Effect of inorganic phosphates on the activity of alkaline inorganic pyrophosphatase in sorghum caryopsis raised through liquid culture

Abstract

1012-1016Detached ears of sorghum (Sorghum vulgare) were cultured in complete liquid medium containing Pi or PPi (20mM).Effect of these inorganic phosphates on conversion of sucrose to starch in relation to the activity of alkaline inorganic pyrophosphatase (EC 3.6.1.1) was studied. Both Pi and PPi reduced the accumulation of biomass and starch in caryopsis and this reduction was more pronounced with advancement in culturing period. Amongst endogenous sugar of caryopsis, the relative proportion of sucrose increased with either of these phosphates. With elevation in endogenous levels of Pi and PPi in caryopsis, there was a corresponding decline in the activity of alkaline inorganic pyrophosphatase. Addition of these inorganic phosphates in culture medium also reduced the incorporation of 14C from (U-14C)-sucrose into EtOH extract (principally constituted by free sugars) and starch of caryopsis. Accompanying this reduction, there was an increase in 14C incorporation into sucrose. Based on these results, it has been suggested that in sorghum caryopsis an inhibition of the activity of alkaline inorganic pyrophosphatase results in lowering starch accumulation