Starch degradation in intact amyloplasts isolated from cauliflower floral buds (Brassica oleracea L.)

Abstract

Abstract. Isolated amyloplasts from cauliflower buds are capable of mobilizing starch. This mobilization is strongly dependent upon the intactness of the plastids and is linear with time for up to 30 min. The degradation of starch occurs via a hydrolytic breakdown and is stimulated by ATP-dependent phosphorylation of products of this hydrolysis. The rate of phosphorolytic stimulation of starch degradation is negligible. Carbohydrates derived from starch degradation do not appear to enter the oxidative pentose-phosphate pathway. Phosphorylation of hydrolytically solubilized intermediates leads to the synthesis of dihydroxyacetone phosphate and hexose phosphates. 3-Phosphoglyceric acid acts as an inhibitor of starch mobilization. The export of labelled phosphorylated intermediates from amyloplasts containing 14C-labelled starch implies the presence of an amyloplastic phosphate translocator in these plastids. The physiological role of varying concentrations of 3-phosphoglyceric acid is discussed with respect to the regulation of a metabolic cycle of simultaneous starch synthesis and degradation.

Sucrose Synthase Catalyzes the de novo Production of ADPglucose Linked to Starch Biosynthesis in Heterotrophic Tissues of Plants

“…1c) (Pozueta-Romero et al 1991, Naeem et al 1997, Shannon et al 1998. Essentially in line with previous investigations describing the occurrence of cyclic gluconeogenic processes in bacteria (Gaudet et al 1992, Belanger and Hatfull 1999, Guedon et al 2000 and animals (David et al 1990, Massillon et al 1995, Bollen et al 1998 in which glycogen synthesis and degradation take place simultaneously, active turnover of starch has been shown to occur in non-photosynthetic tissues of plants (Pozueta-Romero and Akazawa 1993, Neuhaus et al 1995, Sweetlove et al 1996b. Accordingly, the newly proposed mechanistic model of Suc-starch conversion shown in Fig.…”

Developmental changes of enzymes involved in conversion of sucrose to hexose-phosphate during early tuberisation of potato

“…A possible explanation for the requirement of a higher glucose-phosphorylating potential in the tuberising structures than in the nontuberising ones, might be the tuber-initiated accumulation of starch in these organs. There are indications for the existence of a metabolic cycle of simultaneous starch synthesis and degradation (Geigenberger et al 1994;Pozueta-Romero and Akazawa 1993;Neuhaus et al 1995). One of the starch-degrading enzymes, amylase, releases free glucose and resynthesis of starch from this glucose would require an increased glucose-phosphorylating capacity in growing tubers.…”

ADP-glucose drives starch synthesis in isolated maize endosperm amyloplasts: characterization of starch synthesis and transport properties across the amyloplast envelope

“…As AMP represents the counter-exchange substrate for ADPGlc uptake, reduced import of ADPGlc would be the result. (2) We have demonstrated that externally supplied ATP stimulates starch degradation in heterotrophic and autotrophic plastids [44,45]. There is a substantial body of evidence that, in both chloroplasts and amyloplasts, simultaneous synthesis and degradation of starch occurs [46,44].…”

“…(2) We have demonstrated that externally supplied ATP stimulates starch degradation in heterotrophic and autotrophic plastids [44,45]. There is a substantial body of evidence that, in both chloroplasts and amyloplasts, simultaneous synthesis and degradation of starch occurs [46,44]. If we assume that the same holds true for maize endosperm amyloplasts, increased concentrations of ATP might promote starch degradation, leading to a release of radioactivity previously bound in starch.…”