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.
Extracellular invertase of Rhizobium japonicum and its role in free sugar metabolism in the developing root nodules of Sesbania grandiflora L. was studied. The enzyme hydrolysed sucrose extracellularly, and its release was substrate inducible. 0.1 Mβ‐mercaptoethanol released the cell‐bound form of this enzyme. The production of invertase was low when glucose, galactose, mannose, fructose and raffinose were used as carbon sources in the growth medium. In the developing nodules sucrose was the major sugar. The content of fructose was low in comparison with that of glucose – suggesting that in the nodules, fructose is converted to glucose prior to its entry into the bacterial cell. The content of glucose synchronised with the pattern of change in the activity of invertase in the nodules.
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