Effect of the Radicle, and Hormones on the Subunit Composition and Molecular Form of Pyrophosphate-Dependent Phosphofructokinase in the Cotyledons of Citrullus lanatus

Abstract

After initiation of radicle elongation, the pyrophosphate dependent phosphofructokinase (PFP) activity increases in the cotyledons of Citrullus lanatus. A selective increase of the β-subunit and a constant level of the α-subunit is apparent in the cotyledons during early seedling establishment. The radicle plays an important role in the control of the level of PFP activity and β-subunit content in the cotyledons, as removal during the incubation prevented the increase in PFP activity. Radicle removal also largely restricted the increase in specific β-subunit content, observed in the intact embryos. Application of kinetin (0.5 μM) or 2-chlorophosphonic acid (0.1 μM ethrel) to isolated embryos replaces the effect of the radicle. Application of ethrel to isolated embryos increased the specific β-subunit, while the α-subunit content remained constant. Exogenous kinetin resulted in a substantial increase in the specific β-subunit content, while the α-subunit content declined. The PFP isoenzyme ratio differs between the hormonal treatments and the control tissue, probably as a result of their differential effect on the level of the PFP subunits.