Conversion of sucrose to starch in the developing Pennisetum typhoides grain

Abstract

Developing grains of pearl millet (Pennisetum typhoides Burm. S & H cv. PIB 155) were sampled and analyzed for starch and its free‐sugar precursors. The activities of invertase, sucrose‐ADP (UDP) glucosyl transferase and of α‐amylase and β‐amylase in relation to the rate of starch accumulation in the developing grain were assayed. By culturing detached ears, the incorporation of 14C from free sugar precursors to starch was studied. The starch content gradually increased until grain maturity. The rate of starch accumulation was maximum around 12 days after anthesis. Around this period, the activities of sucrose‐ADP(UDP) glucosyl transferase and α‐amylase, β‐amylase were also at a peak. Invertase activity was high during the early period of grain development but gradually declined as the grains matured. In the most actively metabolising milky grains, incorporation of 14C from [14C]‐sugars to starch was maximum in the mid mid‐milky grains. Addition of 20 mM K+ to the culture solution did not affect the incorporation of 14C from supplied sucrose to the free sugar pool and to the starch of the grain, but Mg2+ supply at 20 mM concentration lowered 14C incorporation from exogenous sucrose to grain free sugars, although the utilization of the latter for starch synthesis was enhanced.