Calcium-mediated conversion of sucrose to starch in relation to the activities of amylases and sucrose-metabolizing enzymes in sorghum grains raised through liquid culture

Detached ears of sorghum (Sorghum vulgare) were cultured in complete liquid medium containing Ca2+(0, 3, 10 and 30 mM) and effect of this ion on the c onversion of sucrose to starch with respect to the activities of amylases, sucrose synthase, sucrose phosphate synthase and soluble invertases were st udied in developing grains. Presence of 3 mM Ca2+ in culture medium enhance d both accumulation of starch and activity of alpha-amylase in grain but wi thout having any influence on the activity of beta-amylase. However, with 1 0 and 30 mM Ca2+, the accumulation of starch and activities of both amylase s decreased and with advancement in culturing period, starch accumulation w as further decreased. Irrespective of its concentration, Ca2+ enhanced the activities of sucrose synthase (synthesis), sucrose-phosphate synthase, sol uble acid invertase and soluble-neutral invertase. Increase in the concentr ation of Ca2+ in culture medium was concomitant with an elevation in relati ve proportion of sucrose in the grain reflecting a net balance in per cent increase with Ca2+ in the activities of sucrose-synthesizing enzymes over s ucrose-hydrolysing ones. Based on the results, it is suggested that assimil ation of Ca2+ by grain is essential for maintaining high activity of alpha- amylase to generate starch primers required for the conversion of sucrose t o starch during grain filling in sorghum.