of starch. The levels of sucrose-UDP glucosyl transferase, sucrose-ADP glucosyl transferase and sucrose increased in this organ with the growth of the plant. Sucrose was converted to starch through the intermediate formation of UDP-glucose and ADP-glucose. The activity of sucrose- UDP-glucosyl transferase was much higher than sucrose ADP-glucosyl transferase. Invertase catalyzed the utilization of sucrose for both respiration and starch synthesis at the initial stages of plant growth. At subsequent stages of plant growth, sucrose-UDP glucosyl transferase and sucrose-ADP glucosyl transferase became the major enzymes in the conversion of sucrose to starch. Starch of the storage organ is probably utilized in sprouting and fresh growth following cutting of the plant. Some oligomers, other than sucrose, are synthesized transitionally in the storage organ which are reused for regrowth of the plant.